Metering for flash with 4x5

[the120ist]

Hi all

I've been running some tests using flash with 4x5, and whilst I've been successful in creating some good images (with a fair amount of trial and error) I'm a little confused by the relationship between what my meter is telling me and what I am having to set in order to get a decent image.

I'm shooting in a controlled setting, using a 90mm lens at about 8-9ft, so not much bellows extension to account for. The lens is a fairly modern one, only an X sync port, no M/X switch, and set at 1/60. Lens has a leaf shutter, camera does not have a focal plane shutter.

But, to get acceptable results on the negative, I'm having to overexpose by 3 stops on what the flash meter is telling me. If I shoot at the metered settings I get almost nothing registering on the film.

Would anyone know why this might be? What am I missing?

The main reason I would like to know is that I want to be able to predict what a flash set up will do in a different setting, if I use more lights, in a bigger room etc. If I'm simply working with a 3 stop offset, then that's ok, I can factor that in. But if there is something else going on, which will change the relationship, then I would like to be able to see that coming!

Any insight you can offer would be greatly appreciated!

Cheers

Nick

 

[wiltw]

3 flashes of same power does not result in 3EV difference (compared to one light alone)

If 1 flash = 0EV
2 flashes = +1EV
3 flashes = +1.5EV
4 flashes = +2EV

but only if the flashes all OVERLAP are the power additive. If each flash puts light on a different part of the subject and do not overlap, they are not additive in power!

1. But if you are metering with a flashmeter, the flashmeter should be capturing the proper exposure, if you are using it properly. Are you metering at the subject location?
2. Are you aiming the hemisphere of the meter toward the camera lens?
3. (Sorry for the obvious) Do you have same ISO set as your film, same shutter speed as your lens shutter?

If Yes to all three questions, there might simply be some other flaw of technique or equipment failure.

 

[the120ist]

I get that, the issue is not the flash power, it’s that metering at the subject is giving me a reading that is 3 stops below what I am having to set to get a properly exposed image.

I mentioned the three flashes only to head off people telling me that you can’t use speed lights with large format because they’re not powerful enough.

 

[the120ist]

I’ve edited the original post without the confusing bit about the lights I was using.

 

[BrianShaw]

It doesn’t make sense to me that the flash meter is 3 stops in error unless it’s defective, being used incorrectly, or the film speed is set wrong.

 

[wiltw]

it’s that metering at the subject is giving me a reading that is 3 stops below what I am having to set to get a properly exposed image

So you meter says to use f/11, but you have to set f/4 to get proper exposure?

 

[BrianShaw]

So you meter says to use f/4, but you have to set f/11 to get proper exposure?

I read it opposite. Meter says 11 but aperture needs to be opened to 4.

 

[wiltw]

I read it opposite. Meter says 11 but aperture needs to be opened to 4.

I altered my post before reading yours.
For that behavior, there might be a synchronization issue in the shutter, so it is not timed to be fully open when the burst of light has peaked, but it is delayed so it is catching the falloff tail of light output.

 

[BrianShaw]

That thought crossed my mind, also…

 

[MattKing]

Your shutter's X-synch may be out of adjustment, or the trigger may be incorporating a delay.
One or both could be causing the flashes to fire when the shutter isn't at the maximum set opening.

 

[MattKing]

To check, try triggering the flash manually with the shutter open in bulb mode - in a darkened room of course.

 

[Pieter12]

Are you using a speedlight or a studio strobe? Speedlights can have very short flash durations, so there is a slight possibility of very short exposure reciprocity failure. Is your meter accurate--have you checked it with a smaller-format film or digital camera?

 

[the120ist]

Thanks for the replies. Yes, the flash meter was reading f16, but I was having to open the iris to f5.6 to get a proper exposure. At f16 there was almost nothing on the negatives.

interesting that there could be an issue with the x sync timing. I didn’t know that was possible.

