Figuring out manual flash exposure

lauffray · Apr 20, 2018

I recently bought a small flash for my M body and I'm trying to figure out how to properly expose with it. In a moment of oversight (read impulsion/stupidity) I hadn't realized none of my cameras have TTL metering and I don't have a flash meter. So after doing some reading, I've come to the following understanding and this is where I need some more knowledgeable folk to correct me if I'm wrong. (I could just shoot a bunch of tests until it works but I'd like to understand what I'm doing )

With flash the shutter speed isn't as important as other factors. So I start by setting my camera to the fastest flash sync speed (about 1/45) and from there, using my flash GN I read out that to properly expose a subject at 2.5m (8ft) I need to be at f/8. The GN being for ISO100 and I'm shooting at 800, is it enough then to close down three more stops?

The flash is a Nikon SB22s with a GN of 28 (92ft), from what I can tell there's no setting for power. I have a MP and a M6 body.

Willyekerslike · Apr 20, 2018

The SB-22s can be used in A and M mode, I would start with it in A mode and see how that goes first.

lauffray · Apr 20, 2018

Willyekerslike said:
The SB-22s can be used in A and M mode, I would start with it in A mode and see how that goes first.

Do I just set the mode to A and shoot then? At what speed? How does it work?

AgX · Apr 20, 2018

Flashes that offer a classic autoexposure mode, with metering cell incorporated in the flash, yield one or more distance ranges. For each range, depending on film speed, they offer one certain aperture to be set at the camera. With most flashes of that kind that all is intuitive.

bdial · Apr 20, 2018

Set the shutter to the fastest sync speed. For auto mode, the flash should indicate an f/stop to use for various distance ranges. For manual mode, you can use the chart to determine the f/stop based on your distance.
A manual looks to be downloadable from Nikon.

E. von Hoegh · Apr 20, 2018

bdial said:
Set the shutter to the fastest sync speed. For auto mode, the flash should indicate an f/stop to use for various distance ranges. For manual mode, you can use the chart to determine the f/stop based on your distance.
A manual looks to be downloadable from Nikon.

Yes, when all else fails, read the instructions.

Chan Tran · Apr 20, 2018

Use A mode. Check the manual for the settings. Simply set the flash to A1, A2, A3 or A4.
With ISO 100 A1 use F8, A2 use F5.6, A3 use F4 and A4 use F2.8. It's that simple. You don't need TTL.

E. von Hoegh · Apr 20, 2018

Also, if you go above synch. speed the flash will expose only part of the frame.

lauffray · Apr 20, 2018

Thanks everyone, I must have been overthinking, it seems simpler than I thought. I had read various instructions on flash operations but I was just confused by that stuff, that's why I came here
Tests tonight !

wiltw · Apr 20, 2018

Go online to get a user manual for your flash unit, if you do not have one in print. That is what I did to learn about your flash.

With flash in A1 mode, you set f/8 on the camera and it will use its own photosensor to automatically set exposure, when shooting from 2.0' to 10' for ISO 100, or
With flash in A2 mode, you set f/4 on the camera and it will use its own photosensor to automatically set exposure, when shooting from 2.6' to 20' for ISO 100
Set desired ISO on the control on the back of the flash...the aperture scale window indicates what f/stop provides what distance range is possible at that aperture
Auto mode will be fooled when you have strong backlighting of your subject...it may be better to use Manual flash power rather than photosensor flash
with Guide Number 92 (for ISO 100) you would be shooting f/4 at 23' distance for flash providing primary illumination; or f/4 at 46' distance for -1EV fill flash intensity
with Guide Number 92 (for ISO 100) you would be shooting f/8 at 11.5' distance for flash providing primary illumination; or f/4 at 23' distance for -1EV fill flash intensity

The above information assumes that you are shooting with the normal flash coverage lens

glbeas · Apr 20, 2018

Ive found on most flashes the manufacturer is overly optimistic about the output, and this can change as the flash gets older. Definitely do a test roll and shoot a range of f-stops noting which is what and see if your A setting is close to right or needs a fudge factor applied. Also be aware any flash not used for a period of time needs to be charged up and fired 5 to 10 times to reform the capacitor.

AgX · Apr 20, 2018

This is another argument for the auto mode, as typically not the full capacity is used, thus a reduced max. output due to age would not be of effect.

vsyrek1945 · Apr 20, 2018

glbeas said:
Ive found on most flashes the manufacturer is overly optimistic about the output, and this can change as the flash gets older. Definitely do a test roll and shoot a range of f-stops noting which is what and see if your A setting is close to right or needs a fudge factor applied. Also be aware any flash not used for a period of time needs to be charged up and fired 5 to 10 times to reform the capacitor.

A procedure published some time back, possibly by Vivitar [or for Vivitar flashes] involved loading fresh alkalines, switching on the flash, letting the unit charge up to ready lamp lit, then waiting 30 seconds before pushing the open flash button, and repeating the charge-wait-flash sequence 5 times. It has worked well for me 99% of the time.

Theo Sulphate · Apr 20, 2018

As an aside, I've taken flash units that have been unused for so long that the ready light won't turn on. What I do in that case is put fresh batteries in, turn the unit on, and let it sit while carefully ensuring the unit is not getting hot. After maybe 10 minutes I stop for 10 minutes and repeat this process. I've revived flash units this way in under an hour.

