Recommendations on my next imaging Camera after years with modded DSLRs?

[g__day]

Hi all,

I am thinking I would like to step up from imaging with modded DSLRs and would love advice as to good options to match my gear, seeing and imaging targets.

I currently use two IR modded Canon 40D Dlsr's - a cool boxed one on a F10 C9.25 for DSOs and a uncooled one on a Williams Optics 110 FLT for wider field shots of similar targets. I use Hutech IDAS light pollution suppression filters on both - which probably mean for my night skies I can capture 10 minutes light frames on the WO and 15 - 20 minute subs max on the C9.25 on really dark nights before things just totally blow out the pixel wells.

What I love to try and image are nebulaes like M74, 77, the Helix Nebulae, the Eagle, Trifid or NGC 2070 - things with lots of coloured gas rather than just oodles of stars in them :)

I am aware that at its native resolution the Canon 40Ds with the slow F10 C9.25 - each pixel is seeing 0.44 arc seconds - and the sky here is only fair to average at best - so I am way over sampling the sky.

I don't mind going one shot colour or Mono + filters - I would just like something that can capture more detail, a bit faster and make capturing objects like say M77 which in my locale isn't much above the luminance of the no moon night sky.

At my current location I don't know if this is possible - city glow may be a hurdle if I don't wish to go narrow band - and I don't know if I want to go direcly there.

Budget wise - don't mind anything from $2K - $8K so long as its fit for purpose and will go well with my existing gear. Eventually once I have all the skills I may retire and move to somewhere with darker skies - so the gear can come with me. I want to gain all the skill sets to capture the rather dim objects I am hunting well. Again if folks think to really capture my targets I need darker skies and both larger, and faster OTAs - please do share your insights!

My currently mount (Atlux with the SkySensor2000-PC) guided has no trouble pointing and tracking objects really well for long periods of time, especially guiding thru an OAG - 30 minute shots blow out the pixel wells - but the stars are all lovely and round. ALso since moving to The SkyX witj Tpoint, Dome and Camera add on - using its closed loop slew - targets are dead centred on the Cameras every single time so far.

So I am very keen to hear everyone's advice.

Matthew

[glend]

The ASI1600MM-C, just released in June, is a real game changer camera, extremely low noise, -40C Ccooling, high sensitivity with full gain control.; and less than $2k. Plenty of images from them already, check out the ASI1600 Astrobin group for examples.
Its pixel size is probably best suited to sub-1000mm focal length, so would be a good match for the WO 110. Imaging at f10 is another matter.

[Camelopardalis]

+1 ASI1600 is at an attractive price point. I bought the mono although I've barely been able to use it because of the weather.

I intend to try it with my C8@f/7 which amounts to ~1400mm focal length, sure it's a little oversampled for most seeing, but with the shorter subs necessary with this camera it should capture whatever sharpness the sky chooses to give. So maybe it's worth considering getting one of the 0.63x reducers for your C9.25?

I also reckon it'd be a cracker with the 110.

The advantage with a mono chip is that you can get into narrowband while living in the city and do RGB when you're out.

The other thing about the 1600 is that it's at the lower end of your budget...so if you decide it's not for you, sell it on and you've not lost much.

[Atmos]

At at FL of near 2400mm you'll definitely want larger pixels than that of the ASI1600 which would give you a scale of ~0.33"/pixel. You're better off with a pixel size around the 8+ micron. Although it is very noisy, the 11002 sensor is fine for LRGB imaging.

If you want to keep doing OSC imaging then the ASI1600 colour isn't too bad because you want to over sample anyway.

[billdan]

Hi Matthew,

I went from a DSLR to a QHY12 OSC and have been very happy with the results. However I want more resolution and also do narrowband imaging so I am saving up the pennies for a QHY-16200A. This is an integrated camera with OAG and 2in filter wheel.

http://www.gamaelectronics.com.au/qhy16200a.html

Cheers
Bill

[Shiraz]

reckon I would bite the bullet and change both the scope and the camera. A Mak Newt with a ZWO1600 mono cooled would be great on that mount for high res imaging. The camera needs filters, but you can use 1.25s with the 1600, which is a huge saving if you go narrowband.

of course, the 9.52 would be readily saleable, but if you decide to keep it for imaging, agree with Colin that you will need big pixels. An 11002 or 16200 would seem to be a good way to go, but either is way more expensive than the ZWO approach. An alternative would be to use a ZWO1600 with software binning, but you would end up with only 4m of 7.6micron pixels - still plenty for many DSOs, but not all. In other aspects, a software binned ZWO would be better than alternatives, with lower read noise, slightly better QE (possibly) and much better dynamic range.

[Camelopardalis]

16200 looks a nice sized chip, but the read noise is horrendous by 2016 standards ;)

[Mosc_007]

I bought an Entry Level CCD about 12 months ago. A QHY10 CCD. Is a nice camera but still expensive. Recently I bought a ZWO 1600MC and am very happy with it. And the price is good for such a camera. The Noise on the ZWO 1600MC is so low I dont even bother with Darks.

[RickS]

O noes! I better go and delete all the substandard images I took with that noisy old KAF-16803 :lol:

More seriously, Matthew said he's able to do long subs so the option of a noisier but larger Kodak/Trusense sensor is still worthy of consideration if he's after a larger FOV.

Cheers,
Rick.

[lazjen]

The recent M20 I posted was done at about 1350 mm using the ASI1600MM-C. It seemed to work ok. I do plan moving the camera on to another scope soon (around 700 mm) for its main work, but I was pleased that it did well at 1350 mm.

Keep in mind that if you go mono (highly recommended) you need to budget for all the filters (LRGB, plus Ha, SII, OIII if you make the leap to narrowband), plus a filter wheel. The camera choice may also constrain what filter wheel and filters you can use.

Another thing to keep in mind is the weight of the gear hanging off the back and if that could impact your focuser. Is it up to the task of handling it all? You may find you need to upgrade that as well as some of the CCDs out there aren't that lightweight. :)

[Slawomir]

Hi Matthew,

It might be worthwhile seeing what people have been able to produce with the new ASI camera : http://www.astrobin.com/groups/31/

IMO CCDs still have the edge over CMOS when in comes to DSO imaging, but CCD-based astro cameras are also more expensive. If it was me and if budget would allow for it, I would be seriously tempted to grab a camera with the 16200 chip.

