From: Milton Aupperle <milton@outcastsoft.com>

Date: January 22, 2010 11:13:04 AM MST

To: Astro_IIDC@yahoogroups.com

Subject: Re: [Astro_IIDC] Re: New AstroIIDC user


Hi Kurt;


I totally agree that QE when expressed as a non normalized percentage is the way to compare absolute CCD sensitivity. But they generally don't do that unfortunately and do the peak normalized curves.


And Pixel size is only a direct comparison when your talking the same type of CCD model. A HAD CCD is less sensitive than a Super HAD CCD and a Super HAD is less sensitive than an EXView HAD CCD is.


If you look at the Sony Sensitivity values, a ICX274A (Super HAD) has a sensitivity of 420 and the ICX285AL (EXView HAD) has a sensitivity of  1300, so the ratio is ~3.1 times.


If you were to compare them solely on pixel size we would get 6.45^2 / 4.4^2 and come up with a ratio of ~2.2 times.


So the difference between Super HAD and EXView HAD types comes out to be ~1.4 times, which is a pretty significant difference.


You would need to have a Super HAD CCD with ~7.6 micron pixels to equal the same light gathering ability as a 6.45 micron EXView HAD CCD.


TTYL..


Milton Aupperle


On 21-Jan-10, at 11:40 PM, mihalco wrote:


Milton,

I agree. When comparing the sensitivity of individual pixels, the larger pixels of the ICX285 are certainly more sensitive than the smaller pixels in the ICX274. Sensitivity can be increased at the expense of resolution by binning.  I prefer to compare the QE of the sensors, which is independent of pixel size.  Unfortunately, Sony doesn't provide real QE curves for theirs (only normalized to the peak).  Third parties have measured both the IXC285 and ICX274 QE's peaking right around 60%, with the ICX285's peak a bit broader and centered more towards the red than the ICX274.

Regards,

Kurt