UV filter : useful for image ?

[Bernard_L]

This is not about UV filters as lens protection. I recall reading long ago that UV filters were not needed anymore for color photo because films had built-in UV filtration; maybe was true, maybe not. I don't use UV filters systematically. But I've been occasionally disappointed by color negative pictures (Reala) taken in high/dry desert (Atacama). Slight blue cast, washed-out colors, and not just for distant scenes.

What is you experience in that respect? I.e., is there something to gain in terms of image quality from using a UV filter? Or would a skylight filter be better? Or none? Thank you for sharing your experience.

[Jac@stafford.net]

What you experienced is likely due to color balance issues. A haze or light warming filter might help.

[Doremus Scudder]

A haze filter is a UV filter (many of them even have a slight yellow cast), and yes, it might help if there's a lot of scattered near-UV that your film is sensitive to. The next step up, as Jac suggests, would be a warming filter. As redundant as this seems, you could always try it - take a shot with and without the UV filter and see if it helps. If you don't have one, it would be worth picking up a used one to test with. Hoya HMC filters are great quality and cheap used in common sizes.

Doremus

[Bernard_L]

Jac, Doremus, thank you for your responses. I suspect the issue, if real, may be more than just RGB color balance (whih I do regardless using a picture of a gray card). Maybe some form of metamerism involving the far blue spectrum, around 400nm: real light and real reflectivities involve a continuous wavelength spectrum. See below (reproduced from Portra160 datasheet) how the magenta layer has a sensitivity secondary peak near 400nm, conducive to de-saturation in an environment rich in far-blue/near-UV radiation.
152087

As for experimenting, I was hoping someone would chime in with actual results. I'll have to experiment in the Alps; when I return to Atacama, I need to have the issue sorted out. I had a quick look and indeed Hoya HMC filters can be had used for reasonable prices.

[Bob Salomon]

Jac, Doremus, thank you for your responses. I suspect the issue, if real, may be more than just RGB color balance (whih I do regardless using a picture of a gray card). Maybe some form of metamerism involving the far blue spectrum, around 400nm: real light and real reflectivities involve a continuous wavelength spectrum. See below (reproduced from Portra160 datasheet) how the magenta layer has a sensitivity secondary peak near 400nm, conducive to de-saturation in an environment rich in far-blue/near-UV radiation.
152087

As for experimenting, I was hoping someone would chime in with actual results. I'll have to experiment in the Alps; when I return to Atacama, I need to have the issue sorted out. I had a quick look and indeed Hoya HMC filters can be had used for reasonable prices.

In the mountains, for color a stronger skylight filter, like a KR 3 would be best with color. At lower levels the KR 1.5. For B&W UV is better.

[Willie]

It has been 20+ years ago that Photo Techniques or maybe Camera & Darkroom magazine did a comprehensive comparison of UV filters. Singh Ray filters came out on top and the difference was easy to see.
They did make a difference and the S-R sharp cutoff UV filters were noticeably better than the others.

[Doremus Scudder]

Bernard,

I see your problem. Perusing the B+W filter handbook, it looks to me like the KR 1.5 might work for you. You can compare the transmission spectra yourself; they're at the back of the handbook available here: https://www.schneideroptics.com/pdfs/filters/BWHandbook.pdf

Best,

Doremus

[Bob Salomon]

Bernard,

I see your problem. Perusing the B+W filter handbook, it looks to me like the KR 1.5 might work for you. You can compare the transmission spectra yourself; they're at the back of the handbook available here: https://www.schneideroptics.com/pdfs/filters/BWHandbook.pdf

Best,

Doremus
At altitude, or in very blue shadows, a KR 3 is the proper choice.

[Bernard_L]

First and foremost, thank you all for sharing your experience and taking the time to write up.
@ Willie : one consideration is cost; I can find numerous used B+W skylight filters on the auction site (e**y.fr), but no Lee filter.
@ Doremus : I had gone through the B+W catalog expecting to see the curves on the pages of respective filters!
@ Bob + Doremus : I'll try a 49mm KR1.5 and see how it goes. I use mostly C41 film, so the gray card should take care of color balance per se. Do A/B tests, and if conclusive, proceed with 46mm and 52mm sizes.

