Do filters degrade image quality or do they have no effect?

Yes.

I just ordered some filters, one to put onto a very fine lens.

Today I was asked (yet again) whether filters degrade image quality. Of course they do, and no they don’t!

Regrettably, I own perhaps 150 filters, accumulated over the years in a dozen sizes and colors and functions, many from film days for color balance reasons. I wish I had my money back for most of them, because I rarely use them any more.

Some popular brands alter color balance in undesirable ways, killing off deep blues (for example). To me, this is unacceptable with today’s fantastic DSLRs, just as it was with film.

From what I have concluded over the years both in general use and with some tests:

• Buy only the best filters, like B+W MRC (MRC is scratch resistant, a worthwhile feature);
• Buy only truly neutral UV filters (eg B+W MRC);
• Some popular brands have “neutral” filters that alter color balance in undesirable ways, killing off deep blues (for example);
• Keep them spotless;
• They are needed only for lens protection (specialty filters such as a polarizer are an exception). Sand, dirt, salt spray, heavy pollution, rain, peanut butter fingers, etc.

That’s my take. Skip ’em otherwise, and don’t skimp if you get one.

For more on filters and spectral transmission, read this.