But as it has been already mentioned, a good focuser as well as the cost of filters and FW all need to be taken into account as well.

I'm sure you will have fun with whatever dedicated astro camera you choose :thumbsup:

[gregbradley]

A KAF16200 camera for sure. I am currently imaging with a FLI ML16200 and its a great sensor. I have lots of images with it but none posted yet. Soon.

11002 is no good to you with those scopes. It requires a scope with a wide corrected circle and a flattener. No way the SCT will handle it and the WO FLT perhaps. It needs a 3 inch focuser minimum.

KAF16200 is the best all round sensor for most imagers. Its got a good field of view, low noise (the high noise remark is incorrect) its clean like a Sony sensor, fairly deep wells so blown out stars don't occur as easily and 16mps for that size sensor is quite high resolution. The pixel size means it matches the average persons seeing with an average focal length up to 1500mm. Your SCT will require larger pixels and they are only on full frame or above and it won't handle a sensor that large.

You can always bin the 16200 images on the SCT if the seeing is not good.

As far as which 16200 camera to get your choices are FLI, SBIG (both fairly expensive in AUD). Moravian and QHY. My choice would be the Moravian with the enhanced cooling.

If you wanted a cheaper option then QSI 683 WSG 8's are suddenly fairly common on Astromart for about USD$3,500. I think a lot are upgrading to the 16200.

Greg.

[Slawomir]

Also, Atik claims they will release their camera with 16200 chip in early December, and they promise it will be similarly priced to QHY with the same chip. It will have nice 50 C below ambient cooling, but read noise most likely not as low as in the FLI...

[Camelopardalis]

:lol: just think of all the free hard drive space you'd have :P



Really? Maybe SBIG put the wrong values on their website then... https://www.sbig.com/products/cameras/stxl/stxl-16200/

And QHY are quoting 10e!

"clean" like a Sony sensor...ICX674/694 family are generally ~4e (QSI quote better). Just presenting the facts according to the interweb...

[billdan]

I think the read noise figures are being interperated as some kind of boogie man. The 10e ( or 8e quoted from SBIG) is the same as the QHY12 and other CCD's from 4 years ago. It just means don't do 10sec subs with them, in the majority of sub lengths we do (3 plus minutes) read noise is never an issue.

What would concern me more is being a Kodak chip, RBI can rear its ugly head. I'll ask that question to Theo before I purchase one, if there have been any reports of RBI with the 16200 chip.

Bill

[Shiraz]

I think that read noise can still be the limiting issue with narrowband under some circumstances Bill. With dark skies, very few systems get to be sky limited in NB and dark current can be low with qood cooling, so all that is left is read noise. low read noise is better.

Having said that though, many people do NB imaging under bright sky with moonlight - 10e will be plenty good enough for that.

[billdan]

I have no experience with NB imaging so I trust what you say Ray. However the CMOS chips with very low read noise also have very low full well capacity, so I think that is more important for going deep and getting mag20+ objects.

Bill

EDIT: I forgot about anti-blooming so there probably is no difference - plus dynamic range = full well / read noise, which for the ASI 1600 is 20,000/3.8 and the 16200 is 60,000/10 slightly better.

[Camelopardalis]

Surely what's important for "going deep" is dynamic range and decent QE?

The full well capacity of the 1600 sensor is comparable to the Sony ICX674/694 series, and I don't here a lot of those owners complaining that they can't chase faint objects.

[billdan]

You are right Dunk, it took a while for the penny to drop, but I got there, refer to my edit.
Bill

[g__day]

I am of course happy to upgrade the current focuser - a Meade focuser controlled thru a JMI box to my PC. The C9.25 is carbon fibre so it holds focus extremely well. On the back of the OTA is the Meade, a Lumicon giant OAG, a Meade DSI II Pro Mono and the Canon in a cool box - so that is quite a bit of weight. I did originally have a focal reducer in the OAG - but it introduced coma and Lumicon couldn't explain why so I removed it.

Given I keep the OTA - I would probably go to a Moonlight focuser (had great experience with the last one) into an ONAG into filters (AO if warranted) then primary imaging Camera. I assume with the current set-up I would want large pixels with deep wells, or just bin 2x2 or 3x3 something with smaller pixels?

I'd like to match the camera to my gear - if I were to upgrade OTA - well I would probably upgrade mount as well - then reviewing today's technologies I would go C14 or maybe Riccardi Honders - which could mean all new imaging gear again? I don't plan to go there directly - I want to cut my teeth on this one step at a time.

Given my desired target choice and fact that my night skies aren't that dark - is it all achievable? Do I need faster gear if my targets are only a tad above the night sky luminance?

Appreciate all the thoughts given so far. I notice a lot of Cameras for sale at the moment in the IIS trades - but ponder they aren't quite right for my objectives.

Cheers all,

Matthew

[glend]

If your night sky is polluted then narrowband will be more satisfying, but the filters and filter wheel need to be factored in to your budget. There are sales now and then from Cyclops Optics in Hong Kong on QHY filter wheels, i got the small 5 position 36mm usb wheel from them at a very nice price. Baader NB filters are nicely priced from Tekeskop-Express if you buy the three filter set and they are good filters and all parafocal.
Of course NB means longer subs, and a camera capable of fast narrow band is a real bonus. The ASI1600MM-C is producing very nice NB images with subs of 300 seconds, much shorter than traditional narrowband with less sensitive cameras.
Also short sub broadband can be done, here i mean 30 second subs, to escape skyglow effect, but you need to shoot more subs obviously. Be prepared for a learning curve.

[multiweb]

With the british pound dropping like a stone I'd be looking at a starlight xpress.

[glend]

And if bought from the EU you get the 19% VAT removed for export to Australia.

The Starlight Express filter wheels are export priced from 310-325 euro from Teleskop-Express, depending on size of filter you want to use and number of positions, this equares to $456-480 Aud.

The ZWO electronic 5 position 31mm filter wheel just developed for the ASI1600 is $199 usd ($261 aud ) direct from ZWO Optical and is available bundled with the camera if you wish. Check the ZWO Optical website for details.

