Changing background colour using gels

Canon 12x IS USM (S3 IS built-in Lens) -- 36-432mm (35mm EQ)

05/22/2011 05:56:34 PM · #1

Hi Gurus

I battled through this for the current challenge and now completely beat, I need to ask for help.

I thought I could change the background colour using a gel on the flash...however, it don't seem to get that effect on my pictures.

Do I need to set custom white balance before I apply the gel or after?
Does this work only for gray backgrounds (this is the only thing I couldn't try - since I don't have a grey/gray background)?

On a different note, how far (typically) does the subject need to be from the background to ensure good separation? I understand this is "how long is a piece of string" question, but at this stage I'm frustrated with my results and kinda lost :-)

Thanks
M

GeneralE

Canon PowerShot S3 IS

05/22/2011 06:07:25 PM · #2

I would think you'd need a white background and the flash pretty close (and behind your subject) to accomplish this. The WB should be set to whatever other lighting you're using to light the subject in order to pick up the color of the gel.

If you use the colored light to illuminate the subject you have to then neutralze it (with custom WB) to avoid a color-cast on the subject, defeating the purpose of using the gel in the first place.

Spork99

OM System OM-1

Canon EF 100mm f/2.8 USM Macro

05/22/2011 06:31:18 PM · #3

Another thing to consider it that the higher the flash/strobe power, the less saturated the effect of the gel will be on the BG and vice versa.

kirbic

Canon EOS R5

Canon RF 24-70mm f/2.8 L IS

05/22/2011 06:35:49 PM · #4

I assume you're using a white background, and if so, that should work. As Paul pointed out, you don't do any WB compensation, and you should not be illuminating your subject with the same (gelled) light source.
The keys to success are:
- Setting WB to match your main light(s)
- Gelling only the light for the BG and making sure that light does not spill onto the subject
- Making sure the BG does not blow out (scale back power on the BG light as needed). If the BG blows out, it will be white, by definition.

giantmike

Canon EOS R6

Canon EF 100mm f/2.8L Macro IS USM

05/22/2011 06:40:56 PM · #5

If you are shooting RAW, I don't suspect the white balance matters, as that's easily changed in post. It's more likely that your strobe power is too high as Spork was saying. Also, a pure white background will have less saturation than a grey background, as you suspected.

As for good separation, that depends on the distance from your camera to the subject. For instance, if you camera is 2 feet from the subject, and the background is only 6 inches from the subject, then you will see a lot of the subject, at pretty much any aperture setting. On the other hand, if you move the subject to 4 feet from the background, now you will start to have very nice separation. OF course, this also depends largely on the focal length.

The biggest thing I can tell you is to use the Strobist style of lighting. First adjust the camera to the ambient light via the shutter speed. For instance, use a fast shutter to eliminate the effect of ambient light. Then add in your fill light to your taste. Then add a key light for edge highlighting. Finally, once all of those lights are set to how you want them, then work on the background accent lighting. This is the key piece of information I got from the FlashBus tour, and it has helped my off camera lighting immensely.

Sony FE 200-600mm f/5.6-6.3 G OSS

05/22/2011 07:33:53 PM · #6

Originally posted by GeneralE:

Hmm. I'm gonna post some pictures. I used a white background with a Canon 550EX II gelled with (say) dark pink, but the result was less than satisfactory. I'm gonna try again.

I don't use the coloured light to illuminate the subject - I have a separate flash (non-gelled) acting as fill light (at an angle).. and a white reflector bounce the fill light. Again, will upload my results for you to critique / advise.

Thank you for the reply!

vawendy

Sony Alpha 1

05/22/2011 08:06:34 PM · #7

I know nothing about gels...

but are you layering the gels? My pack has multiple of the same type, and the more I put in, the better the color.

05/22/2011 08:20:35 PM · #8

Update:

It was the flash power - the flash/strobe lighting the background was too strong.

Also, to diffuse / cover a larger background area, I was foolishly trying to diffuse the background light via an umbrella - needless to say that wasn't working...

Thanks guys! Now to cover up for lost time!

Beetle

05/22/2011 08:30:44 PM · #9

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