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Can someone put this in simple terms for me please.
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<blockquote data-quote="WayneF" data-source="post: 109812" data-attributes="member: 12496"><p>I think I read that you had a SB-700. Good flash. It has many Guide Numbers, this is only one of many, depending on the manual power level selected and flash head zoom and ISO for that matter.</p><p></p><p>SB-700 manual page H-23 and H-24 shows much of that. Page H-6 explains it.</p><p>If you need any help, see <a href="http://www.scantips.com/lights/flashbasics1c.html" target="_blank">Four Flash Photography Basics we must know - Guide Numbers</a></p><p></p><p>GN = distance x f/stop, which gives the correct exposure (computing in the inverse square law). This is the overall idea of it. Direct flash only.</p><p></p><p>Normally, if for the power level and zoom and ISO you are using, if that GN is say 80, and if your subject were at ten feet, then the division GN80 / 10 feet = f/8, which is the aperture that gives you the correct exposure. It only works for direct flash, and Manual flash mode of course.</p><p></p><p>Note SB-700 manual page C-11 to C-15 describes a flash mode called GN. This mode already knows zoom and aperture and ISO, so you just dial in the distance, and it sets the power level automatically. This is still considered to be Manual flash mode,, you are setting the flash power for the distance. Again, direct flash only, but it is good stuff for that, because it is independent of the subject.</p><p></p><p>To compare, TTL mode is automatic, it first fires a preflash that the camera meter measures, and sets the flash power level for the shot. But reflective meters see the light reflected from the subject. A lighter or white subject reflects a lot, and the meter cuts it back to come out gray. A darker or black subject reflects very little, an the meter boosts it up to come out gray. So we often have pay attention, and use Flash Compensation as needed. TTL does however handle bounce flash well.</p><p></p><p>But GN just relates the flash power and distance and f/stop to be the right light at the subject, no matter what the subject is. Black things will come out black, and white things will come out white. Which is all generally pretty fine, if you know the distance, and if using direct flash. It is common to guess the distance, and then tweak a bit if necessary. Indoors though, you will probably like TTL Bounce flash better.</p></blockquote><p></p>
[QUOTE="WayneF, post: 109812, member: 12496"] I think I read that you had a SB-700. Good flash. It has many Guide Numbers, this is only one of many, depending on the manual power level selected and flash head zoom and ISO for that matter. SB-700 manual page H-23 and H-24 shows much of that. Page H-6 explains it. If you need any help, see [URL="http://www.scantips.com/lights/flashbasics1c.html"]Four Flash Photography Basics we must know - Guide Numbers[/URL] GN = distance x f/stop, which gives the correct exposure (computing in the inverse square law). This is the overall idea of it. Direct flash only. Normally, if for the power level and zoom and ISO you are using, if that GN is say 80, and if your subject were at ten feet, then the division GN80 / 10 feet = f/8, which is the aperture that gives you the correct exposure. It only works for direct flash, and Manual flash mode of course. Note SB-700 manual page C-11 to C-15 describes a flash mode called GN. This mode already knows zoom and aperture and ISO, so you just dial in the distance, and it sets the power level automatically. This is still considered to be Manual flash mode,, you are setting the flash power for the distance. Again, direct flash only, but it is good stuff for that, because it is independent of the subject. To compare, TTL mode is automatic, it first fires a preflash that the camera meter measures, and sets the flash power level for the shot. But reflective meters see the light reflected from the subject. A lighter or white subject reflects a lot, and the meter cuts it back to come out gray. A darker or black subject reflects very little, an the meter boosts it up to come out gray. So we often have pay attention, and use Flash Compensation as needed. TTL does however handle bounce flash well. But GN just relates the flash power and distance and f/stop to be the right light at the subject, no matter what the subject is. Black things will come out black, and white things will come out white. Which is all generally pretty fine, if you know the distance, and if using direct flash. It is common to guess the distance, and then tweak a bit if necessary. Indoors though, you will probably like TTL Bounce flash better. [/QUOTE]
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Can someone put this in simple terms for me please.
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