[Slawomir]

To my knowledge sensitivity is not only affected by low noise, but also by QE and pixel size - not entirely sure whether the chip used in 1600MM sets a benchmark for sensitivity :question:

[Atmos]

Read noise doesn't directly have anything to do with "sensitivity". The 1600 is a fraction higher than the 8300 and very similar to the 16803 and 16200 over most of the spectrum, little stronger towards the blue though.

Short subs also gain no benefit in "escaping skyglow". The sky glow sets a limiting factor on the length of each sub but has no effect on beating light pollution.

[gregbradley]

That is a main reason I got the FLI, read noise is probably a class leading 6 electrons or less. It certainly seems cleaner than other cameras I have used from FLI which are already very clean. That plus FLI reliability and attention to detail. FLI are the Astrophysics of cameras.

Greg.

[gregbradley]

Really? Maybe SBIG put the wrong values on their website then... https://www.sbig.com/products/cameras/stxl/stxl-16200/

And QHY are quoting 10e!

"clean" like a Sony sensor...ICX674/694 family are generally ~4e (QSI quote better). Just presenting the facts according to the interweb...[/QUOTE]

I am talking about the FLI Microline 16 which is 6 electrons or better. The 694 is around 5 so hardly any difference and to my eye they look much the same. The Sony a touch cleaner. What other manufacturers get out of their electronics may be a different story. Just like QSI seems to extract more out of the KAF8300 than anyone else.

As far as RBI goes I have not noticed this on this and rarely on my 16803 for that matter. I believe these KAF sensors do have RBI but it must be a fairly slight issue as only rarely have I seen it impact an actual image.
Usually something super bright like a plane flying through the frame and you can see the lines of the bright lights for a few subs afterwards until it fades out to nothing again.

Not something I would concern myself as to whether or not to get a particular camera or not. Hardly an issue.

The things that matter are field of view, pixel size to match your focal length, F ratio and seeing, QE and well depth.

Well depth of this sensor is 39,000 electrons. which is quite adequate.

20,000 is starting to get a bit too skinny in my experience.

Greg.

[gregbradley]

I find it hard to believe a one shot colour camera is good for narrowband. The colour filter array means only one pixel in 4 is really getting any signal from each of the usual narrowband filters. Typically a mono sensor leaves a one shot colour sensor in the dust for this sort of imaging.

It may seem OK until you saw an equivalent exposure from a mono camera and the difference would be more apparent.

Greg.

[gregbradley]

The KAF16200 full well is 39,000 electrons and read noise obviously varies with manufacturer but can be as low as 6 or less. FLI is that and I think Moravian is good too.

Greg.

[glend]

Greg, the ASI1600MM-C is a mono camera.

My point in relation the advice i provide to the OP, is that he can probably get the ASI1600MM-C, plus the filter wheel, and a set of narrowband and broadband filters for less than $3K, and that equates to an entry level cheap much noisier KAF-8300 (Atik) alone. He is of course free to spend his money as he choses.

[Retrograde]

This is a great thread full of useful information. Although I'm a long way off making the jump to a dedicated astro-camera myself it's a fantastic resource for the future. Thanks to the OP and all who have contributed so far.



What pros and cons are there between software and hardware binning? Presumably CMOS can only do SW binning because of the underlying HW but are there practical differences in the results you would achieve with each?

[RickS]

Pete,

The only advantage of hardware binning is that you may get a reduction in read noise. The ideal situation is that you get the same amount of read noise reading 2x2 pixels as you do reading a single pixel. In practice it doesn't work perfectly and some sensors get a partial improvement and some get very little (like most of the Kodak/Trusense sensors.)

With software binning you don't get a read noise improvement but you have more flexibility, e.g. you can extract lum from your RGB data and add it to your normal luminance if you image LRGB unbinned. If you do unbinned L and binned RGB as some people do that option isn't available.

If you have the luxury of doing sky limited subs then read noise is irrelevant and HW binning has no value. It may have some utility for NB imaging especially for slow optical systems under dark skies.

Cheers,
Rick.

[Retrograde]

Thanks Rick :thumbsup:

[Slawomir]

On the contrary, I think when assessing sensitivity of any camera, we must consider not only sensor's QE but also noise injected by the camera. Sensitivity determines the achievable SNR which is of key importance in astrophotography, and SNR depends on the camera's capacity to have the signal stand out from the surrounding noise. All else being equal, a camera with higher read noise will have a lesser capacity to detect wanted signal (lower sensitivity), as opposed to a camera with a low read noise that will readily capture faint signal (higher sensitivity). That's how I see it anyway :)

[Atmos]

This is only true if you don't overcome read noise. Take the 16803 which has a very similar QE to the ASI1600 but a RN of 8e- compared to the variable RN of the 1600. As long as they both overcome the read noise, their sensitivity is more or less identical. The 16803 will have to do longer subs to reach that point but it has MASSIVE wells to be able to accomodate for that.

[glend]

I believe people adapt their techniques to work to the strengths of their equipment. For example, with the ASI1600, owners are experimenting with short sub imaging and running large numbers of them, also using the varible gain feature to shoot short NB. With broadband subs of 30-60 secs not uncommon, but hundreds of them. This makes the mount and guiding much less of an issue. Deep wells are not really an issue for a camera with very low noise and short sub capability. Max depth on the 1600 is at Gain 70, but many of us shoot at Unity (Gain 139) and just shoot more subs, we gain our depth through stacking, not sub open shutter duration. As 50 subs at 300" is equal to 300 subs at 50 secs in terms of data acquired. Short subs also are less likely to be sky limited.

Have a look at Ray's Optimum Broadband Sub Length Chart, which shows maximum electron count (after stack) for various Gain settings and suggested sub lengths for those Gain settings.

[Slawomir]

More time needed to reach the same SNR = lower sensitivity :)

[billdan]

I think my old PC would die of a heart attack if it had to stack 300 subs.

[Shiraz]

Rick, I think that you do get a signal-to-read-noise advantage from software binning. With 2x2, the signal goes up by 4x, but the read noise adds in quadrature and only goes up by 2x, so you get a 2x improvement in SNR - probably works out about the same as hardware binning with many chips, except that you also get the full 4x effective well depth (most hardware binning only gives about 2x).

[Atmos]

It does certainly make it a LOT easier on the mechanical side of things doing 30-60s broadband but you also lose considerably more time with dithering, guider/mount settling and the like. With the download speed of the 1600 that becomes irrelevant however.

