# need help calculating aperture with speedlights

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• 11-05-2013, 01:50 PM
BrianShaw
Quote:

Originally Posted by David Allen
... As flash meters were designed to suit the output characteristics of said studio flashes, that is why they gave inaccurate readings with hand-held flashes set to an automatic setting but correct readings when the hand-held meter was set to manual. ...

Maybe Im misunderstanding David's comments, but I never thought it had to do with any kind output characteristic compatability between stobe and meter. My experience with flashes is somewhat limtied but use one of these three options:

1. TTL flash metering (35mm) - let the camera meter work witin the range of the flash output to meter the flash light correctly.
2. Thyristor (on the flash unit) control - let the flash unit work within the range of the flash output to meter the flash light correctly.
3. Flash meter - use a flash meter to determine the appropriate aperture to set on the camera that will correctly expose film for the amount of flash light being used.

and there always is 4. Calculation of aperture using guide number and distance.

I can't even understand how one would use a flash meter in situations 1 and 2 where there is either kind of internal flash metering system being used.
• 11-05-2013, 02:58 PM
jstraw
Quote:

Originally Posted by BrianShaw
Maybe Im misunderstanding David's comments, but I never thought it had to do with any kind output characteristic compatability between stobe and meter. My experience with flashes is somewhat limtied but use one of these three options:

1. TTL flash metering (35mm) - let the camera meter work witin the range of the flash output to meter the flash light correctly.
2. Thyristor (on the flash unit) control - let the flash unit work within the range of the flash output to meter the flash light correctly.
3. Flash meter - use a flash meter to determine the appropriate aperture to set on the camera that will correctly expose film for the amount of flash light being used.

and there always is 4. Calculation of aperture using guide number and distance.

I can't even understand how one would use a flash meter in situations 1 and 2 where there is either kind of internal flash metering system being used.

One wouldn't. One would set the body to "M" and set the aperture and shutter speed manually, per the flash meter. I don't know anyone that uses studio lights that uses the camera's meter or thyristor control with them.
• 11-05-2013, 04:36 PM
wiltw
Quote:

Originally Posted by BrianShaw
Maybe Im misunderstanding David's comments, but I never thought it had to do with any kind output characteristic compatability between stobe and meter.

Second guessing David's underlying understandings, but he did say "when testing the auto settings on my Metz with transparency film but accurate when using the Metz on full power."
Studio flashes tend to be somewhat longer duration light output, while speedlights tend to be shorter duration light output. In the days before today's higher output flash units, most speedlights might be 1/1000-1/10000 or thereabouts, while studio flashes might be about 1/1000. As my experiment showed, when the flash duration gets very short (in my example, 1/10000) my flashmeter is totally fooled and its suggested exposure to totally wrong. That fits David's experience.

The Hassy guy apparently made comments about speedlight output being 'different' than studio flash. Paul Buff's charts might help explain that: http://www.paulcbuff.com/sfe-flashduration.php

You can see that reduced power of (some) studio flash lowers the max voltage, resulting in a lower peak, but fairly uniform duration of light output. OTOH, the IGBT output reduces duration, not the peak amplitude...but that is how speedlights work. Modern studio flash use an approach like IGBT, for example my Dynalite flash duration drops as power is lowered.

My tests showed that the flashmeter could reasonably meter even the abbreviated flash duration of speedlights -- to a point. As I said earlier in this post, when the flash duration gets very short (in my example, 1/10000) my flashmeter is totally fooled and its suggested exposure to totally wrong.

What I can't explain is why my flashmeter's suggested exposure when reading my Metz on Manual power results in a brighter result than one really would want.
• 11-05-2013, 04:49 PM
jnanian
Quote:

Originally Posted by jstraw
One wouldn't. One would set the body to "M" and set the aperture and shutter speed manually, per the flash meter. I don't know anyone that uses studio lights that uses the camera's meter or thyristor control with them.

i have one i use with my lumedyne 244 ...
output can be full 400WS or 2ws or trimmed in between.
its pretty useful ... and i wish everything i used had this feature ..
• 11-05-2013, 06:54 PM
Chan Tran
I have 2 flashmeters and they are both accurate with all kind of flashes. I do use them when the flash is in auto mode just to check if the auto feature is working correctly.
• 11-05-2013, 07:03 PM
BrianShaw
Quote:

Originally Posted by Chan Tran
... I do use them when the flash is in auto mode just to check if the auto feature is working correctly.

If you don't mind me asking, how? Do you set the auto setting, say, to f/8 and then measure to see if the flash meter says something around f/8?
• 11-05-2013, 10:12 PM
jstraw
Quote:

Originally Posted by jnanian
i have one i use with my lumedyne 244 ...
output can be full 400WS or 2ws or trimmed in between.
its pretty useful ... and i wish everything i used had this feature ..

I can see how that would be useful. It's certainly uncommon. I've never encountered anything like it.
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