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Old 01-05-2012, 10:30 AM
pjphilli (Peter)
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Cmos vs ccd

Hi
Having previously used a modified Canon 400D for astro imaging I have recently used a QHY8 CCD colour camera.
I soon noticed that the QHY8 camera is considerably more sensitive (ie
less exposure time required) than the 400D. I see that the 400D CMOS pixels are 5.7microm square whereas the QHY8 CCD pixels are 7.8microm square, ie about twice the area of the CMOS. So I guess this would account for the QHY8 having at least twice the sensitivity of the 400D.
However, I have seen suggestions that for a equal size pixel that CCD is
more sensitive than CMOS. I have looked back on previous threads but got lost in the talk about "quantum efficiency". Could someone put this in terms of a simple fraction?
Cheers Peter
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Old 01-05-2012, 03:57 PM
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gregbradley
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I think its hard to compare as most CMOS sensors are in digital cameras and they have the Bayer colour filters on top that seriously reduce QE.

DSLRs for example are often around 30%QE or less. Some are up around 57-61% (new Nikon D800 57%, Canon 1D Mark iii etc around the 60% area).

I am not sure that CCD are necessarily more sensitive by nature (perhaps they are).

CCD/CMOS both use pixels. CMOS has the amplifier and other circuits next to each pixel, CCD has a separate circuit board for that. So there may be less room used up in CCDs as well that would also add to better sensitivity.

CMOS uses less power and is easier to make.

Greg.
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Old 01-05-2012, 04:02 PM
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Tandum (Robin)
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According to Theo's post here, The sensor board in the original QHY8 was lifted directly from a Nikon D40 ...
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Old 02-05-2012, 04:10 PM
pjphilli (Peter)
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Hi Robin

Further investigation shows that my QHY8 camera has a 6 megapixel
ICX413AQ super HAD CCD chip which has a quantum efficiency of 50%.

Cheers Peter
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