An aside: I have a pair of Vuarnet sunglasses. Landscapes look more beautiful with glasses than without. Incidentally, purple colored flowers become pink, orange, or gray; other than that the auto-white-balance of eye+brain shows me a "normal" image, even the sky looks blue, with improved cloud-sky contrast. I guess these glasses cut out the far blue end of the spectrum, at 420? 450?nm. I tried to take a picture of lanscape+gray card through the glasses, on negative color film. Even after performing the white balance, the colors as recorded by film where nowhere as nice as with eyes through glasses. Such a filter exists in the B+W catalog: UV-Blocking Filter 420, page 26. But, special order, etc... In case you think this business of film reacting differently from the eye sounds like gibberish on my part, see this excerpt from the B+W literature

Because fluorescent tubes are not “thermal radiators”, they do not produce a continuous spectrum like those of the sun and incandescent bulbs. Instead, they emit a sharply defined line spectrum that has high intensity spikes in the green region. Our eyes barely perceive this special green, so the fluorescent light appears to us as nearly neutral in color. However, most color films are especially sensitive to those wavelengths and they react with a strong pronounced cast.

[Bob Salomon]

First and foremost, thank you all for sharing your experience and taking the time to write up.
@ Willie : one consideration is cost; I can find numerous used B+W skylight filters on the auction site (e**y.fr), but no Lee filter.
@ Doremus : I had gone through the B+W catalog expecting to see the curves on the pages of respective filters!
@ Bob + Doremus : I'll try a 49mm KR1.5 and see how it goes. I use mostly C41 film, so the gray card should take care of color balance per se. Do A/B tests, and if conclusive, proceed with 46mm and 52mm sizes.

An aside: I have a pair of Vuarnet sunglasses. Landscapes look more beautiful with glasses than without. Incidentally, purple colored flowers become pink, orange, or gray; other than that the auto-white-balance of eye+brain shows me a "normal" image, even the sky looks blue, with improved cloud-sky contrast. I guess these glasses cut out the far blue end of the spectrum, at 420? 450?nm. I tried to take a picture of lanscape+gray card through the glasses, on negative color film. Even after performing the white balance, the colors as recorded by film where nowhere as nice as with eyes through glasses. Such a filter exists in the B+W catalog: UV-Blocking Filter 420, page 26. But, special order, etc... In case you think this business of film reacting differently from the eye sounds like gibberish on my part, see this excerpt from the B+W literature

Film does not have the same spectral response of your eye, and since the brain is used to interpret the colors you see it doesn't mean that film will respond the same as what you see with your glasses.

[Doremus Scudder]

... @ Doremus : I had gone through the B+W catalog expecting to see the curves on the pages of respective filters!
@ Bob + Doremus : I'll try a 49mm KR1.5 and see how it goes. I use mostly C41 film, so the gray card should take care of color balance per se. Do A/B tests, and if conclusive, proceed with 46mm and 52mm sizes.

Bernard,

The transmission curves for the K1.5 and the K3 (and lots more) are on p. 61 of the B+W catalog I linked to. Don't know why you couldn't find them.

Bob may be right about the K3, but the K1.5 has about the same attenuation of blue at the 400nm spike in the film's response, which is what led me to recommend it. Check out the curves for yourself.

And, Bob is certainly right about film responding differently than your eye. Sometimes you just have to go through a process of trial and error to get the desired filtration effect.

Best,

Doremus

[Drew Wiley]

You need to list the specific color films you intent to shoot. You've mentioned one so far which might or might not be doing what it was engineered to do; but
accurate earthtones isn't something to expect from Reala. I actually keep on hand a variety of UV and sky filters because different films respond differently. As far your extant experience with Reala, there are a number of issues which might have come into play anywhere between condition of the film, the shot itself, and how you are evaluating the final result (prints, scans??). You have to eliminate any repro errors one by one until you truly understand a particular film under your conditions. The learning curve is easier with chrome film because you can just slap it on a lightbox and visually judge. High desert does introduce distinct UV issues. For most color neg films I prefer a pale amber-salmon filter. My favorite is no longer made; but a common competent product is the Hoya 2B. This will counteract not only some of the loss of sharpness due to UV scatter, but the excess blue. It's not a substitute for serious color temperature issues which can
also occur, but suitable for routine tweaking or just leaving on the lens in general. You might try one of those, or a comparable B&W KR 1.5.

