Looking at flats

[StuartT]

Usually I don't bother to look at the master flats that come out of WBPP, but tonight I decided to debayer and stretch and take a look. Clearly some kind of dust on there, but I don't see it on my camera window or filter. It's presumably too in focus to be on the objective, so where is it likely to be? I'd like to clean this off if possible but I need to know where to start looking in the optical train.

Thoughts?

[vlaiv]

That is on filter (my guess).

Use calculator to determine distance of dust from sensor to give you idea what surface it sits on.

https://astronomy.tools/calculators/dust_reflection_calculator

[StuartT]

On 06/10/2022 at 20:33, vlaiv said:

That is on filter (my guess).

Use calculator to determine distance of dust from sensor to give you idea what surface it sits on.

https://astronomy.tools/calculators/dust_reflection_calculator

oh cool! I didn't know there was a calculator for that! Awesome.

Yep. Looks like the filter. 

Edited October 8, 2022 by StuartT

[sharkmelley]

19 hours ago, StuartT said:

Yep. Looks like the filter. 

Or could it be the camera window?

[ONIKKINEN]

Since the backfocus distance of the sensor itself (2600MC i presume) is 17.5mm i would also say that its the sensor window. Nothing else in that range of the sensor really and the filters are much further away.

[StuartT]

Thanks both. The window looks a bit closer to the sensor than that in my 2600MC, but maybe not.

I was also forgetting that there is an OAG between my camera and filter, so that's definitely more than 1.53mm

I'd better try and clean the window then.