Saturday, August 12, 2006

The Myth of Protective Filters?

Since reading Rain Contreras's article in about how protective filters affects the results of your photos or your lens's performance, I have always thought of finding out for myself if there really is such an effect on mine. Later on he opened a discussion thread about the same topic in Flickers Photo Club group and various opinions were shared.
I'm no mythbuster nor am I a myth detector. I just want to share with everyone the exercise I went through and its results.

I have only three lenses in my gear bag, an EF-S 17-85mm f/4-5.6 IS USM, an EF 75-300mm f/4-5.6 IS USM, and an EF 50mm f/1.4. Each one is "permanently" fitted with a skylight filter. When I had my Minolta Dynax 500si film SLR (it's retired now) about a decade ago, I didn't knew much about gears and photography for that matter. It was simply the one I could afford back then but in all honesty, I think it's a very good beginner's SLR camera. Later, I bought a telephoto lens in Singapore and the merchant there advised me to fit it with a skylight filter to protect the front element of the lens. He said that skylight filters are colorless, used to cut down haze but does not affect the amount of light entering thru the lens. I was convinced and so I have been fitting every lens I purchase with a skylight filter.

Now, that article by Rain really intrigued me so I decided to find out for myself. I wanted to see if I could squeeze out just a little bit more of sharpness by shooting without the protective filters. I have not had any complaint on the images produced by the EF 50 so I exempted that from the test. For the other two lenses, there were times when they turn out rather fuzzy images, especially at their longest ends (85 and 300m respectively) so I did my tests shooting that way - the same scene and lighting condition, first with filter and then without. I used aperture priority because that's how I shoot most of the time.

And now, here are the results:

Canon EF 75-300mm f/4-5.6 IS USM, Aperture Priority at f/9, focal length used = 300mm:

Shot with skylight filter.

Shot without skylight filter.

The following two photos are 100% resolution crop from the above images.

Shot with skylight filter.

Shot without skylight filter.

I could not see any significant difference with the results although the one shot without the filter appear to be a little bit sharper. But that's hardly noticeable for practical uses.

Canon EF-S 17-85mm f/4-5.6 Aperture Priority at f/9, focal length used = 85mm:

Shot with skylight filter.

Shot without skylight filter.

The following two photos are 100% resolution crop from the above images.

Shot with skylight filter.

Shot without skylight filter.

I don't see a difference on the results with this lens. They look just the same to me.

One thing I did notice with both lenses is, with the skylight filter fitted, the shutter speed slows down by 1 to 1-1/2 stop which means that my filters do cut down the amount of light passing trough the lens. As far as blurry images, haze cut down, or unwanted reflections. I did not experienced them in this test.

Maybe I conducted my test in the wrong way or maybe I should have done the test in a different situation. But I did this test to find out how the filters really affect my preferences for shooting. This may or may not be of any relevance to you. When I discover a new finding, I will update this topic. But for now, I think I'll start shooting without the filters just to gain that extra shutter speed.




Hocchuan said...

hmmm.. I dont see any difference.. hmm.. maybe I should test this also on my Sigma Lens and see if there's a difference. Thanks for this Alex.

alexdpx said...

I didn't see the difference too. Maybe I should try again, this time shoot towards the light source.

Rain said...

I've actually started to ditch the filter on my semi-permanent Sigma 17-70mm f2.8-4.5 DC Macro lens on the Rebel XT, even if I do shoot with the hood reverted back towards the camera 90% of the time. I guess I really just have to keep a lens cap, and lens cloth, handy.

Alex, maybe you should extend your research to different filter types, and brands. This issue will not stop bothering me, too.

alexdpx said...

Unfortunately, rain, that was not a research but a simple test based on what I have and how I use them. I have a polarizer for my telephoto lens which in fact further reduces the sharpness of my EF 75-300 especially at the longer end.

Sorry for the late reply :)

lenny k said...

ghosting and unintentional flare can be attributed to certain cheap clear filters

i posted sa fpc flickr about doing a simple straight look at the filter.

the cheap filter showed my reflection. the high quality filter looks like there is no glass in front of it.

anyway just my 2 cents, i am firmly in the uv filter on the lens all the time camp :)