Using electronic flash with LF cameras

[Bob Salomon]

I ran my tests again and ended up with essentially an unexposed paper negatives.
I’ve listed below what I know and what I DO NOT know.
I know the shutter [cla’d November 2017] was set to 1/60th sec and f4.7. Also the ‘X’ setting chosen
I know the flash [Cobra D650] was set to ‘manual’ with the hood set at 85 degrees to give a GN 46.
I DO NOT know the exact/current GN of the 30+ year old flash.
I positioned the flash and camera about a metre from the subject and the flash fired when the cable release was pressed.
I use a one shot developer [Ilford PQ Universal] in a Jobo 2509 reel.
I DO NOT know how viable/potent the undiluted developer is.
I used Ilford Multigrade paper but DO NOT know the quality of the sheet used.
So back to square one!
Regards
Tony

GN is easy. What does it say at 3 meters? That’s the GN for whatever ISO you chose.

[Dan Fromm]

Tony, if not specified otherwise the GN is in feet for ISO 100. At three feet -- for this exercise, close enough to 1 m -- with ISO 100 film, the correct aperture if the flash makes its rated output is 46/12 = f/4. Again, close enough to the true value.

Little flashes like the Cobra D650 typically have actual GNs one stop slower than claimed. The only way to be sure is to measure, by shooting a test strip or with a known good flash meter.

Until your flash is proven to make its rated GN, the likely correct aperture with ISO 100 at 1 m is probably f/8. Your paper is approximately six stops slower than ISO 100. Of course you're getting no exposure.

Also, have you verified that on X sync your flash is in fact open when it fires the flash? It should be, but this has to be checked anyway. Remember the strong version of Murphy's law. What can go wrong will go wrong. What can't go wrong will go wrong too.

[Bob Salomon]

Tony, if not specified otherwise the GN is in feet for ISO 100. At three feet -- for this exercise, close enough to 1 m -- with ISO 100 film, the correct aperture if the flash makes its rated output is 46/12 = f/4. Again, close enough to the true value.

Little flashes like the Cobra D650 typically have actual GNs one stop slower than claimed. The only way to be sure is to measure, by shooting a test strip or with a known good flash meter.

Until your flash is proven to make its rated GN, the likely correct aperture with ISO 100 at 1 m is probably f/8. Your paper is approximately six stops slower than ISO 100. Of course you're getting no exposure.

Also, have you verified that on X sync your flash is in fact open when it fires the flash? It should be, but this has to be checked anyway. Remember the strong version of Murphy's law. What can go wrong will go wrong. What can't go wrong will go wrong too.

You also want to know the coverage angle of your flash as these small, cheap units are usually rated in the center of the beam and you may be using more then that.

[Dan Fromm]

Hey Bob, I looked Tony's flash up. If I got it right it is a potato masher and I might have been mistaken in treating its GN as feet, ISO 100. Tony stated a meters GN for it in an early post in this discussion. All that said, what he's getting reeks of massive underexposure.

[tonyowen]

Hey Bob, I looked Tony's flash up. If I got it right it is a potato masher and I might have been mistaken in treating its GN as feet, ISO 100. Tony stated a meters GN for it in an early post in this discussion. All that said, what he's getting reeks of massive underexposure.

Dan,
Potato masher is the correct reference. It is large and [according to the specs] powerful - not quite the big Metz units but getting there.
For information, the GM (metric) is 32 at the 35mm zoom position and 46 at the 85mm zoom position. I calculate the imperial GNs would be 105 & 151 respectively
You refer to a 'good flash meter' but Murphy's Law guarantees the one I get will be 'wrong in some way and how does one prove that the meter is accurate, reliable and consistent!!!

regards
Tony

[Tin Can]

I have proved to myself my flash bulbs, studio flash and modern Nikon flash with DSLR and film.

It all makes sense, then I forget to write it down.

Doing it again soon.

I have a Sekonic 758 and it agrees exactly with my Paul C Buff Cyber Commander.

This time it gets printed in large font in seal a meal, actually the heat plastic stuff whatever that's called

and nailed to the studio wall

Dan,
Potato masher is the correct reference. It is large and [according to the specs] powerful - not quite the big Metz units but getting there.
For information, the GM (metric) is 32 at the 35mm zoom position and 46 at the 85mm zoom position. I calculate the imperial GNs would be 105 & 151 respectively
You refer to a 'good flash meter' but Murphy's Law guarantees the one I get will be 'wrong in some way and how does one prove that the meter is accurate, reliable and consistent!!!

regards
Tony

[Pfsor]

I ran my tests again and ended up with essentially an unexposed paper negatives.
I’ve listed below what I know and what I DO NOT know.
I know the shutter [cla’d November 2017] was set to 1/60th sec and f4.7. Also the ‘X’ setting chosen
I know the flash [Cobra D650] was set to ‘manual’ with the hood set at 85 degrees to give a GN 46.
I DO NOT know the exact/current GN of the 30+ year old flash.
I positioned the flash and camera about a metre from the subject and the flash fired when the cable release was pressed.
I use a one shot developer [Ilford PQ Universal] in a Jobo 2509 reel.
I DO NOT know how viable/potent the undiluted developer is.
I used Ilford Multigrade paper but DO NOT know the quality of the sheet used.
So back to square one!
Regards
Tony

If you tried different flash distances from a very close one you would know what the ballpark you're in is. Like this it seems you want to work on this simple problem for months.

[David Lobato]

In my modest experience paper does not respond the same to electronic flash as film does. I look forward to someone smarter who me can correct my opinion.

I know that reciprocity failure occurs with extremely short exposure times, electronic flash being the most common source. With paper designed for seconds and minutes exposure timnes, that may be the case.

[tonyowen]

I have proved to myself my flash bulbs, studio flash and modern Nikon flash with DSLR and film.
It all makes sense, then I forget to write it down. Doing it again soon. I have a Sekonic 758 and it agrees exactly with my Paul C Buff Cyber Commander.
This time it gets printed in large font in seal a meal, actually the heat plastic stuff whatever that's called and nailed to the studio wall

If you tried different flash distances from a very close one you would know what the ballpark you're in is. Like this it seems you want to work on this simple problem for months.

I know that reciprocity failure occurs with extremely short exposure times, electronic flash being the most common source. With paper designed for seconds and minutes exposure times, that may be the case.

Randy - mine works with film but not paper. [see bottom response]
Pisor - have tried many distances but all (with paper) fail [see above and below}
David - I've come across that before and it matches my experiences. The quoted flash time for the Cobra's 'manual setting' is 1/1000th sec

regard to all
Tony

[Tin Can]

Tony,

Noted, I only shot 2 paper negs with solar pinhole long ago. I tried Harman Positive with strobes but never liked any result.

I will revisit paper negs soon as I do have a project in mind.

Thanks for the tip!