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Old Jun 1, 2006, 12:24 AM   #1
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In almost any discussion of filters that I've seen on various message boards, the universal response to any questions of the form "Should I buy off-brand filter type X?" is "Avoid the cheap, off-brand filters, they're crap". Unfortunately these opinions are never backed up by any evidence, the only jutification being either an implied "They're crap because they're cheap" or an implied "They're crap because they're off-brand".

Being an empirical gnostic, I decided to test some cheap, off-brand filters against not-so-cheap name-brand ones, namely a generic house brand against Hoya. The two I tested were a lens-protector (a.k.a. "UV filter") and a polariser. Living in the country with the highest UV concentration in the world, I figured I could give the, uh, "UV filters" a good workout (even though they're really just lens protectors).

For the lens protector (which should act as much like an optical no-op as possible) I wanted to compare the image quality, and also the ability of the filter coating to prevent lens flare. For the polariser, I wanted to compare the image quality.

In the left corner, a generic house-brand MC UV filter/lens protector and polariser.

In the right corner, a Hoya Super-MC UV filter/lens protector and polariser.

Scaled-down photos are below and in following posts. The first pair is the lens protector image-quality test (the slight tone difference is because the first was at 1/400, the second at 1/320, if I retry this I should probably shoot in manual mode rather than my usual aperture-priority), the second pair the lens-flare test (shooting at a slight angle into the sun with no lens hood, which should be about as bad as you can get). The third pair is the polariser test (the slight differences in tone are because it was hard to get the same polariser settings in both shots). See if you can pick which ones were done with the Hoya filters.

(If anyone wants more/different tests done, or some 100% crops, let me know. There are lots of things you can try, but I didn't want to go overboard with the image-posting).

Update: To fix some glitches in the original attempt (see the followup messages below), I've re-shot the images. So that people won't have to scroll through all of the older shots, I've deleted them from the posts (unfortunately I can't delete the now-empty messages). To see the updated shots, scroll down...
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Old Jun 1, 2006, 12:24 AM   #2
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Old Jun 1, 2006, 12:25 AM   #3
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Old Jun 1, 2006, 12:25 AM   #4
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Old Jun 1, 2006, 12:25 AM   #5
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Old Jun 1, 2006, 12:26 AM   #6
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Old Jun 1, 2006, 1:04 PM   #7
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In my mind, I like the "X" filter in all cases. I can't wait to see the who's who!
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Old Jun 1, 2006, 1:25 PM   #8
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My sense is this:

1. The first series seems to show a real chromatic bias in one or both of the filters. Without seeing the original scene, I would not be comfortable identifying which is biased. I cannot imagine how the chromatic difference could be attibuted to shutter speed. A picture with no UV filter in place would be helpful for identifying which of these (if either) is close enough to transparent for routine use.

2. On the second series, of course, the second image has amuch worseglare problem.

3. On the third pair, the first image clearly shows a polarizing effect in the sky. The second shows little or no such effect. I am not particularly fond of polarizers on color images, so I won't say that I like the first better. But, if you're going to use a polarizer, you presumably want it to polarize.




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Old Jun 2, 2006, 9:16 PM   #9
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When I get time I'll re-shoot them and fix the various problems. I'll do three shots of the first comparison (no filter, UVx, UVy), and a second lens-flare comparison to make sure it's repeatable (also with no filter, UVx, UVy). The polariser is a bit more tricky, because of the FZ30's lag in updating the display it's a bit tricky to find the maximum polarisation-effect point unless there are fairly obvious reflections off glass/water or strong clouds to use as a reference. In this case the differences between min and max aren't very large, and the display delay makes it tricky to find the maximum.
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Old Jun 6, 2006, 6:52 AM   #10
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Here's the re-done tests. The first series is the lens-protector quality test, first with no filter, then brand A, and finally brand B. As tclune pointed out, there seems to be some chromatic bias with brand B, but if you look at the UV filter guide at http://www.cs.mtu.edu/~shene/DigiCam/User-Guide/filter/filter-UV.html (which is far more comprehensive than my basic A / B comparison) there's also some variation there. At least for this single comparison though, it seems that brand A acts as the best no-op lens protector.

The next two are the lens-flare test. With no filter, there's pretty much zero flare (the single bright spot is a piece of dust that wasn't visible either before or after I took the photos, sigh). With brand A there's very mild flare (look just above the dust spot). With brand B... ugh.

Finally, the polarisers. As I mentioned earlier, it's rather tricky getting the exact same setting on both polarisers, both because of the display lag and because on a non optimised-for-polarisers scene it's a bit tricky finding the exact maximum point (or maybe I just oops at this :-)).

I should add some comments on the lens-flare test, this is an absolute worst-case shot. I did a few test shots earlier on and got no flare with either filter, so it could be just bad luck that I got something in this one comparison (note that the small cloud has moved out of the way of the sunlight in the brand B shot, so it could be something as simple as this that caused it).
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