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  #81  
Old 07-10-2016, 07:29 AM
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SimmoW (SIMON)
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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.
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  #82  
Old 07-10-2016, 07:59 AM
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Camelopardalis (Dunk)
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Originally Posted by SimmoW View Post
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.
Dunno what kind of revolution you're looking for, but the ZWO EFWmini and filters are decent value especially when bought with the 1600
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  #83  
Old 07-10-2016, 08:40 AM
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Originally Posted by g__day View Post
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
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.
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  #84  
Old 07-10-2016, 08:51 AM
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lazjen (Chris)
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Quote:
Originally Posted by Camelopardalis View Post
Dunno what kind of revolution you're looking for, but the ZWO EFWmini and filters are decent value especially when bought with the 1600
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.
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  #85  
Old 07-10-2016, 09:30 AM
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Originally Posted by glend View Post
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.
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 :-)
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  #86  
Old 07-10-2016, 01:13 PM
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g__day (Matthew)
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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)!
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  #87  
Old 07-10-2016, 02:42 PM
glend (Glen)
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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.
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  #88  
Old 07-10-2016, 03:17 PM
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lazjen (Chris)
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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).
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  #89  
Old 07-10-2016, 04:02 PM
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Okay - new topic area - Vignetting from filters?
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  #90  
Old 07-10-2016, 04:04 PM
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Quote:
Originally Posted by lazjen View Post
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).
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.
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  #91  
Old 07-10-2016, 09:57 PM
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Originally Posted by Peter Ward View Post
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.
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.
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  #92  
Old 08-10-2016, 02:20 PM
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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.
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.
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  #93  
Old 10-10-2016, 11:42 AM
Placidus (Mike and Trish)
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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.

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

Best,
Mike
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  #94  
Old 10-10-2016, 12:13 PM
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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!
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  #95  
Old 10-10-2016, 08:21 PM
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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.
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  #96  
Old 10-10-2016, 08:28 PM
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Originally Posted by g__day View Post
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!
With 256 subs you bring it from 12 bit back to 16 bit
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  #97  
Old 10-10-2016, 08:30 PM
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In all fairness, 12-bit is still more than I'd get from a DSLR once the ISO is bumped up a bit....
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  #98  
Old 10-10-2016, 08:32 PM
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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.
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  #99  
Old 11-10-2016, 06:02 AM
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Quote:
Originally Posted by Shiraz View Post
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.
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.
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  #100  
Old 11-10-2016, 02:38 PM
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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.
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

Last edited by Slawomir; 11-10-2016 at 03:13 PM.
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