What's considered "high altitude" when it comes to UV filters?

[patrickwiththecamera]

Hi all,

I've searched high and low (no pun intended) for an answer to this question: at what elevation/altitude are longpass (as opposed to skylight) UV filters useful? I'm talking about a Wratten 2A or 2B versus a 1A (or the respective equivalents for other manufacturers) . Like, is 5,000 ft/1500 m high altitude? 8,000 ft/2500 m? 12,000 ft/3,700 m?

I primarily shoot Ilford FP4 on 4x5 at the moment, and would like to do some photos on Mt Rainier around the 8,000-10,000 ft/2,500-3,000 m elevation range. I was contemplating adding a Formatt-Hitech 400nm filter to my kit for this purpose. Any thoughts? I'd put this filter behind a circular polarizer, a 15 or a 24, and possibly a GND.

Thanks!

[Doremus Scudder]

How much UV makes it through to the ground is a function of how much UV gets absorbed by the atmosphere by water vapor and dust. So, even in comparatively low altitudes where the air is dry and clean, lots of UV can make it through (think Death Valley, etc.). Higher altitudes, however, say 5000-6000 feet and above, on nice dry and clear days are where the UV component is highest since the protective thickness of the atmosphere is less. It's a continuum, however, the higher you go, the clearer the atmosphere, the more UV. Judging what filter to use is a matter of judging the way the sky looks; dark, deep blue and clean crisp air would be sign that lots of UV was making it through. Up at 10,000 ft on Rainier on a clear summer day would be just the situation to use filters for eliminating UV.

How much attenuation of the UV you need depends on other things beside the actual amount of UV present, like the amount of distance in your scene (i.e., how much UV haze might be between you and the farthest object) whether there are white clouds in the sky illuminating some of the shadows, etc.

If you're shooting color instead of black-and-white, anything stronger than the 1A or UV filter will warm things a bit, which might be needed for blue-lit shadows, etc. With color transparency material, getting the right amount of attenuation is critical, but with negative materials, corrections can be made when printing. For black-and-white the question would be how much haze cutting is needed.

Here are the Wratten descriptions from the Kodak Photographic Filters Handbook for your information:

The Wratten 1A filter cuts wavelengths shorter than about 380mn, is pale pink, and effectively eliminates UV but not much of the visible spectrum. However, it still transmits about 1% of light in the 310-380nm band. This is the "skylight" filter. The handbook states: "Pale Pink. Absorbs ultraviolet radiation. Reduces excess bluishness of outdoor color scenes photographed in open shade under a clear, blue sky."

There are also UV filters from other manufacturers (e.g., Hoya) that cut rather sharply at about 370-380nm, but appear clear, not light pink. They would act similarly, maybe without so much attenuation of the visible blue.

A 2B filter cuts sharply at about 390nm and a 2A at 405nm. Both cut more UV plus some visible blue light. Kodak does not recommend them for color photography for this reason: "...2A, 2B and 2E filters absorb varying amounts of ultraviolet radiation - more than the No. 1A filter. Because these filters also absorb some blue light, we do not generally recommend them for outdoor color photography." They are recommended rather for cutting progressively more haze in black-and-white photography.

"2A Pale Yellow. Absorbs ultraviolet radiation below 405nm. With black-and-white materials, reduces haze. Acts as a barrier filter in fluorescence photography."

"2B Pale Yellow. Absorbs ultraviolet radiation below 390nm. Slightly more effective when and excess of ultraviolet radiation is present. Attenuates UV for fluorescence photography and for the optical system of color printers."

Moving up the scale is the 2E, which "absorbs ultraviolet radiation below 415nm. Similar to a No. 2B but absorbs more violet."

And the #3, which starts cutting at around the same place as a 2E, but has a longer slope of absorption into about 450nm. It's "Light Yellow. Provides partial correction for excess blue in black-and-white aerial photography and motion-picture photography."

The next filter in the list is the #8 yellow filter.

Note that you don't need a UV filter if you're using other filters that eliminate blue and UV, like your 15 or 24 (or even a #8). They do the job already; you'd just be adding more surfaces that would degrade the image. Only use a UV-cutting filter when you'd make the shot without a filter but are worried that the unseen UV-haze will affect the rendering.

Hope this helps.

Doremus

[Two23]

I usually used a standard yellow filter, FP4 when hiking on Mt. Ranier.