Deep wells are still of importance because your well depth drops faster than the read noise does. As you increase the Gain the dynamic range also drops so well depth is still most certainly a consideration. You may only need 30s but you can blow out parts of an image with 30s as the well depth drops considerably.

The being sky limited is purely having the sky background (the amount of photos emitted by the sky) being brighter than the read noise of the camera. With my QHY22 that happens in about three minutes at my dark site at 4.7e-, with a lower read noise it just hits the required level faster. If I did 10x180s and you did 30x60s it is likely that the results will be more or less identical. On the same telescope theoretically my QHY22 will be deeper as it has a 30% higher QE than the ASI1600.




It takes more time to get over the read noise but 10x300s is the same as 30x100s as long as on both accounts they are sky limited. Under both instances there are the same number of captured photons above noise so the SNR will be very similar.

[glend]

Colin, Jon Rista over at CN, has developed a "Sparse Ditheting" formula which reduces time lost in dithering, ie you only dither after 'n' number of subs, worth a read. Its in the imaging forum.
And SGP now supports dithering every 'n' subs.

[RickS]

Ray, I agree that you'll get a 2x improvement in overall SNR traded off for lower resolution. I was trying, albeit imprecisely, to make the point that you don't get the potential reduction in read noise that comes from HW binning.

The whole point of all this is that there is no perfect sensor or camera at present (perhaps ever.) The "best" choice depends on your requirements and the compromises you are willing to make. I like the big FOV of a KAF-16803 and I'm willing to do the long exposures required to make it work. If I wanted to target small galaxies in isolation then a small, low noise Sony sensor would be a better choice. The new CMOS sensors are interesting but don't appeal to me yet. In a year or two who knows?

Cheers,
Rick.

[Camelopardalis]

Given that many of the modern cooled astro cameras have very low dark current, the read noise is surely the biggest factor in determining the sky limiting exposure length. So, whether imaging LRGB or narrowband, a camera with lower read noise is advantageous unless it is completely outgunned by a camera with significantly better QE.

The quicker the subs are exposed adequately, the more subs you can rattle off in a night. The more subs you can rattle off in a sequence the better the SNR is going to be in the stacked image...to a point. There must be a crossover point where the read noise (additive) from more subs equals the read noise from a stack of fewer subs from a noisier camera. I'm sure one of you maths geniuses could show us the way ;)

By my (possibly incorrect) mental arithmetic, with the "smaller" chip on the 1600 at roughly 1/4 the area of a full frame chip, a mosaic of 4 panels (and 64 megapixels!) works out at about 8e read noise. It'd be an interesting experiment to see how'd they'd compare.

I think this still means we need to deeply consider the best option to go with our kit and techniques...

[gregbradley]

Oh I see. My error. Yes I agree that ASI1600 has the potential to outdo a KAF8300 but you'd have to be good with it as there are some amazing 8300 images out there which is a known and proven path.

Greg.

[gregbradley]

Just my opinion but I feel the 16803 is still the best astro sensor out there despite it now being a bit old. Its a phenomenal sensor.

Greg.

[Atmos]

I agree with you Greg, read noise isn't the only limiting factor to consider for sub length. For instance, the ASI1600 running somewhere around unity gain has a read noise of about 2.3e- from memory. The FLI16803 runs at 8e-. The 16803 is noisier BUT has considerably larger pixels so on the same telescope becomes sky limited 2.15x slower which isn't that much when considering that is the difference between 60s and 130s! You get a much larger FOV but less resolution which can quite easily be recovered a bit by drizzling.

[lazjen]

Well, the 16803 cameras are really a moot point for the budget proposed, particularly if you want to get a FLI. And especially when you add in the extras required. It would be a minimum 5 times the cost (as the ASI1600 setup).

[RickS]

You seem to think that "sky limited" is a bad thing? It actually means that the limiting factor is the unavoidable shot noise from the target and sky glow... which is as good as it gets.



Not even to a point, Dunk :) There are potential advantages of shorter subs but improved SNR is not one of them. For sky limited subs it is only the total integration time that matters. For read noise limited subs, more subs just means the same signal with more noise.

[Shiraz]

Good points Rick. Had put together a summary that tries to say the same thing in a little more detail, so will post anyway - thanks to Dunk for raising the issue. Is in the usual pompous tone - please forgive :P. Matthew, if you feel this is inappropriate for your thread, will happily delete.

The number of photons detected is solely a function of the total exposure time. It doesn't matter if you use short or long subs, you get the same number of photons in total. Same applies to the total dark current, which is also summed over the whole integration time and also does not depend on sub length. Short subs do not give less total dark current and long subs do not give more total photons from faint targets - the total number of photons (signal) as well as the total dark current is completely independent of the sub length for a given total integration time.

The shot noise from the sky background after stacking is the square root of the number of (sky light electrons+dark electrons), so it is also solely determined by how long you image in total - it has nothing to do with the sub length.

The read noise is the only other source of noise and it depends only on how many subs you have - the total read noise in the full integration time is (the square root of the number of subs x read noise per sub), so the more subs you have, the more read noise you have. Low read noise cameras allow you to use more subs (ie shorter ones) before the total read noise becomes objectionable - which it will do if it gets up to a level where it becomes significant compared to the shot noise from the (sky + dark current). That is why the guys with high read noise cameras need to use fewer/longer subs than the folks with low read noise chips. However, with proper sub lengths, both will end up with the same result at the end of the integration. Of course, if there is no sky noise (eg is using NB with dark sky), everybody gets the best results using the longest possible subs (to give the lowest total read noise).

The total signal that you can gather from bright stars before they saturate is determined by the well depth applying to each sub multiplied by the number of subs. For example, 100x 1minute subs with well depth of 10,000e will allow the brightest brightest stars in the stack to reach 1,000,000e before they saturate. 10x 10 minute subs with a sensor having well depth of 100,000e, will allow the brightest stars to reach the same saturation level of 1,000,000e. Well depth by itself does not provide any advantage in terms of saturation or sensitivity - the thing that matters is the dynamic range (well depth/read noise) and there is no need for deep wells if you have low read noise. The other side of the coin is that, if you have high read noise, you must have deep wells.

the above discussion is based on additive stacking. Average stacking is generally used, but that is just additive stacking with everything scaled by the number of subs, so the conclusions are unaffected.

