#41  
Old 07-12-2009, 01:26 PM
Gerald Sargent
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SBIG or QHY

I have ST4000 and QHY8 Pro, former has 15x15mm chip latter 20x15mm,
both colour. QHY is far less noisy than the ST, QHY8's do not need dark
frames. Price difference is significant
I too have had long discussions with Theo and decided that my QHY8 Pro
was the best bet. Think on very carefully your need for the small pixels,
The QHY9 and SBIG restrict you to short focal lengths.
Using the QHY8 (very large chip) and binning to 2x2 or 3.3 on can get
very sensitive "pixels" for long focus work. and still have a decent size chip
The merits of the "for free" software with the SBIG are to my mind
overrated. CCDOps is free anyway and can only be used with SBIG
cameras. CCDSoft - well some use it and like it, but I much prefer the
versatility of Maxim. Nebulosity 2 is also a good alternative and has
drivers for QHY's.
For 2" filters, which I use, the QHY filter wheel is excellent and will fit
any camera that uses "T" threads.Best wishes Gerald.

Last edited by Gerald Sargent; 07-12-2009 at 01:36 PM. Reason: message not complete
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  #42  
Old 07-12-2009, 07:33 PM
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Gerald correct me if I am wrong but the difference in pixel size between the 8 and 9 cameras is 2.4um (qhy 8 = 7.8um and qhy 9 = 5.4um). Both cameras can be binned as can the SBIG so I am not sure how the 9 or ST 8300 would limit you to short focal lengths. Is is always better to over sample so long as it does not get too soft.

Mark
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  #43  
Old 07-12-2009, 07:46 PM
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A lot of people use cameras with small pixels in long focal length setups. Fred (Bassnut) uses his ST10XME in a 12" SCT @ F/10 sometimes, the ST10XME has 6.8um pixels, half way between that of the QHY8/ST4K and the QHY9/ST8300.. Given his results I dare say that you could use the KAF8300 sensor in the same optical configuration without issue.. Granted, the seeing would have to be very good to support the resolution, having said that, Adaptive optics units are becoming widely available for different cameras with Orion making an AO unit for any camera, Starlight Xpress having an AO unit that can be used with any camera...
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  #44  
Old 07-12-2009, 08:30 PM
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Quote:
Originally Posted by marki View Post
Gerald correct me if I am wrong but the difference in pixel size between the 8 and 9 cameras is 2.4um (qhy 8 = 7.8um and qhy 9 = 5.4um). Both cameras can be binned as can the SBIG so I am not sure how the 9 or ST 8300 would limit you to short focal lengths. Is is always better to over sample so long as it does not get too soft.

Mark
The Kodak 8300 CCD may become over sampled when used on a long focal length scope. This is of course way better than under sampled, but pointless because your seeing prevents any benefit. It really benifits a medium to low focal length scope.

Theo
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  #45  
Old 07-12-2009, 09:09 PM
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Quote:
Originally Posted by Gama View Post
The Kodak 8300 CCD may become over sampled when used on a long focal length scope. This is of course way better than under sampled, but pointless because your seeing prevents any benefit. It really benifits a medium to low focal length scope.

Theo
Yes Theo but that is a whole lot different then being unuseable on a long focal scope . Plus 2 x 2 binning will do the trick if necessary.

Mark
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  #46  
Old 07-12-2009, 09:24 PM
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IMO all the above mentioned cameras are fine for long FL (say up to 3m), oversampling is no problem, and anyway the 8300 at 3m FL and bin2 is .74 arcsecs, sweet (and good dynamic range). Decovolute filter (the single most powerfull software tool for post processing) works better with some oversampling also.

Ive considered the 8300 chip too, the low noise is a bonus, but for me QE is very important. 10hrs Ha at 80% QE on an ST10XME becomes 20hrs with the 8300s 40% QE.

Ive lately taken 20min subs with max ADUs in the hundreds (out of 65000!) that were just buried in noise with an ST10. Dark subtraction fixed them right up. Low noise is great, but good darks also do the trick on noisy chips like the ST10.
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  #47  
Old 07-12-2009, 10:23 PM
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Having used a 8300 chip the biggest problem I found was the shallow well depth. It was extremely dificult to take short enough images to capture fine detail while still maintaining star detail and colour. 5 minute exposures almost always over saturated stars. NB imaging was a lot more productive but who wants to only image in NB. Some do I suppose.
The other big thing I did find with the chip was it seemed to generate a lot of hot pixels when taking subs longer than 10 minutes. To reduce this and the noise levels the cooling needed to be crancked right up.
I didn't find sampling to be a major problem even when used on the VC200L at 1800mm although it did improve when the FR was used lowering the focal length down to 1200mm.
I now use a QHY8Pro and contemplated another QHY9 for NB imaging but think I will wait until I can get a CCD with a bit of depth in the well. Having played with a ST4K with a mono chip I would much rather go down this path as I feel the overall results were better.
Hopefully the new pricing will flow on into other cameras in all ranges of cameras and I will think about an upgrade at this point.
Maybe competition in the Astro CCD market will force prices down overall. Lets hope this is just the beginning.
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  #48  
Old 07-12-2009, 10:50 PM
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I have to concur with Fred on the point of QE. I can do things with the ST-10 that frankly you can't with the QHY, merely because of sensitivity.

