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Question about an SB-700 in Manual Mode
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<blockquote data-quote="WayneF" data-source="post: 306785" data-attributes="member: 12496"><p>Right</p><p></p><p></p><p></p><p>Right, full power is full power.</p><p></p><p></p><p></p><p>This part needs work. The really big deal is that flash intensity falls off with distance - the Inverse Square Law </p><p></p><p><a href="http://www.scantips.com/lights/flashbasics.html" target="_blank">Four Flash Photography Basics we must know - Inverse Square Law</a></p><p><a href="http://www.scantips.com/lights/flashbasics.html" target="_blank"></a></p><p>Flash exposure can only be precisely correct at only one specific distance from the flash.</p><p></p><p>The bar graph is showing you this proper distance for the current settings (power level, f/stop, zoom, ISO).</p><p></p><p>There is a concept called Guide Number <a href="http://www.scantips.com/lights/flashbasics1c.html" target="_blank">Four Flash Photography Basics we must know - Guide Numbers</a></p><p>which simplifies the square law concept (is only applicable to bare direct flash).</p><p></p><p>The flash does have its guide number chart in its firmware, and this is what the bar graph is computing and showing.</p><p>The GN chart is also in the manual (at the back for SB-700)</p><p></p><p>GN depends on subject distance and lens f/stop (and zoom and ISO).</p><p></p><p>In use, GN = distance * fstop (for the correct flash exposure - meaning proper full exposure, not partial fill flash exposure). If you know GN, then GN/distance tells you the proper fstop. Or GN/fstop tells you distance. Since there can be many fstops, then this tells the corresponding many distances (for proper exposure). The big point is that it handles the Inverse Square Law for us.</p><p></p><p>Some models (including the SB-700) have a GN mode, which is Manual flash, but you enter the distance, and it knows the rest (from camera hot shoe) to automatically set the flash power level correctly for that specified distance. Only applicable for bare direct flash (not for bounce). </p><p></p><p> The distinction is, GN mode sets the correct power level for the distance you enter. </p><p>Otherwise, M mode bar graph does not know distance, and is advising about the proper distance, the distance where the subject better be, at the current settings (you could of course change settings until it shows the correct subject distance).</p></blockquote><p></p>
[QUOTE="WayneF, post: 306785, member: 12496"] Right Right, full power is full power. This part needs work. The really big deal is that flash intensity falls off with distance - the Inverse Square Law [URL="http://www.scantips.com/lights/flashbasics.html"]Four Flash Photography Basics we must know - Inverse Square Law [/URL] Flash exposure can only be precisely correct at only one specific distance from the flash. The bar graph is showing you this proper distance for the current settings (power level, f/stop, zoom, ISO). There is a concept called Guide Number [URL="http://www.scantips.com/lights/flashbasics1c.html"]Four Flash Photography Basics we must know - Guide Numbers[/URL] which simplifies the square law concept (is only applicable to bare direct flash). The flash does have its guide number chart in its firmware, and this is what the bar graph is computing and showing. The GN chart is also in the manual (at the back for SB-700) GN depends on subject distance and lens f/stop (and zoom and ISO). In use, GN = distance * fstop (for the correct flash exposure - meaning proper full exposure, not partial fill flash exposure). If you know GN, then GN/distance tells you the proper fstop. Or GN/fstop tells you distance. Since there can be many fstops, then this tells the corresponding many distances (for proper exposure). The big point is that it handles the Inverse Square Law for us. Some models (including the SB-700) have a GN mode, which is Manual flash, but you enter the distance, and it knows the rest (from camera hot shoe) to automatically set the flash power level correctly for that specified distance. Only applicable for bare direct flash (not for bounce). The distinction is, GN mode sets the correct power level for the distance you enter. Otherwise, M mode bar graph does not know distance, and is advising about the proper distance, the distance where the subject better be, at the current settings (you could of course change settings until it shows the correct subject distance). [/QUOTE]
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Question about an SB-700 in Manual Mode
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