Effect of filters on sharpness

[Dem Bell]

Bit of Science for y'all:

https://photographylife.com/filters-affect-resolution-lenses

Is it the part where you put a £108 UV filter on a £500 lens and say that if you don't look close, there is no difference? OK, I believe that.

 

[egk4260]

2. It is even more difficult to definitively prove protective benefit so I will continue to avoid them to eliminate potential of image degradation.

But it's really not difficult to prove protective benefit. If you look at the surface of lenses under a microsope/appopriate imaging device, you'd soon see that lenses that have been used without filters would show degradation someway beyond that of lenses that had always been used with filters. I've bought and sold a lot of lenses in my time, and you can tell which ones have been used without filters, easily. I reject any that have been used without filters. These have degraded image quality and lower value.

You may have a point if we all get microscopes, but I guess then we have to once again set the parameters to define benefit. Is benefit defined as absence of microscopic evidence of dust impact to front element or is benefit defined as detectable improvement in images taken from lenses that have had protective filters. Then further if we decide to evaluate resulting images, are those test images obtained with or without a filter respectively. That is, are test images to be obtained with filters for historically filtered lenses, and without filters for historically unfiltered lenses. Do we add that variable to the test as it could be seen to potentially negatively impact test images from the filtered lenses or conversely to inappropriately eliminate that potential filter related image degradation from those lenses that are considered potentially superior because they carried filters. And, of course the evaluators must be a blinded as to filter use in their evaluation of images so as to eliminate observer bias. As to the main part of my response, neither of our opinions are likely to change if this thread proceeds as it does in the monthly reappearances of the past decade or more.

 

[ishwanu]

... I'm backed up by science:

https://clarkvision.com/articles/protection_filters/

Soz, but Science is Science. Y'know, like, fact.

Apparently, 'science' can back up whichever thing a person prefers to do as long as the parts of 'science' that say something else are not mentioned.

 

[John Sheehy]

if an otherwise good filter has physical damage or contaminations of some kind on it, then those things might be hidden at wide apertures and become more apparent at tiny ones.

... if they are in the center. Towards the edges, they are no longer involved as you stop down, with most lenses. With a fisheye lens, however, or a large, clunky FF DSLR super-wide lens with a bulging front element, the pupil moves over a large area as the subject moves in the frame, so almost any blemish is in-path in some part of the frame, even if you stop down.

 

[Mark B.]

2. It is even more difficult to definitively prove protective benefit so I will continue to avoid them to eliminate potential of image degradation.

But it's really not difficult to prove protective benefit. If you look at the surface of lenses under a microsope/appopriate imaging device, you'd soon see that lenses that have been used without filters would show degradation someway beyond that of lenses that had always been used with filters. I've bought and sold a lot of lenses in my time, and you can tell which ones have been used without filters, easily. I reject any that have been used without filters. These have degraded image quality and lower value.

Well I guess I'm glad the few times I've sold a lens the buyer didn't use a microscope to inspect the surface.

So tell us...have you done tests of lenses taken when brand new vs at least 10 years of use with no filter and only a lens hood that can show a definitive difference in image quality? Don't care about what the surface of the lens shows under a microscope; I'm interested in definitive proof that shows on the images.

 

[egk4260]

One post in this thread referenced a little science for us all.

Here is another. It is seven years old, but I suspect filter science has progressed very little since.

https://www.lensrentals.com/blog/2017/06/the-comprehensive-ranking-of-the-major-uv-filters-on-the-market/

My takeaway from this is that filters likely have little effect on image, although subjectives are not addressed. He did show light transmission is only slightly reduced in most, cost does not necessarily correlate with performance.

As always, Roger does inject some of his excellent dry humor.

”Just because the light gets through the filter doesn’t mean it gets through without distortion or aberration. Here’s the opportunity to make fun of marketing (OK, to laugh at the people who blindly buy into marketing). One of the filter manufacturers proudly states they grind their filters flat to 1/10,000 of an inch. Sounds pretty impressive, doesn’t it?

Imaging-grade surface flatness is usually considered 1/4 of a wavelength, which is around 150 nanometers. That 1/10,000 of an inch the marketers are bragging about is 2540 nanometers. So what the advertising actually says is ‘our filters are guaranteed not even to be close to optical grade.’”

 

[Cultius Ponc]

One post in this thread referenced a little science for us all.

Here is another. It is seven years old, but I suspect filter science has progressed very little since.

https://www.lensrentals.com/blog/20...anking-of-the-major-uv-filters-on-the-market/

My takeaway from this is that filters likely have little effect on image, although subjectives are not addressed. He did show light transmission is only slightly reduced in most, cost does not necessarily correlate with performance.