The main advantages of short subs are: increased resolution on the very extremes of lucky imaging; reduced requirement for high quality tracking and guiding; and the possibility that polar alignment can be a bit off, or even that altaz mounts could be used, without field rotation being a major issue. Low read noise does not provide any overall SNR advantage with well exposed broadband subs, but it can help when imaging dim narrowband targets under dark sky, where sky-limited exposures are not possible - if there is no issue with using long subs, you will get better results from a low read noise camera than from one with higher read noise.

[RickS]

Excellent summary, Ray. Hopefully, everybody will read it and we'll never have to have this discussion again :lol:

[g__day]

Folks,

I am really appreciating all this information. I hadn't thought of the ASI1600MM-Cool - but it does look like a really performer. From one of the CloudyNight reviews - it looks like with higher gain it had pretty bad AMP noise - that could be processed out. The idea of Binning 2x2 to get a 80K well hadn't occured to me either. Also pleasing to see Bintel stock it - as I find them 100% reliable to deal with over a very long time!

Be interested in knowing if anyone here has one and is staisfied with it. While the 16803 chip from FLI or S-Big that Greg mentioned looks - the ant's pants - with filters and focusers it probably North of $10K so I would work my way towards that I think - one I am sure of my skills and the set up matches.

I am finding this a very, very interesting thread. The Cloudy Night reviews mentioned the author was going from uncooled DSLR to the ASI1600MM-Cool - wish he had posted some best DSLR versus best ASI pictures for comparision on his edge 8" SCT.

Many thanks all, keep it coming,

Matthew

[Atmos]

That is a very good summary Ray, a lot more succinct than I'd have probably been able to so as I do waffle on a bit at times :P

Getting an FLI PL-16803 with Centreline CFW, Astrodon LRGB and 3nm narrowband filters will cost you about $35,000 AUS at the current USD/AUD rate. So, yeah, it's pretty expensive :P My only concern with the 1600 with your SCT Matthew is that the pixels on the ASI1600 are a bit on the small side. It'll be fine for your refractor BUT at 0.33"/pixel on your C9.25 the sampling is not quite ideal.

The 16200 sensor with 6 micron pixels would be a better all rounder.

[Shiraz]

Matthew, the amp noise is a minor issue. I did an apples-to-apples noise comparison with my (excellent) H694 camera. The noise from an "amp glow" section of the 1600 is shown in the top panel and that from the corner of the 694 in the bottom panel of http://www.astrobin.com/full/253351/0/?real=&mod=Noneattached . The amp glow+read noise in the worst area of the 1600 is lower than the dark current+read noise in the best region of the H694. These are 5 minute darks with bias subtracted, so what you see is the dark current+read noise. The two images have been scaled so that the degree of stretching extends over the same range in photo-electrons. Although the amp glow in the 1600 looks fairly bad by itself, it is actually miniscule when compared to other very good cameras and easily handled with flat calibration.

As to whether it would suit you, maybe as a 4mp @7.6micron chip with software binning on your 9.25 it would be a good match - take Colin's advice though, the pixels are too small without binning. The chip is just small enough to use 1.25 filters as well, which is a bonus. It is a bit different to use though - more parameters than you need to set on other cameras and the USB implementation is not as bulletproof as it might be. Overall though, it is an impressive camera, regardless of price.

[gregbradley]

Well depth by itself does not provide any advantage in terms of saturation or sensitivity - the thing that matters is the dynamic range (well depth/read noise) and there is no need for deep wells if you have low read noise. The other side of the coin is that, if you have high read noise, you must have deep wells.


I don't think that is quite true Ray. Deep wells allow you to capture bright areas in longer exposures before blowing out the highlights. Deep wells allow you to do longer exposures and retain star details and colour.

I have imaged with a few shallow well cameras. It may be the fact of large fast aperture but I found that shallow wells require shorter exposures otherwise your stars will be a mess to process later.

Also images taken with a deep well camera (like the 16803) the stars are very robust and take processing much more than the shallow well cameras.

So there is a very distinct advantage to saturation there. Shallow wells means you really have to do short exposures or use narrowband filters to reduce the light and get longer exposures there but even then perhaps not as long as a deep well camera. Deep wells are a plus not something to be ignored. Personally I am done with shallow welled cameras. Too hard to process well.

The KAF 16200 is at the minimum I would want - around 39K much like the 11002 at around 50K.

Greg.

[g__day]

A slight aside - I see Software Bisque's the SkyX Camera add on manages ZWO cameras directly - does that mean I could manage one of these Camera's from TSX (very useful for Closed Loop Slewing) or do people find its better to control these cameras directly through vendor specific tools?

I could still use it thru the Sky to do the closed loop slew - cause the pointing accuracy that gives me tends to be arc seconds precise.

[Shiraz]

Well that is what I said Greg - shallow well cameras Must Have short subs to avoid saturation. If you don't use short subs with a shallow well camera, you can be guaranteed to have burned out data. But the point is that you can get good results from short subs with low well depth cameras because they also generally have low read noise. That means that short-sub/shallow-well cameras can go just as deep as long-sub/deep-well cameras - provided you take the same total exposure (ie lots of subs for the shallow well cameras).

The red herring seems to be that short subs can look very thin, so the temptation is to make 'em look more gutsy by hitting them with longer exposure. That is a fatal mistake that will burn the data. Short subs with low read noise cameras look thin because they individually carry only a very small fraction of the final signal and so they should look thin and crappy- it is only when you stack that you can see how good the data is and how much dynamic range you have. It is quite scary to use the ZWO1600 with 1minute subs - the target in each sub can look like a light frosting of brighter noise with slight structure, but really deep stuff just pops out when you stack 300-400 of them. I normally set the well depth to around 4000e and rarely have anything saturated in the field - I am quite capable of saturating stuff in processing, but rarely start out that way.

[Atmos]

TheSkyX allows ASCOM camera control so it doesn't matter either way. Right now I use TSX which uses the camera via MaximDL. This allows me to have several programs at a time using the the camera :) I can take a photo in MaximDL, FocusMax, TSX and Sequence (ASA mount control) all without having to reconnect the camera.

