52mm? vs 48mm?

One of recent common questions on IDAS filters, especially from full frame camera users, is 52mm filter? or 48mm? I’m always answering 52mm IF your optical system allows to set 52mm. Simply larger is better.

See a following shot.

Clockwise from upper left : Canon R adapter, Nikon Z, 52mm filter and 48mm

43mm and 47mm are the effective aperture. So 48mm(or 2″) doesn’t mean 48mm(or 2″) clearance. Meanwhile the diagonal of full frame sensor is about 43mm. So in my opinion, filter’s 43mm aperture is not obviously large enough. Even 47mm might not be a plenty of room in particular optical design either. It is subject to the factors of optical design and filter location etc though.

I understand 48mm(described as 2″ normally) is quite universal. It should be standard in our industry. But it seems to be the time for full frame camera users to carefully review the size of your filter and its location.

I suggest to take two test shots with a filter and without if your illumination drop doesn’t look what expected in your image result. It doesn’t seem clear to figure out mechanical vignetting? or native optical drop-off as designed if a filter is set further from the sensor.

BTW, Nikon Z mount is 55mm opening while Canon R is 54mm. Unlike Nikon traditional F mount, 55mm is quite large opening now. It should be good match with telescope’s optical design.

~ by tedishikawa on December 27, 2019.