Manual flash calculations with accounting existing light

BrianShaw said:

Matt... flashmeter (you know this, I’m sure): one or two pops results in guide number.

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Yeah, but where is the fun in that!
It is a good idea though to do the flashmeter test in the same conditions - outside at night without a lot of reflective tests.

Fundamental concept: Any flash expsosure is the combination of TWO light sources...

1. in some cases, one source predominates to make the shot
2. in other cases, each source contributes equally to make the shot
3. and there are all the situations between the extremes of #1 and #2

Let us look at ambient and how it adds to flash exposure, with four situations...

• In Situation 1, let us assume that flash guide number says to use f/4. Let us assume that ambient light is weak, needing 1/4 shutter at f/4 (but your camera shutter is set to 1/60. The flash exposure lights the subject fully, and the -4EV anbient does not register at all
• In Situation 2, let us assume that flash guide number says to use f/4. Let us assume that ambient light is weak, needing 1/15 shutter at f/4 (but your camera shutter is set to 1/60. The flash exposure lights the subject fully, and the -2EV anbient is not strong enough to cause a significant change to overall exposure.
• In Situation 3, let us assume that flash guide number says to use f/4. Let us assume that ambient light is subdued at bit, needing 1/30 shutter at f/4 (but your camera shutter is set to 1/60. The flash exposure lights the subject fully, and the -1EV anbient adds 50% to the light falling on the subject, so the subject is slightly overexposed (by 0.5EV) by light from both flash+ambient
• In Situation 4, let us assume that flash guide number says to use f/4. Let us assume that ambient light is strong, needing 1/60 shutter at f/4 (and your camera shutter is set to 1/60. The flash exposure lights the subject fully, and the anbient adds 100% to the light falling on the subject, so the subject is overexposed (by (+1EV), by light from both flash+ambient

This is how it looks when you get greedy with ambient light in a lowlight situation. You can actually see exactly what is ambient and flash since I used a blue filter over the flash and the ambient is tungsten.

vedostuu said:

I have figured out how manual flash calculations work. For example my FlashQ has GN 20 at ISO 100 with 1 meter distance and 1/8 power I should use f8. OK........

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1. If the flash asks for f8 set f11 on the lens.
2. Then set the shutter speed that gives proper ambient exposure at f11.
3. Shoot.
4. Job done.
What you have just achieved is full ambient exposure with 50% flash fill. This is the easiest, most basic, nice looking way to combine flash and ambient light. Beyond this many complex variations are possible.
The only precaution is to make sure the shutter speed you set is equal to or longer than the flash synch speed for your camera.

Trouble with film and flash is that it all depends on the vintage of your equipment and the setting.

You’ll make things easier on yourself with a TTL continuous exposure check capable camera. But
But of course that leaves out some great gear.

In a studio like setting, sure a flash meter is just the thing.
But if you are out and about, photographing real life indoors and outdoors, you won’t have to time to step up to the subject with a flash meter and do a test-pop.
There you need to rely on gut feeling and experience.

Direct flash is easy unless your gun is ancient. The photocell will ensure a good enough exposure. Same with a simple bounce.
Most flashguns from the last forty years or so, has an exposure check, where you test fire the flash and a little light shows you that a good exposure is possible.

For more ambient, just set the shutter speed higher or lower, or set the ISO higher on the flash.
When you want to fire more than one flash it gets complicated.
But again, film takes light overexposure a lot better than digital.
Don’t assume that every extra flashgun just ups the exposure with a set amount.
It all depends on placement and bounce or direct, umbrella or reflector, etc.

Two light source relative contribution variable...

• If ambient contributes 1 part of light, and flash contributes 8 parts of light (3EV brighter), the total on subject is only 12.5% more than flash alone or about 12.5% overexposure of the subject...scarely noticable.
• If ambient contributes 1 part of light, and flash contributes 4 parts of light (2EV brighter), the total on subject is only 25% more than flash alone, or about 25% overexposure of the subject...modestly noticeable
• If ambient contributes 1 part of light, and flash contributes 2 parts of light (1EV brighter), the total on subject is 50% more than flash alone, so there is 0.5EV overexpossure of the subject.
• If ambient contributes 1 part of light, and flash contributes 1 parts of light (same brightness), the total on subject is 100% more than flash alone, so there is 1EV overexposure of the subject.

