High F ratio dust and bunnies

[kirkster501]

Hi, Ive noticed when I use my barlow (Powermate x 4) and my ASI1174M on my Meade 14" there are a lot of bunnies and flecks visible in the live video. This is of course imaging at F40 and nigh on 10m of focal length.  These go away if I don't use such a powerful barlow.  The optical surfaces of these things is immaculate.  This is not visible if I dont use the Powermate.

What causes these bunnies please and what do you do to get rid?

[Peter Drew]

All you can do is to keep the sensors as clean as possible. The Barlow actually tends to focus on dust and specks which shows them up more noticeably.      🙂

[Merlin66]

Yeah!

I've  just spent three frustrating days trying to clean motes from my ASI 1600 sensor.

Looked OK when tested at f5....but add the PM and "they're back".

A real PITA.

 

[kirkster501]

Ok guys, thanks.  The surfaces of the PM and sensor window look immaculate otherwise.

What about using some form of flats for this?

[Merlin66]

I only do solar imaging.....getting a good flat is problematic.

 

[vlaiv]

2 hours ago, kirkster501 said:

What about using some form of flats for this?

^ I think this is best solution.

You should certainly try to do full calibration. Although most "imperfections" are not strong enough to be seen in single sub, after stacking and when trying to sharpen up things, better to have "clean" data rather one containing bias patterns and PRNU.