Quote:
Originally Posted by RickS
I have heard a couple of people suggest that binning a KAF8300 doesn't appear to give a significant increase in effective well depth. I haven't ever tried binning on my SX H18, but I might have a play with a light box on the weekend (if it's cloudy) and see if I can test this hypothesis.
Cheers,
Rick.
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Here's a link that explains it if you can understand it. The writer hasn't bothered to define the unusual words but you get the idea that the way the CCD is read affects the result when binning and it isn't a straight quadrupling by binning 2x2 but there is an increase.
7.4 micron would not be in the middle of 200 and 400mm focal length but much longer.
It comes down to sampling theory.
My understanding of this is the Nyquist theory of sampling which states a good sample requires a minimum of 2X to get a good sample.
In other words you want your pixels to be of a size that will gather enough data to get decent resolution but not too many that simply reduces down too much the sensitivity ie several pixels trying to get the same amount of light - its spread too thin. You don't want it spread too thick (undersampling) and you don't want it spread to thin (oversampling).
One way to work it out on a simple easy to follow rule is 1 arc sec/pixel.
So if your seeing is 3 arc seconds you plug in the focal length, aperture and pixel size of the camera into the Wodaski CCD calculator and you get an arc seconds per pixel number.
I shoot for .66 arc seconds per pixel but what you will find with super short focal lengths is that number will get large even with small pixelled cameras.
Having said that this is just a guide. There are numerous awesome FSQ106 images using 16803 chips with 3.6 arc seconds per pixel.
One way of looking at that is it makes the system less prone to the effects of seeing.
These calculations I think are more important for long focal length scopes where small pixels will wreck an image. Larger pixels in shorter focal lengths will still be good but not the other way round.
Take other factors into consideration as well like QE, well depth, read noise.
But recent Kodak chips largely have similar performance one to the next once you get past the 16803. The really large chips tend to have very poor performance characteristics for astronomy. Like the KAF39000, 40000 (one of the better large chips) and 50100. Really low QE, small wells, noise is fine.
KAI versus KAF. As pointed out there are 2 main advantages of the KAI chips - electronic shutter and no ghost images. KAF tend to have higher QE though. KAI only go up to 28.8mp, KAF go up to 50mp.
The KAI series seem to have more of the new True Sense one shot colour matrix with far better low light performance.
If you were doing one shot colour I would try out the KAI4050 before the tried and true KAF4021 one shot colour. Noone has posted an image with one but on paper the KAI4050 should be better as a one shot colour.
Most True Sense sensors are 5.5 microns which is quite small for Kodak and only the 8300 is smaller with 5.4 microns (insignificant difference in size).
I have seen for myself the difference with 8300 in fast refractors. Definitely the small pixels shine. The 9 micron pixels are a good compromise but the small ones take on an edge in APOs as they tend to be fairly short in focal length (given good seeing that is).
I hope this helps a bit.
Probably more important than the chip is the camera itself. A FLI or Apogee and QSI as well as Starlight Express seem to be the current leaders. SBIG has a good range and lots of accessories. Moravian are yet to be proven and perhaps still working out the little bugs.QHY are popular because of price and seem to be good bang for buck so is Atik. How they compare in other areas I don't know. Processing cleans up a lot of the little differences.
The main points to evaluate cameras are:
1. Price/value. No point in looking at a $6000 camera if your budget is $2500. Its a very competitive market these days and the cheaper cameras seem to make big strides forward.
2. Cooling. There is no substitute for powerful cooling and cooling solves almost all CCD problems and if anything no brand cools hard enough. FLI and Apogee have the most powerful cooling, Apogee takes 30 minutes plus to get there plus the firmware takes over so you can't utilise alll of the cooling power available. It is a flawed cooling system with incorrect engineering assumptions. FLI is best, QSI Series 6 is excellent, Apogee is great with small chips (if you're patient). SBIG ST8300 may have reasonable cooling but possibly a bit weak but good enough for 8300 chip.
Professional CCD cameras cool to -100C which is where some chips need to be to fully handle ghost images (more for back thinned chips).
