BetterPhoto Q&A
Category: New Questions

Photography Question 
Jason Rogers

Lighting Ratios and Flash Photography

Hello everyone. I'm new to this site and just came across it after reading some great posts in the forums. I have a question about calculating lighting ratios. I'm using a two light setup with a main and fill light. Let's say I want a 4:1 lighting ratio. Assume I'm using F8 on my camera. To get a 4:1 ratio, that would be two stops from F8, so F4 would be my fill light setting if my calculations are correct. Here's where I'm confused. Would I then set the main light at F8 with or without the fill light on? I hope my question makes sense. I'm very new to using flash, but I'm trying to learn as much as possible to keep it fun!

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12/8/2006 11:18:23 AM

Jason Rogers   P.S.--The reason I'm asking this is that I found an F Stop calculator at

In the instructions, it says to set the fill light first, (F4 in the example above) and then turn the main AND fill on and set the main at F8. My flash meter manual says to set them both separately and once you have your ratio, then you determine the overall exposure settings.

Thanks again.

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12/8/2006 11:28:48 AM

Kerry L. Walker   Set them separately and then turn both on to get your exposure setting.

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12/8/2006 1:15:21 PM

John H. Siskin
BetterPhoto Member
John's Photo Courses:
4-Week Short Course: An Introduction to Photographic Lighting
  Hi Jason
I am not a big fan of ratio lighting. If you want it to work according to predictions, you need to use small light sources, which means harsh light on the face. But you asked about doing this, not about whether you should do this. :-) 1:4 lighting means that your fill light puts one unit of light on both sides of the face and the main light puts three units of light on one side of the face. So if your fill light is f4, your main light should be 1.5 stops brighter, or about f6.3. So I think the answer to your question is that you would meter the main light with the fill light on and you would want to consider the fill light in your exposure calculations. You might check out a BetterPhoto article I wrote about working with just one light. Itís also on the magazine article page at my website: Good luck!

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12/8/2006 1:15:41 PM

Kerry L. Walker   Let's do it the easy way. Assuming your light sources are of equal intensity, just set your fill light twice as far away from the subject as your main light. Then meter for exposure.

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12/8/2006 1:25:03 PM

Jason Rogers   Kerry,

Thanks...I have read about controlling it via distance, but the room I'm using to shoot in isn't that big and I would have to put the main light pretty darn close to the subject.


That's a great article! I have printed it out and will be trying it this weekend.

Thanks again to both of you for your replies...Very helpful!

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12/8/2006 1:30:06 PM

W.    Hi Jason,
I dunno what gear you got, but if you "have to put the main light pretty darn close to the subject", why not halve the output power of that flash?
And, since you want to keep the ratios the same, you ought to halve the fill light's output as well, of course.

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12/8/2006 1:41:32 PM

Kerry L. Walker   Jason, first off let me say that my experience with studio photography is very limited and I plan to keep it that way. LOL. Not exactly my cup of tea (or coffee for that matter.) For some good advice, contact Debby Tabb. She is the resident expert on studio photography. At the top of the page, right side, you will find a box with a small magnifying glass next to it. Just type her name in there and it will direct you to her page. Send heer an email and she will reply.

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12/8/2006 1:45:07 PM

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