UV filters, unscientific test

Started 6 months ago | Discussions thread
sybersitizen Forum Pro • Posts: 21,350
Re: Try it with a much longer lens

Phil A Martin wrote:

sybersitizen wrote:

Regardless, the point I wish to make here is that any sharpness degradation caused by a filter will be most apparent at much longer focal lengths. I wasn't convinced that focal length mattered in that regard until I did my own testing with some poor filters.

Why do you think that is?

I don't know. It was actually contrary to my expectations before I did testing, but evidence keeps turning up.

For the following pairs I used an old Cokin gradual ND filter (A 121). It's not the worst of all filters, but definitely not the best, either. It's held sideways and slightly shifted so that only the extreme right side is affected by the darkening. As in the other tests, the camera was well secured and the self-timer was used.

In these 55mm shots, I don't see a strong degrading effect:

With filter

No filter

But with these 280mm shots (about 5x the magnification), the degradation is more apparent, in my judgment. For example, look at the way the poultry wire in the lower left corner is rendered. In fact, all the corners and the center look worse to me:

With filter

No filter

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