[Zuts]

Hi,

Thanks for all the replies, I have decided to wait for the 2 inch filter drawer. One of the reasons I was asking about distance was because I thought the further away the less chance of reflections and halos around stars, then I read it is the exact opposite?

Originally Posted by Camelopardalis

Paul, it’s better to have the filter as close to the sensor _if_ their sizes aren’t too dissimilar. If the filter is much larger than the sensor, then it can be further away before causing an obstruction to light.

FWIW, 1.25” filters usually work out about 28.5mm clear aperture. How noticeable any obstruction is will depend on the focal ratio of your scope/reducer combo.

A 2” filter is substantially larger...

Thanks Dunk, I hadn't considered the fact that the clear aperture of the filter is less than the actual aperture by over 10% in this case.

Originally Posted by jahnpahwa

Hi Paul, I think your sensor is smaller than APS-C, at 17.7x13.4mm, and 1.25" filters are ok for that size. That said, 40mm seems a long way from the sensor so still may throw up an issue. Are there any secret threads inside spacers or adapters closer to the sensor that you could mount it in?

Hi JP, the ASI 2600 MC is (23.5 x 17.5mm) with a diagonal of 29.3, maybe you were thinking of my ASI 1600 MC which I have replaced now. While I am waiting for the filter drawer I can use an M48/M42 adaptor but this will increase the spacing from reducer to chip by an extra 1mm beyond the recommended 55mm.

Originally Posted by DiscoDuck

Paul, it depends also on your scope's focal ratio. There is a calculator here https://astronomy.tools/calculators/ccd_filter_size where you can plug in your numbers.

Thanks for the link Paul. This convinced me to wait for the filter drawer and not get a 1.25 inch filter.


Cheers
Paul