Questions tagged [guide-number]

For questions about the metric describing flash power.

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What is the guide number of a smartphone "flash"?

I know that smartphones have a LED "flash" which is not really a real flash that would produce a very intense short-lived pulse of light, but rather is a continuous light that is turned on ...
juhist's user avatar
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0 votes
1 answer
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Nikon flash guide number

I have recently purchased a Nikon SB-28 flash for my Mamiya 645 1000s camera. Since I can use the flash only in the Manual mode, I am trying to create a guide in order to be able to calculate the ...
Jose Ramon's user avatar
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2 answers
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Are guide number rules still valid over unusually high distances?

Theoretically, a combination of a speedlight of GN 45m@ISO100, an F1.1 lens, and a full frame camera capable of results at 51200 ISO should achieve a reach of almost a kilometer - or two when using 4 ...
rackandboneman's user avatar
1 vote
2 answers
574 views

What is the theoretical relation between zoom length and guide number for a flash?

The point of a guide number is to specify the relation between aperture number and distance. For zoomable flashes there are still extensive tables considering ISO number and zoom length. The ...
user82428's user avatar
3 votes
2 answers
4k views

Godox V860II Guide Number at different zoom steps

Is there any specification for the Guide Number at different zoom steps for the Godox V860II flash? Some manufacturers make this information available. I couldn't find this at the Godox website, nor I ...
Diogo Bento's user avatar
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1 answer
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Why doesn't the distance scale on my Yongnuo flash properly change with aperture?

My Yongnuo YN600EX-RT has a distance scale that is not working properly. For example, with flash in manual mode, ISO100, 35mm, Power 1/1, GN=128 ft: The LCD display gives 10ft for both F8 and F11 ...
Jim K's user avatar
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3 votes
2 answers
690 views

Why does the Guide Number have a distance given with it? [duplicate]

I am learning photography and looking to buy a flash. I learned the basics of the flash, and as far as I saw everywhere, the Guide Number had a feet unit with the ISO number; e.g. 160' at 100 ISO. I ...
Suthan Bala's user avatar
2 votes
2 answers
2k views

Flash guide number f/stop calculation

I have been reading the B&H Speedlight Buyer's Guide. I am confused specifically about the guide number calculation. I understand the principle and how the inverse square law is used. Here is the ...
Albert Savage's user avatar
5 votes
4 answers
909 views

Do flash guide numbers assume some amount of ambient light built-in?

My flash shows its potential range in meters, but is that indoors or outdoors? The question came up the other day when I was trying to work out whether fitting a diffusion dome would be suitable for ...
connersz's user avatar
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3 votes
2 answers
514 views

What flash guide number do I need to underexpose a "sunny" background?

I'm familiar with the maths behind flash usage (guide numbers, etc.). Here's a more practical question that doesn't yet seem to have an answer on photo.se: Consider a subject, outdoors, on a regular "...
Nils L's user avatar
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Guide number and exposure [duplicate]

I am having a bit of a difficulty calculating this. Guide#= 32 feet at ISO 100 X sync speed= 1/250 Min ISO= 100 Max ISO= 800 What exposure values to expose to capture subject that's far away? What ...
user17651's user avatar
8 votes
2 answers
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How do I set exposure with a manual flash?

I recently got an old Canon AE-1 film camera back in working order. I'd like to use my modern 430EXII Speedlight flash with it, however since there is no TTL metering, I have no idea how much the ...
Bill's user avatar
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2 votes
2 answers
225 views

Old Flash from the 70's

I have an old Consul 400 flash. It was distributed by Braun North America. I would like to figure what is the GN number at ISO 100, f/4, 10 feet.
gjw's user avatar
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3 votes
1 answer
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What is the relationship between Guide Number and flash power level?

From this post, I understand that the flash guide number (GN) is given by the following formula: $$ \text{Guide Number} = \,\frac{\text{Shooting Distance}\times \text{f-number}}{\text{ISO factor}} $$ ...
CadentOrange's user avatar
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10 votes
4 answers
7k views

What is the quantative relation between flash guide number and ISO?

I found that formula on the Internet: $$ \text{Guide Number} = \frac{\text{Shooting Distance}\times\text{Aperture}}{\text{ISO Sensitivity}} $$ Is it correct? If it is could someone please explain why ...
lanan's user avatar
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6 votes
5 answers
5k views

Does adding additional strobes cumulatively add to the flash power?

I've been reading articles that talk about using multiple strobes next to each other, all pointing in the same direction: as a means to add more light over what one flash can do. Does the addition of ...
Daniel T.'s user avatar
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