Blue filters and fog

Photo Engineer

Subscriber
Joined
Apr 19, 2005
Messages
29,018
Location
Rochester, NY
Format
Multi Format
Physics is important in understanding light, but photographic materials are a small subset of that entire field. For example, we do not need to include optics in designing a photomaterial but do need to just include a "flare factor" for the average lens. This narrows the field enough that we need only consider R/G/B/C/M/Y to do the job correctly. It is like an approximation. We don't need PI to many decimals to get a good value for the area of a circle for example.

We do need to know what the effects are when a dye is changed even by a tiny fraction, and we need to know it for all possible colors. And so, this tiny subset of C/M/Y dyes, can reproduce the colors seen in Kodachrome, Ektachrome, Agfachrome, Ciba/Ilfochrome, Fujichrome and all of the negative films and papers as well. One tiny error will upset the entire thing.

And so I think that post 100 is right to the point!

PE
 

Q.G.

Member
Joined
Jul 23, 2007
Messages
5,535
Location
Netherlands
Format
Medium Format

It is.

But what point exactly?


Anyway. You do know now.
 

Ray Rogers

Member
Joined
Aug 27, 2005
Messages
1,543
Location
Earth
Format
Multi Format
Points...

Q.G.,
In summary, What is your answer to...

Q.
[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?
 
Last edited by a moderator:

Q.G.

Member
Joined
Jul 23, 2007
Messages
5,535
Location
Netherlands
Format
Medium Format
Fog and mist are (as was mentioned by someone - can't find the post in a hurry, so no specific attribution. Sorry!) white light reflected off water. A blue filter will do nothing to enhance that.
(Try a blue filter on clouds - very dense fog/mist - and see whether they stand out more )

Aerial haze however is blueish, and a blue filter will leave that alone while toning down the non-blue part of the light behind, or rather mixed in with, the blueish veil. So the haze will be enhanced a bit.


P.S.
You asked about the foreground vs background, i forgot. The above only concentrated on the fog/mist/haze itself.
Anything that is not mist, and of a colour that will be darkened by a blue filter (red flowers?) will be darkened by that blue filter, while the white fog/mist will not.
So if the scene is a bank of mist rolling in front of a field red with poppies, the contrast between mist and field will be enhanced using a blue filter (and reduced using a red filter).
 
Last edited by a moderator:

Ray Rogers

Member
Joined
Aug 27, 2005
Messages
1,543
Location
Earth
Format
Multi Format
Do you think photographically,
Haze can sometimes be confused with (or look like) Fog?
 

Q.G.

Member
Joined
Jul 23, 2007
Messages
5,535
Location
Netherlands
Format
Medium Format
Ray Rogers said:
Do you think photographically,
Haze can sometimes be confused with (or look like) Fog?
Click to expand...

I think everything can get confused with anything.
Particularly when fog/mist and haze are not mutually exclusive natural phenomena.

P.S.
Another p.s., lest you think i'm just being flippant.
Whether the right conditions exist to use a particular filter on weather has to be determined, tried, almost on a case by case basis.
It's easy when there is a thick fog/mist, because you know that there is no filter that will change anything about it (though it may have an effect on bits that are not behind that fog/mist).
Aerial haze however can be just that, or a mix of haze and fog. And if only a haze, it can be strong, or weak. You'll just have to see what a filter does or does not do to it.
 
Last edited by a moderator:

Ray Rogers

Member
Joined
Aug 27, 2005
Messages
1,543
Location
Earth
Format
Multi Format
Purple Haze...

Q.G. said:
Fog and mist are... white light reflected off water.

Aerial haze however is blueish...
Click to expand...

Yes, but what color did the haze start out as?
Haze isn't part of the spectrum, right?
 

keithwms

Member
Joined
Oct 14, 2006
Messages
6,220
Location
Charlottesvi
Format
Multi Format
As I think I mentioned some time back in the thread, for haze/fog particle sizes you get Mie scattering across the wavelength spectrum and a whitish effect. So you start with the solar spectrum and get roughly equal Mie scattering power across that spectrum... and thus fog looks white. Mie scattering also accounts for the whiteness of clouds.

So... whitish appearance usually means Mie scattering is the dominant mechanism; colour shift (e.g. at sunrise or sunset) usually means Rayleigh. Rayleigh is typically dominant when particle sizes are quite small relative to the wavelengths.
 

Lee L

Member
Joined
Nov 17, 2004
Messages
3,281
Format
Multi Format
Photo Engineer said:
Keith;

Are you sure that the color at sunset and sunrise isnt Magenta?

PE
Click to expand...
Sunset is a figment of your imagination. If you were standing somewhere else on a sufficiently large scale, you wouldn't even see it. :confused:

Lee
 

Lee L

Member
Joined
Nov 17, 2004
Messages
3,281
Format
Multi Format
Just reading some in reference to Keith's post. Water particles are close to the size of visible light wavelengths. Gas particles are much smaller. So it's Mie scattering for water particles and Rayleigh scattering for atmospheric gases, both effects driven by their particle size relative to the wavelengths of visible light. The answer to both 'why is the sky blue?' and 'why are clouds white?'.

So my assumption that Adams may have been talking about lower water vapor concentration and greater numbers of water vapor particles over distance in an earlier post doesn't hold. It's really the greater scattering of blue wavelengths by greater intervening volume of gas that causes the effects that can be more readily enhanced/exaggerated by blue filtration.

Thanks Keith.

Lee
 

Ray Rogers

Member
Joined
Aug 27, 2005
Messages
1,543
Location
Earth
Format
Multi Format
Title of Gum Printers Exhibition: Pigments of My Imagination

keithwms said:
As I think I mentioned some time back in the thread....
Click to expand...

Thanks Keith - I hadn't really forgotten , I just thought it might be helpful to focus our attention on that for a moment....
not sure yet of the outcome, but at the very least, it resulted in a few good jokes!
 

Poisson Du Jour

Member
Joined
Jul 1, 2008
Messages
5,462
Location
.
Format
Digital
I'm a bit foggy on where this thread is heading... we ring-side observers are waiting for the next bout...
 

Ray Rogers

Member
Joined
Aug 27, 2005
Messages
1,543
Location
Earth
Format
Multi Format
It's OK.
Perhaps we should all have a drink somewhere central like DC... say,
Foggy Bottom?
 
Last edited by a moderator:

Steve Smith

Member
Joined
May 3, 2006
Messages
9,109
Location
Ryde, Isle o
Format
Medium Format
Ray Rogers said:
Haze can sometimes be confused with (or look like) Fog?
Click to expand...

I have at least one photograph where the haze looks just like mist.


Steve.
 
You must log in or register to reply here.
Menu
Log in
Register
Cookies are required to use this site. You must accept them to continue using the site. Learn more…