User error is absolutely a possibility. I can’t think what I could have been doing wrong, but I am prone to the odd silly mistake!

I don’t think the meter is defective, I use it every day for ambient and constant light, but not usually for flash (but it is a flash meter btw).

All messages very helpful though, thank you. I’ll go back and read the manual again, double check I’m not being an idiot, the do the bulb test and see what that throws up.

 

[the120ist]

Are you using a speedlight or a studio strobe? Speedlights can have very short flash durations, so there is a slight possibility of very short exposure reciprocity failure. Is your meter accurate--have you checked it with a smaller-format film or digital camera?

Ahh interesting! Yes I am using speed lights. Multiple speed lights linked together to boost the output, but still speed lights.

so a short exposure can cause issues with film just as a long exposure does? I didn’t know that.

I haven’t used these speed lights with film for quite a few years, only digital, and to be honest I work with them so often on digital that I don’t meter them, I can generally get close just with experience and can of course tweak as I go along.

 

[MattKing]

It was unfortunate that you edited out the reference to the three lights and the trigger, because you could have synch issues arising there as well. It would be worthwhile also checking to see if a single flash directly connected does give correct exposure at the exposure recommended by the meter.
The same applies to a single flash triggered through the trigger.

 

[the120ist]

It was unfortunate that you edited out the reference to the three lights and the trigger, because you could have synch issues arising there as well. It would be worthwhile also checking to see if a single flash directly connected does give correct exposure at the exposure recommended by the meter.
The same applies to a single flash triggered through the trigger.

apologies, I thought that the information was confusing the issue.

More elements to test though, thank you.

 

[mshchem]

To check, try triggering the flash manually with the shutter open in bulb mode - in a darkened room of course.

EXCELLENT suggestion!
Something is really wrong.

 

[mshchem]

Ahh interesting! Yes I am using speed lights. Multiple speed lights linked together to boost the output, but still speed lights.

so a short exposure can cause issues with film just as a long exposure does? I didn’t know that.

I haven’t used these speed lights with film for quite a few years, only digital, and to be honest I work with them so often on digital that I don’t meter them, I can generally get close just with experience and can of course tweak as I go along.

No argument that it could be an issue. Kodak, back in the mid 20th century even warned about cold, not only a sluggish shutter, a obvious issue, but film losing a bit of sensitivity. Still modern film is pretty good.

 

[mshchem]

apologies, I thought that the information was confusing the issue.

More elements to test though, thank you.

What sort of film?

 

[BrianShaw]

What sort of film?

… and in the holder correctly? Shooting with the film backward could cause “under exposure”.

 

[the120ist]

What sort of film?

Foma 400, but I metered at 320 to account for the usual Foma underexposure.

 

[mshchem]

… and in the holder correctly? Shooting with the film backward could cause “under exposure”.

Oh. Good suggestion!

 

[the120ist]

… and in the holder correctly? Shooting with the film backward could cause “under exposure”.

I shot maybe 15 sheets across three sessions of testing, gradually increasing flash power and/or opening iris and noting down settings. I was getting consistent results, so I don’t think I got any sheets backwards.

 

[removed account4]

are they speedos attached to the same battery pack ? don't forget every light plugged in reduces the output of the flash so 1 head at 200Ws 2 at 100 each 3 at 50.. have you tested your flash to make sure its running at the right speed ?
sorry for obvious questions, but sometimes I am looking for my keys and holding them in my hand..

 

[the120ist]

are they speedos attached to the same battery pack ? don't forget every light plugged in reduces the output of the flash so 1 head at 200Ws 2 at 100 each 3 at 50.. have you tested your flash to make sure its running at the right speed ?
sorry for obvious questions, but sometimes I am looking for my keys and holding them in my hand..

Im all ears to the obvious suggestions! I quite often look for my keys and find them in my hand! The most likely cause of this is me, for sure. But shooting speed lights, so they are all individually powered.