[Bob Salomon]

You need to list the specific color films you intent to shoot. You've mentioned one so far which might or might not be doing what it was engineered to do; but
accurate earthtones isn't something to expect from Reala. I actually keep on hand a variety of UV and sky filters because different films respond differently. As far your extant experience with Reala, there are a number of issues which might have come into play anywhere between condition of the film, the shot itself, and how you are evaluating the final result (prints, scans??). You have to eliminate any repro errors one by one until you truly understand a particular film under your conditions. The learning curve is easier with chrome film because you can just slap it on a lightbox and visually judge. High desert does introduce distinct UV issues. For most color neg films I prefer a pale amber-salmon filter. My favorite is no longer made; but a common competent product is the Hoya 2B. This will counteract not only some of the loss of sharpness due to UV scatter, but the excess blue. It's not a substitute for serious color temperature issues which can
also occur, but suitable for routine tweaking or just leaving on the lens in general. You might try one of those, or a comparable B&W KR 1.5.

Just "slapping a chrome on a light box" is not necessarily the best way to evaluate the slide unless you know what the K temperature and CRI is of that box. If it is not a high CRI, daylight balanced box then you can not accurately evaluate the film.

[Bernard_L]

Film does not have the same spectral response of your eye
@ Bob: agreed. My little anecdote was meant to illustrate two points: this one, and the fact that, before the continuous spectrum is recorded in schematic form as just three colors, subtle things can happen that cannot be explained by just RGB balance or even matrix transforms.

Don't know why you couldn't find them.
@ Doremus: because I expected to find them on the pages of the respective filters. Looked up filters that were potentially useful, did not read the document front-to-back.

Sometimes you just have to go through a process of trial and error to get the desired filtration effect.

accurate earthtones isn't something to expect from Reala. I actually keep on hand a variety of UV and sky filters because different films respond differently.
@ Doremus, Drew. Note taken: I need to practice more, make systematic tests, and find out about filter-film interactions, change from Reala to Portra for certain uses. I certainly do not have the same level of experience and knowledge as you. At some point I was under the illusion of covering all issues by recording a pic of a Wolf Faust target (each film) and making a curves-matrix profile with Argyll.

Again thanks to all who contributed. Time to prepare the backpack, climb, and make systematic tests.

[Bernard_L]

An afterthought. Sensitivity curve of Reala, from Fuji datasheet. Extends more beyond (lower than) 400nm than in the case of Portra (my post #4). Possibly an explanation for my problems with Reala in high desert light. In retrospect, that is where I should have started looking. Although, the curves have a look of "hand-redrawn". Well...
152235

[The Joker]

plain glass blocks most most UVB (non visible) wavelengths but passes approx 75% of UVA which is closest to visible light. But lenses with coatings may well stop some UVA light but not necessarily all. How much effect the UVA light will have obviously depends on how far below approx 400nm your film is sensitive too but also how much of it there is in your subjects spectrum. So a UV filter may have a significant effect in some lighting situations and very little or none in other situations.
At high altitude less UVC and UVB will be blocked by the atmosphere so could have a greater imapct on film depending on how low its sensitivity goes below 400nm so a UV filter could have a more significant effect at high altitude depending on film but remember plain glass stops most UVC and UVB anyway but there could be a lot more UVA light at altitude since there is less atmosphere to block it.

If in doubt try out a couple or three filters on same subject at same time to see the differences but also note the lighting conditions and altitude to get a feel for when conditions suggest a UV filter may be benficial in future.

[The Joker]

Vuarnet sunglasses are designed to give high contrast in low light. They have a strong yellow/orange filtration. i.e. minus visible blue but will probably also cut a fair amount of UVA. They also have ND to cut light levels as most sunglasses designed for altitude do. Life always looks sunnier through a pair of vuarnets. ;)