Coated clear-glass-filter *behind* older optics for digital?

[Blcak]

I just had this idea, certainly not new, I'm not even sure about my premises, but let me sketch it out:

Premise 1: I've read that new, "digital optimized" lenses have a specially coated back element to mitigate reflection effects by the sensor.

Premise 2: I doubt many of the enlarger lenses in use for our hobby were designed with this in mind.

Idea: A coated filter, preferably otherwise irrelevant for the visible spectrum (clear glass/UV) somewhere behind the back element of a lens could maybe help with this. Maybe at the other end of extension tubes or the bellows.

A further non-optical effect could be that you don't have to dust off the sensor that often.

Has anyone ever tried this? I might give it a try otherwise, I just don't have the proper filter yet.

[rjlittlefield]

A clear filter can help with dust. It will not help with reflections. Consider: the best clear filter you could put in would have no reflections at all. But that would be just like air, which you already have.

In theory, you could kill reflections by putting in a circular polarizer, properly oriented with the normal back side facing out. (Google circular polarizer mirror test.) I expect that would cause other problems, but it could be an interesting test.

--Rik

[Photo-DIY]

Old thread but I want to add:
Digital optimized lenses are calculated with the AA + IR-Cut filter glass in mind.
Old lenses are designed to have no glass between last lens and film.

From this it is better to reduce parallel glass behind the old lens system (like the filters in fisheye lenses) to optimize it for DSLR use.
But I have to admit: I see no striking IQ difference with the Zenitar 16 I tested this.
And you have to correct back focal length.

To add filters is worthless for perfect IQ.