Landscapers – why is that blue filter in your bag?

[Heroique]

Last week, I used my blue filter (#47) for the first time in years, though it’s always with me.

It was a b/w mountain scene in which I wanted to reduce overall contrast, at the expense of light values for the dark, evergreen trees whose details I’m otherwise careful to capture. It worked, but it looks like I added haze to the distant air. :(

I don’t foresee using this filter again anytime soon. At this point, I consider it “dead weight.” Not a whole lot of dead weight, but every ounce counts where I hike. Our relationship might be coming to an end.

On the other hand, I also have a Lee 80d filter (below) whose only purpose is to correct my B+W 10-stop ND filter’s strange, golden-brown cast on transparency film. This 80d filter costs me 2/3 stop, and adjusts color temperature about +1000 K. The B+W ND filter isn’t neutral at all, despite the “neutral” in its name, but the Lee 80d filter forces it to behave. So I’ll keep this blue filter.

If you have one, why do you use it?

[Mark Woods]

"ND" filters, with few exceptions, are not neutral. They generally shift a bit "warm" or lower the color temperature. I've proven this using a densitometer, and with the electronic capture (i.e., digital), it's obvious to cinematographers that the QC is a problem. There are various filters "recommended" to sold the IR problem, but it's really an issue with the difficulty of making a true neutral density filter. Use whatever works.

[Bill_1856]

My blue filter came with a large set of Linhof filters I bought several years ago. They are in a beautiful fitted case, so I carry them all but have never used the blue one. (Unfortunately, the Polarizer has delaminated.)

[Heroique]

I’ve proven this using a densitometer, and with the electronic capture (i.e., digital), it’s obvious to cinematographers that the QC is a problem...

That’s interesting about QC. I once borrowed a color meter to do some unscientific testing – a Nikon 2-stop ND produced a +160 K shift (more blue). And a Tiffen 3-stop ND caused a +340 K shift (a little more blue than the Nikon). But these non-neutral shifts would, I imagine, produce little if any noticeable difference to the naked eye. What’s strange about the B+W 10-stop ND is the pronounced and noticeable DROP in temperature, about -970 K, which is why my Lee 80d stays in my pack for pretty good correction. I wish the 80d under-corrected (leaving more warmth) rather than over-corrected by +30 K, but life isn’t always fair.


I carry them all but have never used the blue one...

I’m beginning to think there’s potential here for a new club. ;^) This afternoon, I was paging through AA’s The Negative and noticed a couple of landscapes w/ blue filters. In each case, the caption’s tone suggests an indifference toward the filter, as if he included the images for illustration only.

[Kirk Gittings]

A lot of William Clifts work is with a blue filter. It appears to me that he is chosing to exagerate atmospheric haze so that the landscape becomes very ethereal in the distance. This is a terrible reproduction (lifeless) but you'll see what I am talking about.

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[John Kasaian]

I like shooting in fog. Blue seems to help in making fog look a little bit foggier.

[Merg Ross]

I like shooting in fog. Blue seems to help in making fog look a little bit foggier.

John, you beat me to it, and you should know about fog! Yes, the blue is also my filter for fog.

Hope all goes well down your way.

Merg

[Leszek Vogt]

I like shooting in fog. Blue seems to help in making fog look a little bit foggier.

John, all you need to do is get over to Kerman Jct....they used this filter over the entire area.

Les

[Doremus Scudder]

I carry a Wratten 44 or 44a when I can, which turns panchromatic film orthochromatic. Blue-green sensitivity only can be very gratifying in shots with lots of foliage and rather dark blue-sky lit shadows, rendering both a lot lighter and turning what would otherwise be a harsh scene into something softer and more voluptuous. It is also useful for lightening skies and enhancing atmospheric effects (a 47 filter will do this too, to a bit greater extent).

An 80B color-correction filter has much the same effect, and I carry one of those when I don't have room for the book of gel filters. I use it for the same reason.

A 47 filter will reduce the film's sensitivity to blue only, approximating the look of the earliest emulsions. If you like this look, that would be a good reason to use a sharp-cut blue filter. I prefer the ortho look to this, hence my preference for the 44 or the 80B.

