Manual Flash Query

marsbars · Dec 25, 2007

I know the process for calculating the use of a manual flash. However one thing that I have not gotten a grasp of is changing from the norm. What I mean is my flash, which has an automatic sensor on it, says to set the x-sync and use the calculated f/stop. The thing that I am not grasping is my F3 syncs at 1/80 and my nikkormat syncs at 1/125. How does using the same f/stop produce a good exposure. That is close to a whole stop difference. Also if for instance I want to use a slower shutter speed to add motion or allow for more exposure in the background. Do I have to adjust the f/stop to compensate for the added exposure time. I want to experiment with slower shutter speeds and my flash. I hope that this makes sense to all of you.

Nick Zentena · Dec 25, 2007

A full out flash blast is ALOT faster then your fastest shutter speed. Lower power blasts are even quicker.

If you want to expose the background set the shutter speed for the background. Set the F/stop for the foreground.

JBrunner · Dec 25, 2007

The sync speeds are the fastest speeds you can safely use a flash with the particular camera in question. Run faster, and kiss the stripe.

Nick Zentena · Dec 25, 2007

And the flash is still faster then those.

JBrunner · Dec 25, 2007

Yes, which is why you can use them, and any speed slower than the sync speed. The flash impulse is super fast, and a curtain shutter can't keep up. The sync speed or slower makes sure the film gets even exposure while the light is a poppin. You should be able to shoot the nikkormat at 1/80 for sync if you wish, just not the other way around.

RobC · Dec 25, 2007

The sync speed given is usually the maximum sync speed. And also usually, the sync is first curtain sync so the flash fires as soon as the first curtain is fully open. You should be able to set your nikormat to the same speed as your F3 and it should work. But if you set your F3 to 125, then the second curtain has started to close before the first curtain has fully opened which won't work.

Nick Zentena · Dec 25, 2007

But if you switched to a faster synching camera the flash would still be faster.

My point is there is no real difference between 1/80 and 1/125. The flash has popped off and gone off to recharge long before the shutter closes. Unless you're using a real big flash that might be slower then a fast syncing leaf shutter.

RobC · Dec 25, 2007

I agree with Nick, The flash length is very short and depends on your flash system. Maybe between 1000th to 20000th so providing the shutter is fully open, the actual shutter speed is irrelevant as regards the flash. [edit] (but not irrelevant as regards the overall exposure)[/edit]

Incidentally, I was just reading about some flash units which actually pulse at very high speed (but lower output on each pulse) and allow you to use shutter speeds in excess of the quoted max sync speed. (Just to confuse the issue)

David A. Goldfarb · Dec 25, 2007

rob champagne said:
Incidentally, I was just reading about some flash units which actually pulse at very high speed (but lower output on each pulse) and allow you to use shutter speeds in excess of the quoted max sync speed. (Just to confuse the issue)

Yes, this is how some modern SLRs with focal plane shutters do high speed sync. The downside is that to get that fast pulse rate the output is reduced, so it's not as much of an advantage as it seems for the purpose of balancing flash with bright ambient conditions.

Leaf shutters sync at all speeds in general without having to reduce the flash output, which can give you more options in balancing flash with daylight.

johnnywalker · Dec 25, 2007

The bottom line is use 1/80 (or less) and the same f-stop for both cameras and you will have the same exposure. The shutter speed controls the background exposure, the f-stop the flash exposure.

JBrunner · Dec 25, 2007

What Mr. Walker said.

marsbars · Dec 25, 2007

So what you all are saying is that changing the shutter speed to a slower speed doesn't change the exposure as far as the flash pop is concerned. I think that I am getting the idea now.

RobC · Dec 25, 2007

correct

PatTrent · Dec 25, 2007

Nick Zentena said:
A full out flash blast is ALOT faster then your fastest shutter speed. Lower power blasts are even quicker.

If you want to expose the background set the shutter speed for the background. Set the F/stop for the foreground.

Marsbars:

Nick is correct. You can also use exposure compensation (depending on your camera and flash unit) to adjust the background and foreground levels, and you can adjust either without needing to adjust the other. It's a matter of what you want to achieve.

pat

Richard Kelham · Dec 30, 2007

marsbars said:
Also if for instance I want to use a slower shutter speed to add motion or allow for more exposure in the background. Do I have to adjust the f/stop to compensate for the added exposure time. I want to experiment with slower shutter speeds and my flash. I hope that this makes sense to all of you.

The limiting factor is the ambient light level. The ratio between your chosen f-stop and the light level, at a given ISO, will determine how slow a shutter speed you can use I presume you after a blurred image with sharp flash shot on top like Martin Parr used to do though you might find reducing the flash exposure by a stop helps avoid washing out part of the image: experiment!

Unfortunately, this sort of thing is usually more successful if you use rear curtain sync, but the F3 and Nikkormat can't do that. The F90X and later cameras can however.

Also try using (colour) neg film at first as it is more tolerant of over exposure. Above all, have fun!

Richard

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