Blue filters and fog

[36cm2]

I recently read an interesting post that noted that blue light is diffracted by air more easily than other colors. The post mentioned that Ansel Adams exploited this effect by using a blue filter to accentuate mist across distances in some of his landscapes.

Is this correct? E.g., if you are photographing a setting with thin fog, will the use of a blue filter accentuate the fog and increase its impact from foreground to background?

Thanks for any insight.

Leo

 

[w9cae]

I have read the same also. Last time we had some fog I was not privy to this info & tried some other filters with varying results. Hopefully next time there is some fog I will get the opportunity to try, and I will post back here.

 

[Rick A]

I've used a blue filter with modest success. I'm still not sure if I like the effect, I'll have to use it more with different situations to be certain. I havent had chance to use it with large scale landscapes and fog banks, I think that is where it would prove itself.

 

[bsdunek]

I have a 'haze blue' filter I got from Spiratone about 40 years ago. If there is fog or mist in the air, it does emphasize it to some degree. I don't have any examples handy right now.
The other thing it can do is make 'night scenes'. On a sunny day, add the blue filter and underexpose a couple of stops and it looks like bright moonlight. That's what they used in the movies for night scenes years ago.

 

[w9cae]

I have a 'haze blue' filter I got from Spiratone about 40 years ago. If there is fog or mist in the air, it does emphasize it to some degree. I don't have any examples handy right now.
The other thing it can do is make 'night scenes'. On a sunny day, add the blue filter and underexpose a couple of stops and it looks like bright moonlight. That's what they used in the movies for night scenes years ago.

Turn day into night what a wonderful idea. But I guess one would have to be careful with the subject matter ? Cars might ruin the effect ?

 

[Steve Smith]

On a sunny day, add the blue filter and underexpose a couple of stops and it looks like bright moonlight. That's what they used in the movies for night scenes years ago.

I thought a red filter was used for this (black and white film).


Steve.

 

[Marco B]

I only tried it once, and have attached two scanned contact sheets of four negatives of two shots. The upper contact prints are just normal without filter. Lower negatives in the sheets with blue filter. There is a visible effect, but it is relatively small, and in this case, I decided on a print of the upper left negative where the filter was not used.

The difference between the contact sheets is that one is printed at grade 2 and the other at 3. Grade is written with pen in the upper right image.

Marco

 

[pentaxuser]

I thought a red filter was used for this (black and white film).


Steve.

That was my understanding as well. Isn't this why the contrast between the clouds and sky stands out and makes the night light look a little artificial. It was moonlight on steroids : "Americaine Nuit" I think it was called. The older B&W cowboy films often used the technique.

A blue filter in effect reduces the blue of the sky to a uniform white on the print which would not be the effect desired. Wasn't a blue filter recommended for shots where the photog considers the sky to be "unwanted" allowing another sky to be imported into the scene for a better print?

pentaxuser

 

[Photo Engineer]

Just as a yellowish filter is a haze filter, by removing blue and UV light, a blue filter passes blue light and accentuates any haze or fog. A red filter does nothing in this regard except incidentally by removing blue and UV, it decreases haze. It can also increase contrast between the blue of the sky and the white of the clouds. But then a good yellow filter will do that as well.

PE

 

[Ian Grant]

Just shoot straight in fog, works perfectly.

I had a huge row back in the early 90's when I said I was off out shooting in the fog, my then partner screamed at me that I wouldn't be able to get any images

She was very wrong, (also a photographer & film maker - she should have known better). One of my best selling images was made that day in thick heavy fog

Ian

 

[Ray Rogers]

I have a 'haze blue' filter...
The other thing it can do is make 'night scenes'. On a sunny day, add the blue filter and underexpose a couple of stops and it looks like bright moonlight. That's what they used in the movies for night scenes years ago.

bsdunek, Steve, pentaxuser

The blue filter is used for this effect with color film....

Ray

 

[keithwms]

Yes Leo, a blue filter can sometimes enhance fog. You may also find that a polarizer turned the 'wrong' way may also enhance fog for you. You might also try ortho film. It really depends a lot on the scene, the light, the direction of the light etc.

The best way to get good fog, though, is timing... if you understand dew point then you're probably going to know exactly when to be in the right spot and what angle to shoot from. My attempts with various filters never delivered results as dramatic as getting out of bed early and applying some patience

By the way, I suspect that primary mechanism for scattering from ground fog and haze is Mie scattering, in which the size of the water droplets has a correspondence to the wavelength scattered. The droplets are quite random in size and hence all wavelengths are quite equally scattered, producing whitish scattered light. Quite often people speak of Rayleigh scattering and its 1/wavelength^4 dependence, which suggests much stronger scattering from shorter (bluer) wavelengths than IR, but my feeling is that Mie normally plays the larger role with ground fog. A point of confusion is that there are two scattering regions one must consider. There is (1) scattering in the upper atmosphere between your subject and the sun, and (2) scattering between yourself and your subject. I think Rayleigh applies mostly to (1) and Mie to (2). I haven't put much thought into it though, honestly.