As chips age they get more hot pixels or develop lines. Strong cooling fades these defects away. I noticed I have a vertical line in my Microline 8300. I don't notice it because its only there at warmer temps. At normal cooling it completely disappears. I run it -35C in summer and -40C in winter.
3. Sealed CCD chamber with inert gas installed. This prevents frosting. SBIG uses a desiccant plug and whilst this works well it is just something you have to service from time to time.
4. With the sealed chamber comes the option of no cover slip on the CCD which gains you an extra 2% QE and also no small halos on bright stars in fast systems from the cover slip (minor issue really but its something).
5. Download speed and instant connection. My main dislike of SBIG cameras (STX may not have this problem) is the download of the driver from the computer when it powers up. It makes it lag, sometimes it fails, if the power or any cable is disturbed it stops, and needs to have CCDsoft shut down, repower the camera and then reboot CCDsoft - a real drag. If you have a reliable SBIG camera and reliable cables and power supply this is probably no big deal. I have not experienced that and I estimate I have had to do this 300 times.
I love the instant connection of the FLI and Apogee cameras. They have a built in memory buffer and the driver is on board. Once turned on you can unplug them from the computer and they are still going once plugged back in. You can't do that with an SBIG camera except perhap STX (I assume). For me that is a deal breaker but for you maybe not.
6. Download speeds. FLI are fastest. I think the new QSI series 6 are now fast as well. Apogee is quite a bit slower but fast compared to other brands. My FLI cameras download 1x1 in 1 second. Great for dusk flats etc.
Also self guiding in SBIG cameras gets stopped during downloads. An STL11 takes 26 seconds to download a 1x1 image. That means your tracking has been building up errors and you need to program in at least a 30 second delay for the guiding to catch up before the next exposure.
Not so with STX. Also not with FLI or Apogee or QSI or others as they use a different guide chips.
7. Accessories. SBIG has the best range. FLI has filter wheels and focuser but no guide cameras nor offaxis guiders. Apogee also. Starlight Express has the next best range. QSI also offers the filter wheel and guider in one package which is a fabulous idea and better than SBIG's self guiding as you can guide normally though narrowband filters.
8. Noise level of electronics. This should really be up higher on the list.
I am not sure of the others but FLI, Apogee and Starlight Express have super low noise electronics and you almost don't need darks.
9. After sales service and resale value. Speaks for itself.
10. Futureproof.
The STL design had a flaw in that they made the opening too small. So advances in CCD size meant they couldn't fit the next generation chips in the body. A big and costly mistake. FLI and Apogee have very large openings and will be able to handle any size chip for some time. FLI can put in any chip even the Kodak 50mp monster with no sweat.
QSI 6 series is limited to the KAF8300 at the largest and are working on another body for the larger chips. All the others seem to be able to accomodate up to 16803 at this time. FLI Microline can handle any sized chip. Apogee Ascent only KAI chips and limited to 29mp, Alta body anything. QSI the 8300. Starlight Express offer up to 16803, QHY and Atik I think both offer up to 16803.
11. Reliability. Obvious.
12. Weight:
Here is a loaded one. FLI Proline is arguably the best but its main problem is it is very heavy. I don't know what an SBIG STX weighs but it may well be the Proline is the heaviest of all these cameras. Apogee Alta is a few lbs lighter. But the good news is FLI Microline is lighter and more compact than a lot and can handle any chip. On a 16803 chip apparently the Microline cools to within 3 or 4C of the Proline. That may mean -30C instead of -35C on a 16803 chip. You would get -25C with a standard Alta Apogee or similar with the DO9 body (but that probably makes the Alta the same weight as the Proline).
Weight is a big issue with some scopes. Many scopes can not handle the heavy weight of a Proline, some can. A lens is not an issue as it will not be supporting the camera.
Phew - I did not mean it to be such a long post but there is a lot to take in on CCD cameras and its such a big investment you want to make sure you get it right.
If I were getting another 8300 camera I'd go QSI Series 6 as I like the idea of built in filter wheel with cheaper smaller filters and a built in offaixs guider. I love my FLI Microline though.
If I were getting another large chipped camera I would go with FLI Microline. Its a bit cheaper but mostly because it is way lighter and being lighter like heavy cooling, saves you a lot of problems.
Greg.