Using electronic flash with LF cameras

[Phil Hudson]

I have been using paper negs in an old passport camera. In the studio I use 3 x 500w flash heads on full power with softbox diffusor screens removed pointing at a subject at a distance of about 1.5 m. It looks about right at f/16. Scaling that back to your scenario I would say that you need lots more light.

[tonyowen]

I have been using paper negs in an old passport camera. In the studio I use 3 x 500w flash heads on full power with softbox diffusor screens removed pointing at a subject at a distance of about 1.5 m. It looks about right at f/16. Scaling that back to your scenario I would say that you need lots more light.

I’ve found a reference that states: As a rough rule of thumb, multiplying the square root of the (wattsecond) Ws number by 4 gives a indicator of the metric GN at ISO 100.

Therefore assuming your shutter is set at 1/60th second and your studio lights give 1500w power

We get 1500 x 0.017 = 25Ws

Therefore GN = SQRT(Ws) x 4 = 20

Both of my flash guns have a higher GN at 100 ISO

However, as stated above this is a rough rule of thumb.
regards
Tony

[Bob Salomon]

I’ve found a reference that states: As a rough rule of thumb, multiplying the square root of the (wattsecond) Ws number by 4 gives a indicator of the metric GN at ISO 100.

Therefore assuming your shutter is set at 1/60th second and your studio lights give 1500w power

We get 1500 x 0.017 = 25Ws

Therefore GN = SQRT(Ws) x 4 = 20

Both of my flash guns have a higher GN at 100 ISO

However, as stated above this is a rough rule of thumb.
regards
Tony

It has to be very rough as watt seconds is not a rating of output.

At any given WS the output will change with reflector size, reflector shape, length of the connecting cable, etc.

Base output on BCPS or ECPS.

[Pere Casals]

... but the paper may be ISO 5 or less, so you may need x20 more flash power in the flash than with TMX.

[tonyowen]

It has to be very rough as watt seconds is not a rating of output.
At any given WS the output will change with reflector size, reflector shape, length of the connecting cable, etc.Base output on BCPS or ECPS.

Agreed, but it surely is some form of indicator even if it is out 10 fold

... but the paper may be ISO 5 or less, so you may need x20 more flash power in the flash than with TMX.

Post #31 refers to 1500w when using paper negatives [ie low ISO] therefore I've assumed apples v apples

regards

Tony

[Pere Casals]

Post #31 refers to 1500w when using paper negatives [ie low ISO] therefore I've assumed apples v apples

yes...

...but I'd take your own exposure working well for ISO 100 film, and I'd multiply x20 the light, around 4 or 5 stops in aperture or light power.

Or easier, use a DSLR, adjust for a good digital shot at ISO 100 and give 5 stops more light.

A DSLR is a perfect flash meter for LF, we only need to understand the relationship in the look. Also I manage to shot the DSLR at the same time than the Norma, so I preview face expresion and if eyes are open.

Not that weird, Hollywood's cinematographers still using film also record video to know if the have the scene. Digital is amazing.

[Bob Salomon]

[QUOTE=tonyowen;1483480]Agreed, but it surely is some form of indicator even if it is out 10 fold

It is no indicator of output at all. It is an indicator of input. And the most efficient flash units are only able to discharge about 80% of their input!

And, since output changes with reflectors, umbrellas, soft boxes, cable length, efficiency of the flash tube, number of connections, etc. watt seconds are the last thing you want to rely on.

Just think, a given unit with say 500 watt seconds will have different outputs with a polished reflector, a matte reflector, an elliptical reflector, an umbrella reflector a snoot, a background reflector or when used bare bulb. But all were 500 WS. How can that WS rating relate to a consistent f stop?

There is no formula to convert a watt second into a f stop without knowing the loading of the capacitors, and no flash manufacturer includes that specification.

On the other hand there are easily found formulas that are accurate that convert a BCPS or an ECPS rating directly into a guide number or f stop.

[John Kasaian]

Now here's an electronic flash worthy of LF photography
The K-17 was, IIRC 9.5" x 9.5

http://invention.si.edu/seeing-dark-...naissance-wwii

[Tin Can]

Very interesting and I love the quote,


“If you don’t wake up at three o’clock in the morning and want to do something,” Edgerton quipped, “why, you’re wasting time.”

[tonyowen]

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