Quote:
Originally Posted by Peter Ward
Sorry Phil but I suspect you analysis is flawed. You are comparing 23 units of flux vs 15 (and even that isn't correct...but I'm lazy and couldn't be bothered with the math  )
In terms of time to get data, then certainly things get a little muddy.
But in terms of spectral flux hitting the sensor its pretty straight forward.
The performance of CCD's, particularly with low flux, is significantly superior....as is their read noise.
An easy acid test is narrow band.
Expose, say 5 minutes, with an SII filter with a DSLR, then do the same with a mono CCD.
London to a brick you'll have usable signal with the CCD, but the DSLR will be mainly noise. |
do you under-estimate me that much Peter?
http://www.iceinspace.com.au/forum/..../winking70.gif
i don't claim the test to be the final answer and it was done very early in my CCD days. but like a good little scientist, i've put all the details there so anyone can see exactly what i did and make their own interpretation.
but equivalent imaging time was certainly my main interest (i didn't get the bonus "50% more clear dark sky package" when i bought my CCD
). so at the time i wanted to see what i got on the new CCD vs the cooled SLR that i was familiar with in the same amount of time, since a few hours on an object at a dark sky site was all i was lucky to get. (i do quite a lot of comparative testing of my gear at times, different ISO, binning, settings etc.. it's one of the ways i learn).
one of the common misconceptions i hear from people comparing mono-CCD to DSLR is that SLR imaging is quicker because you don't have to take images through separate filters. but as anybody who's used a nice sensitive CCD knows, you can get good (enough) binned colour data pretty damn quick and still easily match DSLR resolution. so my primary aim of the test was to show that CCD will outperform DSLR even in the same (short) time.
my surprise was how small the difference was in that case. narrow-band obviously different and clearly the much greater strength of mono CCD.
having said all that, i thought DSLRs were pretty good from a read-noise point of view, but nowhere near as good in thermal noise. quantum efficiency also lower but that's partly an RGB vs mono argument rather than CCD vs DSLR technology.
Phil
Edit.. P.S. why is that winking emoticons rarely work for me? hope i don't come across as too serious!
