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flash output indication

Ralph Honsbeek

New member
Hi there ,

totally love this forum ,

Question about flashes , just was curious to know how I can know the maximum output
of a flash unit just by reading the outside numbering.
For example , Canon 430 EX , Canon 580 EX , Vivitar 285 , just be looking at these numbers
can I assume that the output is 43 watt 58 watt and so on ? Really haven't a clue that's why I ask

thanks

Ralph
 

Will Thompson

Well-known member
Hi Ralph!

They are not watt seconds they are Maximum distance guide numbers, well at least the canon flashes are.

The 430 has a Max guide # of 43 meters and the 580 has a Max guide # of 58 meters.

Typically Max guide numbers are stated by canon as proper exposure at ISO 100 using a f1.4 at X meters.
 

Asher Kelman

OPF Owner/Editor-in-Chief
Guide to understanding "Guide number" flash output of electronic flashes!

Hi Ralph!

They are not watt seconds they are Maximum distance guide numbers, well at least the canon flashes are.

The 430 has a Max guide # of 43 meters and the 580 has a Max guide # of 58 meters.

Typically Max guide numbers are stated by canon as proper exposure at ISO 100 using a f1.4 at X meters.

Will, Doug or anyone else,

Can you try to translate this to W/S? Of course, it all depends on the reflector, but can we have some estimates?

Asher
 

Doug Kerr

Well-known member
Hi, Asher,
Will, Doug or anyone else,

Can you try to translate this to W/S? Of course, it all depends on the reflector***, but can we have some estimates?Asher

*** And many other things!

Simple answers to questions in this area are very dangerous. It's a little bit like saying, "I have a vessel full of liquid to a depth of 6 inches; how much can we estimate the liquid to weigh?"

For those really interested in the topic, I suggest this reference:

http://doug.kerr.home.att.net/pumpkin/Photoflash_Output.pdf

Then, once you understand the real question, some of the estimated equivalence factors in the paper can be applied in a meaningful and practical way.
 

Doug Kerr

Well-known member
Hi, Ralph,

What about the Vivitar 285 , does it cover 285 meters you think > ?

Well first, if you mean "is its guide number 285 meters", that certainly wouldn't mean it "covered 285 meters".

If you don't have the manual or a spec sheet, you can determine the manufacturer's opinion of the guide number by considering the exposure calculator on the unit (I don't have a 285, nor the manual for one, so I can't do it here).

For the Vivitar 285HV, the claimed guide number (ISO 100 basis) with the zoom set to "Tele" ("105 mm) is 140 ft (43 meters).

With the zoom set to Super wide ("28 mm") the claimed guide number is 70 feet (21 meters).

Best regards,

Doug
 
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