Metering for flash with 4x5

[mshchem]

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

Look at Foma date sheet online. Foma 400 shows normal exposure 1 second to 1/1000th. 3 stops more exposure at 100 seconds.

There's only 1 data sheet that I could find. Only difference is what base it's coated on (rolls vs sheets)

 

[the120ist]

Look at Foma date sheet online. Foma 400 shows normal exposure 1 second to 1/1000th. 3 stops more exposure at 100 seconds.

There's only 1 data sheet that I could find. Only difference is what base it's coated on (rolls vs sheets)

interesting, so if the flash duration was shorter than 1/1000 then it would behave abnormally. I need to check the t.1 and t.5 time on the speed lights. I was linking up flash units to try to keep the power down, but that would give shorter durations. Any ideas what behaviour you could expect from Foma at shorter than 1/1000 exposures?

 

[removed account4]

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.

oops. I took speed lights as being speedotrons sorry for my cluelessness! just realized you meant nikon speed lights...
have you done this same set up with non 4x5 film ? and does it register correctly with a different camera ( no matter analog or electric )? is there a setting on the speed lights so they sync up and are slaved to a master light? maybe 1 light goes off and the other 2 don't
if it all works with other cameras, it might mean your lens needs servicing ...

 

[the120ist]

oops. I took speed lights as being speedotrons sorry for my cluelessness! just realized you meant nikon speed lights...
have you done this same set up with non 4x5 film ? and does it register correctly with a different camera ( no matter analog or electric )? is there a setting on the speed lights so they sync up and are slaved to a master light? maybe 1 light goes off and the other 2 don't
if it all works with other cameras, it might mean your lens needs servicing ...

They work perfectly with digital. I haven’t tried with other analogue formats for quite a while, I’ll have to give that a go tomorrow.

unlikey to be one unit not firing I think, as the metering was done via flash meter at the subject, and the results consistent.

 

[the120ist]

interesting, so if the flash duration was shorter than 1/1000 then it would behave abnormally. I need to check the t.1 and t.5 time on the speed lights. I was linking up flash units to try to keep the power down, but that would give shorter durations. Any ideas what behaviour you could expect from Foma at shorter than 1/1000 exposures?

struggling to find a flash duration chart for the ones I was using, but comparable canon models suggest that at 1/4 power the duration could be as low as 1/2800…

 

[benveniste]

Is there any chance you can borrow a different shutter? I don't think it's a film issue as much as either a sticky shutter or a synchronization issue.

 

[cramej]

What film?

What meter?

How are you metering? I.E how are you triggering the strobes when you take a meter reading?

What mode are your strobes set to? A, M, what power?

 

[mshchem]

What film?

What meter?

How are you metering? I.E how are you triggering the strobes when you take a meter reading?

What mode are your strobes set to? A, M, what power?

Very good questions.

 

[mshchem]

I would try 1 strobe, manual full power.

Have you considered a skylight

 

[mshchem]

Kodak TMY-2 400 ISO. No exposure adjustment from 1/10,000th to 1 second, add 1/3 stop at 10 seconds.

 

[MattKing]

It certainly isn't impossible that you are seeing the results of short duration reciprocity failure.
But I think it unlikely.
If you are working at 8-9 feet, and your meter suggests f/11, and you are using 3 flash tubes, that usually doesn't indicate the sort of immensely quick flash that brings rise to a 3 stop reduction of film response.

 

[mshchem]

I think it's the shutter. Got to love film.

 

[the120ist]

Is there any chance you can borrow a different shutter? I don't think it's a film issue as much as either a sticky shutter or a synchronization issue.

I have another lens in its own shutter, I'll give that one a test today, see what results I get.

 

[the120ist]

What film?

What meter?

How are you metering? I.E how are you triggering the strobes when you take a meter reading?

What mode are your strobes set to? A, M, what power?

Meter is a Sekonic Flashmate L-308S. I have tested in both cord flash mode - with the TX of the remote trigger plugged directly into the flash meter, and in cordless timed mode, triggering the TX in my hand. Same results with both methods.

Flash units are all on full manual, no auto and no slaves, all fired directly via PC socket. I tested through a range of power outputs from 1/16 to 1/1, each time metering after changing the power output and then comparing metered light with results on the negatives.

 

[the120ist]

Thanks everyone for all your suggestions. I'll be setting up to run all the tests you guys have suggested this evening, including different formats, different lenses, different shutters and different trigger methods! Busy evening ahead for me, but I'm excited to get to the bottom of what's going on. Will update for anyone interested to know the findings.

Thanks again.

 

[the120ist]

I would try 1 strobe, manual full power.

