Help Request - How to expsoure for Rim and Backlighting

[chilli_vision]

Hey Guys,

Can you help. I am trying to workout how to both rim light and back light a subject to make the more 3D, i.e standout from the background or look less flat. I have been having a few issues in getting the correct exposure when adding a second speedlight behind or to the side of my subject. I exposure for my subject using say a softbox slight left of camera. Then add a speedlight behind my subject firing off against a wall to catch a circle of light on the wall behind his/her head.

Is it mainly flash power you use to adjust the exposure of the 2nd flash when back lighting, i.e. trying to place a circle of light on a back wall, or is it a combination of both flash power and the Inverse Square Law, i.e. moving the subject further away from the back light so that the light from the 2nd speedlightfalls within a smaller f stop than I am using to expose the subject, i.e. with a softbox?

Does the same principles work for say rim lighting when i am using a speedlight fired directly at the subject from say back left to create the nice halo affect?

Cheers for your advise

 

[Garry Edwards]

Is it mainly flash power you use to adjust the exposure of the 2nd flash when back lighting, i.e. trying to place a circle of light on a back wall, or is it a combination of both flash power and the Inverse Square Law, i.e. moving the subject further away from the back light so that the light from the 2nd speedlightfalls within a smaller f stop than I am using to expose the subject, i.e. with a softbox?

You've over-complicating it, forget about the ISQ.
There are 2 subjects here, the front one (person in this case) and the back one, which is the background. your circle of light on the background is a separate light on a separate subject and has no direct relationship to whatever lighting you're putting on the front subject. Just set the power to whatever gives you the result you want. Here is an example of sorts (NSFW) in picture one. I say 'of sorts' because although it's a perfectly good shot, it isn't exactly a circle of light. In that particular example, a higher exposure would have produced a larger and more pastel-coloured circle of light and a lower one would have produced a smaller and more deeply saturated circle of light.

Does the same principles work for say rim lighting when i am using a speedlight fired directly at the subject from say back left to create the nice halo affect?

The same link shows some other useful examples. Nude 2 and nude 6 are purely rimlight/backlight and so the exposure reading is taken from the parts illuminated by the light, i.e. the exposure is correct for the parts that are lit, allowing the rest of it to go into shadow. Nude 4 is the opposite, there is an on-axis fill that is lighting all of the subject seen by the camera (which is what a fill light does) and the exposure has been set for that. The rimlight here is - well, just being a rimlight - so it's overexposed.

 

[chilli_vision]

HI Garry,

Thanks for your comments. I will be running some testing tomorrow and will incorporate the points you made. The idea is for me to learn how to achieve the back and rim lighting I am looking for as at present I am impacting on the subjects lighting with the back light which I know has something to do with the background wall, I think I am getting to much reflection back into the lens.

But, it is good to start to understand lighting behind a subject. I really appreciate the time spent in helping me. Cheers.

Matt

 

[Garry Edwards]

You're welcome.
BTW, I forgot to mention...
The first shot was against a white background, the reason that it's almost black is that care was taken to prevent any light (except for the gelled light) to reach the background. The other shots were taken against a black background.

We used studio flash on the Lencarta Lighting Workshop, it's easier because they have modelling lamps, but we may do a bit with hotshoe flashes on future courses, now that we have hotshoe flash > S fit adapters. But don't worry about it, it can still be done with hotshoe flashes, it's just a bit more fiddly when there are no modelling lamps, so you may have to do a bit more experimenting to get it right.