Messed up WB with Rosco CTO 3/4 gels

[Skysi]

I just tried Rosco CTO Cinigel 3/4 for the first time while doing a residential shoot. I put the gel on my two flashes and put my 5D on 3200K. The lighting in the house was tungsten with some daylight of a cloudy day coming in.
Shooting in the basement, I only had my flashes against tungsten light.

Funny thing was that on the camera monitor the images looked perfect. After importing into Lightroom/CDPP they are all pinkish/purplish and very hard to fix. This applies to both, shots with some cloudy daylight and shots done in the basement where there's no daylight
1. Should I have used 1/2 or perhaps full CTO.

2. Should I switch to Lee CTO? (I remember someone saying Rosco's are on a red side
3 If none of the above, what mistake am I making here?

I 'm thinking maybe it depends on the ratio of tungsten to flash?

I was shooting at: 1/40, f8, ISO 500. Both flashes were shooting in the white ceiling (one was 580EX II and the other SB 26) and were at 1/2, 1/4, sometimes the on-camera 580EX II was at full.
I could have overpowered the tungsten with other flashes that I got plenty of, but the agent wanted all the lighting fixtures of the house on and as much ambiance as possible.
Here're some examples

Picasa Web Albums - Serge - Misc

Picasa Web Albums - Serge - Misc

Picasa Web Albums - Serge - Misc

Picasa Web Albums - Serge - Misc

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skysi
Sergi Yavorski

[highbarger]

Originally Posted by Skysi

3 If none of the above, what mistake am I making here?

It doesn't look right with the WB set to tungsten and the daylight visible in the windows. I think that if the strobes are gelled to match the tungsten light, the windows should also be gelled to match. It might work to use your strobes without filtration and use full spectrum light bulbs in the fixtures that are showing in your shots.

[Ed Shapiro]

Here are the problems and hopefully the answers.

When using the Rosco CTO 3400 series you have to consider the primary light source first. For example; Roscosun 1/2 CTO converts daylight at 5500 K degrees to 3200K Kelvin degrees so as to convert daylight to tungsten 3200 K photo lamps. Problem is the color temperature of daylight varies with the time of day, the degree of cloud cover and reflections from nearby building or large objects. Electronic flash is supposed to match daylight but it may not be exactly the same. If you ave thyristor controlled auto or TTL flash units, their color temperature also varies with flash duration. As you know the thyristor circuitry clips some of the flash duration i order to control flash output thereby enabling automatic exposure with flash. Even if you manually control a studio type or portable flash unit the exact color temperature will vary with the power output. The xenon gas in the flash tube is being ionized a differed rates when the voltage or capacitance to the tube changes.

when converting daylight to tungsten via flash filtration, because there are the aforementioned variations you have to do a bit of testing to find out which CTO filter to use to best match the existing light. If you have the Rosco sample book you will also see the light transmission information on the interleaves. You can' t really tell on the camera's screen so you would need a laptop to verify the results as you test.

As you might have noticed in you images, there is no feeling of ambient lighting and mood- the flash wiped all of that out and there is considerable fall of as per the inverse square law.

Gelled flash is not my favorite method of interior photography- there are easier ways.

The first thing to do is figure out what the dominant light source is going to be- the lights that give the mood of the room. If daylight is the most prominent source all I do is expose for the natural light comming in through the windows and GENTLY fill in with a wink of electronic flash. Another easy method is to buy some inexpensive blue photo flood lamps (photo flood #1B- 250 watts) and use bare bulb or light bounced of a pure white ceiling or wall to act as fill. I sometimes place the photo floods in table and floor lamps and fill in as mentioned above- that mixed with window light makes for a natural look. When do the table lamp thing- turn on the lights, make your reading as placements and then shut the light off if the setup is taking a bit of time. Theses lamps generate a lot of heat and can set fire to cloth lampshades or burn out the lamp sockets if left on too long. 5 minutes at a time is OK. In a case like this you are going for a near daylight custom white balance.

If the dominant room lighting is tungsten, simply expose and white balance for the the existing light and fill in gently with a simple tungsten light bulb or a quartz lamp bounced off a white umbrella or a pure white piece of Foam-Cor board.

The reason I am suggesting continuous light sources is that you can better judge you lighting effects and ratios visually and make sure you are not over-filling and wiping out the ambiance.

The problems you are experiencing with color balance is most likely due to the aforementioned color temperature discrepancies and a mixture of daylight seeping into the mix.

When bouncing light off walls and ceiling you need to make sure there are no serious tints in the paint, otherwise you must use umbrellas of pure white reflector boards. Never aim the bounce light into the picture area- use the walls and ceiling behind the camera. Light bounced onto the ceiling toward the camera's view of the room will tend to over fill and show up in the images a an overexposed ceiling.

It is better to have a slightly darker fairground- this leads the eyes into the room. If other rooms show in your composition, the should be lighted as well.

The other problem I see is linear distortion- converging vertical lines. This distortion will cause a rooms to appear out of square ot give the impression that walls and pillars are falling over. If you don't use a view camera, you can maintain the perpendicularly of vertical lines by setting up the camera on a tripod midway between the floor and the ceiling and keeping it totally level, If you have too much ceiling or floor in the resulting image, simply crop for the best composition. As soon as you tilt the camerae up or down you are inviting distortion.

I hope this helps, Ed

[Skysi]

Thanks, highbarger. Could be a good idea with those full spectrum bulbs.

[Skysi]

Thanks so much, Ed for taking time to respond and your detailed advice -- very informative.
I never thought of those blue flood lights. They are 3400K if I'm not mistaken, so I'm surprised they balance with daylight. I wonder also if full spectrum lights would be OK for this purpose?
I do have a few hot lights (500W) that I was about to sell )...

[Ed Shapiro]

Blue photo floods are near daylight- just slightly warmer. There is a blue tint in the lamp's frosting thus the number 1-B. The number 1 photo floods is frosted the same as regular light bulbs- they are about 320000 K or slightly more when they are new. They only have a life of about 4 hours and become warmer as they age. The blue lamps have the same effect as using Rosco #3202 (full Blue) which takes 3200K to 5500K. Again, testing and a custom white balance should give you a trouble free file.

Ed