Diagonal banding on Artemis 285

[Tom How]

I've had a long standing problem with an old Artemis 285 camera.

The bias frame contains some faint diagonal banding.

Stack of 20 bias frames:
http://astro.neutral.org/tmp/CalibrationFrames.jpg

http://astro.neutral.org/tmp/CalibrationFrames.fit

Single bias frame:
http://astro.neutral.org/tmp/singlebias.fit

I've played around endlessly with power supplies, different computers etc, but this slight banding always seems to be there. I've also inspected the camera and clean any dirt etc I can find.

I do a lot of astronomy DIY  - I originally built this camera - so I don't mind ripping it apart and tweaking it - however I can't fathom what might be causing this sort of interference.

I don't know if it means anything, but horizontally the cycle is about 45 pixels.... if the data is coming out at 1.5Mbit / s then this is a frequency of 2khz or so.

I'm not looking for answers on a plate here.... but and pointers on avenues to investigate are most welcome!

I can sort of get around this with a bit of dithering, but obviously it would be better to be without it!

[Tom How]

As a further example, even a bright region like the Crescent is effected by the problem if I don't dither the guiding.

NGC 6888 Crescent Nebula in Ha

[Tom How]

The other bit that puzzles me, whatever I do, the bands appear in the SAME place on every frame - which is why the co-add in the stack

[1275rob]

Hi Tom,
Only just seen this post I don't look very often. I have seen this myself on my Artemis and the first thing that comes to mind is the Peltier. Do you know if it is working OK?
As you have a separate supply for the Peltier it should be easy to check. Another thought the silicon paste may have dried and effecting the performance.
Just a couple of ideas.
Bob.

[Tom How]

Hi bob, only just seen this! Thanks for your reply.

I am 100% confident the peltier is working, there is no vertical gradient typical of an uncooled sensor.

It is still unexplained, especially how it appears in the same place on each frame which I wouldn't expect with a ground loop

Tom

[1275rob]

Hi Tom,
I don't know if you have found the answer but I was messing around with my Artemis CCD  and I had exactly the same diagonal banding. What I had not done was to select the FIFO. As soon as I did this the next download was OK.
I have always selected this option as a matter of course and in ArtemisCCD the FIFO setting is remembered.
According to the original build manual the FIFO was an option but I am glad I installed it as I always needed it because I had a slow LapTop. I now use a powerful MacBook Pro but I still have the issue.
I hope this helps.
Cheers,
Bob.