FWIW, B+W used to make a 081 filter, coated glass in a brass mount, that has a similar transmission spectrum to the Wratten 44 filters (it's somewhere between the 44 and the 80B). I've been trying to get my hands on one or two of those in 52mm and 67mm for years, but have not been able to come up with one. If you've got one and don't need it...

There was a thread on fog and blue filters here or maybe on APUG some time ago. I think I made the point there that if you are in fog, I mean, completely enveloped by it and it is filtering the light that illuminates the scene you are photographing, a blue filter will just give you a longer exposure and have the predictable effect on colored subjects; it won't, however, "enhance" the fog in that case. Now, if the fog is a part of a scene lit by the sun, or if the fog is patchy or thin in places, then the blue filter will enhance the fog, since it lightens the blue light coming through it in relation to the other illumination.

Best,

Doremus

[Struan Gray]

Fog is made water droplets which scatter light by wavelength-independent Mie scattering, and so is white. A coloured filter will not emphasise it.

Haze from smaller particles of dust (or oil from gum trees or heather) is famously blue, for the same reason that the sky is blue - you are seeing light scattered by Rayleigh scattering, which is stronger at the blue and UV end of the spectrum than the red. A blue filter will emphasise this because it cuts out the longer wavelengths coming from whatever is beyond the hazy air.

[Brian Ellis]

I bought a blue filter (and others) when I got back into photography and bought a Nikon F4. I don't remember now why I bought it but I never put it on the camera. I think it still sits in its original plastic container somewhere in the house.

[Heroique]

Many of my b/w prints with distant mountains surprise me for being more hazy than I remember.

Probably because in addition to the blue scattering, which the eye can see, there was also a high-violet (not quite UV) scattering, which the eye has trouble seeing but is still picked up by the film.

Kind of like using a blue filter even though you left it at home!

[Arne Croell]

I do not carry a blue filter, but a blue-green one (B+W 470). I use it occasionally in redrock country, for increasing contrast between sandstone layers (red sections vs. beige sections); also to lighten foliage green and open up the shadows in forest scenes.

[Doremus Scudder]

Fog is made water droplets which scatter light by wavelength-independent Mie scattering, and so is white. A coloured filter will not emphasise it.

Haze from smaller particles of dust (or oil from gum trees or heather) is famously blue, for the same reason that the sky is blue - you are seeing light scattered by Rayleigh scattering, which is stronger at the blue and UV end of the spectrum than the red. A blue filter will emphasise this because it cuts out the longer wavelengths coming from whatever is beyond the hazy air.

That may all be true, but still, the color temperature on a cloudy day or in fog is much higher (bluer) than on a sunny day, and much more blue than what color film is balanced for (hence the use of correction filters by many on cloudy days, especially when white balancing video).

That would lead me to believe that using a blue filter with black and white film in a situation where there is light transmitted through fog together with light transmitted from a clear sky (i.e., sunlight) would lighten the bluer (higher color temperature) light and objects lit by it in relation to the objects lit by the warmer (lower color temperature) sunlight. This has been my experience as well. Whatever is meant by "emphasize," the blue filter will have an effect on such a scene; and, if you use a blue filter on an overcast day or in the middle of the fog, it will affect everything equally, in essence having no effect on relative values, just an overall effect on exposure.

Now, reflected light from fog is the same as reflected light from clouds...

Best,

Doremus

[Mark Woods]

Fog and an overcast day have the same color temperature as the sun, roughly 5600* K. It's an urban myth that fog and overcast has a higher CT. It's one of the questions I've put on tests at AFI after I take the class outside on an overcast day with my CT meter. The sun is illuminating the overcast, hence the CT is roughly equivalent to the sun's 5600*K. Not so different from putting a silk lit by the sun over a set will have the same CT as the sun (if the silk is neutral and no color shift, unlike unbleached muslin). Light reflected from fog, etc., will be roughly the CT of the original source. Lowering the CT in an overcast situation makes the image more pleasant to look at for many people. If you have a CT meter, take it out and see for yourself.

