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Flash Distance Compensation - Large Format


leighton_mcdonnell

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Hi

 

I have just dug out my Gowland 4x5 and an old notebook after a few years with digital but may have forgotten some basic formulas. I may have to waste some film I think but if I photograph at night with flash only and:

 

Focus on a subject say at 60" (measured from film holder to subject) do I have to compensate for exposure (using flashmeter) if flash (Metz 45) on full power (manual) is closer to subject than the film (such as adjacent to to lens on its own tripod). I have a suspicion I do. Is there a formula for calculating this or simply trial and error.

 

Many thanks

 

Leighton

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You would use the flash meter reading for your initial calculation subject to increasing exposure to compensate for magnification on film. I normally start to worry about that at 1:4 where you would need to open up by 1/2 a stop over a meter reading.
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I have always used flash to subject distance in calculating the flash exposure.

Except he is not shooting in a normally illuminated room with normal reflecting surfaces. He is shooting in a dark area and that will absorb a lot of light. Especially if there are normal sized and colored walls and ceilings.

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Except he is not shooting in a normally illuminated room with normal reflecting surfaces. He is shooting in a dark area and that will absorb a lot of light. Especially if there are normal sized and colored walls and ceilings.

 

True,

In a "normal" room I used the calculator on the back of the strobe.

Outdoors or in a BIG room, I opened up 1 stop, to compensate for lack of reflective surfaces.

 

A flash meter would be good to have, as it would eliminate guessing on the reflectance or lack of reflectance of the environment.

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Leighton, do you have a flash meter? The original post mentioned this. If yes, compose the scene and trigger the flash with the meter. In other words, use the flash meter as per the normal procedure. The flash meter will tell you the exposure.

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Hi

I realised 20 minutes after posting thread that all I needed to do was move the flash 7 inches (length of bellows extension) and calculate the aperture difference. It was just 16.7 and 16.8 for iso 100 (but slightly more for iso 400 (0.2) in large living room. Incidentally I always use a bulb release not the cable release. The latter will cause camera shake. This is easily seen if you try both with the camera (such as an old 35mm or blad) plonked in a cheap kitchen scales (the ones where the scale dial quivers before settling) and check out the scale of needle needle quiver from each cable. The quiver from the 500cm was a shocker. if I remember from either release.even with the mirror up, simply because the release is not connected directly to the lens like a large format..

 

Many thanks for all replies.

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It doesn't matter what format or camera you're using; the principles of flash exposure remain the same.

 

As others have said, and you've worked out, a 7" difference in flash distance is of absolutely no consequence except at macro distances.

 

A metered exposure should need no compensation - with provisos. A reflected flash exposure reading at 60 feet won't be accurate IMO. For example: if the background is well beyond the subject it will be darker and the meter will tend to indicate overexposure. OTOH any foreground will be more brightly illuminated and tend to meter for underexposure.

 

The only reliable way to use a flashmeter is to take an incident reading at the subject position with the meter pointed back at the camera. No compensation will be required regardless of flash-to-subject or flash-to-camera distance.

 

BTW, you shouldn't rely on Guide Numbers. I used to think that the old Metz Cx45-x hammerheads were as powerful as claimed. They're not! They have a metered GN of around 34 (metres/100 ISO), and as such aren't much more powerful than a good quality hotshoe speedlight. Given their long recycle time, short battery life and cumbersome size my old Mecablitzes lie unused in favour of Nikon SB-25s that are far more versatile.

Edited by rodeo_joe|1
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It doesn't matter what format or camera you're using; the principles of flash exposure remain the same.

 

As others have said, and you've worked out, a 7" difference in flash distance is of absolutely no consequence except at macro distances.

 

A metered exposure should need no compensation - with provisos. A reflected flash exposure reading at 60 feet won't be accurate IMO. For example: if the background is well beyond the subject it will be darker and the meter will tend to indicate overexposure. OTOH any foreground will be more brightly illuminated and tend to meter for underexposure.

 

The only reliable way to use a flashmeter is to take an incident reading at the subject position with the meter pointed back at the camera. No compensation will be required regardless of flash-to-subject or flash-to-camera distance.

 

BTW, you shouldn't rely on Guide Numbers. I used to think that the old Metz Cx45-x hammerheads were as powerful as claimed. They're not! They have a metered GN of around 34 (metres/100 ISO), and as such aren't much more powerful than a good quality hotshoe speedlight. Given their long recycle time, short battery life and cumbersome size my old Mecablitzes lie unused in favour of Nikon SB-25s that are far more versatile.

You have to compare output over the same angle of illumination. So a small flash may only cover 30 degrees while another might cover 50.

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"So a small flash may only cover 30degrees while another might cover 50."

