UV Filters with the RD_1.

[Doc William]

A recent post by one of our members, "RD-1 #4 letting me down", brought about a wonderful dialogue in diagnosing a relatively simple problem (sans one diparaging post). It came down to a UV filter causing lens flare at night time.

I noticed that many people mentioned that they never use filters. Why not (besides the aforementioned problem of night time lens flare)?

The selling point to me has always been getting a scratch or dust on my $70 filter rather than my $2800 Leica lens.

Are their any other problems I should be looking for or situations where it is a definite NO to use a UV filter?

Thanks in advance and again, great work in diagnosing our fellow forum members problem.

 

[RML]

Doc, I'm one of those who never use a filter. Why? Because on a rf camera I find it difficult to anticipate the effect. And secondly, a $70 filter is more expensive than my J-8: I could buy 3 for that price. 🙂

 

[jaapv]

Any lens has internal flare because of reflections. The better the coatings of the lens, the smaller the intensity of the reflections and with that the degradation of the (theoretically possible) image. One would think that the addition of two reflective surfaces to an optical system with, say, six elements is not that bad, but unfortunately the number of reflections is governed by Snellen's law which is R=N(N-1)/2 where N is the number of air/glass surfaces. So a Summicron with 6 elements and 12 surfaces has 66 [ 12(12-1)/2 = 132/2 = 66 ] reflections. If you add 2 surfaces you will have 91 reflections [14(14-1)/2 = 182/2 = 91 ]!Just try stacking filters and adding four or even six surfaces in this formula 😱 Depending on the situation this may really influence contrast. Lenses with more elements and/or less effective coatings will be even more at risk. This is about the type of flare called veil, which usually can only be seen in direct comparison, as it is an overall degradation of the image. The type of flare that produces "UFO's" or diaphragm reflections. is of course well known, but it follows the same laws. Then there is direct reflection of the filter called ghosting, which will result in highlights being reproduced once at a certain distance of the original image, sometimes upsidedown. We had some beautiful examples of that in the RD1 forum a short while ago in the thread you mentioned and that was with a Summicron 35 and Hoya filter. Not the worst combo by any means. The next problem is especially with wide-angle lenses: The light travelling at right-angles to the filter will have a considerably smaller distance to go through the filter than light striking it at an acute angle, resulting in a difference in refraction and with that in loss of sharpness. Again, the problem is of a character that it will only be seen in direct comparison.
As for protection, in my opinion and experience a lens hood and lens-cap when not in use offer far more protection than any filter without having the chance of degrading the image and as a last resort there is always insurance. But, in the end, if you feel more comfortable with a "protective" filter and are happy with your results, what reason would there be to do otherwise.... 🙂 ? As long as you are aware of the theoretical considerations, that , as always, must be subject to the final result. And remove the filter and use a lens-hood in any high-contrast situation.
Just for completeness sake, a filter for UV protection is not needed with nearly any post-1960 lens.

 

[LCT]

Very interesting Jaap.
Thanks.
LCT

 

[Donald Mann]

Jaap . . . does ancient refer to you or your Leica? 😉

 

[jaapv]

Unfortunately both. I still have my first Leica (I bought it second-hand in the seventies), a 1954 M3. Me? I knew Father Christmas when his beard was brown...........Oh- and I've just worked out I have used 27 camera's since I started photographing at the tender age of 7. 🙄

 

[pfogle]

A little byway to this thread if I may 😉

I bought a 50/2 Hexanon, which I was excited by, having previously owned an AF Hexar, with the 35/2 lens. However, it came with a UV filter I could't get off, so I never felt I'd really seen what it could do.

Then I tried a technique I'd previously used on a stuck 77mm - I screwed in a step-up ring (not too tight!) and then bound them together with a thin strip of gaffer tape (duct tape). You can then easily remove them both, using the larger grip.

I now feel I have a new lens, and the 50 is my current favourite 🙂

 

[hamsong]

I have used B+W filters on all of my lenses for the past 15 years, and have never had a problem with flare. In fact, the slight warming of the B+W Skylight filter is nice to make the skin tones in digital a bit more film-like. I've done comparison shots with the filter on and off, and I can never tell the difference, whether looking at negatives or digital files.

