Can a filter diminish the quality of your pics on good glass

[PJ]

I'm sorry if this topic has already come up but I searched the forums with no luck.

I'm curious about something.

The glass makes the lens right!
Then is the $20-30 UV filter i'm putting on the front of my multi hundred dollar lens diminishing the quality of the image?

I plan on doing some tests tomorrow to see if i notice a difference but I wanted to hear what you experts had to say.

If it does diminish the quality I'm sure i'll still keep the filter on anyway for protection.

thanks

PJ

[Pekka]

Good quality multicoated UV / UV haze filters (Hoya Pro, B&W) do not really make any difference. I use those mainly in situations when I need glass protection (rock concerts, wind, rain etc). If you are shooting in situation where you have strong (side) lights touching the filter then contrast may be better without filters but if you keep hoods on all the time this is not an issue either.

[drisley]

Read this recent thread.
It shows what can happen when you use a uv filter in a low light situation.

http://photography-on-the.net/forum/showthread.php?t=37765

[sdommin]

Lenses are designed to be at their best without a filter.

That being said, a good quality filter will make very little difference in your everyday photos, and it's doubtful whether you'll even notice in a side by side test.

[Tom W]

Yes, a filter can degrade an image under certain circumstances. As drisley pointed out, the image linked in the other thread that he showed us shows one of the effects of a poorly-coated filter - ghosting. Flair is also an issue.


Why? Because the non-coated or poorly-coated surface will reflect approximately 5% of the light back in the other direction. Since the sensor filter (and film to a lessor extent) has some reflective characteristics, very bright images are first reflected off the sensor filter and then back again off of any glass surface that isn't properly shaped or coated to prevent back-reflection. Good lens construction and coating lets this reflection either pass out of the lens, or reflect in a direction where it is absorbed by the interior flocking of the lens or mirror box.

Using good-quality multi-coated filters such as Hoya Pro or Hoya Super HMC or B&W as Pekka points out will minimize or eliminate these effects in all but the nastiest of situations.

Note that there are a few lenses out there that might exhibit the same effect without the aid of a filter, but they are few and far between. Usually very cheap lenses that skimp on quality and engineering.

[msvadi]

Hoya S-HMC has six coatings (on each side?) and 99.7% of the light passes. HMC has 4 coatings. One can notice the difference between two, probably, only under extreme conditions.

[WestFalcon]

I have mentioned this before several times but modern photography or popular photography magazine did tests with and without filters using AirForce resolution charts and found that there was no degradation of the image with medium to top quality filters like Hoya, Canon, Tiffen. I don't believe that they tested for flare which is another variable but unless you are shooting in a flare situation(into a bright light source), a filter will not degrade your image...not my conclusion but the conclusion of the research back in the 70's .

[drisley]

I've seen tests that show comparisons of images shot without a filter, with a generic filter, with a multi-coated filter, and with an expensive super-multicoated filter.
The test was for contrast, flare and ghosting.
The best image was the unfiltered lens.
The super-multicoated fitler was second, but did exhibit flare, loss of contrast and some ghosting.
The results on the generic filter, and even the multi coated fitler were pretty bad.
Since I shoot mainly in situations that would be affected by flare, and ghosting, I never use a UV filter. That is what lens caps and lens hoods are for.

[Tom W]

I have mentioned this before several times but modern photography or popular photography magazine did tests with and without filters using AirForce resolution charts and found that there was no degradation of the image with medium to top quality filters like Hoya, Canon, Tiffen. I don't believe that they tested for flare which is another variable but unless you are shooting in a flare situation(into a bright light source), a filter will not degrade your image...not my conclusion but the conclusion of the research back in the 70's .

Realistically, under most circumstances, the filter won't affect the image unless it has some curvature or dirty glass. But flair and ghosting are issues whose effects are increased significantly if the filter isn't properly coated to maximize transmittance and minimize reflection. So while the test chart probably didn't show any difference, it is far different than shooting outside on a sunny afternoon when the sun is sometimes just in the wrong place. Or, in a stadium with very bright lights (and in fact, in most dusk or night-time cityscape-type photography).

Frankly, while I think it is much safer to risk scratching a filter during cleaning, there are some situations where one might want to omit the filter altogether.

[PJ]

Thanks for the info all. Answered my question and more.

appreciate it. :)

PJ