Whether used or not, I pop my flashes every month (i.e. put batteries in, turn them on for 10 minutes, fire the flash, wait 10 minutes, remove batteries.

jim10219 · Apr 20, 2018

Theo Sulphate said:
As an aside, I've taken flash units that have been unused for so long that the ready light won't turn on. What I do in that case is put fresh batteries in, turn the unit on, and let it sit while carefully ensuring the unit is not getting hot. After maybe 10 minutes I stop for 10 minutes and repeat this process. I've revived flash units this way in under an hour.

Whether used or not, I pop my flashes every month (i.e. put batteries in, turn them on for 10 minutes, fire the flash, wait 10 minutes, remove batteries.

That's a sign that the electrolytic capacitors need reforming, or are leaking or drying out. In any case, when I encounter that problem, I usually replace the capacitor(s). They're usually just a few bucks and fairly easy to DIY replace (if you can solder). Just make sure to get the same (or as close as you can find) capacitance value, the same or higher voltage value, the same or smaller physical size (so it will fit), and the same type of leads (axial or radial to make the installation easier). Then, when you install it, make sure to orient the new cap with the same side connected to ground as the old cap (there should be a marking on the cap indicating which is which). Word of advice, if you do this yourself, be sure to short out the cap before proceeding. That just involves making simultaneous contact between the two terminals on the capacitor with something conductive. Sometimes that can spark and scare people, so you may prefer to use something like a 100 Ohm 1/2 watt resistor to shorten the capacitor with. The resistor will prevent the spark at the cost of slowing the draining process down, so be sure to hold the resistor there for about 30 seconds to drain the cap to a safe level.

A small Speedlight shouldn't have enough juice to kill you, but it might give you a nasty burn and a hell of a scare. Now the big studio flashes probably could kill you. So I don't really recommend messing with one of those if you're not pretty experienced with high voltage electronics.

ic-racer · Apr 20, 2018

Inexpensive flash meters are still around. I got one like this for $15. Solved all my 'manual flash' problems.

wiltw · Apr 20, 2018

A number of us with flash meters have found that with speedlights typically the flash manufacturer is about 1EV optimistic in their Fuide Number ratings. This is regardless of the brand of flash and regardless of the brand of the flash meter. We have speculated that the conditions under which the flash manufacturer measures and rates their flash units is somehow different than what we measure in our own homes, and all of them are standardized upon some specific test conditions which we do not understand

lauffray · Apr 24, 2018

Thanks again for your help folks, I shot a couple of test rolls in A mode as suggested, will come back with samples when I've developed them

Sirius Glass · Apr 24, 2018

lauffray said:
I recently bought a small flash for my M body and I'm trying to figure out how to properly expose with it. In a moment of oversight (read impulsion/stupidity) I hadn't realized none of my cameras have TTL metering and I don't have a flash meter. So after doing some reading, I've come to the following understanding and this is where I need some more knowledgeable folk to correct me if I'm wrong. (I could just shoot a bunch of tests until it works but I'd like to understand what I'm doing )

With flash the shutter speed isn't as important as other factors. So I start by setting my camera to the fastest flash sync speed (about 1/45) and from there, using my flash GN I read out that to properly expose a subject at 2.5m (8ft) I need to be at f/8. The GN being for ISO100 and I'm shooting at 800, is it enough then to close down three more stops?

The flash is a Nikon SB22s with a GN of 28 (92ft), from what I can tell there's no setting for power. I have a MP and a M6 body.

Guide numbers are related by the square root of the film speed. So the guide number for ISO 100 would be GN100*Square root(800/100) = GN100*2.8

AgX · Apr 24, 2018

There are several Guide Numbers given for a flash.

1) dependant on length unit. Foot or Meter
2) dependant on film speed. Early flashes got one based on 18DIN, later ones on 21DIN
3) on the reflector or reflector setting. In the past it typically was the setting for a 35mm lens. Today the tele setting is used ...

Of course one may calculate one into the other, but first one must know what the given GN was based on. A look ast the dial should reveal such better than some manual.

lauffray · Apr 25, 2018

Sirius Glass said:
Guide numbers are related by the square root of the film speed. So the guide number for ISO 100 would be GN100*Square root(800/100) = GN100*2.8

This just blew my mind, thanks !

AgX · Apr 25, 2018

The square root is a most important factor in several photographic calculations.

Mainecoonmaniac · Apr 25, 2018

lauffray said:
I recently bought a small flash for my M body and I'm trying to figure out how to properly expose with it. In a moment of oversight (read impulsion/stupidity) I hadn't realized none of my cameras have TTL metering and I don't have a flash meter. So after doing some reading, I've come to the following understanding and this is where I need some more knowledgeable folk to correct me if I'm wrong. (I could just shoot a bunch of tests until it works but I'd like to understand what I'm doing )

With flash the shutter speed isn't as important as other factors. So I start by setting my camera to the fastest flash sync speed (about 1/45) and from there, using my flash GN I read out that to properly expose a subject at 2.5m (8ft) I need to be at f/8. The GN being for ISO100 and I'm shooting at 800, is it enough then to close down three more stops?

The flash is a Nikon SB22s with a GN of 28 (92ft), from what I can tell there's no setting for power. I have a MP and a M6 body.

That would be 3 stops down from ASA 100. As for shutter speed, the fastest synch speed is the upper end. The speed where you don't get your flash exposure blocked off by the shutter. However, you can shoot slower shutter speeds which will increase the ambient exposure of your scene. It all depends on what you want.

Sirius Glass · Apr 25, 2018

AgX said:
The square root is a most important factor in several photographic calculations.

Strangely related to the inverse square law.

lauffray · May 26, 2018

Hi everyone, finally back with some scans of the tests I made. Everything turned out great, thanks again for the help !

Figuring out manual flash exposure

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