Flexible auto-thyristor flash for use with fast films

Dan Fromm · Jul 16, 2014

BrianShaw said:
it is always easier to use flash in manual mode and a flashmeter to establish the proper balance of flash-to-ambient.

Guide number arithmetic still works.

BrianShaw · Jul 16, 2014

Oh... but that requires arithmetic.

Chan Tran · Jul 16, 2014

Jim Jones said:
To reduce flash output, the flash can be filtered or masked. B&W sheet film evenly exposed and developed makes a practical neutral density filter for low power flashes. Really strong flashes can fry the film. A durable mask can be fabricated from thin sheet metal by drilling an array of holes in it. An array of many small holes shouldn't affect the flash pattern.

Simply bouncing the light would reduce the intensity greatly but the OP wish to have an flash that works on auto with relatively high ISO and large aperture. Putting ND on the flash won't solve the problem as in auto mode the flash will try to put out more light to compensate. Manual mode and flashmeter is easiest but does take time and the OP doesn't want to do that either.

BrianShaw · Jul 16, 2014

Chan Tran said:
... Manual mode and flashmeter is easiest but does take time and the OP doesn't want to do that either.

Yet that (flash meter or guide number arithmatic) is the way to achieve the goal. Suggestion to OP: Review this handy-dandy instructional booklet. The concept works even if using a non-Norman strobe. Syching with sun is about the same as synching with interior lighting, only the levels of light will be different.

http://normanlights.com/pdfs/applications/SyncroSunlight.pdf

or this, which discusses the benfits/limitation of thyristor auto modes and fill-in flash too.

http://finearts.uvic.ca/sim/equipment/manuals/_photography/vivitar_285.pdf

p. rex · Jul 16, 2014

Jesus, tough crowd. I have an idea of how guide numbers work, and could do it manually if circumstances permitted. However, I want to take candid pictures. If flash power is going to require constant adjustment based on distance to the subject, that's not a great solution. I would much rather be thinking about composition and interacting with subjects than computing distances and guide numbers or waving around an incident meter. That said, I plan on buying a flash with manual control, and probably eventually picking up a flash meter. Obviously, that provides more precise control than you could get in any automatic mode, and I assume that after you've been doing it for a while, you begin to pick up a more intuitive grasp of how it all works.

*edit* Perhaps I should rephrase that -- I'm not necessarily looking for candid pictures, but I do want to maintain a certain informality. I am, after all, taking pictures of friends and family.

Dan Fromm · Jul 16, 2014

I figured that it would make sense to expose the ambient light at about two stops below the flash. This would require me to set shutter at 1/60 (no choice here), aperture at f/4, and the flash at 1/8th power (assuming five feet to subject, a guide number of 80, and a half-CTO gel on the flash).

Hmm. If 1/8 power gives GN = 80, ISO/feet then without the gel GN arithmetic (80/5 =16) says the flash exposure wants f/16.

According to Rosco a CTO gel cuts light by ~ 1 stop, a half CTO by 1/2 stop. See http://www.rosco.com/filters/cinegel.cfm?menuReturn=quickFilmTV&CategoryID=2

So a half CTO will give you, counting on my fingers, 4, 5.6 (-1), 8 (-2), 11 (-3), 3.5 stops brighter illumination from the flash than from ambient. If you want ambient to be 2 stops below flash, you'll have to put 1.5 stops of ND gel on the flash or expose at ~ 1/20.

I gather you're going to be shooting people indoors. Suggest that if you have time to experiment before the event or whatever that you have to shoot you try using only flash and at an aperture/flash power setting that make sense for the kind of shots you want to take. You may like the results. I make the suggestion having been pressed into shooting office parties. I used ISO 100 color negative film, flash (283 equivalent) on auto, and f/11.

BrianShaw · Jul 16, 2014

For a party wher you want to interact with the guests rather than fiddling with lighting calculation I just use auto (preferably with TTL metering) or the Vivitar sensor (which I've grown to understand and trust). The bacground somewhat falls wherever it does, but the party experience is enhanced and the pics are generally quite nice. Balancing lighting takes effort and a bit of experience. Sometimes it is better to give up the pusuit of perfection and go straight documentary. Sorry if we are seeiming tough on you; just trying to help. Amen.

p. rex · Jul 16, 2014

No, thanks for the advice! I think I understand: blending with ambient is somewhat dicey business, and difficult to manage without a lot of planning and manual control. I think I'll follow your advice and start with using the flash at a more normal automatic way -- if I get one with manual control, I can always try more advanced stuff later.

jp498 · Jul 16, 2014

If you use the vivitar auto sensor, and set your camera to -1 stop exposure compensation, and the flash to -1 also (by adjusting the film speed too high on the calculator), you'll be at a good balanced exposure.

p. rex · Jul 16, 2014

JP, I'm trying to figure out how to do that on a fully manual camera. It's tough to adjust ambient light exposure independently of flash because the only variables I control are 1) aperture, and 2) flash power. Now, when using a digital camera, my habit was to apply -1 stop of flash exposure compensation. I guess the way to do this would be to set the sensor on the flash to expose for an aperture one stop larger than the one actually selected?

Steve Smith · Jul 17, 2014

p. rex said:
It's tough to adjust ambient light exposure independently of flash because the only variables I control are 1) aperture, and 2) flash power.

You can control ambient using shutter speed. As long as it is below the sync. speed with a focal plane shutter (or any speed with a leaf shutter) the flash exposure will not be affected.

EDIT:

p. rex said:
I will be using this with a Pentax ESII, an early 70s SLR with maximum 1/60 sync speed.

Yes, that does restrict it a bit.

Steve.

Chan Tran · Jul 17, 2014

Yes said:
It doesn't because the OP doesn't need speed higher than 1/60 as his ambient light is expected to be quite low.

Flexible auto-thyristor flash for use with fast films

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