[Drew Wiley]

The old blue-sensitive plates often produced a kind of monumental scale to the landscape. The sky could just be too blank at
times, but I still admire the sense of atmosphere and distance this could achieve under skilled use. Once in awhile I'll tote a blue filter, but rarely actually use it. In the mtns I seem to be able to fine-tune the same look just thru thoughtful film exp, dev and printing. Here on the coast I let real fog do the work for me.

[Sal Santamaura]

There is no blue filter in my bag. A UV filter, however, is on every one of my lenses. Unfortunately, most of the planet already exhibits enough haze.

Those who do have a blue filter in their bags will be prepared in case there's a sudden elimination of air pollution. Then they can use the filter to make pictures that remind them of the "good old days." :)

[ROL]

I rarely, and specifically, only carry the dead weight of the orphan blue when I want to accentuate the atmosphere (i.e., fog, spray, etc.) between the camera and important compositional elements. As I referenced in an earlier post, I have no present interest in purposely lightening blue skies, though that is also a common use for some.

But I'll go further (so that I can travel farther;)) with the thought. Overall, I have standardized all of my good glass (B+W) carry filters at 67mm with step up rings on both LF (5x7 variety) and MF lenses. I only carry (one size of) filters specific to do the job at hand.

Monochrome:


Most of the time I carry only yellow and deep yellow, occasionally including either a warming polarizer, mainly to add "density" to some specific effect, and/or a sky/haze only to protect the lens from water or blowing dust/sand. Mostly, I can get along only with the yellows, though the polarizer has occasionally given me a somewhat preferable negative to work under the enlarger, in certain circumstances.

In red rock country, I generally carry only a single green filter, as it encompasses most of the reasons I would need a yellow and enriches reds tonally. I add yellow in the fall (see below).

In the spring, I carry my usual yellows, with the green included to enhance new foliage. Conversely, in the Autumn I match the most significant compositional tones to one or the other of my usual yellows.

Though I have them, I neither use nor carry either orange or red for normal natural light panchromatic work.



Color:

I rarely shoot color film any longer, as I now view that to be entirely within the realm of digital. When I did (do – never say never), I only include the (double duty) polarizer, and possibly the haze*.


That makes my normal (carried) filter pack from 1 to 3 filters total, lessening dead weight quite a bit. Now, if only I could find a way to remember that the intended filters are in the pack at the start of each trip.





* though I might be a bit hazy on this.

[Drew Wiley]

A couple years ago I was trying to get above a lot of forest fire smoke snaking thru the canyons in Sequoia, and finally stopped smelling the smoke at a very pristine off-trail lake at about 10,000 ft, with some spectacular pointed crags in the
background. There was still enough "atmosphere" between the foreground and peaks at the other end of the lake, in fact, way
too much. I could hardly see detail at all, just silhouettes of the crags. So I stuck on a red filter for a couple of shots, including one with a very long lens aimed at the summite area of one of the crags. When I got home and made a large print,
right there on the exact pointy summit was a golden eagle in perfect focus - it was way up there, so even in the print looks
tiny - but right smack dab on the center of attention anyway. Sometimes filters help, sometimes dumb luck too.

[E. von Hoegh]

"Landscapers – why is that blue filter in your bag?"

There is no blue filter in my bag. I have used one though, to bring up detail in open shadows. One might also be useful if one wanted to replicate the look of wetplate, with a featureless sky.

[Heroique]

AA lists four practical observations about color temperature in The Negative, which photographers here may want to compare to their own experience. I don’t think anyone should view them as statements ex cathedra, but rather go by what they experience in the field, and learn how this experience translates in personal darkroom and scanning work:


1. The sun gives warmer (redder) light early and late in the day. Clear blue sky is very strong in blue, violet, and ultraviolet, especially at high altitudes.

2. A clear blue sky gives colder (bluer) light than hazy or partially cloudy sky in which the haze or clouds scatter sunlight.

3. The light on an overcast day is about the same color temperature as the light from sun and clear sky.

4. Shadows illuminated by open sky are colder (bluer) when the sky is clear than when it is misty, partly cloudy, or overcast.

If you merely glance over these observations, they may seem a bit contradictory, but read carefully, they support each other. Personally, the key lesson I take away from them is that shadows on a sunny, blue-sky day are being illuminated by the blue sky, not by the direct sunlight. The higher up the mountain > the more clear the blue sky > the more blue light illuminating (and being transmitted by) the shadows.

