Gels against Black Background

[pacific]

Okay, I'm trying to use a red gel against a black background. I am using studio strobe (interfit 600) and no matter what I try, I cant get a blue background. What am I doing wrong? I am shooting 1/125 and tried all kind of f stops.

[awad]

hm. have you tried a blue gel to get a blue background?

[TMR Design]

Am I missing something here? A red gel on a black background will never give you a blue background.

Any more information or correction of a typo would be great.

[MikeMcL]

post a pic maybe?

I have found that my gels work best on a dark gray BG, they look completely awesome. black is ok, white is ok... gray is top notch.

red and black dont make blue.

[suyenfung]

haha this thread is awesome.

pacific, you lose a lot of light using a gel and bouncing off of black. make sure your light is up all the way and pretty close to the background. open up your aperture all the way. take a picture. if it is white, close down the aperture. if it is red, then good. if it is black, turn up the iso. eventually it should turn the color of the gel.

i've found that usually when i use a colored gel on black, my background light is turned up all the way or close to it, and my other lights are turned down quite a bit. this is to compensate for the loss of light.

and if you have a meter this is very easy to do.

[TMR Design]

Based on the OP's question about usoing a black background and red gel, wanting it to be blue, it doesn't make sense to talk about power of the light, ISO or other variables.

We use black, gray or white backgrounds differently but each one can be controlled without any problem. Which we use will depend on what is at our disposal and what degree of saturation we want.

If you want a black background to change color you use a colored gel but there is nothing that says the strobe's output has to be at any particular level and even with the output way down you will still get the deepest, most saturated color of the gel, so you can't just generically say that a certain color bckground works best. Turning the power up all the way will undoubtedly give you either an extremely light, unsaturated color or end up being blown out and appearing almost white.

Gray is in the middle so it is easy to hit it with light and change color but if you are looking for a deep saturated burgandy you're not going to get it with gray and black will work much better. If you wanted a powder blue or light pink then gray may still be too saturated and white would be a better choice.

If you can only have one color background then gray would be the most versatile but not always the best solution. We can turn a white background black or a black background white but this can be problematic if you don't have very good isolation between subject and background and can be limiting in terms of the aperture used for the shot. You, the photographer wants to make that decision and not have the power output of the strobe be the controlling factor. Gray can go either way but when using colors it's not always that simple, depending on the actual color and level of saturation you desire. Turning a black background white means you have to hit that background evenly with quite a bit of light and without excellent separation you're going to end up with a lot of that light returning to the subject and affecting your taking aperture.

If we could get the specifics of what the OP wants to do it would be much easier for us to help.

[TMR Design]

To further demonstrate how this works I figured I would take some test shots as examples. This is basic portrait lighting using a main and fill light, 2 stops apart, with the subject about 6 feet from the seamless background. I placed a blue gel on an Alien Bees B800 and feathered it in from the side. I did not take the time to get the background lighting completely uniform and I didn't adjust exposure, but you can get the idea.
Since I do not use my AB's at any power level less than 1/16 I fired shots going from 1/16 power to 1/8, 1/4, 1/2, and full power.

You can clearly see that the black seamless gives you the most flexibility because it can go from deep blue to a rich saturated blue. The grayis already leaning towards the lighter, less desirable blues and the white is pretty much useless except for the shot at 1/16 power.

Additionally, the black seamless can easily be used to create the same colors as in the samples using gray by adding more light to the background.

Hope this helps.