To UV, or not to UV, that is the question.

To UV, or not to UV, that is the question.

When acquiring a new lens, many folks will buy a “clear” filter to protect the front surface. The most common type of filter is a “UV” filter that appears to human eyes to be clear. 

There’s some controversy about how such a filter affects image quality. Theoretically, the more glass surfaces the more problems they can cause. But in practice does that really matter?

I have a newish Tamron 17-28mm lens for my Sony E-mount cameras. It’s a nice lens. Thus far my only complaint is the lack of a lens correction profile for Photoshop and Lightroom, though I’m sure it’s in the works.

I hadn’t yet purchased a protective filter. Today I was digging through a bag of free filters and noticed a vintage Vivitar Skylight 1a filter. My guess is this filter was made in the 1970’s or 80’s. It does not have multicoating and has a slightly warm cast to it.

Voila, I have a filter to test! In fact this test is ideal, because the filter itself is not. So if a mid range, non coated filter from decades past is acceptable on a thousand dollar new lens that pushes the extremes of what’s possible optically today that says something!

So I grabbed my tripod, wiped as much of the Schmutz off the filter as I could and walked over to one of my favorite photo spots. I work on a college campus that has many historic buildings. What is now the back side of our Art Museum was once the front side. A freeway replaced the road leaving the grand front entrance sealed shut and unused. But it is a beautifully grand ornate portal etched with the words “Fine Art” atop the doors.

I took four photos in total for this test. I set the ISO to 100, vibration reduction off, 2second timer, manual focus, and then took:

1. A photo with the Vivitar filter on the lens and the lens hood on
2. A photo with the Vivitar filter on the lens but no lens hood
3. A photo with no filter and no lens hood
4. A photo with no filter but the lens hood back on.

Left Image: Skylight filter on lens, Right Image: no filter. Note no apparent loss of sharpness or contrast.

Left Image: Vintage Vivitar Skylight Filter 1a (uncoated), Right Image: No filter. Note added flare when using filter.

Only versions 1 and 4 are shown. 

One tricky bit to the test is that this lovely entrance is virtually always in deep shade, and much of the day (including for this test) has a strong backlight. So flare is always a problem. 

And it appears that the only disadvantage of using even such a relic of a UV filter is flare and a little loss of contrast in the most extreme circumstances. So I’d say as a general rule, it makes sense to use a protective filter. On rare occasions where you need no lens protection but image quality may suffer, simply unscrew the filter and pocket it until you’re done.