Changing a CCD chip

[anthony]

I will quickly demonstrate my complete ignorance here but I thought I'd ask you nice, kind and knowing people so that you could (with consideration rather than laughter and pointing) point out why this wouldn't work………..

The SXV H9 has a lovely sensitive chip with low dark noise. The SBIG ST2000XCM (now discontinued) has a built in guide chip but much noisier imaging chip.

Is it possible to place the ICX 285 chip in place of the Kodak KAI2020 (or whatever it is) and have best of both worlds. I am sure that to those familiar with electronics that this question is a bit like "why don't we look down the wide end of a telescope?", but go on, enlighten an ignorant!

[ronin]

No.

The chip is very closeley tied to the software and how data is read off.

The reading of the data is an art close to black magic.

The chip is a grid and the software does not read direct from the chip, it reads a row of pixels one pixel at a time, but not a row that is directly on the chip..

Imagine something like 200 rows of 200 pixels, R1 to R200

R1 is moved down to R0, R2 is moved to R1, R3 to R2 ,,,,,,,,,,

Then R0 is moved left or right one pixel at a time.

This pixel is then read.

Move the row again one pixel and read the next, etc, etc until the end of the row.

Move the "new" R1 to R0 and repeat the whole move down, move left/right until all rows and all pixels are read..

The software to read a chip is a lot of nested loops doing copy and reads, not difficult just messy at times.

So a different chip is a different size, will probably not have the same structure as in is the Row that is read R0, or one above the "top" row in the above R201. The chip could read a column not a row and the level for "White" on one chip will differ to another. Finally the chips will be different sizes and pin arrangements.

[NickK]

No.

The chip is very closeley tied to the software and how data is read off.

The reading of the data is an art close to black magic.

The chip is a grid and the software does not read direct from the chip, it reads a row of pixels one pixel at a time, but not a row that is directly on the chip..

Imagine something like 200 rows of 200 pixels, R1 to R200

R1 is moved down to R0, R2 is moved to R1, R3 to R2 ,,,,,,,,,,

Then R0 is moved left or right one pixel at a time.

This pixel is then read.

Move the row again one pixel and read the next, etc, etc until the end of the row.

Move the "new" R1 to R0 and repeat the whole move down, move left/right until all rows and all pixels are read..

The software to read a chip is a lot of nested loops doing copy and reads, not difficult just messy at times.

So a different chip is a different size, will probably not have the same structure as in is the Row that is read R0, or one above the "top" row in the above R201. The chip could read a column not a row and the level for "White" on one chip will differ to another. Finally the chips will be different sizes and pin arrangements.

This. There's also different timings between the chips too for each pixel, along with other electronic design for supporting the chip (supply circuits, PIC controllers etc). Interlaced vs non-interlaced etc.

This is why I don't like all-in-one cameras. If I want to change the 383L I can (and do - to the titan) whilst still maintaining the filterwheel and 16IC for guiding. I remember accidentally ripping out the USB port on the 383L and sent it back for repairs but I could still image with the titan.

[anthony]

Thanks guys. I reckon I knew the short answer (i.e. No!) but it is appreciated having it fleshed out a bit.

[ollypenrice]

Also those SBIG built in guide chips are a nightmare.

1) you have to rotate the camera to land a guide star and you may even have to move the mount as well, doubly compromising your framing.

2) this prevents you moving between objects in a night or obliges you to to reframe with rotation included, which is hell and slow.

3) it means that you need new flats for each new image, whereas without rotatiing the camera you don't.

4) there is no reason 4 because the first three are all terminal reasons in themselves.

Olly

[anthony]

Hi Olly,

I liked number 4 the best, made me chuckle.

I have to speak in defence of the SBIG though and not just because I own one . I have owned both cameras for years (my attempts at getting them to breed in captivity have never worked). The prob with the SBIG for me is a noisy OSC kodak chip. I would have sold the SBIG a while ago if it was not so very convenient and good in many other ways. I'd agree with each point you make but there is nothing that renders SBIG belly up in the water for me. Of course, your set up will determine very different demands than mine.

The SBIG always works a treat and rare is the problem of getting a guide star. Faffing with camera rotation chasing guide stars is also rare for me and I image directly over a police car park to the east, astro turf pitches to the south and Bristol to the west. Mind you, I do not use it to chase super dim extended objects with few stars nearby.

If the SBIG had the lovely sensitive, low dark current SXV H9 mono chip it would be great. I guess my original post was in hope! My old Mx7c was swapped out for mono by Terry Platt and enquiries to SBIG confirmed (if I was willing to pay enough) I could get the mono chip or even the bigger 4000xm chip (but still a noisy Kodak chip). There was a dim, faint hope that a bit of blu tac would happily take care of transplanting an ixc285 into the SBIG and banishing the noisy OSC colour chip that it has.

Anthony