[Mark Woods]

Hello Heroique, there are all excellent observations. The thing about going up higher is that there is less atmosphere to cut the UV, hence the yellow haze filters. This is all in line with what I posted earlier. In the morning and evening, particularly if a fire has been burning, the sun's color temperature can be as low as 2800* K. I measured it when there was a fire in the Hollywood hills. Also, as the CT is lower approaching the CT of a flame, the meters one uses can be off by as much as a stop to give a reading that will make a thin neg. If one is going to shoot in this environment, one should really shoot some tests.

[Drew Wiley]

47 and 47B are sharp-cutting and will totally darken any true green as well as red (most green foliage is not true green, so
will still have some response, but not much). I'd rather use a deep cyan, though these are not particularly resistant to fading
over time. But I just go the lazy way, and grab a tungsten-conversion blue filter from my color film kit, when I want to use
this approach. At least I've got something coated that way. Pollen haze etc get quite a bit higher in altitude that many people realize, usually at least up to 8000 ft. Above timberline the rules of the game change somewhat, or out in parts of
our SW deserts. I like a jump start with orthopan films like ACROS in such circumstances - saves me some filter factor. A
dense 47B might cost you four stops, 47 at least three!

[Struan Gray]

the color temperature on a cloudy day or in fog is much higher (bluer) than on a sunny day, and much more blue than what color film is balanced for

This is wrong.

I'm more used to thinking in terms of spectra than colour temperatures and mireds. Sea level sunlight looks like a 5500 K blackbody superimposed with absorption bands from the main atmospheric gases and water. Light from the blue sky is canted by the Rayleigh 1/(lambda)^4 law and has proportionately more blue and UV than red and IR. Saying that this has a higher colour temperature is sometimes done, but it implies that the spectrum is still roughly black body, just with a bit more blue. But it isn't really, which is why you get such strong shifts between perceived colour and recorded colour when photographing gentians at altitude.

On cloudy and overcast days the diffuse light from the blue sky is overwhelmed by diffuse light from the clouds, which has pretty much the same spectrum as the sun itself. The colour temperature is unchanged from direct solar irradiation.


I agree that if you have a situation where the background is lit by bluer light and the intervening mist or fog by redder light, then a blue filter will cut through the fog and boost the background. I've only encountered this situation on a couple of occasions - both were red rainbows at sunset - and in those cases the last thing I wanted to do was emphasise the background.

Most of the time you have white fog (which you'll need IR or teraherz wavelengths to cut through) or blue haze, in which case a blue filter will emphasise the haze over the background.


As it happens I do own a blue filter, for using daylight film in tungsten lighting. Oddly, I haven't had much call for it when shooting landscapes.

[Robert Langham]

I keep a blue thinking I'm going to use it to open up a shadow and flatten the tones in a sky.....ought to give up a couple sheets of film and test it I guess. I did use a green in Canyon de Chelly on a couple shots.

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[jb7]

Nice Robert- I wouldn't have thought of green...
That's a big shadow...

[Mark Sampson]

If you live in the humid East like I do, the problem is usually skies that are too light and shadows that are too open. So a blue filter is rarely necessary- yet I carry a Wratten 44 gel and have used it occasionally.

[ROL]

True enough. I have always thought that if forced to live east of the Continental Divide for any great length of time (shivers up spine, involuntary retching*), I would investigate making those conditions work for me in interpreting landscape. I always feel it best to go with what you got, unless one's visualizations are more hyperbolic than natural. As a devotee of natural light photography, my maxim is always to dance with the one that brung ya, errh natural light. In more general art terms, I'd be thinking more Hudson River School than California Plein Air. While Western Light (in)famously pervades much of the most widely appreciated landscape photography (insert name(s) here) the challenge for me in photography as fine art has always been finding regionally relevant compositions expressed in visually compelling tones.




* I did live in Vemont and New Hampshire for a couple of winters, having driven across the country twice (and back) in a VW bus – there are many wonderful landscapes of specific character not available in the West.

[Robert Langham]

Shiprock sized!

