Filter ... bigger or small in the back ...

[InTheSky]

I was searching for a Polarized filter to put in the back of the big monster 400mm 4.5 APO, and found that you cannot really get one under ~325$ US (or CAD ...). The front lens of the 400mm is 95mm compare to 42mm in the back.

I'm curious if someone ever try to use a big front polarized filter instead of putting one in the back. Because for me, follow physic law ... it is probably more difficult to make good optic has small as 42mm of surface to cover a 35mm sensor than using a big surface like 95mm.

I'm thinking that I should get a 95mm filter for about half the price and probably get better optical quality that the one in the back. Just thinking about a dust in the front where it is almost impossible to see where the one in the back scrap the image. Well the hood can be not fun to move to adjust the effect but usually once you are in horizontal or vertical it is almost done ...

Do we really need to keep the hood on a lens where there is a polarized filter in the front ?

What is your idea about that ?

Frank

[David Kilpatrick]

It's very difficult to make a really good 95mm pol but very easy to make a rear one in a smaller size to exceptional quality. There is a good reason why long lenses use drop-in filters, and it's not just the size.

If I owned a 400mm, I would get the rear slot filter. Easier to operate, lens hood is actually very important, optical quality is better, two less air to glass surfaces when in use compared to a front mounted polariser, less space in outfit, less weight, faster rotation, probably a superior type of polarising layer unless you buy the most expensive (B+W) front filter - etc.

David

[InTheSky]

Thanks David, I will follow your recommendation.

Frank