Wb issues with studio flash, advise sought please.

Cris_L

Cris_L

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Please could someone give me a clue regarding the colour cast I'm getting in my studio. I'm using lencarta smartflash. painted white walls with a wooden lowish ceiling. the back wall behind where I stand is painted a dark greyish (does have a very slight hint of colour, but its basically grey).

Normally if I set the WB to 5500 its all pretty close but now I seem to be getting a slight reddish cast. I'm pulling the WB back to around 5350 but its still a bit red as can be seen here.


IMG_2046 by Cris_L, on Flickr


Please could I have some ideas on a) what is causing it and b) the best way to sort it.

Many thanks

more here
 
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Hi Chris,

Not sure why you would be getting a red tint with that choice of WB setting sorry but are you sure it's not your monitor that needs calibrating?

I know my desktop screen hasn't been calibrated recently but I'm not seeing it on either my laptop or my desktop and the white background seems to pretty much identical to the white background of the flickr site?

Edit: I've just looked at IMG_2041 and can see the skin looks a bit red but the background looks ok, Is it the skin or the background that's bothering you?
 
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Hi Chris (very similar names we have!) my monitor is calibrated and a couple of other people have pointed out the red cast / skin tone. Though I'l be honest on this laptop (not my main pc) it looks better.

I think I may have just over saturated in pp, although one of the people who noticed the red skin tones is a very well respected experienced wedding and portrait tog. he also said the BG has red in it.

hmmm. Maybe i should do a custom WB and see from there.
 
I'm not seeing it either Cris (never calibrated monitor though).

If you're worried why not set a custom WB in camera?
 
I notice that if I open IMG_2041 in CS3 it's a lot less saturated than the web version?
 
Thats odd...do you think the problem may be more a saturation issue than wb? i definately do need to reduce the wb from 5500 which is where I used to find these flash heads ok in my spare room before moving to the shed-studio.
 
I'm not sure sorry but when I tried to upload an edited version it had the same over saturated/red tint to the boys skin.

I'm sure someone more PS savvy than me can correct me if I'm wrong but if I hover over the white background using the eye dropper tool it shows a consistent value of 255 which I thought meant it was pure white?
 
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If the background is completely blown I'm guessing it's going to show 255 regardless of any colour cast?

Looking at the RGB and also CMYK values there is definitely a red cast. Teeth, eyes and white markings on the clothes all have high red values.

Perhaps a silly question but do you use a grey card? Also, would the wooden ceiling cause a warm cast?
 
If there is a colour cast, and it's not something else, then it's got to be coming from somewhere. Presumably the wooden ceiling.

The background is also excessively over exposed, so there's bound to be loads of light bouncing around picking up colour contamination.

Anyway, a custom white balance will fix it in two seconds. Fiddling with colour temperature is a crude and not very accurate way of doing it. Or include a white/grey test card in a reference shot and use that to correct in post. Either way should be easy.
 
Cheers guys, looks like a custom wb is the way to go.

I wonder if the wooden ceiling is causing part if the issue? The bg is lit from a strip softbox above he subjects, I'll have to try turning it down until it's just blowing the bg.
 
Cris_L said:
Oh, daft question but when doing a custom wb in the studio I assume we fire the flash?
Click to expand...

Yes. The light for a custom WB must be exactly as it is in the final photo. Get your subject to hold a card/paper, facing the camera, and just make sure the centre circle of the viewfinder is covered.

The inherant nature of the white background look is tons of light flying about, much of which bounces around the room and finds its way to the camera side of the subject. Ceiling, walls and floor, even furnishings and clothing will all contaminate it.
 
Cris_L said:
Oh, daft question but when doing a custom wb in the studio I assume we fire the flash?
Click to expand...

Yes. There's a very long winded video on fridayphotoschool where Will (Why use one word when you can use ten?) Crockett is demonstrating different flash equipment and modifiers. Every time he changes the lighting he fires off a quick WB calibration shot, with the model holding a grey card in front of her face. Different lights have different temperatures. Different modifiers can have a different effect. Different mixes of ambient vs flash or bounced vs direct light all can cause a slight shift. If you really want to get it right then a custom WB is probably the answer.

In your example above, if you want to adjust the shots you've already taken, rather than fiddling with temperature have a look at the green-magenta balance. You may want to nudge the balance a fraction towards green.

EDIT : The video is called "Indoor Basics". It is free to download. Free registration is required (no spam).
 
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Custom white balance is the way to go, with the flashes firing. I'be started using a CBL from 7dayshop to set mine.
 
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