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[Doremus Scudder]

Fog and an overcast day have the same color temperature as the sun, roughly 5600* K. It's an urban myth that fog and overcast has a higher CT. It's one of the questions I've put on tests at AFI after I take the class outside on an overcast day with my CT meter. The sun is illuminating the overcast, hence the CT is roughly equivalent to the sun's 5600*K. Not so different from putting a silk lit by the sun over a set will have the same CT as the sun (if the silk is neutral and no color shift, unlike unbleached muslin). Light reflected from fog, etc., will be roughly the CT of the original source. Lowering the CT in an overcast situation makes the image more pleasant to look at for many people. If you have a CT meter, take it out and see for yourself.


... Sea level sunlight looks like a 5500 K blackbody superimposed with absorption bands from the main atmospheric gases and water. Light from the blue sky is canted by the Rayleigh 1/(lambda)^4 law and has proportionately more blue and UV than red and IR. Saying that this has a higher colour temperature is sometimes done, but it implies that the spectrum is still roughly black body, just with a bit more blue. But it isn't really, which is why you get such strong shifts between perceived colour and recorded colour when photographing gentians at altitude.

On cloudy and overcast days the diffuse light from the blue sky is overwhelmed by diffuse light from the clouds, which has pretty much the same spectrum as the sun itself. The colour temperature is unchanged from direct solar irradiation...

Gentlemen:

I stand corrected! I was referring to numerous sources on color temperature and white balancing on the web that indicated the usual 5500°K for sunlight and color temperatures ranging from 6000°K to 7500°K for light from an overcast sky (see: http://en.wikipedia.org/wiki/Color_temperature and http://www.schorsch.com/en/kbase/glossary/cct.html for two such sources; there are scores more that agree with them).

However, I deem your expertise to be a better and more trustworthy source of information that most web sites, so I will concede the point and rethink my idea of why a blue filter "enhances" fog and mist in a scene.
BTW, I hate the use of the word "enhance" in this discussion, which is why I put it in quotes. Do we mean lighten or darken when we say we use a filter to "enhance" the fog? What I strive for when using a blue filter to accentuate fog is to render it lighter than it would be without the filter.

Many photographers (including Merg Ross earlier in this thread) do use a blue filter to lighten fog and mist in a scene. If the color temperature really does not vary much from that of daylight, then I wonder what mechanism is at work here. Possibly there is a lot of haze in conjunction with the fog, possibly something else is making it "bluer" so as to render it lighter in the final print.
What I assumed (albeit incorrectly) was that light passing through water vapor in the form of clouds or fog was filtered in a similar way to light passing down through water, i.e., becoming proportionally bluer with increasing amount of absorption/reflection from the water (red light is reduced significantly in water after just a few meters).

That said, I use my cyan and blue filters less for fog and mist than for achieving a quasi-orthochromatic look and boosting shadow values. In many cases that would otherwise be rendered rather harsh, getting rid of the red sensitivity of the film gives a pleasing smoothness and luminous, detailed shadows. This effect is particularly gratifying in scenes with lots of foliage or harshly-shaded whites.

Best,

Doremus

[Struan Gray]

Doremus, experiment trumps theory every time. If a filter works for you, full speed ahead and damn the torpedoes.

[Heroique]

Possibly there is a lot of haze in conjunction with the fog, possibly something else is making it “bluer” so as to render it lighter in the final print.

A mixture is what I suspect too.

It’s a crazy, complicated, mixed-up world out there.

Mother Nature is trickier than schoolroom blackboards.

[Doremus Scudder]

On a related note: I've noticed that the shaded areas in clouds can vary a lot in color. Often the shadows are lit by surrounding skylight, making them rather bluish, sometimes they are lit by the setting sun, warming them up substantially. During or before big thunderstorms, the darkest areas of the clouds often take on a greenish hue. Filter choice in these cases would be based on the desired effect and the color of the shadows.

I can imagine that something similar happens to fog, which is really just a cloud with an altitude problem. Fog shadows lit by skylight would lighten considerably with a blue or a cyan filter. This is likely what I am experiencing when I use a filter for that effect; reducing the contrast in the fog somewhat and rendering the shadowed areas a bit lighter. A yellow-red filter would have the opposite effect.

Best,

Doremus