# Speedlite guide number question



## duydaniel (Nov 21, 2013)

Hey guys, I have a question.

Let's look at an entry 430EX speedlite, according to Canon, the 43 is the guide number (43 = f x distance in meter).

My question is why this entry speedlite has larger guide number than the pro class Nikon SB-910 (guide number only 34) let alone the 600EX which is almost double the Nikon.

Why is it so far off?

Thank you


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## neuroanatomist (Nov 21, 2013)

Because their respective specifications aren't comparing apples to apples. Nikon specifies their guide numbers (GN) with the flash zoom head set to 35mm, Canon specifies the GN with the head at the maximum zoom (105mm for the 430EX II). The 600EX-RT and 580EX II have the same flash tube - Canon specifies a higher GN for the 600 because the head zooms to 200mm instead of 105mm. 

At a zoom head setting of 35mm, the 600EX-RT has a GN of 36 and the 430EX II has a GN of 31, compared to the Nikon SB-910's GN of 34.


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## AcutancePhotography (Nov 21, 2013)

neuroanatomist nailed it. 

I would like to add one thing. Larger guide number is not the only attribute for a flash. A "pro level" flash does not always mean a higher guide number just like a "pro level" camera does not always mean a higher MP.


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## neuroanatomist (Nov 21, 2013)

AcutancePhotography said:


> I would like to add one thing. Larger guide number is not the only attribute for a flash. A "pro level" flash does not always mean a higher guide number just like a "pro level" camera does not always mean a higher MP.



+1

The built-in catchlight panel and the additional freedom of head movement (180° in either direction, and downward tilt) of the 580/600 flashes vs. the 430 are often more useful than the additional power.


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## duydaniel (Nov 21, 2013)

Wow interesting indeed! Thank you!


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## Random Orbits (Nov 21, 2013)

neuroanatomist said:


> AcutancePhotography said:
> 
> 
> > I would like to add one thing. Larger guide number is not the only attribute for a flash. A "pro level" flash does not always mean a higher guide number just like a "pro level" camera does not always mean a higher MP.
> ...



LOL, yes, but it's hard to go the other way. After using a 430/600, I got used to how much light they could put out. I got the 270 for the M, and it is barely adequate for boucing off 8-ft ceilings. I'm glad that I didn't get the 90.


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## Harv (Nov 21, 2013)

Also, the 580/600 can be used as a master and the 430 can only be used as a slave.


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## Hillsilly (Nov 22, 2013)

I recently came across a flash where the manufacturer compared their GN to some competitors. I thought that was a smart move as it removes a lot of potential confusion. Still it is interesting to see that GN 110 = GN 60 = GN 34. (and, of course, some of these measurements are in feet and others in metres, which also makes it a little harder to make direct comparisons.)

"Every company measures guide number differently. At LumoPro®, this is how we measure guide number: 
GN= Distance x f/stop,
Distance = 10ft, F/stop at 105mm, ISO 100, Full Power = f/11
10ft x f/11 = 110, GN = 110
The LP180's power is *roughly equivalent to the Canon Speedlite 600EX-RT or the Nikon SB-900*."


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## duydaniel (Nov 22, 2013)

Hillsilly said:


> I recently came across a flash where the manufacturer compared their GN to some competitors. I thought that was a smart move as it removes a lot of potential confusion. Still it is interesting to see that GN 110 = GN 60 = GN 34. (and, of course, some of these measurements are in feet and others in metres, which also makes it a little harder to make direct comparisons.)
> 
> "Every company measures guide number differently. At LumoPro®, this is how we measure guide number:
> GN= Distance x f/stop,
> ...



yes GN = distance x f stop is the formula on Wikipedia. Only American and probably UK use feet while the rest of the world uses metric system. I prefer the Canon GN more because they included the zoom in their GN number while Nikon only gives GN based on 35mm and you need to calculate the rest.


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