Have you considered a skylight

Ha! Of course there is always the option of not using flash... but I'm in too deep for that now!

 

[AgX]

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?

Speedlights are in about the 1/300 to 1/1000 range . Unless set in manual to a fraction of output or set to AE.

For fractional output of a speedlight Metz for instance gives for 1/8 output a duration of 1/4000sec.


The classic studio flashes controlled output by the number of capacitors employed. So the duration does not change, but there are tricks to shorten the duration.
With modern monolights the output is controlled by duration.

 

[shutterfinger]

1. with the lens/shutter off the camera set the aperture to wide open, shutter speed to 1/15 through 1/100 or 1/125 whichever you have. attach 1 flash to the shutter, powered on. point the flash and lens at a light colored wall. looking through the rear of the lens trip the shutter. you should see the wall at full aperture as it would be if you were looking through it on T or held open on B.
think of the shutter as a variable aperture that goes from closed to full open in .0001 second, being held open for the selected time then being forced closed in .00001 second. at some point on opening it is 2 or more stops below the toe of the film and again on closing. the opening and closing speeds are such as not to effect exposure. if you can see the shutter blades in the lens while the flash is firing then the flash sync is off. a 3 stop error will be the flash is firing when the shutter is 80% open. another way to test is with the flash attached and powered on trip the shutter on 1 second or B but hold the cocking lever and allow the shutter to open slowly and note where the shutter blades are when the flash fires. shutter blades 95% open will not have a determinable effect on exposure, less than 1/3 stop approximately.
2. after testing the shutter flash sync block the auto sensors on the flash and test again with film.

 

[RalphLambrecht]

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

there could be something wrong with the flash synchronization, but you can test for that. If you try your set up in a totally darkened room and fire the flash wth the¬ens opened at the meter setting.This will give you the same illumination as the meter is seeing and the exposure should be as the meter predicted, if not, the flash synch of the lens is not working properly. Also, please tell what aperture you're using.

 

[the120ist]

there could be something wrong with the flash synchronization, but you can test for that. If you try your set up in a totally darkened room and fire the flash wth the¬ens opened at the meter setting.This will give you the same illumination as the meter is seeing and the exposure should be as the meter predicted, if not, the flash synch of the lens is not working properly. Also, please tell what aperture you're using.

Thanks Ralph, I'm going to try this tonight, after sunset. My "studio" (garage) is not fully light tight, so I'll need to wait til it's dark. But I'll bring the sheets straight in once I've tested and develop, see what's what.

I tested a range of apertures, but got best results at f5.6, when the meter was telling me to be at f16!

 

[the120ist]

1. with the lens/shutter off the camera set the aperture to wide open, shutter speed to 1/15 through 1/100 or 1/125 whichever you have. attach 1 flash to the shutter, powered on. point the flash and lens at a light colored wall. looking through the rear of the lens trip the shutter. you should see the wall at full aperture as it would be if you were looking through it on T or held open on B.
think of the shutter as a variable aperture that goes from closed to full open in .0001 second, being held open for the selected time then being forced closed in .00001 second. at some point on opening it is 2 or more stops below the toe of the film and again on closing. the opening and closing speeds are such as not to effect exposure. if you can see the shutter blades in the lens while the flash is firing then the flash sync is off. a 3 stop error will be the flash is firing when the shutter is 80% open. another way to test is with the flash attached and powered on trip the shutter on 1 second or B but hold the cocking lever and allow the shutter to open slowly and note where the shutter blades are when the flash fires. shutter blades 95% open will not have a determinable effect on exposure, less than 1/3 stop approximately.
2. after testing the shutter flash sync block the auto sensors on the flash and test again with film.

That sounds like a good test, I'll try that this morning. Thank you!

 

[removed account4]

Is there any chance you can borrow a different shutter? I don't think it's a film issue as much as either a sticky shutter or a synchronization issue.

+1

 

[tezzasmall]

Although you are using flash units, have you tried taking some exposures outside in daylight? Using the same meter, expose a couple of sheets of film. To my mind, if these are also underexposed, when exposed at the meter reading, then it's the lens shutter not working properly.

Terry S

 

[Chan Tran]

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.

It's about right if the OP using the flash meter in reflective mode and use in in the incident mode fashion.

 

[the120ist]

Although you are using flash units, have you tried taking some exposures outside in daylight? Using the same meter, expose a couple of sheets of film. To my mind, if these are also underexposed, when exposed at the meter reading, then it's the lens shutter not working properly.

Terry S

Yes I've been using this lens/shutter/camera/light meter combo for quite a while, never had any issues until I started trying to use flash indoors!