I do weddings all over the world, including very dusty places, and when you see what the filter looks like, you are just glad it's there. I'd much rather wipe off or replace a $25 filter than have to deal with damage to the front element. If you look at old Leica 50mm lenses, you'll see the most commonly listed condition note is: "barrel perfect, slight cleaning marks". At least I can prevent cleaning marks when I pass these lenses on to my kids...

 

[jlw]

Oh- and I've just worked out I have used 27 camera's since I started photographing at the tender age of 7. 🙄

Relax, we've got people here who have used 27 cameras in the past week...

 

[Fred]

Very interesting reading Jaap.

I tend to use filters on all my lenses that will take them, possibly through habit. My kit goes out in all sorts of conditions that I'd prefer to keep the end element as protected as possible. I also use a hood most of the time and the cap stays on when not shooting. If I'm shooting a scene that will likely cause flare I can always unscrew the filter (if I think about it and remember).

I'll have to do some tests of the with and without filter. Cirtainly when I had a day with Leica UK we were given the chance to use any kit they had and none of it had a filter attached. For me, the jury is still out.

 

[hamsong]

The surface to air discussion is interesting reading, but real world results with the addition of filters tend to be less dramatic. As a an example of current lenses that are highly regarded and test well with MTF rating at photodo.com of 4.6 is the Canon 70-200/f2.8 "L" IS lens, which has 23 elements in 18 groups. As a photographer who has used this lens quite a bit, I can tell you that there is no shortage of contrast, even with the 77mm UV filter on the front. The nice thing about the R-D1 is that you can quickly test the effect of a UV filter yourself and get results immediately. Take the same shots in a variety of lighting situations (backlight, front light, side light, etc) with and without a UV filter. Depending on the filter, you'll find that there is no quality loss, no contrast loss, and rarely any additional flare.

Nothing turns an APO 90 Summicron ASPH into a paperweight faster than a scratch on the front element. Since I have not seen flare in this lens in the tens of thousands of shots I've taken with it, I will keep my filters on and my lenses safe. I clean fingerprints and dust off of them after every job. I wouldn't want to do that to the front element...

 

[pfogle]

The surface to air discussion is interesting reading, but real world results with the addition of filters tend to be less dramatic. As a an example of current lenses that are highly regarded and test well with MTF rating at photodo.com of 4.6 is the Canon 70-200/f2.8 "L" IS lens, which has 23 elements in 18 groups. As a photographer who has used this lens quite a bit, I can tell you that there is no shortage of contrast, even with the 77mm UV filter on the front. The nice thing about the R-D1 is that you can quickly test the effect of a UV filter yourself and get results immediately. Take the same shots in a variety of lighting situations (backlight, front light, side light, etc) with and without a UV filter. Depending on the filter, you'll find that there is no quality loss, no contrast loss, and rarely any additional flare.

Nothing turns an APO 90 Summicron ASPH into a paperweight faster than a scratch on the front element. Since I have not seen flare in this lens in the tens of thousands of shots I've taken with it, I will keep my filters on and my lenses safe. I clean fingerprints and dust off of them after every job. I wouldn't want to do that to the front element...

I agree with these comments, but would like to add a couple of points to this discussion.

Firstly, the addition of 2 extra surfaces won't make much difference to image quality IF the filter is (multi-) coated on both surfaces.

Secondly, filters are particularly troublesome with bright sources in the picture because the surfaces of the filter are plane, so cause recognisable reflections. Most lens surfaces are curved, so the reflected images are defocused.

That said, I don't use filters now, and haven't scratched a lens in over 30 years of photography, a lot of it as a working pro. When I did use filters, it was mainly to warm up the images with transparency film, something that's no longer necessary with digital.

However, that doesn't mean I don't think it's a good idea to use filters, especially when working under difficult conditions - I was probably just lucky, and mainly worked in a studio. Also, I have to admit, I was too lazy and probably too stingy to bother 😉

Phil