On the subject of oversampling, I'm yet to be convinced that it's a bad thing, I suppose I'm spoilt as I have the QE, but I find that I can tell the difference in resolution between binned and unbinned images.

For instance have a look at two subs from the recent NGC 2070 images I have done. One is Ha unbinned, the other is red and binned 2x2.

I can definitely see that the binned image stars are blocky.

Cheers
Stuart
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  #49  
Old 08-12-2009, 06:56 AM
Hagar (Doug)
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Quote:
Originally Posted by rat156 View Post
I have to concur with Fred on the point of QE. I can do things with the ST-10 that frankly you can't with the QHY, merely because of sensitivity.

On the subject of oversampling, I'm yet to be convinced that it's a bad thing, I suppose I'm spoilt as I have the QE, but I find that I can tell the difference in resolution between binned and unbinned images.

For instance have a look at two subs from the recent NGC 2070 images I have done. One is Ha unbinned, the other is red and binned 2x2.

I can definitely see that the binned image stars are blocky.

Cheers
Stuart
Hi Stuart, I don't consider this a very true representation of a binned and unbinned image. If both images were Ha or both were red channel images I would expect this to be a much more accurate representation. Ha images by default will have smaller stars purely by virtue of the narrower wave length of the light collected.
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  #50  
Old 08-12-2009, 07:10 AM
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Hi Doug,

Why would this be so? I can't think of a good reason why filtering out all the spectrum except a narrow band in the red region is better than a wider band also in the red region?

It's not the overall size I was trying to point out, it's the sampling. The red stars are blocky, i.e. not as well sampled as the Ha stars, which show a nice curve to them. The images weren't taken on the same night, so the seeing conditions may not have been the same. The nebulosity doesn't seem to be affected by the sampling at all, so I suppose if you're only interested in diffuse objects then the sampling rate doesn't matter that much?

FYI according to CCDStack the FWHM of the red image stars is 3.1 - 3.3, the Ha is 3.4 - 3.6, depending on the star involved.

Grab the images and blow them up a bit (but don't resample them), you'll see what I mean.

Cheers
Stuart
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  #51  
Old 08-12-2009, 01:57 PM
Gerald Sargent
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SGIB or QHY9

In reply to the questions put to me about oversampling, I agree
that over sampling is not necessarily a bad thing, I am generally
concerned (for my own imaging) with getting the image within
the available space on the chip, in which case oversampling is
not an option that is of concern to me
What did get my interest was the possibility of getting better
image of those small targets, ie many of the small "balls of fluff"
that are galaxies unresolvable by 7.4 micron pixels, a case where
say 2-3 micron pixels would be of use but then the QE starts to
become an issue. So I suppose I must recourse to barlows to get
around this problem. Gerald.
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  #52  
Old 08-12-2009, 02:41 PM
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I'd like to see a Sony data sheet that shows an absolute QE for their sensors. Every (Sony) data sheet I've seen to date has relative QE's....a useless figure IMHO.

As far as I know, Sony don't publish this data...hence I'd question (QHY's) claims of 50% QE in H-Alpha for *any* Bayer matrix sensor.

I'd however be very happy to be shown a suitable web link.....
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  #53  
Old 08-12-2009, 04:18 PM
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Quote:
Originally Posted by Peter Ward View Post
I'd like to see a Sony data sheet that shows an absolute QE for their sensors. Every (Sony) data sheet I've seen to date has relative QE's....a useless figure IMHO.

As far as I know, Sony don't publish this data...hence I'd question (QHY's) claims of 50% QE in H-Alpha for *any* Bayer matrix sensor.

I'd however be very happy to be shown a suitable web link.....
You may want to change the "QHY" claim and put everyone that sells cameras with this chip in it, so get YOUR facts right Peter before blowing your horn !.

On your question though, its the sensor that has a total QE, NOT after debayer film QE. The "True" final product actually hitting the surface of the Sensor, is of course less. But is still advertised as the sensor QE. And before you say anything else, SBIG also do this too. They will put the same QE for the mono and color of the same chip, e.g 11000M/CM.
Further, take the ICX-285 from Sony also shows a "Relative" QE of xx but Sony DONT state the "Absolute" QE on this either except as a relative value, yet everyone (FLI, APOGEE, etc) prints the QE as an absolute value with reference to 100 % . Go tell them, oh wait, you wont..

Lastly (I hope) the thread is on a different subject, NOT the Sony Sensors QE.


Theo

Last edited by Gama; 08-12-2009 at 04:59 PM.
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  #54  
Old 08-12-2009, 05:43 PM
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..., so get YOUR facts right Peter before blowing your horn !.

.................


Theo
Que? All I asked for was an absolute QE curve for Sony sensors.

If the QHY guy can't supply a link, I can only assume Sony doesn't publish them.