Kent in SD

[patrickwiththecamera]

Thanks for the detailed response, Doremus!

The bit you wrote (paraphrashing) "there's always UV" is basically the crux of my question. Some photogs never take their UV filters off - ever. And I'm guessing overall sales of 1A filters to 2A filters are 10,000:1. I just got to thing - after I got extremely cooked on Rainier last weekend despite applying sunblock every hour - "I know I need a UV filter, but how strong?"

I got so wrapped up in thinking about the UV filters that I wasn't considering how my other filters were affecting that part of the spectrum! This saved me a chunk of change for the couple of photos I have in mind!

Note that you don't need a UV filter if you're using other filters that eliminate blue and UV, like your 15 or 24 (or even a #8). They do the job already; you'd just be adding more surfaces that would degrade the image. Only use a UV-cutting filter when you'd make the shot without a filter but are worried that the unseen UV-haze will affect the rendering.

Doremus

[Drew Wiley]

Depends on how clear the air is. Sea level can have high UV issues. People get sunburn especially quickly on some beaches, for example. My wife sure learned that the hard way in Hawaii, where the air can be pristine. What you didn't state is if you are intending to shoot color film too, because the ideal UV or skylight filter for color all depends not only on the specific film, but certain other issues too. I see absolutely no reason to stack a UV filter with a contrast filter, or anything like a redundant ND grad for FP4 purposes. It will merely add more reflective surfaces and end up being counterproductive. Even a basic light yellow or yellow-green contrast filter will kill all the UV, with deeper orange or red having the significant benefit of cutting through more haze too. But as per the topic per se, UV does tend to increase with altitude, depending. Here in our California Sierras, manmade smoke and smog tends to thin out around 6,000 ft; natural pollen haze and lighter smoke around 8,000. Then as you get still higher, UV increase with air clarity, and can be a significant factor between 12,000 to 14,000 ft up. But that's nothing compared to what one might encounter in the much higher Andes or Himalayas. If you intend to work with color film at high altitude, then re-post the question with a specific film in mind. Otherwise, I'd totally ignore the issue for black and white work, and simply take a basic selection of contrast filters - and I have abundant experience with quite a variety of UV and skylight filters, having done decades of high-altitude photography, both color and b&w, FP4 included. As far as quality, I strongly recommend multi-coated glass screw-in filters in the mountains, not only for their anti-reflective properties, but for ease of cleaning and sheer durability. Gel and resin filters might suffer. Multicoating is even more important when someone simply leaves a filter on for sake of routinely protecting the lens itself. A couple years ago I got a steal on a Fuji 6x9 RF that had a totally mauled skylight filter on it the whole time, yet the primary lens itself didn't even have a speck of dust. But if I had that custom in relation to b&w shooting, I would simply leave on my most used (or most potentially used for a specific outing) black and white contrast filter instead.

[Jerry Bodine]

Attached is a scan of a print on Galerie paper I made of the Winthrop Glacier on Mt. Rainier from a ridge at 7800’ altitude a few years back. At that time I wasn’t too versed with filter effects, so it was an experiment. I made three exposures fairly quickly with gel filters, #8 (yellow), #15 (G) deep yellow, then # 25 (red), so no glass in front of the lens. I selected the negative that I preferred (can’t recall which filter). The film was HP5 Plus, but checking the spectral sensitivities against FP4 Plus in the data sheets, there’s little difference between the two. I did know, however, that the filters closer to red would deepen the shadows more, as they were illuminated by blue skylight, but I made no exposure allowance for that. So I’d conclude there was no issue with UV under these conditions. AND I suffered no sunburn.

[Jim Andrada]

How high is high? Good question. Tucson is around 2700 feet, which in and of itself isn't so high, but the amount of water vapor in the air can be really low - I think it's the skin capital center of the US due to the high UV and overall absence of shade.

[J. Patric Dahlen]

I would just use the #15 deep yellow filter. It blocks all UV, cuts through the haze enough to sharpen up the details in the distance and darkens the sky without giving that unnatural look you can get with a red filter or a polarizer. That last bit is of course a matter of taste.

[BrianShaw]

It seems that altitude is just one factor in UV level. Right now I’m at near sea-level but experiencing an extremely high level of UV.

https://www.epa.gov/sites/production...vradiation.pdf

[Alan Klein]

Any special recommendations with Velvia 50?