 Vadim Boriskevich |
Guide Number for SB-600 I'm looking an easy way to quickly get a correct guide number for my Nikon SB-600. I saw those formulas in the booklet that comes with this flash. I thought there could be an easier way to figure this out. I'll be shooting this Sunday on my wife's birthday. Nikon D80, NIKON 50MM F/1.4D AF LENS, SB-600 with Gary Fong Cloud diffuser. Option 1: On the sunny deck in the afternoon. In my D80, I'm using FV lock option with a FUNC button. It measures and lock the flash exposure. Then, every photo I take, the flash doesn't fire before the photo is taken. Any tips are appreciated. Thanks.
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W. |
Hi Vadim, the GF diffuser is useless outside, because there is nothing to bounce off of. Worse than useless, because it cuts your flash' range to a 1/4. I don't have a D80+SB600 combo, but all modern camera/flash gun combos – if correctly set – communicate the correct flash exposure value from camera to the flash gun, so you don't need to change settings for every shot. "1/1 or 1/32", etc. refers to the SB600's power output. Relative to its Guide Number. You had better stay at 1/1 for now, and let the processors do the thinking. "If you change the distance to the subject, the same flash exposure will be used in all other shots?" Have fun!
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Cathy Barrows |
I had a SB-600 (or should I still have but don't use) because it nerver put out enough flash power to properly light up any object. Have you used the flash before and had good results?
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Alan N. Marcus |
Hi Vadim, Calculating a guide number for a flash is easy. In surrounds similar to your shoot location, position your subject 10 feet from the camera. Shoot a series of exposures, each at different apertures (f/numbers) select the best shot based on exposure. Note the aperture that was used. To calculate an accurate guide number, multiply aperture used times subject-to-flash distance. Example: Best frame shot at f/16. Distance flash-to-subject 10 feet. Thus 16 x 10 = 160. This is your calculated guide number. You perform this exercise with the camera set at a specific ISO value. You can carry out this excurse at any ISO setting and you may choose a different distance so long as you don’t exceed the effective range of the flash. Once the guide number has been established, during the shoot, estimate subject-to-flash distance. Divide guide number by distance to obtain a suitable f/number setting. Assume guide number is 180 and subject-to-flash distance is 15 feet then: Modify guide number: Should a guide number prove continually off by under or over exposing. Multiply guide number by 0.70 to adjust + 1 f/stop Best of luck,
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Vadim Boriskevich |
WS, I'll test the GF outside, and will point the SB-600 directly to the subject, since there is nothing to bounce off. Hi Cathy,
Thank you for the detailed explanation. What does this mean: 40.0/131.2 ?
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Alan N. Marcus |
Hi again Vadim, To the rest of the world the US and Liberia are pretty stupid. Seems only these two continue to use the English system of feet in inches. The remainder of the world uses the more logical metric system. Page 35 explained. Your flash unit is able to accommodate different fields of view. When the flash field of view is more concentrated, at the longer zoom positions, the flash is brighter thus the guide number is greater for 85° (40/131) vs. 14° (14/46). You can round these values. It is dim-witted to work and publish 45.9 so we round to 46. (Guide number aren’t that accurate anyway) Look at 40/131 – the fist number is posted for those folks that use the metric system. The second number is for those folks that use the English system. Consider a subject 10 feet flash-to-subject. That’s 120 inches ÷ 39.37 = 3.05 meters. So English 131 ÷ 10 = f/13.1 – whereas metric 40 ÷ 3.05 = f/13.1 (same answer) This is a table based on the geometry of circles (the lens is circular). To modify a guide number + 1 stop we multiply by 0.70 to modify + ½ stop we multiply by 0.84 to modify – ½ stop we multiply by 1.2 – to modify – 1stop we multiply by 1.4. Nobody said it’s easy! Alan Marcus (marginal technical gobbledygook)
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Alan N. Marcus |
Perhaps a better explanation of the ISO sensitivity factors bottom of page 35: The guide numbers are provided for ISO 100 only. Should you choose to use a higher or lower ISO you are directed to use the ISO sensitivity factors to calculate the Guide number revision. Example for a flash zoom head position 50° the published Guide Number is 118.1 additionally this value is for a camera setting of ISO 100. Should you choose to shoot with a camera setting of ISO 200 you must calculate a revised Guide number. To accomplish you multiply the published value of 118.1 times 1.4 thus 118.1 x 1.4 = 129.9 (I suggest rounding to 130. Should you choose to shoot at ISO 400 the factor is 2 thus the math 118.1 x 2 = 236.2 Should you choose to shoot at ISO 50 the math is 118.1 x 0.71 = 83.8 Nobody said it’s easy. Now you know why I call this stuff technical gobbledygook. Alan Marcus
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Vadim Boriskevich |
Alan, I got this mathematics, but it'll be difficult to calculate it for every shot.
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