[Camelopardalis]

Even better :D

Having read all this good stuff makes me think I'm going to be (eventually) trying the 1600 on my SCT (with reducer) too ;) I originally jumped in with both feet thinking it would let me continue imaging through the QLD summer and maybe dabble with some narrowband from the inner city...

[Peter Ward]

I don't agree...as the argument falls apart with very low flux emitters, where you can't ignore shot noise.

If you are only capturing say...one photon every five seconds...then a 1 second sub will likely fail to capture anything 4 or so times out of five.
This is assuming you have zero read noise and perfect QE....which is simply not available at present....the reality is you won't capture anything but noise.

But if we go deeper...a five second exposure will capture that photon. A ten second exposure will capture two etc.

Yes, you need exposure time, but reduced to is absurd conclusion, a million millisecond exposures is unlikely to produce anything useful.

[Shiraz]

That isn't how it works Peter - it is perfectly sensible to count subs that have no target photons. The signal is the total of the photoelectrons and the noise is the combination of shot noise and (read noise*sqrt(numbersubs)). For deep narrowband, the shot noise may be almost non-existent compared to the read noise, so the SNR = totalphotoelectrons/RN*SQRT(numbersubs). This equation applies to any sub length - there is no requirement for every sub to have signal in it.

To prove the point, have a look at M&Ts wonderful deep Helix. http://www.iceinspace.com.au/forum/showthread.php?t=127240
The outermost regions are identified to be equivalent to 9 photoelectrons/pixel - detected in 16x 1 hour subs ie, about half of the subs had no target electrons at all. But there's the signal - really beautiful and very faint shock fronts.

The 16 subs with the 16803 would have produced about 40e rms noise total. A camera with 2e read noise would produce the same 40e total read noise using 400 subs over 16 hours, so you could get the same result using 400x 2.4 minute subs - and you would still only have target photons in 9 of the subs. ie, all else being equal, identical results to M&Ts could have been produced by a hypothetical low noise camera using vastly more short subs. Of course, with broadband the situation is dominated by sky noise, but but the two systems would be equivalent in this environment as well.

[RickS]

I see that Ray replied while I was writing this. I'll post it anyway in case it helps someone understand this apparently slippery subject...



The argument doesn't ignore shot noise. Shot noise is a function of the number of photons detected in a total integration but is indifferent to the length of the individual subs.



So, if you take an "average" 10 second sub it will see 2 photons. If you take 10 x 1 second subs, on average two of them will see one photon and the rest will see none. You still get two photons in the same integration time.




Read noise has relevance as already discussed. QE has the same effect on long or short subs.



Doesn't matter because we're integrating the subs. It's the averaged total that's important.



Not with current sensors, but without read noise a million one millisecond exposures will produce the same result as one 1,000 second exposure or 100 x 10 second exposures. BTW, we're not suggesting you can ignore read noise as should be clear from the discussion above...

The maths is very clear. The problems arise when we use intuition to reason about signal and noise. Like conditional probability it seems like our brains aren't wired to grok it.

[codemonkey]

I've been thinking about this recently... In the above example, the signal is present in just over 2% of the subs. You'd be at risk of these being rejected in the stacking process by the same rejection parameters that protect you from sat trails and cosmic rays, so unless you were to go with a straight average (i.e. no rejection), there might still be a benefit in longer subs for very weak signals.

[Peter Ward]

Sorry, still don't agree.

I have taken a similarly deep image to M&T's helix (attached) ..and my early attempts with 10 minute subs were no where near as successful as my later attempts at 30+ minutes.

Read noise wasn't the problem....it was a pure lack of photons...i.e. shot noise.

Hence I don't accept it is ".. perfectly sensible to count subs that have no target photons" if that is all you are counting.

The physical reality, as opposed the the mathematical nirvana, is you need to capture photons.

If you reduce subs to the point photons are not recorded more often than not, the noise from outside the camera will swamp the signal.

[Shiraz]

don't think it is a problem Lee. depend on the rejection algorithm, but 1 photoelectron is not going to be anywhere near the threshold needed to reject aircraft, cosmic rays etc. In any event, in a sub, a photoelectron will be hidden in the read noise and will only be visible at all after stacking - you probably could not reliably reject such low signals even if you deliberately went out of your way to do so.

[Shiraz]

No need to apologise. I doubt that we are going to agree, even with M&Ts clear (non-Nirvana) results. Your better results at 30 minutes are easily explained - your camera has relatively high read noise. You would not have detected more photons in total using 30 minute subs cf 10 minute subs, but you would have generated much less total read noise when combining the longer subs.

I cant' think of any "noise from outside the camera" - once the signal is digitised, that's it. It could be sent on a mobile phone carrier from Pluto and still arrive in perfect condition.

[codemonkey]

Hope so Ray, I've been planning on doing some very short, high gain work and that's been a concern--been meaning to start a thread on it.

[Peter Ward]

Given the fact I routinely image through a glowing atmosphere, I can assure you the sky emits flux, and it is a noise source ...not sure why you are ignoring this. :shrug:

[Shiraz]

surely sky noise is detected inside the camera Peter.

In any event, the physics is pretty much identical if you add in sky noise. I am sure that M&Ts marvellous image included a little sky noise (they must have imaged through the atmosphere), but they were still able to detect a clear signal where photoelectrons were present in only about half of the subs.

[g__day]

Hey Peter,

What advice would you offer about cameras given my gear, sky and goals? I see it as a stepping stone to learn up and get really serious about gear if that's my post retirement plan.

Matthew

[RickS]

Lee,

The dimmest target I've managed is the jet, R4 in NGC 1097. I don't remember the actual numbers but it was at the level where you could count the photons on your fingers in a 15 minute sub and the number of e- measured was less than the read noise. Through the magic of stacking I got a faintly visible signal and pixel rejection wasn't a problem.

Cheers,
Rick.

[Peter Ward]

OK just so we are clear.

Shot noise, is a noise source from outside the camera, that is due to the random arrival of photons to individual pixels.

If you sample at too short an interval, this noise will become dominant.

Due to its physical and statistical nature, Shot noise is *reduced* by longer individual exposure times, regardless of other parameters the camera might have.

