Flash question

[basiltahan]

I am trying to shoot some 8x10 paper negatives (or positives on Harman Direct) in the studio.

If I can only get f8 power from a flash setup (at ISO 3) can I simply trigger the flash multiple times with the shutter open to get more power (still life)?

For example, to get from f8 to f11 fire the flash twice.

Then to get to f16 from f8, fire the flash 4 times.

Hypothetically, if I want to shoot at f45 but can only achieve f8 at full power (8 11 16 22 32 45- five stops), can I just open the shutter and fire the flash repeatedly 32 times?

I think the answer is obviously yes, but don't want to be missing something.

[Jim Jones]

Your math is correct, although there may possibly a slight discrepancy due to reciprocity failure. Multiple flashes work well if the camera and subject don't move between flashes and the ambient light isn't strong enough to affect the image.

[Drew Bedo]

Years ago I did some larger than life size macro of some flowers on 8x10.. It was a shoe-string set up with a $10 oscilloscope lens and out of date film. With bracketing these shots took 8 to 15 Pops of the little strobes that I had then.

My Set-Up
8x10 Kodak 2D at near max extension.
75mm Ocillo-Parago set to f-1.9 to focus, stopped down to f-11 or f-22 for shooting
Two Vvitar 283 strobes
Ektachrome 100

A few years later I took a Daguerreotype workshop. The instructor described his success in making a few portraits using one pop of a HUGE bank of studio strobes.

[Leigh]

Hypothetically, if I want to shoot at f45 but can only achieve f8 at full power (8 11 16 22 32 45- five stops), can I just open the shutter and fire the flash repeatedly 32 times?

That's correct, but a word of caution...

Be sure you don't overheat the strobes.

A strobe generates significant heat internally each time it's fired.
In regular usage, this heat dissipates before the flash is fired the next time.

For flashes in rapid succession, monitor the housing temperature and do not fire if it's uncomfortably warm.

Note that some strobes have internal thermal links that will open to protect the device if the internal temperature rises too high. The strobe is then dead until that component is replaced by a repair shop.

- Leigh

[lenser]

If you are using a flash with a modeling light, that will accumulate as ambient light on the film, causing an over exposure.

Do your set up, turn off the room lights and modeling light, and then fire away slowly, (as Leigh warned), to avoid over heating the flashes.

A dim light in the room at some distance away from the subject (such as a plug in nigh light) shouldn't cause any problem and allow you some sense of vision in your work space.

Tim

[DG 3313]

Run tests...take notes.....you are painting with light and it does accumulate on the neg (paper or film).

[basiltahan]

Run tests...take notes.....you are painting with light and it does accumulate on the neg (paper or film).

Thank you to all. I will post the results.

I think the flash would overheat, so I'll try an 8 flash shot at f22 first. Still quite shallow for what I want to do but at f8 there is almost nothing in focus.

[Doremus Scudder]

The other alternative of course (and since you are going to have your shutter open for a long time anyway...) is to simply use continuous lighting and a long exposure. I've done still-lifes like this for a long time, using either natural light or incandescent lighting. Meter at your desired aperture, adjust for bellows extension and reciprocity, set everything up, open the shutter, leave the room for 20 minutes... ... Come back later and close the shutter (same procedure in dark canyons too). Flowers sometimes have a tendency to change position during long exposures, but often enough don't. Static subjects work fine this way. It does take longer.

Best,

Doremus

[basiltahan]

The other alternative of course (and since you are going to have your shutter open for a long time anyway...) is to simply use continuous lighting and a long exposure. I've done still-lifes like this for a long time, using either natural light or incandescent lighting. Meter at your desired aperture, adjust for bellows extension and reciprocity, set everything up, open the shutter, leave the room for 20 minutes... ... Come back later and close the shutter (same procedure in dark canyons too). Flowers sometimes have a tendency to change position during long exposures, but often enough don't. Static subjects work fine this way. It does take longer.

Best,

Doremus

I am not sure, but ISO 3 and f45 could be a very very slow combination. Could be several hours with ambient room lighting.

Two people have mentioned reciprocity failure. I was under the informed assumption that paper did not have reciprocity failure. Am I wrong?

[Leigh]

Two people have mentioned reciprocity failure. I was under the informed assumption that paper did not have reciprocity failure.

Any photographic emulsion will exhibit reciprocity-law failure at both ends of the exposure-time range.
The difference being that the "normal" exposure times for paper are much longer than for film.

Experimentation would be needed to determine the characteristics of your particular paper.
Fortunately for the wallet, you only need a small piece of paper for each time, not a full sheet.

- Leigh