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Correcting Colour Casts


Ian-Jones 17 133 2 United Kingdom
28 Jan 2004 4:12AM
Could anyone help with a prob? I'm addicted to Velvia & usually like the colour casts which happen with artificial lighting or reciprocity failure. But, comments on Disappearing Into The Mist made me think about trying to correct this when I take the picture, rather than after processing.

I think the green in the above image is down to mercury vapour lighting & using a specialist film could be the way to go. Which one would compensate for mercury/fluorescent lighting?

Using another film might not always be practical 'cos I'm unlikely to shoot that many pictures which are this heavily affected. Could any square filters do the same job? Any other ideas?

Any help would be great, thanks.


Ian
tim franklin 17 2.7k
28 Jan 2004 7:19AM
Possibly Fuji Reala might be the best bet, as I believe it copes pretty well with artificial lighting.

Filtration depends on the type of tube you're shooting under. The easiest choice is an FL-D filter (for use with normal daylight film) or FL-B (for tungsten balanced film). The other option is to use one or more colour correction filters.

That said, for the picture in question I can't think of any method that could correct this "in camera". Like most of the respondees I really like the effect here. If this picture was shown to a picture editor (together with a bunch of other Eiffel Tower shots) then this would make it jump out and demand to be looked at.
fraser 17 631 14 Scotland
28 Jan 2004 8:45AM
You can compensate for reciprocity failure by increasing the exposure. The correction factor varies with individual films, so it's basically a case of trial and error.

The problem with your shot (which is great, by the way) is that this would probably burn out the highlights. Experimentation is probably worth a try the next time though.
Ian-Jones 17 133 2 United Kingdom
29 Jan 2004 1:02AM
Thanks for that folks. Tim, I take your point about the pic - I liked the effect. However I'd like to take a range of identical pics with different filters etc. with a rough idea what'll happen(!). So, thanks for the tip about FL filters. You mentioned other CC filters. What did you have in mind? I've got my head around ND & grey grads but not much else!

Fraser, you were spot on with your comment. Longer exposures were burnt out. Unfortunately, shorter ones were v dark - further experimentation, possibly with a grey grad, is needed!

Cheers

Ian
tim franklin 17 2.7k
29 Jan 2004 8:46AM
Ian,
I'm no expert on filtration or lighting, so what I can say here is merely a basis for further investigation, but as you have asked.....

To correct a green cast you will need to use a CC Magenta Wratten type filter. These come in various strengths as I'm sue you know. I have here Lee Frost's book on filters in which he recommends a CC30 magenta to partly but not wholly correct this effect. The problem you face with reading up on this is that most/all writers will be thinking of pictures taken indoors under flourescent lighting rather than outdoors as yours is. A more detailed chart provided by Frost suggests again differing requirements for different types of tube. I will reproduce the daylight film part here: (copyright is of course with Lee Frost).

Tube Type - Filters
Daylight - 40M+40Y (+1 stop)
White - 20C+30M (+1 stop)
Warm White - 40C+40M (+1.3 stop)
Warm White de luxe - 60C+30M (+2 stops)
Cool White - 30M (+0.6 stop)
Cool White de luxe - 20C+10M (+0.6 stop)

The bracketed figurs are exposure increases in stops.
Ian-Jones 17 133 2 United Kingdom
18 Feb 2004 3:41PM
Thanks again Tim for taking the time. That's very useful info - looks like the book is well worth tracking down!

Cheers

Ian
deviant 16 3.1k 1 United Kingdom
18 Feb 2004 4:25PM
Yeah I bought it and have to say it's fantastic. Though also a lot take in for a newbie like me !

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