QE 101:

Absolute Quantum efficiency (AQE) is the number of photons detected by a sensor, divided by the total number of photons. A perfect sensor detects 100 out of 100 photons.

Relative quantum efficiency is AQE * K where K is a number less than or equal to 1.0

The number K could be 0.5 or 0.25 making the *real* AQE of a sensor
lower by a factor or 2x or 4x. Knowing K is *really* important. Capish?

Kodak do publish AQE curves.

I am not saying Sony chips are rubbish....they have some commendable traits.

All camera manufacturers rely upon the CCD foundry's data, yet Sony don't seem to make this *rather important* data freely available.

If they did it would be nice to be able to compare Apples with Apples.
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  #55  
Old 08-12-2009, 06:07 PM
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I asked you why you keep refreing to QHY, your comment should be a generalised question. As i said, and of course you dont listen, why would you, all camera manufacturers including FLI, and Apogee etc use the same Sony sensors, but you say squat about obtaining the same info from them.. Peter, blab on..

Start another thread if you want, but leave this to the questions originally asked.

Theo.
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  #56  
Old 08-12-2009, 06:23 PM
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Quote:
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I asked you why you keep refreing to QHY..
Yes, I suppose once is a constant *referal*.

I have no axe to grind here Theo. Fli and Apogee don't have the data either.

Lighten up.

P.S. The Sony datasheet for this CCD can be found here
http://www.datasheetcatalog.org/data...y/a6803068.pdf (relative QE's only I'm afraid)

Last edited by Peter Ward; 08-12-2009 at 08:21 PM.
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  #57  
Old 08-12-2009, 09:30 PM
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Quote:
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Start another thread if you want, but leave this to the questions originally asked.
Umm, not to be a smartar$e, but the original question was SBIG or QHY9.

Seems valid that Peter should refer to the two manufacturers in question. For the uninitiated questions of QE, pixel size, sampling etc. can seem a bit esoteric, but these numbers do mean stuff. Whether any of these is particularly important to your specific imaging equipment is something only you can decide, but you have to learn about them.

Peter refers to the QE because, in general, SBIG have used Kodak chips that excel in this area. If sensitivity is high on the list that becomes important.

Theo refers to chip size as the QHY range typically get you a larger chip for the price. If maximum FOV is important to you then that moves chip size up the list.

Then there's the quite complex issue of sampling. Ideally you should match the pixel size of your camera to the focal length of your scope, but that would require far too much equipment for most, particularly if you like to indulge in both long and short FL imaging.

You'll notice that virtually nobody refers to megapixels anymore, as this number is pretty much meaningless other than the general relationship that more pixels equals smaller pixels.

Cheers
Stuart
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  #58  
Old 08-12-2009, 10:27 PM
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Umm, not to be a smartar$e, but the original question was SBIG or QHY9.
Your dead right Stuart. The question was about which camera to purchase an SBIG 8300 or QHY9 (8300) Both pretty well the same cameras at least as far as the CCD is concerned but Peters comments could easily be construed as a direct attack on the QHY range of cameras. As an SBIG dealer Peter appears to be holding up the SBIG Halo and making an open attempt to degrade the standing of the QHY range in general at least from a performance point of view. This really is irrelevant to this question.

Cameras are and will always be purchased on terms such as performance, price, personal requirements and aftersales service. I doubt the need for such an attack.
In this case QHY have priced the QHY9 well below the SBIG but then SBIG produce a much bigger range of CCD's than QHY so we all have plenty of cameras to choose from at lots of very diferent prices with very diferent features.
Great to have some choice.
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  #59  
Old 08-12-2009, 11:05 PM
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I am just glad SBIG and hopefully other manufacturers have seen the light and are making an effort to cater for this sector of the market. I believe QHY have played a big part in not only dropping the cost of CCD ownership but also producing excellent cameras to boot giving us a greater choice. For us as amatures this can only be a good thing. I would imagine the new ST8300 will be an excellent camera as I belive the QHY9 is so the worst dilema you have is which one to buy. Great times indeed .

Mark
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  #60  
Old 08-12-2009, 11:29 PM
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The Sbig and Qhy camera being discussed in the OP use the Kodak chip. What is the purpose of raising an issue about a Sony chip that is not even in the camera's being discussed. Based on the OP the discussion is comparing two camera with the same Kodak sensor, can we stay on topic here guys. I to am tossing up between these two cameras down the track and would like to see more from actual users.

My only experince with a SBIG was my friend ST-237 and it was the first hands on i had with a CCD camera. It was awesome compared to the later borrowed DSI experience i had. The software, the camera, the filters it all just worked. I would like to know how true this is for the ST8300 and the Qhy9 users.

I would suggest a seperate thread to discuss AQE, as it seems to merit discussion on weahter such a curve could be derived for the Sony's.

Also its worth considering that it is the very comppetivie pricing of the Qhy that has brought abou the recent response in lowering of prices by other establisedh companies. Were it not for Qhy what would the ST8300 cost? competition is good and glad its there in this. I would like to see more affordable cameras like this in the future.

Last edited by netwolf; 08-12-2009 at 11:40 PM.
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