Stupid Question time - Lighting background from behind

[WelshNoob]

So I've watched lots of lighting videos and read lots of lighting books including techniques and sample setups. What I haven't really seen is lighting a background from behind. If I've got a white translucent background, would it not be simple to place a light source behind it in order to have a bright white background or would the spill from doing that be the reason for not doing it?

 

[Garry Edwards]

Yes you can, and you will get very similar results to using a softbox (such as the Hi-Lite) as a background - same benefits, same disadvantages.

 

[WelshNoob]

Makes sense Gary - so it would turn the BG into a large modifier. Slowly getting my head around it. Was thinking about shooting at home where there are 2 rooms separated by double doors, would give me more space to have the BG in the doors and the light in the other room behind it rather than trying to light the BG in the same room as the camera, models (children) and the other modifiers.

 

[Phil V]

Makes sense Gary - so it would turn the BG into a large modifier. Slowly getting my head around it. Was thinking about shooting at home where there are 2 rooms separated by double doors, would give me more space to have the BG in the doors and the light in the other room behind it rather than trying to light the BG in the same room as the camera, models (children) and the other modifiers.

Definitely a good use of the space, giving you less to worry about in front of the bg and less chance of a subject disturbing the lights.

 

[WelshNoob]

Another question while I'm amassing equipment and can't experiment myself. Would the power of the flash behind the BG remain constant to provide a white 'blown' if you like, background regardless of what I do with the power of the modifier in front of the background?

Definitely a good use of the space, giving you less to worry about in front of the bg and less chance of a subject disturbing the lights.

Good stuff, I've ordered some very expensive gels (£1.37) from HK which will change the white background to any colour in an instant very easily I'm guessing.

 

[simonbarker]

Another question while I'm amassing equipment and can't experiment myself. Would the power of the flash behind the BG remain constant to provide a white 'blown' if you like, background regardless of what I do with the power of the modifier in front of the background?

If you don't change the aperture or the relative position of the light you're using on it then the background should remain white regardless of what you do with any other lights (also assuming you're using enough power to ignore ambient or in a controlled environment).

Generally excess light hitting something you've already exposed properly is undesirable but as it's a pure white background more light won't change how it looks. The brighter you light the background the harder it becomes to avoid spill on other subjects in the shot but as we're probably talking about a light you're increasing for the benefit of one of those other subjects I would assume this wouldn't matter too much to you (or perhaps it may).

 

[sk66]

Another question while I'm amassing equipment and can't experiment myself. Would the power of the flash behind the BG remain constant to provide a white 'blown' if you like, background regardless of what I do with the power of the modifier in front of the background?

It could remain constant, but IMO that would be a poor choice. As you add light to the front, the amount of backlight required for "white" will be reduced. If you reduce the power of the backlight correspondingly it will remain white while reducing the issues of lens flare/bloom.

Of course, this will be variable with the amount of spill and where it's hitting the BG.

 

[HoppyUK]

You will still have the same issues lighting the background evenly. Ideally, for pure white the background should be only just blown, and evenly exposed all over. Never easy. TBH I'm not sure this is such a great idea. Convenient maybe, but if you're tight on space then a Lastolite HiLite is a better solution.

Yes, the front light will influence the background brightness just as it would any other way. There is always at least some light spill. Could be quite a lot, but it's not usually anything you can't work around.

 

[WelshNoob]

Never easy. TBH I'm not sure this is such a great idea. Convenient maybe, but if you're tight on space then a Lastolite HiLite is a better solution.

Thanks for the suggestion. I baulked at the price when I googled what the Lasolite was. I can't justify spending that to have a play at something at home unfortunately.

 

[juggler]

I've done it a few times. It works well with a softbox or double thickness of shower curtain, not so well with a sheet. It gets trickier as the size of the backdrop increases.

I often find I need to manipulate the contrast in post, too.