From: "mihalco" <mihalco@yahoo.com>

Date: January 22, 2010 12:29:09 PM MST

To: Astro_IIDC@yahoogroups.com

Subject: Re: New AstroIIDC user

Hi Milton,

I agree that when normalized for area, the ICX285 is ~1.4 more sensitive than the ICX274. Part of this difference is due to the smaller pixel size on the ICX274, where the non light collecting interconnects are a larger percentage of total surface area.  

Comparing identical geometries, as in with the ICX258 and ICX408 (both with 6.35 x 7.40 micron pixels), the ExView HAD technology is about 18% more sensitive that Super HAD (sensitvity 1000 vs 850).  So, you would need a 7.00 micron sq SuperHAD for equivalent sensitivity to a 6.45 micron sq ExView HAD pixel.

Regards,

Kurt

--- In Astro_IIDC@yahoogroups.com, Milton Aupperle <milton@...> wrote:

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