PDA

View Full Version : Multiple Exposure Question



IanBarber
1-Oct-2017, 13:03
I am wanting to try out some multiple exposure on the same negative of the same scene on some coastal work tomorrow.

Scenario:
The meter reading is 1/4 second at f22 but to use 1/125th second at f22, divide 125 by 4, the answer is 31 multiple exposures at 1/125th.

Is there anything else I need to be aware of or will the 31 exposures at 1/125th give me the same density as a single exposure at 1/4

Jac@stafford.net
1-Oct-2017, 13:24
Nooooo. Exposures are not linear. The good news is ~ five exposures.

IanBarber
1-Oct-2017, 13:26
Nooooo. Exposures are not linear. The good news is ~ five exposures.

Can you explain how you arrived at 5 please

Jac@stafford.net
1-Oct-2017, 13:30
Can you explain how you arrived at 5 please

1/4 to 1/8
1/8 to 1/15
1/15 to 1/30
1/30 to 1/60
1/60 to 1/125

Five stops

I am sure someone will correct me if I am wrong.
.

IanBarber
1-Oct-2017, 13:35
1/4 to 1/8
1/8 to 1/15
1/15 to 1/30
1/30 to 1/60
1/60 to 1/125

Five stops


What would happen if I took 31 exposures at 1/125th. Would the density on the negative not build up to equal one exposure at 1/4

jamesaz
1-Oct-2017, 14:14
And then some.

jamesaz
1-Oct-2017, 15:18
I'd never given it much thought but it seems like it would be way over exposed. If I did feel the need to put 31 exposures on a sheet of film though I'd start with close to proper exposure and build (or subtract) from there likely using a combination of film, developing, and neutral density. The OP seems to want to use 1/125 so shutter speed doesn't seem an option. Could be an interesting experiment, not for me but maybe someone somewhere.

Jac@stafford.net
1-Oct-2017, 15:26
I'd never given it much thought but it seems like it would be way over exposed. If I did feel the need to put 31 exposures on a sheet of film though I'd start with close to proper exposure and build (or subtract) from there likely using a combination of film, developing, and neutral density. The OP seems to want to use 1/125 so shutter speed doesn't seem an option. Could be an interesting experiment, not for me but maybe someone somewhere.

The OP is not wanting to make 31 exposures. He simply wants to know how many exposures to equal a certain exposure.

Charlie Strack
1-Oct-2017, 16:03
5 stops is correct, but stops are on a logarithmic scale with a base of 2: each stop doubles the exposure; shutter speeds are on a linear scale , though the speeds on the dial have been chosen to reflect a doubling with each step (with slight fudging, e.g. 125th should actually be 1/128th). So 5 stops amounts to 2 to the 5th times the exposure which is equal to 32.

However, not all multiple exposures act linearly, as film tends to have a minimum exposure threshold, and the shorter exposures might not meet it in the shadows. You may find a bit higher contrast with the multiple exposures, and deeper shadows. Experiment to find out. Ansel Adams used pre-exposure to provide a minimum exposure to control contrast in certain situations for this reason. Pre-exposure is using an out of focus single tone subject placed at Zone 1 to give the entire piece of film an exposure equal to base black. It is out of focus to be sure there is no texture recorded.

xkaes
1-Oct-2017, 16:14
1/4 second at f22 - 1 exposure
1/8 second at f22 - 2 exposures
1/15 second at f22 - 4 exposures
1/30 second at f22 - 8 exposures
1/60 second at f22 - 16 exposures
1/125 second at f22 - 32 exposures

You were WAY off!!!

LabRat
1-Oct-2017, 16:34
This subject has been throughly discussed here (at length) at least a couple times over the past couple of years... Please go through the archives and find it...

No matter what, even if you photograph something on a black background, it will build-up base and overall density differently than a single exposure, and not the same (much flatter contrast etc), and I really don't understand why so many exposures would be needed on a sheet of film, when other sheets could be shot, and combined later somehow... (Limited subject matter/choices & overall density problems...) There are times to split exposures (CC filter changes/color, movement, adding elements, montage, etc), but without masking, the image gets terribly complicated, and harder to print every step of the way...

