light blue filter for street/ documentary photography

[steven_sherwin]

I heard that some people use light blue filters for black and white street/documentary photography. I have never

heard this before and was wondering what effect this would produce? Thanks

[Spearhead]

I've never heard that anywhere. Have a reference?

[james_ollinger]

I haven't heard of it either, but that means nothing. A light blue will lighten (no pun intended) blues and darken yellows. A light blue would do it a little bit, probably just enough to give you the effects but not enough to be make it obivious. It would wash out the sky, probably wash out a lot of things in general (a lot of things in the world are painted pale blue), and bring out the pigment spots and imperfections in human skin. I suppose it would look very un-cinematic, hence "documentary" feel.

[Craig_Cooper11664875449]

Its not going to do a lot... as a <i>light</i> blue, it will slightly darken your yellows (which will affect your

reds, oranges & greens, see below) as well as lighten blues. Never heard of it either. If any filter is regularly

used on B&W street as a generic filter its probably a light yellow, which would do the exact opposite of the

light blue.

<p>

Its pretty easy to think about the effect: RGB just plays off against CMY(K);<BR>

Red <--> Cyan <BR>

Green <--> Magenta<BR>

Blue <--> Yellow

<p>

Red is the absence of Cyan; cyan is actually an equal mix of Green and Blue<br>

Green is the absence of Magenta; magenta is actually an equal mix of Red and Blue<br>

Blue is the absence of Yellow; yellow is an equal mix of Red and Green

<p>

<i>Basically, if you write RGB and CMY (k) against each, other as above, if you add a filter of a particular

colour, that colour will lighten and everything else that is either horizontal or vertical to that colour in the

table will darken. eg. Magenta filter; magenta colours will lighten, horizontal, green will darken, and

vertically, cyan and yellow will darken. How much is dependent on the strength of the colour filtration</i>

<p>

You can make 3 layers in Photoshop of red, green and blue then turn one off an a time and "screen" blend them and

see this. Other things to understand is the colour of light in places that aren't always obvious such as shadows,

which hold a lot of blue light so where a red/yellow filter will block the blue light, this will darken shadows

even more., whereas a blue filter would help to open them up.

[manut]

Are you refering to skylight blue filter?

[frank uhlig]

Could you ask your "some people" about why; and what this their light blue filter actually is?

[mark_brown14]

Steve,

I posted a comment to the earlier thread on this topic. To go into greater detail, I can refer you to the commentary

on 'White House Ruin' in Ansel Adams' 'Examples', which is where I first learned of this technique. Basically he

figured a blue filter 'like the No. 47' would pick up the reflected light in the shadowed recess of the Canyon de Chelly,

and give him the luminosity he so admired in earlier, blue-sensitive emulsions. (Unfortunately, he goes on to tell us

in his characteristically disarming manner, he had mislaid his blue filter and was unable to achieve his

previsualization.)

 

This is the example that always comes to mind when I'm faced with the problem of how to lighten shadows out of

doors.

 

Of course, you also have to take into account the effect of that blue filter on other parts of the scene...