Fuss and bother! The Nikon SB 800 not only will do that automatically, but also do it with a bounce flash.

Maris said:

1. If the flash asks for f8 set f11 on the lens.
2. Then set the shutter speed that gives proper ambient exposure at f11.
3. Shoot.
4. Job done.
What you have just achieved is full ambient exposure with 50% flash fill. This is the easiest, most basic, nice looking way to combine flash and ambient light. Beyond this many complex variations are possible.
The only precaution is to make sure the shutter speed you set is equal to or longer than the flash synch speed for your camera.

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Great recipe! Because manual flash photography is a bit "weird" I think this kind of simple instructions are needed.

Sirius Glass said:

Fuss and bother! The Nikon SB 800 not only will do that automatically, but also do it with a bounce flash.

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Does this flash work with manual cameras? How?

wiltw said:

• If ambient contributes 1 part of light, and flash contributes 8 parts of light (3EV brighter), the total on subject is only 12.5% more than flash alone or about 12.5% overexposure of the subject...scarely noticable.

• If ambient contributes 1 part of light, and flash contributes 4 parts of light (2EV brighter), the total on subject is only 25% more than flash alone, or about 25% overexposure of the subject...modestly noticeable

• If ambient contributes 1 part of light, and flash contributes 2 parts of light (1EV brighter), the total on subject is 50% more than flash alone, so there is 0.5EV overexpossure of the subject.

• If ambient contributes 1 part of light, and flash contributes 1 parts of light (same brightness), the total on subject is 100% more than flash alone, so there is 1EV overexposure of the subject.

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If flash calculation is done without accounting ambient light, we end up with always overexposed photo. The good thing is that negative film copes this very well! So maybe compensation (1 stop down from flash) isn't always needed?

I need to shoot some film and see how this works. Electro 35 + ColorPlus + Christmas -> probably 100% good stuff.

vedostuu said:

Great recipe! Because manual flash photography is a bit "weird" I think this kind of simple instructions are needed.




Does this flash work with manual cameras? How?




If flash calculation is done without accounting ambient light, we end up with always overexposed photo. The good thing is that negative film copes this very well! So maybe compensation (1 stop down from flash) isn't always needed?

I need to shoot some film and see how this works. Electro 35 + ColorPlus + Christmas -> probably 100% good stuff.

Click to expand...

Indeed, since color neg well tolerates even +3EV overexposure, and that becomes 'hidden' in the final print, manual flash power in the presence of equally strong ambient light makes it invisible to the photographer, and unless they inspect negs for density it remains hidden to them!

But since manual flash power has largely disappeared from common usage, due to first photosensor flash and then due to TTL flash, the flash automation cut its power output for the unthinking photographer, and only pros shooting transparencies with manual flash power know better! Nor have I used manual powered flash without a flashmeter since the early 1980s.
My gawd, I personally have not used a manual-only on-camera speedlight since the early 1970's!

wiltw said:

Indeed, since color neg well tolerates even +3EV overexposure, and that becomes 'hidden' in the final print, manual flash power in the presence of equally strong ambient light makes it invisible to the photographer, and unless they inspect negs for density it remains hidden to them!
But since manual flash power has largely disappeared from common usage, due to first photosensor flash and then due to TTL flash, the flash automation cut its power output for the unthinking photographer, and only pros shooting transparencies with manual flash power know better!
My gawd, I personally have not used a manual-only on-camera speedlight since the early 1970's!

Click to expand...

Overexposing isn't problematic at all, but good thing is that the information is there, but one needs to dig out both. This might be really difficult when doing print, depends on the scene. Surely the frame should be exposed "correctly" - what ever that is.

This is the fun part of the photography; I can shoot frames but learn new techniques at the same time. When widening understanding the basic things comes easily, I think. Transparency manual flash photography? That is the black belt level for sure

vedostuu said:

Does this flash work with manual cameras? How?

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Yes, I use it that way all the time. The sensor cuts off the flash when it has seen enough light from the scene and the flash. That is how I use it with my Hasselblad. RTFM. The Hasselblad has its TTL system which reads the light off the film but I do not have that strobe system.