Well there you go. I've scoured the internet for any other scientific tests which can prove stuff, but there is literally nothing that proves any significant degradation of image quality in general use. Now whenI say 'general use', I refer to the type of everyday photography that the vast majority of photographers do. I do believe there are times when one might not want to use filters; astrophotography comes to mind. You'd surely want as close to 10% as you can get. Other forms of scientific photography might benefit from the lack of a filter. And then; other forms actually require specialist filters; using UV light for eg, where you want ONLY the UV light to pass through the filter. But we're into extremely specialist territory here.

 

[BirdShooter7]

One post in this thread referenced a little science for us all.

Here is another. It is seven years old, but I suspect filter science has progressed very little since.

https://www.lensrentals.com/blog/20...anking-of-the-major-uv-filters-on-the-market/

My takeaway from this is that filters likely have little effect on image, although subjectives are not addressed. He did show light transmission is only slightly reduced in most, cost does not necessarily correlate with performance.

Well there you go. I've scoured the internet for any other scientific tests which can prove stuff, but there is literally nothing that proves any significant degradation of image quality in general use. Now whenI say 'general use', I refer to the type of everyday photography that the vast majority of photographers do. I do believe there are times when one might not want to use filters; astrophotography comes to mind. You'd surely want as close to 10% as you can get. Other forms of scientific photography might benefit from the lack of a filter. And then; other forms actually require specialist filters; using UV light for eg, where you want ONLY the UV light to pass through the filter. But we're into extremely specialist territory here.

Science doesn’t really “prove” anything. Basically evidence is gathered and analyzed and an idea is either supported by the evidence or not. The idea is then refined based on the evidence.

With protective filters, I’ve found that not all filters are created equally. In one extreme case I purchased a used EF 70-200mm f/4L USM lens used from someone in my area. The seller mentioned that he had installed a protective filter as soon as he took the lens out of the box when he purchased the lens new from a retailer. It turns out that the filter was part of an accessory package that the retailer sold him along with the lens. The lens looked brand new and the glass looked flawless.

When I took the lens out for my first photo outing everything seemed to go well until I got home and downloaded the photos. Every single one looked as if I was shooting through a gray haze and if I viewed the images at 100% everything looked a little bit fuzzy. I immediately thought that I’d been sold a faulty lens and started to think about how to go about asking to return it. When I finally calmed down it occurred to me that I should try taking off the protective filter and see if anything would change. When I did I noticed a drastic improvement in image quality. Everything was crisp and sharp just as I would expect from this lens.

The filter was a brand I had never heard of and I immediately tossed it in the trash. My next step was to order a B+W multicoated filter to replace the junk filter with. The good quality filter cost me around $65 and when I did some testing with it I didn’t notice any difference between with or without the filter so I went on using the filter for the rest of the time I owned the lens.

Now there might have been certain situations where the filter could have still caused some degradation in image quality. Maybe if I was shooting into the sun or something… Anyway I used the lens for years and was very pleased with the results I got with the multicoated filter in place.

 

[Aaron801]

... who often uses a clear or UV filter to protect the lens. I get that the extra piece of glass on there can theoretically suck up some of the sharpness, but in reality, I don't think that it really does that most of the time. There are situations though where I notice that the filter can cause problems, so I take it off. That's whenever I'm shooting someplace that's very dark, with single point light sources, like on the street at night or in a theater with stage lights...

 

[bridge77]

... who often uses a clear or UV filter to protect the lens. I get that the extra piece of glass on there can theoretically suck up some of the sharpness, but in reality, I don't think that it really does that most of the time.

There are situations though where I notice that the filter can cause problems, so I take it off.

answers all the questions: take it off as needed.

The End

That's whenever I'm shooting someplace that's very dark, with single point light sources, like on the street at night or in a theater with stage lights...

 

[John Sheehy]

does that mean that a poor filter will not have much effect on degrading a macro image shot with a normal macro lens.

I don't know. I haven't tried to test that. Macro magnifications typically reduce the effective size of the pupil, though.

The apparent absolute size of the pupil can shrink at very close subject distances, but that does not necessarily mean that the angular size of the pupil (from the perspective of the subject matter) has also shrunk. It may be just reduced returns on the pupil angle when getting closer. At great distances relative to focal length, like 100 feet and 200 feet with a 20mm lens, the angular pupil diameter from 100 feet is almost exactly 2x what it is at 200 feet, but every halving of distance will fail to double the diameter as you start getting much closer.