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FORUMS General Gear Talk Flash and Studio Lighting 
Thread started 17 Oct 2011 (Monday) 09:22
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Some stupid lighting questions...

 
TijmenDal
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Oct 17, 2011 09:22 |  #1

Hello boys 'n girls!

Time to be a PITA and ask some, probably, really annoying questions.

The first question is about snoots and grids. I read up on why to choose either (or both), but I don't quite understand why the grid works how it does...

IMAGE: http://i54.tinypic.com/105cmma.png
I made a little illustration of how I think it works, but I'm not sure.
Obviously the grid is the top image and the snoot the bottom. I haven't had physics, so made the yellow lines I drew are total balonie but that's the way I figured the light beams would reach the most outer edges of whatever it's lighting. My questions is: does the pink not 'work' or something? Because if the light bounces, it can reflect at a much more diffuse angle, right? Or is it, because the grid is black, that it doesn't reflect much light and the light it reflects is almost negligible.

Second question:
Umbrella's!
Recently I picked up my first flash (YN-560) and I really love fiddling around with it, but a friend of mine asked me (Raspberry-rouge.com asked me to shoot her (with a camera, not a gun) some time. She has a blog (Raspberry-Rouge.com DISCLAIMER: Only for females who are obsessed with fashion!) and because it's getting dark earlier she asked me if I could do a shoot in the dusk.
Basically, it sucks for her I'm a bum and can't afford anything expensive, so my options are pretty limited on lighting and diffusing. I pretty much settled on an umbrella setup (unless anyone has a better solution), but while I wait for 'em to get shipped I have a few questions.
I ordered two white shoot-through umbrella's, because I figured it would be a good starting point (and they were the cheapest ;) ), but I'm also interested in reflecting umbrella's. I scavenged the interwebz for the differences but a lot of the articles I read didn't have a clear view on when to use which or which was better.
Maybe someone here can?


Now, when I start using my umbrella's it's probably gonna be a bummer how hard it is (not the only thing hard in our hobby), so maybe someone could answer these questions:
- As a guideline I've read that shoot-throughs let about 2/3 of the light coming out of the strobe through, is this about right?
- I've got a lovely zoom feature on my flash, but how does this work with umbrella's? Of course it diffuses the light and makes it much more soft because it's a bigger source, but should I use the zoomnumber I'd normally use or should I go wider/narrower? It would save me a lot of time if I knew this beforehand.
Maybe the next picture would make it a little bit clearer what I mean, which lines does it follow?
IMAGE: http://i51.tinypic.com/k4y06o.png

My questions so far, maybe something will pop up in my head but then I'll just edit this post or ask in another post.

Thanks a lot in advance.

//Tijmen
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Executive ­ Images ­ Photo
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Oct 17, 2011 09:39 |  #2

With snoots or grids you are narrowing the beam of light (light spread). A snoot or grid keeps the light into one central area allowing you to control over flow (spill) of light. Most of the time girds will be use for a hair light or a back light. Remember when narrowing the beam of light it will make the light spread SMALLER thus making the light harsher on your subject.

With an umbrella you are doing the opposite. Weather you are bouncing the light or using a shoot through umbrella you are widing the light spread thus making the light softer.

Most of the time (especially with fashion work) a modified light (flash with umbrella or softbox) and a bare light is used. Bare light used as a back light/side light and the modified light used to light up most of the subject.

Remember, making a subject look 3d in a photo is made using lights and shadows. Hope that helps you. :-)


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Curtis ­ N
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Oct 17, 2011 09:40 |  #3

1) Grids are black, to absorb the light that hits them. The photons represented by your pink line will be absorbed by the grid and converted to heat, rather than being reflected. So the only photons that escape are the ones that don't hit any of the sides of the grid. Think of a grid as a bunch of mini snoots assembled together. The light spread is determined by the size of each cell, relative to its depth.

2) My testing with white nylon umbrellas indicates approximately half the light travels through the material and the other half is reflected off it. So no big difference in efficiency either way. Use the widest zoom setting on your flash unit and use the entire length of the umbrella shaft to fill the umbrella as much as possible.


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TijmenDal
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Oct 17, 2011 09:57 |  #4

Curtis N wrote in post #13261278 (external link)
1) Grids are black, to absorb the light that hits them. The photons represented by your pink line will be absorbed by the grid and converted to heat, rather than being reflected. So the only photons that escape are the ones that don't hit any of the sides of the grid. Think of a grid as a bunch of mini snoots assembled together. The light spread is determined by the size of each cell, relative to its depth.

2) My testing with white nylon umbrellas indicates approximately half the light travels through the material and the other half is reflected off it. So no big difference in efficiency either way. Use the widest zoom setting on your flash unit and use the entire length of the umbrella shaft to fill the umbrella as much as possible.

Thanks a lot, that's both really helpful!
One question about the second answer though:
By using the entire shaft you mean having the flash close or far away from the umbrella?
I can imagine when having the flash far away a lot of the light will spill, and if you use it too close to the umbrella the umbrella won't do what you should use it for.


//Tijmen
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Curtis ­ N
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Oct 17, 2011 11:49 |  #5

Keep the umbrella as far from the light as possible so the light spreads out to fill the umbrella. You won't spill much.


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Some stupid lighting questions...
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