Multiple exposure - dumb question

Johnboy2978 · May 9, 2005

Hey all, there are a couple of pics in my head that I wanted to try out soon with multiple exposures. When you are doing that, do you need to have a lower aperture setting though so that it doesn't get overexposed? I mean, it seems to me that if you are taking 2-3 shots on the same frame, that unless you adjusted it some to begin with, white areas would really be blown out when you exposed it 2 or 3 times. Am I right, and if so, how much would you change it?

(shooting with b/w film that is)

Hertz van Rental · May 9, 2005

I think I have posted this before.
If you are doing 2 exposures then you halve the indicated meter reading and use that for each exposure. If you want 3 exposures on one frame then divide the meter reading by 3 and so one.
If the exposure is 'A' and you give it 2x(A/2) then you are effectively giving it 'A'.
A=3x(A/3) A=4x(A/4) and so on. The end result is the same.

Meysha · May 10, 2005

Ok So what hertz here makes sense to me. But my photos don't.
I'm famous for double, triple, even quadruple exposing my damn Holga. But my photos are never over exposed.
I dunno how to explain it in film terms, so I'll do it in PS terms. The first exposure is usually exposed correctly, then the following exposure(s) are as if they are a layer in PS but the opacity has been turned down. I was expecting one of my shots to come out all blown out because of the 4 exposures - but it just looks like 1 shot with 3 other faint shots over it.
Does anyone know why this happens?

Big Mike · May 10, 2005

Hertz van Rental said:
I think I have posted this before.
If you are doing 2 exposures then you halve the indicated meter reading and use that for each exposure. If you want 3 exposures on one frame then divide the meter reading by 3 and so one.
If the exposure is 'A' and you give it 2x(A/2) then you are effectively giving it 'A'.
A=3x(A/3) A=4x(A/4) and so on. The end result is the same.

That what I thought but I wasn't quite sure. Thanks Hertz for laying it out difinitively for us. Your posts over the last few days have been especially informative. Thanks.

Hertz van Rental · May 10, 2005

If you want to get really fancy...
You could give one exposure at half of that indicated and two at a quarter of that indicated.
Exp A = A/2 + A/4 + A/4
A half plus a quarter plus a quarter = 1.
Once you have the basic principle you can fiddle around with it providing the total exposure is the same as what is indicated by the light meter. It gives you a lot of creative possibilities - and can be fun, too.

As for your query, Meysha. I'd need to see the negs to give you a definitive answer. There are a number of variables that could work together in different ways to give the results you get. Different exposures - either through changing camera settings or changes in light levels, development, et al. There are also some effects due to quantum physics that could account for what you get (in part, anyway). As Holmes used to say: 'it is a mistake to reason without data'.
You could try playing around with a roll and shooting off various multiple exposure combinations to see if you can produce anything similar. Best I can do off the top of my head. Maybe someone else like KSMatt could be more help...

Johnboy2978 · May 10, 2005

Okay, that makes sense. Let me throw some numbers out to get it in my head. Suppose the proper exposure for the setting is f8 with shutter speed of 1/125, and I am going to have 3 exposures. I would go to f32 and leave the shutter at 1/125 or go up 3 stops with an f of 22? If my numbers are off what would they be? I am still trying to get a firm grasp on terminology and how it all fits together.

ShutteredEye · May 10, 2005

:roll: Sheesh what newbie question.:roll:

Soo....uh.....er.....Hertz....??

[/patiently waiting for answer to be revealed.]

:mrgreen: :mrgreen: :mrgreen: :mrgreen:

Hertz van Rental · May 11, 2005

f8 @ 125th = 2x f11 @ 125th OR 2x f8 @ 250th for 2 exposures. (1 stop is halving or doubling the exposure)
so
f8 @ 125th = 4x f16 @ 125th OR 4x f8 @ 500th for 4 exposures.

For 3 exposures you want the exposure between these two. That's the easy way of working it out.

OK. You can't do it with shutter speed sooo...

125 @ f16 + 1/3stop. Put the aperture to f16 then move the ring around 1/3 of the way to f11. Most lenses only realy allow you to move half way between f-numbers. This is OK - you will get a little bit of overexposure but it is within acceptable limits.
Work out the maths to see how it works.
To be honest 3,5,7 et al odd number exposures are b*stards to work out - with a high risk of getting it wrong (I expect KSMatt to come in here and tell me I've done the 3 exposure calculation wrong - I've not been well Matt....) so I admit to avoiding them like the plague. Stick to the easy numbers - 2,4,8...