[Shiraz]

That's not clear at all Peter. Shot noise increases with longer subs - it is the square root of the signal count and the longer the sub, the higher the count and the more shot noise you get. The read noise is fixed for a sub. With low signals from short subs, the read noise dominates. eg if you get 10 photoelectrons in a sub, the shot noise will be about 3e rms. That is much less than the read noise in an SBIG camera. You need about 100 photoelectrons to get up to the read noise level of such a camera.

When you stack, you get shot noise that is the square root of the total photoelectron signal - that is independent of the sub length and it doesn't matter at all which subs the photons appear in.

[Shiraz]

:lol::thumbsup:

sorry about your thread Matthew

[g__day]

It's all useful learning curve for me Ray! There aren't too many guides to help you step beyond cooled, IT modified DSLRs - so the advise of this forum is priceless!

[Peter Ward]

Yes, agreed, but CCD's in reality have all sorts of noise sources, and these simply can't be ignored. e.g.

Dark current
Dark Current non uniformity
Dark current spikes
Spurious Charge
Transfer noise
Residual surface image
Residual bulk image
Cosmic rays
Cosmetic defects
Blem Spill
ADC Quantizing noise
EM interference.

Read noise is but one of many sources that derail the "mathematical ideal"
way to capture an image being espoused here.....as to work... it requires a perfect camera that simply doesn't exist.

But if you expose longer with a less than perfect camera...gosh..you get more signal. ;)

And if you stack hundreds of deep subs, the signal gets really impressive at the expense of noise.

Rest assured I get the math.

And when I can buy a camera with Perfect QE and zero noise, I'll seriously consider shorter subs.

[Peter Ward]

I never meant to imply shot noise did not increase with flux. I did however say at low flux levels shot noise can dominate.

But by your own math, If the signal is 1, so is the shot noise. Making the exposure nine times longer, we get signal 9, shot noise 3. QED ?

[SimmoW]

Chomping on my popcorn chaps. Good debate!

Although I already have the 1600, I'm still very curious at the technical advantages of the sensor, learning ASAP how to take advantage of its strengths.

The cam is definitely a disruptor, price wise. Just under $2k from Bintel, compared to almost $7k for a QSI683WSG? I upgraded to a cooled Astro cam 1-2 yrs sooner than I expected due to the price difference. And I fully expect to upgrade again within 2 yrs assuming CMOS development goes as well as I think. Good times for the hobby.

[Slawomir]

In terms of the cost, you need to add FW and OAG but it is still about half the cost of 683wsg; however, QSI cameras are extremely reliable and known to last for years. If one needs to "upgrade" / replace the camera every 2 years then it may not be so economical in the long term. Oh no! I just had a vision of landfills covered with astro cameras...:lol:

[lazjen]

Except that you're likely to recover a portion of your costs in the upgrade as there will be a 2nd hand market. And that's also good news as the entry point for those buying 2nd hand will be a lot lower than it currently is now. It will make things more accessible all round.

Now we need a similar "revolution" in the tech/price of filters and filter wheels... :)

[glend]

There is no evidence of any quality or reliability issues with the 1600 at this point (after nearly five months), and i am using mine a lot. The only upgrade i would considering changing over for is say the rumoured APS-C chip format that ZWO 'may be working on'., or commercialisation of sCMOS astro cameras. Rather than landfill i believe what is more likely is a big reduction in resale value of some cameras.

As to QSI, a brand is no guarantee of quality, i know of one member here on IIS, that bought a QSI for over $6k from Bintel, and was never able to get it to work. I watched him on dark site trips struggling to get it to produce an image. It didn't help that he was a beginner and probably got in over his head. He eventually got the s**ts with it and took a long caravan trip. By the time he tried again the warranty was over. He found out the camera was a dud from the factory i believe.
How many times do we hear of high end ccds with bad columns, or similiar pixel issues, right out of the box; or guys that have repeatedly returned these cameras to the manufacturer for fixes or debugging.

To date i have not heard, on CN or IIS, of one ASI1600 failure. Yes Beta testers uncovered some control concerns and as a result there have been a few driver updates but mostly these were required for inter-working with particular control software, like SGP. Not unusual for a new camera and Sam has quickly resolved any reported problem.

[SimmoW]

Yeah Suavi, I suppose every 2 yrs was an exaggeration. But don't many of us upgrade our mobile phones at a similar rate? Would you not want to update if the improvements were compelling?

Sadly I doubt there will be a revolution in filters, wheels or scopes, they're not reliant upon sensor tech or indeed any CPU factors.

[Camelopardalis]

Dunno what kind of revolution you're looking for, but the ZWO EFWmini and filters are decent value especially when bought with the 1600 ;)

[Peter Ward]

I use a SBIG STX16803. But candidly admit it's too big a camera and sensor for many, as it will test everything from your mount to focuser to the correction of your optical system.

As I image from light pollution central, maximizing signal and minimising noise are important to me, so I use every tool possible to make that happen e.g. well corrected optics, deep cooling of the sensor, seeing limited tracking, adaptive optics, accurate calibration data, etc.

For me the STT8300 delivered most bang for buck as it allowed all the above without being too over the top price wise...though candidly the Chinese stuff, while it does not have all the bells and whistles....is a good deal less expensive.

My ideal camera would have full frame chip, 4K res, ultra low read noise,
ultra-deep cooling, SBIG's self guide CFW and AO compatability.

[lazjen]

Filters: something to drive down the cost per unit; electronic id system on each filter to read the details of the filter - for automatic setup and discovery, information, etc.

Filter Wheels: Hold more filters (maybe a cartridge/magazine style?) particularly of the larger sizes, less overall/more compact, "real estate" used; easier access to individual filters for maintenance; quiet motors (still USB powered only, no extra power required); read the electronic id system mentioned for filters above; "self-cleaning" system for filters to remove dust; provide USB hub.

Some of the above exists for filter wheels, but certainly not all of it. Really, as it stands now, this part of the 'ecosystem" is quite primitive. :)

[Slawomir]

I did not mean to suggest that these new cameras do not last - I was referring to us upgrading astro cameras very often without any concerns in terms of environmental sustainability...

I really hope these new cameras will last many many years and will prove to be reliable and trouble-free products :-)

[g__day]

Next newbie question - for that camera and my listed targets - what filters and filter wheel are recommended and why (preferably a PC controlled filterwheel unit with ASCOM drivers that MaximDL and TSX + Camera add on can control)!

