UV filter sharpness frustration

icefox · Sep 4, 2009

I was shooting the beautiful full moon with my Canon 70-200 f4L on 400D. I realize that my UV filter is degrading the sharpness significantly. See the enlarged (original size) pictures w/o and w/ the filter.

You must be thinking the filter is a $5 ebay crap. Sorry, but in fact it's a Hoya. I trashed my last cheap UV filter when I found it reduces sharpness in a similar test. But I never thought a Hoya would do no better; in fact it is even worse.

This is quite frustrating. Do you guys think this level of reduction of sharpness is normal? Would you recommend buying an even more expensive filter, or leave the front element naked? I'm thinking of latter. Note that sharpness reduction is most severe when shooting far away objects, so if you want to test your own filter, do shoot the moon with a telescope.

Pure · Sep 4, 2009

Personally, I only use UV filters when shooting in dirty/dusty places where particulate can enter the lens. Other than that, just a hood.

icefox · Sep 4, 2009

Pure said:
Personally, I only use UV filters when shooting in dirty/dusty places where particulate can enter the lens. Other than that, just a hood.

I guess I'll do so as well in the future. I never thought a single layer of glass can blur the image so badly.

soze · Sep 5, 2009

ouch, I'm going to have to test this out as well.

Garbz · Sep 5, 2009

icefox said:
You must be thinking the filter is a $5 ebay crap. Sorry, but in fact it's a Hoya.

Which Hoya, there's about 5 different kinds, and 3 of them are ****. The SHMC and Pro1 series of filters give no visible difference zoomed in 100% in my tests. The rest of them ... yeah.

Sw1tchFX · Sep 5, 2009

this is why i don't use UV filters unless the conditions are going to be SERIOUSLY bad. Which is almost never here in oregon.

HeY iTs ScOTtY · Sep 5, 2009

I NOTICED THIS AS WELL. I ALSO NOTICED IT MAKES THE COLOR LOOKED WASHED OUT. I REALLY ONLY USED IT FOR LENS PROTECTION SO NOW I ONLY USE IT WHEN THE ENVIRONMENT CALLS FOR IT LIKE WHEN I'M AT THE BEACH. I DIDN'T NOTICE IT AT FIRST BUT AFTER A FEW PHOTO SESSIONS I NOTICED MY PICTURES LOOKED A LOT CLEARER AND COLORFUL WHEN I FIRST GOT MY CAMERA. I THOUGHT I MIGHT OF MESSED WITH THE SETTING OR SOMETHING. I STARTED SHOOTING ON THE VIVID SETTING FOR A WHILE BUT THEN I REALIZED ITS THE DAMN FILTER. :er:

Phranquey · Sep 5, 2009

Garbz said:
icefox said:

You must be thinking the filter is a $5 ebay crap. Sorry, but in fact it's a Hoya.

Click to expand...

Which Hoya, there's about 5 different kinds, and 3 of them are ****. The SHMC and Pro1 series of filters give no visible difference zoomed in 100% in my tests. The rest of them ... yeah.

That's why for the filters that I do use, like the CP and neutral densities, I buy good ones....crap ones do affect quality. Like most, I do keep a UV filter on the lens for protection in bad conditions or if the cap pops off in the bag, but 99% of the time it comes off for shooting.

Dwig · Sep 5, 2009

icefox said:
...Do you guys think this level of reduction of sharpness is normal? ...

Yes, its in line with my expectations and experience.

It should be noted that you used the correct term, "sharpenss". "Sharpness" is something that does not exist in the real world. It is a mental opinion that you get when your eye/brain sees a range of image attributes including detail level (~=resolution) and various aspects of contrast.

Given that shooting the moon against a black sky is a massively flare inducing situation, the addition of two glass to air surfaces (rear of filter and front of lens) to the optical path can cause a noticable increase in flare even with modern multi-coating. Also, even the best multi-coating isn't enough. The edges of the glass disk must be ground and blackened, just like the elements in a good lens, or their will be additional internal reflections that the coatings can do nothing about.

Additional optical problems can be introduced if the filter isn't perfectly flat and perfectly perpendicular to the optical axis. Warping is not uncommon when atmospheric pressure and/or temperture changes and when the filter is torqued onto the lens too tightly. In ancient days, Nikon took steps to avoid the warping issues. They used a hard bronze for the metal band and the filter was held in with a spring clip. This kept the glass from being put under stress. They also edge blackened the glass flat to avoid the internal reflections.

icefox · Sep 5, 2009

thank you guys so much for the careful explanation! I'm a relative newbie in photography and your advices do help a lot.

Now if only someone could show me how your more expensive filter would affect shooting the moon at 200mm focal length.

Derrel · Sep 5, 2009

That's Hoya Quality for ya! :lol:

cfusionpm · Sep 5, 2009

icefox said:
Now if only someone could show me how your more expensive filter would affect shooting the moon at 200mm focal length.

That would be interesting to see. I can't stand using UV filters as they just don't do anything to help the image. I use a lens hood for protection and only put on a filter if an application calls for it.

KmH · Sep 5, 2009

HeY iTs ScOTtY said:
I NOTICED THIS AS WELL. I ALSO NOTICED IT MAKES THE COLOR LOOKED WASHED OUT. I REALLY ONLY USED IT FOR LENS PROTECTION SO NOW I ONLY USE IT WHEN THE ENVIRONMENT CALLS FOR IT LIKE WHEN I'M AT THE BEACH. I DIDN'T NOTICE IT AT FIRST BUT AFTER A FEW PHOTO SESSIONS I NOTICED MY PICTURES LOOKED A LOT CLEARER AND COLORFUL WHEN I FIRST GOT MY CAMERA. I THOUGHT I MIGHT OF MESSED WITH THE SETTING OR SOMETHING. I STARTED SHOOTING ON THE VIVID SETTING FOR A WHILE BUT THEN I REALIZED ITS THE DAMN FILTER. :er:

Well, you figured out what the problem was.