Quote:
Originally Posted by gregbradley
I don't think its 3-4 times but it might be 2 to 3 times depending on the CCD of course.
Depending on the DSLR. I have a link somewhere to the various sensitivities of various brands and models but they typically are between 30 and 60% QE. QE is quantum efficiency which is what percentage of photons that hit the sensor get converted to electrons (signal).
Your average CCD is about 45-55% or less. But because they are monochrome every pixel counts whereas DSLRs take 4 pixels to make one colour dot in an image so that reduces the sensitivity a lot.
CCDs usually have minimal gain applied to the signal. So say for example the Nikon D800, ISO 1600 is close to minimal gain like a CCD. That ISO level would vary also with brands and models of cameras.
My Nikon D800E has 59% QE and my astro CCD cameras are mostly 60%. The difference is mainly the mono of the CCD versus the colour filters
on the DSLR. A closer approximation of sensitivity is a one shot colour CCD camera and a DSLR. There is still usually a greater sensitivity with the one shot colour but the difference is less. Mostly due to the cooling reducing the noise. Sometimes the sensors are the same for example the Starlight Express M25 one shot colour uses the same CCD sensor as the old Nikon D70.
Greg.
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Thanks Greg,
the fact is that CCD out performs Bayer matrix CMOS every time.
I was amazed at the difference it made when I switched to CCD.
I went from this:
http://www.flickr.com/photos/2471943...in/photostream
to this - using the same telescope:
http://www.flickr.com/photos/2471943...in/photostream
cheers
Allan