moire pattern ?!

soulbouy

Hi all
Sorry if this is covered elsewhere, not found anything like this though ...

After some months not imaging through our UK summer, a few nights ago I decided to have a go capturing M16. My imaging camera is the ZWO ASI 071 MC. I used this at the end of last winter, at the end of my William Optics Z66. Never had any problems in the past with this set up.
However when I tried taking images, I was getting a moire patten, example is shown attached. This was a single 5 mins exposure. I got the same pattern with different exposures. Got the same pattern pointing elsewhere in the sky. Shining a light down the optical train, I can see nothing that would explain this.
The only thing different to when I last imaged, was that I'm using a laptop borrowed of a friend. His laptop is a quite old Pentium, whereas my laptop (currently in repair) is an 8 core Intel machine with much higher spec.
So advise please... could a low spec laptop be causing this ? I don't understand how the optics would produce this effect. many thanks

w7ay

soulbouy

That does not look like Moiré. Moiré tends to have a much finer repeated pattern whose pattern changes as you magnify the image.

What you have looks suspiciously like ice on the sensor.

If it is an icing problem, are you cooling the ASI071? If so, do not take it directly to the target temperature.

Take it to just above freezing first and let it sit there for 5 or 10 minutes, before taking it down below freezing. Even better, take it down in multiple steps, +10ºC, +5ºC, 0ºC, -5ºC, -10ºC for example, resting for a couple of minutes between the steps.

It may also be time to swap (or recharge) the desiccant tablets in the camera.

Chen

soulbouy

many thanks for the advice Chen. I thought about ice but I would have expected a more random effect. Also, I tried the camera yesterday during daylight hours, not cooled at all, and could still see the pattern, with the camera at c + 17C.