Using electronic flash with LF cameras

[Pere Casals]

Output as expressed by a GN, an Fstop, BCPS or ECPS over a given degree of coverage is the only accurate way to determine exposure with a flash.

The only exception to this were/are studio strobes with a quartz halogen modeling light centered in the flash tube and both covered with a frosted glass dome with a power pack with fully proportional modeling light control and constant flash duration at all power levels.
With this type of flash a standard light meter can give the proper flash exposure.

Of course I agree that aperture will be determined by GN and strobe to subject distance...

But strobe capability is told by WS.

Imagine you illuminate a group portrait, say 4m x 3m. If flash angle is narrower you will have to place it farther... So if placing the flashes at the distance that will cover all the group then what rules performance is WS.

Same with a softbox, GN is irrelevant, what counts is WS in that case.

[Bob Salomon]

Of course I agree that aperture will be determined by GN and strobe to subject distance...

But strobe capability is told by WS.

Imagine you illuminate a group portrait, say 4m x 3m. If flash angle is narrower you will have to place it farther... So if placing the flashes at the distance that will cover all the group then what rules performance is WS.

Same with a softbox, GN is irrelevant, what counts is WS in that case.

Get your head into the facts. WS are only a measure of energy storage, it is also referred to as joules. They have no relationship with the output of a flash and the most effective flash can only output 80% of its stored capacity.

Learn to use the correct terms, BCPS, ECPS, GN or f stop and get input capacities out of your head.

[tonyowen]

[QUOTE=hsandler;1485360 ..... the effective ISO of the paper being much less than 6 when using flash due to its orthochromatic response and possibly reciprocity (paper not intended for brief intense flash) and I think your results are explainable. Your equipment seems to function; you just need a lot of light.[/QUOTE]

Please can we get away from the rants and discuss my original query.

Okay, does anyone challenge the above quote from Hsandler?

It seems to match my observations and tests, but I do not understand the why and wherefore
My post #59 and result #2 infer that the effective flash GN was/is between 3 and 4 [ f4.7 @ 0.7m]
In turn, given my flash has a GN of 46 at ISO100 then the apparent paper ISO is less than 1.56 [www.scantips - understanding flash guide numbers]

regards
Tony

[Pere Casals]

paper ISO

Tony, just calculate it...

First this is not an ISO Speed, but a suitable EI, (Exposure Index).

I insist. Take a DSLR at ISO 100 and see the right flash power/aperture. Then make a bracketing with paper until you find the right flash/aperture. Comparing the DSLR vs paper then you have your suitable EI for paper.

[Tin Can]

I may have time today.

Tell us exactly what paper you are using.

You only stated Ilford MG.

FB or RC, matt or glossy, guess the age as none is dated.

Any other variables you know of.

Thank you

[tonyowen]

I may have time today.Tell us exactly what paper you are using. You only stated Ilford MG. FB or RC, matt or glossy, guess the age as none is dated. Any other variables you know of. Thank you

Randy, the following is off the box - both sides

Ilford MGIV RC de luxe; 8x10 sheets 100 box; medium weight, Pearl;
MG4RC44M; 09C501C91; 1455 2089; Harman Technology Ltd

Age unknown - best guess circa 10 years????????

regards

Tony

[hsandler]

Please can we get away from the rants and discuss my original query.

Okay, does anyone challenge the above quote from Hsandler?

It seems to match my observations and tests, but I do not understand the why and wherefore
My post #59 and result #2 infer that the effective flash GN was/is between 3 and 4 [ f4.7 @ 0.7m]
In turn, given my flash has a GN of 46 at ISO100 then the apparent paper ISO is less than 1.56 [www.scantips - understanding flash guide numbers]

regards
Tony

Tony there's yet another factor that I think may have been lost in the discussion. In your post #69 the photo of the table and chairs established the GN of your flash is indeed fairly consistent with its rating of 46 in metres at ISO 100. In your post #59, a paper negative photo outdoors established the paper exposed at EI 6 is indeed fairly consistent with ISO 6 for continuous daylight exposure with your development process (negative looks a little thin to me though in the photo, but these things are hard to tell--it's in the ballpark anyway). But way way back near the beginning of the thread, you used GN and paper EI and distance to establish what you predicted should be the right aperture for your still life photo; however, you just summed the distance from the flash to the bounce surface and from the bounce surface to the subject. That's going to be way off, especially for a bounce surface that is not a large mirrored surface. The rule of thumb for bounce flash is you lose 1-2 stops in bouncing off a white ceiling, and that's in addition to the extra distance of the light path. The reason is that a lot of the light is absorbed or scattered off in other directions by the bounce surface. You can verify this by doing a bounce flash photo of something with your digital camera (set it on B in the dark and manually flash your Cobra flash off the ceiling with measured distances and see).

So you have three factors that could account for your underexposure: calculation ignored bounce loss, ortho paper may be less sensitive to bluish flash than daylight or tungsten, and paper may have reciprocity loss for brief flashes (1/1000s at f16 may give less density on the negative than 1/60s at f4).

The thread has gotten very long, and perhaps I missed if you verified these last two things by doing a paper exposure with direct flash but not bounced. The tests with flashing right into the lens only showed that your shutter is working fine on X synch.

[Tin Can]

I have not got to my test yet.

Agree a bounce off the ceiling vastly changes flash effect

[Luis-F-S]

I use a flash meter. Using guide numbers in general and for large format is a fallacy.

[Dan Fromm]

I use a flash meter. Using guide numbers in general and for large format is a fallacy.

Has always worked well for me for closeup work. But my GNs, not the manufacturer's.