Well, that's another drawback of the Metz 45 series hammerheads; no "zoom" to adjust coverage angle. And you have to attach a Mecamat to get any useful degree of manual power control.

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The 60 series are also subject to the standard flash manufacturer's hyperbole of adding one whole stop to the rated Guide Number. They measure as having a GN of around 44.

 

I believe that the quantum Q-flash and similar Godox wistro 360 are a lot more powerful while still having a shoulder-pack design. They're not so common used though, and considerably more expensive.

 

Sunpak's 120j ii has about the same power as a Metz 60 and is reasonably priced new. It's also more compact, lighter, takes standard batteries and is more convenient all round.

 

FWIW, I think your estimate of f/16 in a large living-room for the Metz 45 is highly optimistic. At 60 feet outdoors with 100 ISO film you'd realistically be looking at using an aperture of f/2 using direct flash and 100 ISO film. Even 400 ISO only buys you another 2 stops and would need an f/4 lens.

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I've been using Sunpak auto 611's for literally decades.

They are auto or manual power ration potato masher units (no separate battery pack its all in the head & handle) with a REAL g/n of 160 ISO/Ft.

You will need a voltage dropper for the trigger circuit though as its in the 180v. range.

They are a non-dedicated hot shoe or pc cable unit. If you want similar, but dedicated look at the Sunpak auto 622.

Being "old" they sell for a song on e-bay.

upload_2017-6-13_9-36-13.jpeg.22403e8f69efb1053898659ee8b0125d.jpeg

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"You will need a voltage dropper for the trigger circuit though as its in the 180v. range."

 

- Shouldn't be a problem with the all mechanical Compur, Copal or Prontor shutters commonly used with LF lenses.

 

Not sure what shutter was used on the Gowland, but chances are a bit of high voltage on the P-C socket won't harm it.

However, I wouldn't lick the flash synchro plug!

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I've been using Sunpak auto 611's for literally decades.

They are auto or manual power ration potato masher units (no separate battery pack its all in the head & handle) with a REAL g/n of 160 ISO/Ft.

You will need a voltage dropper for the trigger circuit though as its in the 180v. range.

They are a non-dedicated hot shoe or pc cable unit. If you want similar, but dedicated look at the Sunpak auto 622.

Being "old" they sell for a song on e-bay.

[ATTACH=full]1192420[/ATTACH]

 

The good thing about the 611 and 54x series is that you can replace the NiCd batteries with NiMh batteries and the batteries last longer when shooting. It is like a massive upgrade to the flash. 500ma for a NiCd AA vs. 2,000ma for a NiMh AA battery = 4x the capacity and longer shooting time before a battery change. The C cells in the 611 would have a similar boost in performance.

 

But, I prefer the external battery pack, for the FAST recycle time.

Yes, I'm spoiled. Once you get used to FAST recycle, it is really hard to go back.

 

I get wider coverage on my flashes by putting a piece of frosted plastic milk carton in front of the flash. It diffuses the flash to give me wider coverage. Yes not as good as a wide angle lens made specifically for the flash, or a zoom head, but not all my flashes had a wide angle lens. And today, even those that did, it is hard to find those small accessories.

 

Being an old battery pack guy, I've been thinking about getting the Sunpak 120 that RJ mentioned. It is like a cheap version of the Quantum Q flash.

Personally, I like the idea of taking the weight of the battery out of the flash, to make the flash, that I have to hold in my hand, lighter and easier to handle.

My old workhorse was the Honeywell Strobonar 800.

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Yes I'm using "C" cells of the hybrid variety. Both recycling speed & number of flashes are vastly improved.

Sorry about the voltage dropper comment earlier, it wasnt (obviously) meat for camera equipment designed for 200+ voltage use, but with all the concerns of low & medium voltage issues with digital synch I felt it worth mentioning before someone had an accident with delicate equipment because they weren't aware of the fact.

 

Also there was a separate battery pack or 2 available, one was the high speed 510V pack, but there was one that took 8 "D" cells. If you could find one it would be awesome with modern battery technology!

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Yes I'm using "C" cells of the hybrid variety. Both recycling speed & number of flashes are vastly improved.

Sorry about the voltage dropper comment earlier, it wasnt (obviously) meat for camera equipment designed for 200+ voltage use, but with all the concerns of low & medium voltage issues with digital synch I felt it worth mentioning before someone had an accident with delicate equipment because they weren't aware of the fact.

 

Also there was a separate battery pack or 2 available, one was the high speed 510V pack, but there was one that took 8 "D" cells. If you could find one it would be awesome with modern battery technology!

 

I use both the Quantum Turbo and Lumedyne Megacycler HV packs with my flashes.

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