Question about flash rigs

paddler4

What is the purpose of moving the flash head back from the front of the lens? Most of the DIY flash rigs I have seen are like this, which is (or was) Phil's. I have been using this:



The cap is a sto-fen, with foil around the sides, extra layers of diffusing plastic inside, and two layers of paper towel on the outside. It has generally worked well, but I am wondering whether this close position is why I sometimes get unwanted glare on the image, as in this one:



Thanks very much.

Dan

JulianNell

I don't know a lot about flash rigs, but I have been told that the closer the flash is to your subject, the softer the light will be.

basflt

IMO your diffuser is too small diameter , and also to close to the flash-unit

me , i would go for about 4 inch , both diameter and length
then move the unit backward so that the front of the diffuser is near the front of the lens

here old setup of Brian

paddler4

IMO your diffuser is too small diameter , and also to close to the flash-unit
i would go for about 4 inch , both diameter and length
then move the unit backward so that the front of the diffuser is near the front of the lens

I know people often do that. I was asking why. What are the effects of positioning the light source farther back? However, your reply adds another question. That is, what are the effects of increasing the size of the front end of the diffuser, given that both the light source and the subject are very small?

Canon's MT-24EX macro flash unit (not a ring flash) has two very small heads, both held very close to the front end of the lens.

basflt

it is because the diffuser itself reflects on the subject
a large diameter looks more natural

i use MT-24EX and it shows as 2 duffusers > http://basflt.smugmug.com/Myphotos/macro/Jumpers-springspinnen/i-BN76frW/0/L/IMG_5748-Edit-L.jpg
one large one would be much better , but i found no way yet for the MT-24EX ( still working on that )

on my SB-700 however , it is about four and a half inch diameter ( front exactly same distance as front of sun-hood )

paddler4

OK, thanks. I constructed one of Brian's coke can diffusers tonight, although not very tidily. I'm going to try a double sheet of baking parchment paper for a diffusing surface to start; it's what I have been using recently for ambient-light macros.

Lord Vetinari

As Basfit says - a few things going on. You are trying to get a large effective light source close to the subject. The diffuser should act as the light source. So both the material and the size affect the softness of the light. Think of cloudy day natural light versus direct sun. The clouds act as a huge light source and diffuser.

Brian V.

paddler4

Thanks, Bas and Brian. I'm eager to try out the new diffuser.


Sent from my iPad using Tapatalk