Open Flash

tonyowen · Apr 19, 2020

What exactly is open flash in terms of single shot portraiture?
I know that generally open flash 'can' mean long exposures with multiple 'pop' of a flash gun.
I've tried electronic flash guns [metric GN40 @ iso100] with paper negatives [iso8]., but the single activated flash has no effect ie no exposure.
What is the guesstimated minimum wattage of a single light that would allow exposures of say 1/50s?
Any and all response welcome
regards
Tony

MattKing · Apr 19, 2020

With open flash, one normally doesn't use 1/50 of a second, one uses "T" - the shutter is left open.
With that flash, with ISO 100 materials, and the flash 5 meters from the subject, f/8 (40/5) should work.
So with ISO 8 materials and the same flash to subject distance, you need 12.5 times the exposure (100/8) so you would need to "pop" the flash 12.5 times.
That should give you a starting point -most likely you will also run into some reciprocity issues, so experimentation is in order

tonyowen · Apr 19, 2020

MattKing said:
So with ISO 8 materials and the same flash to subject distance, you need 12.5 times the exposure (100/8) so you would need to "pop" the flash 12.5 times.

I can see multiple pops for subjects other than portraiture, where ideally I want a single exposure.
Regarding your 12.5 pops, I think that this value should be around 4. Halving the iso value decreases the 100iso value by square root of 2. So metric GN @ iso50 is 28
At iso8 the modified GN of 40 becomes circa 10.
regards
Tony

wiltw · Apr 19, 2020

MattKing said:
With open flash, one normally doesn't use 1/50 of a second, one uses "T" - the shutter is left open.
With that flash, with ISO 100 materials, and the flash 5 meters from the subject, f/8 (40/5) should work.
So with ISO 8 materials and the same flash to subject distance, you need 12.5 times the exposure (100/8) so you would need to "pop" the flash 12.5 times.
That should give you a starting point -most likely you will also run into some reciprocity issues, so experimentation is in order

To clarify the statement about ssue of flashes vs. relative amount of light.
If 1 Flash = 0EV light, then
2 flashes give 1EV of exposure
4 flashes give 2EV of exposure
8 flashes give 3EV of exposure
16 flashes gives 4EV of exposure, etc.

ISO 8 is -3.66EV compared to ISO 100, so it needs (about) 8X the amount of light as ISO 100 light sensitive material. The sequence of ISO values (the very low values of 12 and 6 are questionable as standard tables usually don't go that low!)

6
8
10
12
16
20
25
32
40
50
64
80
100
125
160

So to 'open flash', start with an open shutter (and presumably very dim ambient light), and then you would flash 12 times and then close the shutter...to expose with ISO 8 material to the same level as you would have achieved using ISO 100 material and achieving a good exposure on that when illuminating it with one flash. it would work for still life, but for a live subject it would likely be disastrous (unless you were intentionally wanting 12 ghosted images set in front of a background)

John Koehrer · Apr 19, 2020

#4 above: There's also reciprocity failure to consider with multiple exposure*.

*The other definition of "open flash" is using a flash without a reflector.

MattKing · Apr 19, 2020

wiltw has the progression correct. The guide number system makes linear what would otherwise be logarithmic.
You could also divide the distance between flash and subject by 12.5 (down to 0.4 meters) and work with a single "pop".
I could be wrong, but I think that what John Koehner is referring to is "bare bulb" flash.

Sirius Glass · Apr 19, 2020

I have only used an open flash for filling in the foreground during a night photograph.

tonyowen · Apr 20, 2020

wiltw said:
So to 'open flash', start with an open shutter (and presumably very dim ambient light), but for a live subject it would likely be disastrous /QUOTE]
My point exactly, hence the question(s) - how about single point illumination [without fancy or and reflectors etc]
regards
Tony

R.Gould · Apr 20, 2020

years ago I used to use open flash to paint with light, at night I would set my camera on a tripod to, say, photograph a small rock formation, lens open at B, aperture at around 11 with fast film, then I wouhld fire the flash from different angles, making sure I was not in front of the camera, it was quite a fad over here, and worked well, if done well you could get an almost surreal look to the photo by building up the photo bit by bit around the object

MattKing · Apr 20, 2020

tonyowen said:
My point exactly, hence the question(s) - how about single point illumination [without fancy or and reflectors etc]
regards
Tony

Bare bulb flash is interesting to work with, but you need either fast film or a lot of patience, because a significant amount of the light intensity from flash comes from the built in reflectors and lenses.
In days of yore, to render rooms "naturally", people actually put flash bulbs in light fixtures and put the shades back on.
Flip the switch and the resulting light was natural, but the flashbulb pop was impressive.
For very simple lighting, consider bouncing a normal flash off of a side wall.

jtk · Apr 20, 2020

tonyowen said:
What exactly is open flash in terms of single shot portraiture?
I know that generally open flash 'can' mean long exposures with multiple 'pop' of a flash gun.
I've tried electronic flash guns [metric GN40 @ iso100] with paper negatives [iso8]., but the single activated flash has no effect ie no exposure.
What is the guesstimated minimum wattage of a single light that would allow exposures of say 1/50s?
Any and all response welcome
regards
Tony

FWIW, I think the common term for flash-without-reflector is "bare tube flash." I used a Graflex bare tube flash gun with my 200WS portable , sometimes usefully and sometimes not usefully. Common use generally relied on a small room, using all of the walls as reflectors. Very bizarre use involved a nude dancer in a very dark room...produced a somewhat science-fiction-looking image with cat eyes. Ektachrome X preceded by some testing.

R.Gould · Apr 20, 2020

MattKing said:
Bare bulb flash is interesting to work with, but you need either fast film or a lot of patience, because a significant amount of the light intensity from flash comes from the built in reflectors and lenses.
In days of yore, to render rooms "naturally", people actually put flash bulbs in light fixtures and put the shades back on.
Flip the switch and the resulting light was natural, but the flashbulb pop was impressive.
For very simple lighting, consider bouncing a normal flash off of a side wall.

I well remember using flash bulbs to light up rooms, once I had to light a hanger with a Glen Miller tribute band over her, had to show both the band and the audience in the one shot, I set up 50 flash units and flash bulbs, and very big ones at that, very nerve racking as I only had one chance to get the shot right, I was terrified untill I developed the the film, all went according to plan
Richard

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