"Bubble" spots on images

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Carlo Paschetto avatar
Hi all,

one of the issues I'm used to deal with it's due to spots on the images shaped as large bubbles, which I experience with different distribution and size depending on the camera I use. The attached image shows an example just taken with an almost brand new ASI533MC Pro, which perhaps I used nno more than 5 o 6 times.
I'm wondering whether these bubbles are most probably due to spots on the camera sensors or to the telescope / flattener lenses. At a first sight, lenses seem to be perfectly clean, but on the other hand the 533MC is almost new.
I have often noticed the same effect using my Canon DSLR. I sent it to a laboratory for the sensor to be cleaned and the situation seemed to be improved, but after a couple of sessions small bubbles have begun to appear again.
Of course, same bubbles appear by shooting the flat frames and btw using flats helps to reduce the problem in the final image. Nevertheless I'm wondering which cause I should probably look at and the best way to avoid this issue. 

Than you got your tips and support.
Habib Sekha avatar
These are dust specs (although condensation droplets can look the same).

Take a Flat, rotate at the rotator and take another Flat. If the position of the specks changes the tey are located between the rotator and camera. Now you could try the same but by only rotating the camera.

Dust can be on the protecting glass of the camera, filters, reducer/flattener etc.
Helpful Concise
Dale Penkala avatar
Agree with @Habib Sekha these are dust motes. Take flats and they should calibrate out for you.