I like to put problems before solutions, instead of solutions that are looking for a problem (but that's just me)... And try not to hold technical concepts as "koool", and that being the underlining reason to do it... (Or I could be printing epic photographs on the heads of pins... Cool, right!?!!!)

(Don't mind me, I'm in a weird mood today...)

Steve K

Jac@stafford.net
1-Oct-2017, 16:36
1/4 second at f22 - 1 exposure
1/8 second at f22 - 2 exposures
1/15 second at f22 - 4 exposures
1/30 second at f22 - 8 exposures
1/60 second at f22 - 16 exposures
1/125 second at f22 - 32 exposures

You were WAY off!!!

Were you ignoring that each exposure accumulates to the final result?

xkaes
1-Oct-2017, 16:41
I really don't understand why so many exposures would be needed on a sheet of film

Here's one that I've used myself many times. I'm at the beach with a bunch of rocks. I can take one exposure at short or long shutter speeds -- at whatever f-stop. With the longer exposures I get more blurrrrr of the waves crashing. Or I can take 64 exposures of the same scene with a short exposure time with the waves frozen at different positions. Completely different effect.

xkaes
1-Oct-2017, 16:44
Were you ignoring that each exposure accumulates to the final result?

Last time I checked 1/8 + 1/8 = 2/8 = 1/4. But it's been a while since I took calculus.

LabRat
1-Oct-2017, 16:49
Here's one that I've used myself many times. I'm at the beach with a bunch of rocks. I can take one exposure at short or long shutter speeds -- at whatever f-stop. With the longer exposures I get more blurrrrr of the waves crashing. Or I can take 64 exposures of the same scene with a short exposure time with the waves frozen at different positions. Completely different effect.

Just more complicated... (You mean 64 underexposed exposures???)

Get to the beach much???

Steve K

xkaes
1-Oct-2017, 16:58
Just more complicated... (You mean 64 underexposed exposures???)

Get to the beach much???

Steve K

Yeah, I know, math is complicated. Even more complex than getting to the beach. FYI, it works on rivers and streams as well, as I and many other photographers, who know how to divide, can attest. Go buy a calculator and try it yourself.

LabRat
1-Oct-2017, 17:12
Yeah, I know, math is complicated. Even more complex than getting to the beach. FYI, it works on rivers and streams as well, as I and many other photographers, who know how to divide, can attest. Go buy a calculator and try it yourself.

Go figure...

Steve K

IanBarber
2-Oct-2017, 01:02
Here's one that I've used myself many times. I'm at the beach with a bunch of rocks. I can take one exposure at short or long shutter speeds -- at whatever f-stop. With the longer exposures I get more blurrrrr of the waves crashing. Or I can take 64 exposures of the same scene with a short exposure time with the waves frozen at different positions. Completely different effect.

This is exactly what I am trying to achieve. So going back to my initial question, do I have the math right in order to calculate the number of required exposures

Doremus Scudder
2-Oct-2017, 02:41
This is exactly what I am trying to achieve. So going back to my initial question, do I have the math right in order to calculate the number of required exposures

Ian,

Your math is correct. The way xkaes figures, one comes up with 32 exposures, but the difference is trivial. In this case, Jac is wrong (uncharacteristically). You need a lot more than five exposures at 1/125 to equal 1/4 sec. Think of it this way: 1/4 second is 250 milliseconds; 1/125 second is 8 milliseconds. Divide 250 by 8 to find how many exposures you need. Answer: 31.25.

However, keep in mind that there is such a thing as the intermittency effect, which basically states that many short exposures do not exactly equal one long exposure. If I were in your place, I would use 40 or more exposures.

FWIW, I use cumulative exposures to make up one total exposure all the time, although usually only 4-10 different exposures. It's a great way to stop wind, keep passers-by and cars out of your shots and get rid of blinking lights.