 

[Poohblah]

Yes Leo, a blue filter can sometimes enhance fog. You may also find that a polarizer turned the 'wrong' way may also enhance fog for you. You might also try ortho film. It really depends a lot on the scene, the light, the direction of the light etc.

In theory, isn't using a blue filter on pan film equivalent to using ortho film?

 

[Photo Engineer]

In theory, isn't using a blue filter on pan film equivalent to using ortho film?

No.

PE

 

[Poohblah]

No.

PE

Explain. Does pan film react differently to blue light than ortho? The response curves vs. frequency I have seen suggest that both pan and ortho are equally sensitive within the blue end of the spectrum. Or is it simply that blue filters don't filter all green-red light?

 

[Marco B]

Or is it simply that blue filters don't filter all green-red light?

I think the issue is not the fact that many of these blue filters, like you say, transmit some of the green-red spectrum (see for example the spectral transmission curves here: http://www.rosco.com/us/filters/supergel.asp#Colors), but actually, that they transmit to little of the green-red spectrum.

If you look at the spectral curve of an orthochromatic film, you will notice that it actually extends way into the green-yellow region, and only fails in the yellow-red part of the spectrum, whereas a blue filter will block a substantial part of that green-yellow part of the spectrum.

For example, look here, and compare that with the transmission curves of some of the blue filters on the Rosco site:
Dead Link Removed

Marco

 

[Sirius Glass]

Explain. Does pan film react differently to blue light than ortho? The response curves vs. frequency I have seen suggest that both pan and ortho are equally sensitive within the blue end of the spectrum. Or is it simply that blue filters don't filter all green-red light?

If it were that simple, ortho films would not be made.

Look at the transmission curves of blue filters.
Look at the information data for available pan films.
Calculate the effect of blue filters on pan films.
Look at the information data for available ortho films.
They are very different.

What needs to be explained?

Steve

 

[Photo Engineer]

Explain. Does pan film react differently to blue light than ortho? The response curves vs. frequency I have seen suggest that both pan and ortho are equally sensitive within the blue end of the spectrum. Or is it simply that blue filters don't filter all green-red light?

Ortho films are Blue and Green sensitive. If you use a blue filter on ANY film, you only see the Blue component and therefore this filtration does not equal either ortho or pan sensitization.

Also, in the use of any filter, the result does not equal the unfiltered sensitization. It is, in a way, the product of the bandpass of the filter and the spectral sensitivity of the film. Thus 0 x 0 = 0 or 1 x 0 = 0!

PE

 

[Q.G.]

But if you have two emulsions, with the same spectral responese except for extended sensitity towards the red for one, if you filter out only that extra bit the longer spectrum film also records, there should be no difference.

So the thing hinges on a) the accuracy of a filter (and i'm sure there must be some that work) and b) any difference in spectral sensitivity in the part not filtered.

 

[Photo Engineer]

In any case though, blue filtration of a blue sensitive film, blue filtration of an ortho film and blue filtration of a pan film yields only the blue sensitive portion of those films modified by the bandpass of the filter. This thus cuts out any green and red portion of any film's sensitivity.

If the blue filter allows green light to pass, then you will see an impure blue color to the filter and you will have some component of the ortho sensitivity remain in the exposure. If the blue filter allows some red light to pass as well, then the filter becomes grayish, and functions merely as a lopsided neutral density filter.

PE

 

[Q.G.]

In any case though, blue filtration of a blue sensitive film, blue filtration of an ortho film and blue filtration of a pan film yields only the blue sensitive portion of those films modified by the bandpass of the filter. This thus cuts out any green and red portion of any film's sensitivity.

If the blue filter allows green light to pass, then you will see an impure blue color to the filter and you will have some component of the ortho sensitivity remain in the exposure. If the blue filter allows some red light to pass as well, then the filter becomes grayish, and functions merely as a lopsided neutral density filter.

PE

Sure.

But if we dig out the Wratten filter guide, i'd be very surprised if there's no filter in it that fits the bill.
There's blue and there's blue. A filter that cuts out red appears blueish when held in white light.

 

[Ray Rogers]

A filter that cuts out red appears blueish when held in white light.

???
Doesn't a Green filter cut out Red?
So green should look blue, correct?

The Japanese often call a green stop light "Blue"
Humm, you must be correct!

 

[fschifano]

I thought a red filter was used for this (black and white film).


Steve.

The red filter will do just the opposite. It will reduce the appearance of haze and fog.

 

[Q.G.]

The red filter will do just the opposite. It will reduce the appearance of haze and fog.

But can be used for day-for-night on B&W film.

 

[Q.G.]

???
Doesn't a Green filter cut out Red?
So green should look blue, correct?

It also cuts out blue, if it is a true green filter.
And that's why it's green.