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Old Apr 16, 2010, 8:46 AM   #1
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Default Guide Numbers = Worthless Info???

Has marketing finally won, publishing "official" guide numbers that may be accurate but defy comparison? It appears, in most cases they quote iso 100 figures, they have eliminated other common denominators - such as lens. Consider the following, data from manufacturers site:
Nikon
SB-900 34/111 lens not specified (40/131 with 35mm per B&H)
SB-600 30/98 35mm
SB-400 30/98 18mm and ISO 200 (gotta love that stretch!)
Canon
580 EX 58/190 105mm
430 EX 43/141 105mm
Sigma
530 (both) 53/174 lens not specified (53/174 105mm per B&H)
Metz
58 42/___ 50mm
48 38/___ 50mm

It goes on but I won't bore you with data from other manufacturers. I can understan why, as I downloaded the SB-900 manual to see if it specifid the lens and there is a 2 page table of guide numbers for both FX and DX. It is enough to make ones head spin!

It seems like there should be some sort of industry-wide standardization.

Right now, I am considering add a flash to my current SB-600 as I explore multi off camera flash. The obvious decision questions another SB-600? SB-900? Sigma or Metz models - and while they support TTL, do the also support Nikon's CLS in either commander or slave modes? With those normal questions, it seems like a standardized guide number would have minimized the confusion!

Last edited by tizeye; Apr 16, 2010 at 8:50 AM.
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Old Apr 16, 2010, 9:09 AM   #2
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Trying to make sense out of the above, I did the un-manly thing and went to the SB-900 manual.

From the tables @ ISO 100 discovered:
FX:
35mm = 34 (what Nikon site qouted without stating lens)
50mm = 40
105mm = 49.5
DX
35mm = 40 (what B&H site used in their quote)
50mm = 46
105mm = 52.5

That at least gives some standardization, but one should not have to go to that effort!
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Old Apr 16, 2010, 9:38 AM   #3
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Yea... It's getting to where you need to download the manuals to see how well they do at a given focal length (or zoom head setting).

You also have different zoom head designs between them (i.e., some may be designed for the narrowest flash beam at 85mm, and some may be designed with an expanded zoom head out to much further (like the Nikon SB-900). So, it's getting to where you may need to download the manuals to see how they compare, as some manufacturers quote more conservative numbers using a wider focal length and some may quote GN at max zoom head position on the flash.

As for Metz, the 58 AF-1 can work as master or slave. See the camera specific section on this page:

http://www.metz.de/en/photo-electron...formation.html

See page 111 and 112 of this manual for the English language wireless flash section to see how that works and the features supported:

http://www.metz.de/fileadmin/fm-dam/..._NL_GB_I_E.pdf

Make sure to download the latest firmware and install it if you go that route. See this page:

http://www.metz.de/en/photo-electron...1-digital.html

The lower priced Metz 48 AF-1 will only work as a slave, so you'll want to go with the 58 AF-1 if you want a flash you can use as a master/controller, too.
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Old Apr 16, 2010, 10:27 PM   #4
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Guide numbers are needed to shoot in manual, and then you need all the additional information. If you use the flash in auto mode, by itself, then it isn't as improtant. Guide numbers also tell you the power of the flash so you can relate it to others. If you really want to spend your time calculating flash ranges, have fun.

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Old Apr 17, 2010, 12:27 PM   #5
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Quote:
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Guide numbers also tell you the power of the flash so you can relate it to others.
brian
That was just my point. When shopping and comparing, you can say Flash 1 and a Guide # of "X" and Flash 2 has a guide # of "Y". Whit "x" being a larger number than "Y", "x" is more powerful. That conclusion is not possible when "x" os based on a 35mm field of coverage, and "y" is based on a 105mm field of coverage.
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Old Apr 17, 2010, 12:39 PM   #6
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The honest truth is that many flash manufacturers tend to "fudge" a little on their guide numbers. Guide numbers are no longer as accurate as they were when we all used manul flash.

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Old Apr 17, 2010, 2:42 PM   #7
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Quote:
Originally Posted by tizeye View Post
That was just my point. When shopping and comparing, you can say Flash 1 and a Guide # of "X" and Flash 2 has a guide # of "Y". Whit "x" being a larger number than "Y", "x" is more powerful. That conclusion is not possible when "x" os based on a 35mm field of coverage, and "y" is based on a 105mm field of coverage.
As long as the free market system continues to exist(forever. I hope), we will have virtually no industry wide standardization. Competition will assure that the market place remains confusing to the consumer. If all products took the same battery, lens mount, etc. the companies that manufacture the hardware, software, and consumables would lose their edge to the consumer, and we know that ain't happenin'...

This is not to say there aren't savvy shoppers out there, but they are not the majority, would be my guess...
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Old Apr 17, 2010, 3:02 PM   #8
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You make a very good point, Robert-

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Old Apr 17, 2010, 3:38 PM   #9
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Cameras with variable ISO settings, and flash heads which have zoom capability make things more complicated than they used to be. Even the 'old days' were not that easy. GN for flashbulbs depended on the bulb type and reflector type - basic electronic flashes had fixed GN, but that changed if you bounced the flash.
Just be glad you don't have to do the math in your head anymore.

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Old Apr 17, 2010, 4:23 PM   #10
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Quote:
Originally Posted by VTphotog View Post
Cameras with variable ISO settings, and flash heads which have zoom capability make things more complicated than they used to be. Even the 'old days' were not that easy. GN for flashbulbs depended on the bulb type and reflector type - basic electronic flashes had fixed GN, but that changed if you bounced the flash.
Just be glad you don't have to do the math in your head anymore.

brian
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