[glend]

Well ZWO have just released a compact filter wheel for the ASI1600MM which is ASCOM controlled. They can lalso supply filters and it can all be purchased as a bundle. It uses 31mm filters and they are located close to the sensor so vignetting is not an issue. Other filter wheels like Starlight, and QHY, work fine but you need to consider how you attach or the adaptor used, and spacing distances. I use a QHY wheel with 36mm filters which negate any vignetting risks, and the 1600 screws directly onto the wheel housing. Filters can be expensive, but there are some good value ones available as bundled sets, narrowband and broadband purchased together will save you money. I like the Baader filters.

[lazjen]

The Xagyl Filter wheel works wheel and it's very thin. I already had filters (1.25"), but if/when I buy more, I'll be going for a larger size set - at least 36mm like Glen has done. I can get the filter wheel and the camera closely connected such that I barely have any vignetting now - and I think I should be able to get rid of it with flats (fingers crossed).

[g__day]

Okay - new topic area - Vignetting from filters?

[Shiraz]

agreed, I find that the 1.25s are juuust big enough at f4. Would also get something slightly bigger if buying from scratch. Vignetting? - signal is down roughly 30% in the corners, but that only makes a slight difference to the SNR after flat fielding.

[RickS]

Actually, you can ignore many of them when comparing a sequence of short subs with a long sub of equivalent length because they have exactly the same effect in both cases. Many of these items aren't even noise, but sources of unwanted signal... the difference is significant. But there's little point in discussing further if you think that physics and mathematics aren't up to the task of modelling a sensor enough to derive useful imaging parameters.

Cheers,
Rick.

[Peter Ward]

I suspect we are talking about the same thing but coming at it from different perspectives. SNR increases linearly with time if your quarry is down at the read noise limit of your camera. Adding multiple short images however does not improve the SNR in a linear fashion here. It only improves the the square root of the number of exposures. So adding say 10 ten second exposures will improve things by about a factor of 3, compared to a factor of 10 if we take a single 100 second exposure.

This all changes when the signal level pops up a bit, and puts us into the shot or photon noise limit of your camera. In this region, SNR improves by the square root of total exposure time. One long exposure is also likely to be hammered by other noise sources (eg cosmic rays) so it makes sense to take sufficiently many subs to weed out any noise using statistical techniques.

Quality telescope time is however what I don't get a lot of....which I also suspect is being ignored here. Yes, the theory is sound...but how much time is practically required to get the data? (just downloading a sub takes 13 seconds with my camera)

My experience has always been: better data with less telescope time by taking deeper subs. What others choose to do is up to them.

[Placidus]

I agree with Peter's comments about very faint targets where read noise is the primary problem. Ignoring light pollution and sky glow, I've had a crack showing this quantitatively here (http://www.iceinspace.com.au/forum/showthread.php?p=1274920#post127492 0).

I don't think I'm disagreeing with anything that Rick or Colin has said, either, just trying to make it quantitative.

Best,
Mike

[g__day]

Question on the ASi 1600MM- Coolded - why did they only go for 12 bit DAC and will this limit the camera on faint shots?

BTW - liked the linked post on the SNR thread - thanks!

[Camelopardalis]

It's a micro 4/3 sensor so they had to go with whatever ADC was on the chip.

Legend has it that you can gain back the extra bits of precision through stacking.

[Atmos]

With 256 subs you bring it from 12 bit back to 16 bit :)

[Camelopardalis]

In all fairness, 12-bit is still more than I'd get from a DSLR once the ISO is bumped up a bit....

[Shiraz]

almost all 16 bit cameras generally only have 11-12 bits of real information - the bottom 4-5 bits are dominated by read noise, so are useless. 16 bit files from the ASI1600 have the bottom 4 bits full of zeros - I guess they could have put noise in there, which would have been equally useless. They have not lost any real signal by using 12 bits. Some CMOS chips are going over to 14 bits (quite possibly for marketing purposes?), but they are not yet available in mono cooled cameras.

[gregbradley]

That may be but 16 bit medium format cameras are known for subtle transitions between colours and tonality. The extra differentiation 16bit provides does add something to the image.

Greg.

[Slawomir]

Just a question out of curiosity - how many bits are dominated by read noise in ASI1600 at unity gain or when adjusting the gain for longer subs?

Would this be a correct way to determining how many bits are really available for signal in my case?

Gain = 0.16 meaning 1 electron results in 1/0.16 = 6.25 ADU
Read noise = 4e thus 4 x 6.25 = 25 ADU equalling about 5 bits (2^5) taken by read noise leaving me with 11 bits per sub for data?

Ta
Suavi

[Shiraz]

that's the way I would do it Suavi. gosh that read noise is low :thumbsup:.
I think that the dynamic range data on the 1600 can be read off from the graphs on the ZWO website

[Camelopardalis]

From measurements with my ASI1600 and plugging the numbers in as Suavi did, I get...

Gain = 75 => 16.4 ADU
Gain = 139 => 25.6 ADU

Methinks at a dark site I'll be using gain=75 and suck up the longer exposures ;)

[Slawomir]

Does it mean that at unity gain one is left with 12-5= 7 bits (or thereabouts) available for real information?

[glend]

The original poster, and others, may find the QHY163M Beta Testing thread, on Cloudy Nights, worth following. The initial testers seem to be encountering some of the same things that that ASI1600 testers did. One bonus on the QHY163M is a heated sensor window (Not that I have had any problems with ASI1600 fogging or internal condensation), but it would be a nice feature to have imho.

Thread is here:

http://www.cloudynights.com/topic/551681-qhy163m-beta-is-in/

[Camelopardalis]

Nah I was using 16-bit numbers so it's just over 11 bits of dynamic range at unity gain (=139) and 12 at gain=75

[Slawomir]

I thought 16bit files from ASI have first 4 bits = zero :question:

[Shiraz]

the bottom 4 bits are padded with zeros after the ADC conversion (ie the noise is multiplied by 16 as well as the signal). At unity gain, the maximum signal is either 4000 electrons or 64000 ADU and the noise is either ~1.6 electrons or ~25.6 ADU - take your pick on how to represent things, but it is an extra complication when trying to understand this camera.

[Slawomir]

Thanks Ray, I think I have enough info for now :)