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Old 01-11-2011, 03:33 PM
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gregbradley
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Join Date: Feb 2006
Location: Sydney
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Peter makes some good points. SBIG's strength has long been their self guiding cameras, a good range of accessories and good customer service. Their prices generally are reasonable and there are many fabulous images on the net.

I have had 4 SBIG cameras - ST2000XM, 2 STL11's (one shot colour and mono class 2) and an ST402 (I still use).

These cameras are ruggedly built and reliable generally. I was able to take good images with them and the self guiding is very handy when doing LRGB imaging. I particularly liked the STL11's with the integrated filter wheel.

I don't know much about the STX apart from it being a sophisticated camera with many potential and perhaps not fully sorted guiding features.

My main critique of SBIG cameras would be cooling could be a bit stronger in the case of the STL11 (mine did 43C below ambient which is quite strong really). STX on paper sounds to have good cooling.
I understand the point about accurate cooling and callibration and I have seen that effect Peter is referring to myself. Try using a 30C dark on a -35C image with a large chipped camera that requires very accurate flats and you will have big trouble.

So with regards to noise defects etc the first and most important feature of the camera for a given chip is powerful cooling and clean electronics. Not all cameras have the same read noise - they vary.

The next main thing would be the reliance on a computer for the driver when it powers up. This places too heavy a dependence on the computer. This may not be a problem for most. I found it was an issue far too often. STX again I believe has onboard memory for the drivers (I hope!).

SBIG also seems to have poorer performing electronics in terms of noise. Whilst my STL cameras with the KAI11002 chip would dark subtract well, the images were rather noisy. I thought this would be the same for every camera with that chip as the noise was coming from the chip.

Not so. Mike Sidonio posted a 10 minute dark from his FLI Proline 11002 and I posted my old 10 minute dark same temp from my STL11 class 2. Totally chalk and cheese. The STL was way way noisier. So the readout electronics boards or the analogue to digital to converter electronics vary a lot in quality. As Peter says this dark subtracts out so perhaps not the biggest problem in the world if other factors are good. However I would point out it does place more emphasis on accurate darks.
Both my Apogee and FLI cameras were quite clean in their electronics and dark subtraction is far less important.

I found both FLI and Apogee to cool to the same accuracy (or at least I think so, they both state a temp readout to 3 decimal places) as my SBIGs. Perhaps the SBIG is a bit more accurate there. I am not 100% certain of this but I can say the darks match the lights very accurately of both Apogee and FLI. My opinion is that the darks matching the lights with these very clean electronics brands is more important with larger chips to get accurate flat fielding (there is always some vignetting) than with smaller chips.

With regard to the importance of cooling. Powerful cooling has several
advantages. Apart from less noise which is the obvious advantage there are less artifacts. With my STL11 it had a vertical line that did not always dark subtract out and would present a problem late in the processing. The line itself is not really a fault of the camera but heavier cooling makes these lines almost totally clear away. Like -35C.

A sealed CCD chamber is also important. No desiccant is needed to be serviced. I believe the Argon gas also helps protect the CCD itself. It also allows a no cover slip option.

I know Peter had an expensive U47 Alta which is a high end ultra sensitive chip known as back thinned (they literally thin the chip so its quite thin and it is mounted back to front and these show the patterns of the thinning process easily). These back thinned chips require accurate flats and are prone to residual bulk images (ghosting). This requires an infrared flash and flush several times before the actual image to fill up the deep substrate where the ghost image gets trapped. This flush stops a ghost image from forming but it means extra noise as this flush leaks out during an exposure. Only powerful cooling handles that. FLI at -35C for a large chip is one of the strongest cooling and technically that is insufficent (-100C is). But it works in practice with slightly elevated noise. Apogee has a ghost image fix (I believe the FLI system is the superior one). Ghost imaging is a problem with KAF Full frame sensor technology and not KAI series chips due to different chip architecture.

One of the best images I have seen on the net lately are done by Wolfgang Promper with a 16 inch ASA Cassegrain (Philip Keller) and a FLI Proline 4240 which is one of these high QE (sensitivity) chips by a company called E2V. 90% QE and those images are routinely brighter and more luminous compared to other images of the same object, often he does this with modest exposure times.

As far as shutters go from Apogee or FLI I found both to be good but yes you need at least 3 seconds for a 20,000ADU flat (ADU is a measure of brightness on a chip) to not show the shutter. That may be very difficult with a back thinned 95% QE chip.
Perhaps with one of those illuminating panels a lot are using where you can control the light it may have been more practical. I use 3-10 seconds for flats and the inside of my observatory is painted matt black and a bit of light comes in from the gap of the wall and roof. I put the
white material over the end of my CDK17 and I can do 10 second flats in the middle of the day. Very handy. Flats work well once flat dark subtracted.

KAI chips have an electronic shutter video output option so you can take really short shots without a shutter.

I would use an SBIG again. Although I have become spoilt by instant and stable connections, 1 second downloads, super low noise, powerful cooling. I think the Proline is quite heavy and can be a problem for some scopes unless they have a beefy focuser. That would probably be the same for STX and Apogee Alta. The FLI Proline also has a minor defect in that some brighter stars have a little diagional spike on them almost like a diffraction spike. The same chip in a FLI Microline does not have these. I personally don't mind them but they should not be there. My ML8300 has no spikes.

SBIG does have a good range of accessories that are integrated and the many fabulous images prove they are good. Non STX models though are getting a bit dated and need a bit of a refresh (cleaner electronics, faster downloads, self guiding that does not get interrupted by downloads, sealed chambers, an image memory buffer, more powerful cooling, a larger and cleaner guide chip) to remain competitive as there are now a lot of camera makers and they all seem to be improving their models each year. QSI seems to be developing their models the fastest and the current go getters. Their range of chips is limited though until they get the bigger model out which could be a while. Then they will need to do the 1-2 year sorting out of issues that arise in the field.

No one camera is perfect for your needs. Some chips give big widefield images others close up detail, some super sensitive others not bad, some one shot colour some not. Like scopes, you end up wanting a few to be able to capture a particular image!

Greg.
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