Best,

Doremus

IanBarber
2-Oct-2017, 02:46
Ian,

Your math is correct. The way xkaes figures, one comes up with 32 exposures, but the difference is trivial. In this case, Jac is wrong (uncharacteristically). You need a lot more than five exposures at 1/125 to equal 1/4 sec. Think of it this way: 1/4 second is 250 milliseconds; 1/125 second is 8 milliseconds. Divide 250 by 8 to find how many exposures you need. Answer: 31.25.

However, keep in mind that there is such a thing as the intermittency effect, which basically states that many short exposures do not exactly equal one long exposure. If I were in your place, I would use 40 or more exposures.

FWIW, I use cumulative exposures to make up one total exposure all the time, although usually only 4-10 different exposures. It's a great way to stop wind, keep passers-by and cars out of your shots and get rid of blinking lights.

Best,

Doremus

Thanks for the clarification, I was not aware of the intermittency effect, is it just a case of adding a few more to take this into effect or do you calculate it through a formula

LabRat
2-Oct-2017, 03:01
But what will the effect (on water) look like??? With enough exposures, it ends up looking murky, as there's only chopped (short) exposures, not enough time to build up proper (normal) highlights, and not enough collective "frames" to have a completed event image... With many exposures, it might start looking like a time exposure, as snapped elements start to join... Or something murky with something foggy over it...

You might as well just get a heavy ND filter, as exposure + reciprocity are easily calculated, as one of the benefits is that in a body of moving water, different flow patterns tend to replicate, so with a long enough exposure, the patterns emerge and become visible...

Actually doing some real tests reveal what the camera/film image "sees", rather than what we (think we) "want"... And do we like what we get???

Test, test, test...

Steve K

xkaes
2-Oct-2017, 05:59
You don't need a calculator -- other than the one you have in your head. Just determine the correct exposure for a scene/subject, as you normally do. Then, determine the number of exposures you want to take. If nothing else, just guess. I first used this approach with a Minolta SLR that had double exposure capability, but a LOT of "double" exposures is a pain -- MUCH, MUCH easier with large format.

Make sure your camera is secure to a steady tripod -- you don't want to waste a lot of time by having your camera move after 50 exposures.

Then start "doubling" your exposures -- as far as you want to go. Every time you double the number of exposures, you simply switch to the next faster shutter speed:

2 exposures = 1 shutter speed change
4 exposures = 2 shutter speed change
8 exposures = 3 shutter speed change
16 exposures = 4 shutter speed change
etc.

Pretty simple. If you run out of shorter shutter speeds, add NDX filters -- BEFORE you start, of course.

Sure, the intermittency effect exists, but it depends on how bright your subject is as well as how many exposures you take. The darker the subject and the more exposures, the more compensation you will need. My experience? Find something more important to worry about -- like being struck by lightning. You are more likely to run out of "a next faster shutter speed" or "time" before you need to worry about intermittency. And even if it is there -- to whatever extent -- you might like the effect. My best results were taken on Long Island Sound, shortly after sunset with Kodachrome 25 and colored filters. I did not even attempt to guess at how much to compensate for intermittency.

170432

The effects will be different depending on how many exposures you take. The more you take, the more it will be like a single LONG exposure, but still will be different. And remember that you can make other changes inbetween exposures, such as filtration changes, which you can't do with a single LONG exposure. Once again, you are only limited by your imagination.

Jac@stafford.net
2-Oct-2017, 08:24
Thanks to all who corrected me. I went so far afield I got lost.

pjd
2-Oct-2017, 22:04
This is exactly what I am trying to achieve. So going back to my initial question, do I have the maths right in order to calculate the number of required exposures

Fixed it ;) Unless you are an American exiled in Doncaster, in which case please accept my apologies.

About the original question, why not make two negatives (one with split exposure) and see if you can spot a difference (in negative density, not in the waves or whatnot). Also check which prints better.