Comparison of CCD chips

Hi,

I'm comparing a couple of CCD chips at the mo and would like some advice please:

* Large, high resolution Kodak KAI4021M CCD chip, with 4,194,304 x 7.4uM square pixels in a 15.15 x 15.15mm array.

* Monochrome

* High sensitivity, 55% QE at peak (green light). 45% at 400nm. 30% at 650nm.

* Anti-blooming

Versus

* Very large, high resolution 'SuperHAD' CCD chip, with 6,000,000 x 7.8uM square pixels in a 23.4 x 15.6mm array. Size equivalent to APS film.

* Single-shot colour, using a Bayer matrix of R, G and B on-chip filters. No filter wheel required.

* High sensitivity, equivalent to 60% QE at peak of green filters. 50% roll-off at 400nM and 650nm

* Anti-blooming

The first one is relatively large, monochrome, but the QE drops off in the red.

The second has a bigger area, higher QE in the red and is colour, which would save on a filter wheel and RGB filters.

What do you think?

Cheers,

The first one has square pixels so no need to go stretching afterwards to get the right aspect ratio. It's monochrome and you would think it should be more sensitive than the colour chip but it doesn't appear to be. If then specs are to be beleived the second one has it beat hands down.

Its a really hard call. On the face of it I'd go for the second because of the better QE, larger pixels and the fact it is colour. What do these pixel sizes relate to in arcseconds per pixel on your scopes?

Michael

Try and get more data if you can. For the same chip, the mono version will always perform better.

For the two chips you're looking at, see if you can get any reviews (in any camera body) or try and talk to vendors that offer both types of chip (I think SBIG use only Kodak).

I would need confirmation that a manufacturer can apply a Bayer matrix to a single 7.4 um pixel extremely accurately and reproduce that for the other 5,999,999 pixels

Judging by recent advances though, a few of the top-end photographers seem to use single shot colour CCD's - so they can't all be bad. That said, the majority use mono CCD's - but perhaps that's because of Ha imaging.

And on that subject, I don't know how a colour CCD works with filters - if you wanted to do any non-RGB filter work (hydrogen, oxygen, sulphur) perhaps a colour CCD would prevent you.

Its never a smooth path...

Let us know how you get on with the research.

Dave

Michael,

The Kodak chip is the same one that is in my H16 and despite the figures I find it very sensitive.
I have used one shot ccds with higher QE but needed a much greater exposure time which means tracking/guiding needs to be spot on.
I will not be going back to imaging with a one shot ccd.

Kieran

A piece of info re the colour ccd chip:

Most competitive brands of CCD camera require a ‘dark frame’ to be subtracted from your images to achieve the best results. A dark frame is simply a picture which was taken with the same exposure as your ‘light frame’, but with the telescope objective covered, so that no light can enter. It records only the ‘hot pixels’ and thermal gradients of your CCD, so that these defects are largely removed when the dark frame is subtracted from the light frame. The SXV-M25C CCD is quite different from those used in other brands of camera and generates an extremely low level of dark noise. Indeed, it is so low that subtracting a dark frame can actually INCREASE the noise in your images! This is because the statistical noise of the dark frame can exceed the ‘pattern noise’ from warm pixels and hence add to that of the subtracted result. If your test pictures have an exposure time of less than about 30 minutes (as above), then don’t bother with a dark frame, just ‘kill’ any hot pixels with your processing software.

In terms of h-alpha imaging with the colour camera, the bumff says:

Would you like a single-shot colour imager, but also need to capture H-alpha images with it? The excellent red light sensitivity of the SXV-M25, combined with our special narrow-band processing software, can give you the best of both worlds!