Quote:
Originally Posted by Atmos
With the sensor thread heating up recently I have been doing some dirty calculations and from what I can tell the KAF-16803 is probably one of the cleanest on the market at the moment (haven't compared it against anything without ABG but they should be even cleaner). Although the PL16803 has a read noise of 10e- and comparing it against the MLx814 which has a read noise of 2e-, you may at first consider the MLx814 to be far cleaner but in reality it isn't. This is where well depth becomes important as well, the 16803 has 100,000e- depth while the 814 has ~ 15,000e-, with a gain of 1.53e-/ADU and 0.23e-/ADU.
Ray can correct me if I am wrong here but that would ultimately make the 16803 ~ 33% cleaner? It may have a much higher read noise but the gain offsets it. That is my understanding of it anyway. This is meant irrespective of focal length, just in generalisation.
|
Hi Colin. My understanding is that the read noise determines how long the subs must be to reach the point where read noise is overwhelmed by sky noise. The 16803 requires >20x as long to get to "sky limited" as the 814, based on the figures you quote, so the 16803 needs much longer subs. Happily, it can handle longer subs without overloading, because it has very deep wells. As a generalisation, if you give the 814 lots of short subs and the 16803 a few long subs, you should end up at about the same point after roughly the same total integration time (ie, the final image will have about the same SNR and very roughly about the same dynamic range). So yes, I think that the 16803 could end up about as clean as the 814, but at the cost of requiring very much longer subs - it does seem to be a very nice chip.
In the situation where read noise dominates (eg narrowband), I think that the 814 will end up with an advantage, but of course it has small pixels, so you will be limited in how big a scope you can use - the 16803 can be used with much bigger aperture scopes, which is a major advantage in theory. However, the issue of scope size is also not clear cut. For illustration of this, consider that a 694 is well matched to ~ 1.2 m fl scopes and there are a few of these at f4 or thereabouts, including some low cost corrected Newtonians. 16803 pixels match to ~2.4 m scopes, but f4 scopes at these fls will be either hideously expensive or very unwieldy - so most scopes for the 9 micron chips end up around f8 (ie they have ~the same apertures as the fast scopes used for the smaller chips). Thus this potential performance advantage of the 9 micron chips is not fully realised at present. If GSO ever brings out an affordable 20inch f4 RH, the shouting will all be over - 9 micron will reign supreme if you have a strong enough mount to carry a large fast scope.