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#11
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Hi Alan & bruce
The book is "The New Guide to Sea & Sea" [cameras & strobes], Joe Liburdi & Cara Sherman, 1977, ISBN 0-9621111-3-9. (quote) p.82 "How to bracket" "When shooting with an external strobe in TTL mode:" "It's impossible to bracket in the same manner as when using the strobe in manual mode. No matter which f-stop you select, the TTL sensor will automatically compensate for the measured light refelecting off the film plane. Therefore, we must intentionally over or underexpose to create different exposures. 1. Bracket by altering strobe to subject distance. Take your first picture at the recommended f-stop & strobe to subject distance. Then remove your strobe from the base plate and handhold it. One foot forward or backward will efectively change your exposure by one f-stop. 2. Bracket by changing shutter speed. Change it one speed faster and one speed slower than the recommended exposure. Do not change f-stop." (end quote) I don't see how either of those two recommendations can affect the exposure. Surely the TTL sensor will quench the strobe after 'x' amount of light has been received by the film, regardless of strobe to subject distance, f-stop, and shutter speed? Hope that you can shed some light on this! Is the book just wrong, full-stop? TIA, TC |
#12
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Hi Alan & bruce
The book is "The New Guide to Sea & Sea" [cameras & strobes], Joe Liburdi & Cara Sherman, 1977, ISBN 0-9621111-3-9. (quote) p.82 "How to bracket" "When shooting with an external strobe in TTL mode:" "It's impossible to bracket in the same manner as when using the strobe in manual mode. No matter which f-stop you select, the TTL sensor will automatically compensate for the measured light refelecting off the film plane. Therefore, we must intentionally over or underexpose to create different exposures. 1. Bracket by altering strobe to subject distance. Take your first picture at the recommended f-stop & strobe to subject distance. Then remove your strobe from the base plate and handhold it. One foot forward or backward will efectively change your exposure by one f-stop. 2. Bracket by changing shutter speed. Change it one speed faster and one speed slower than the recommended exposure. Do not change f-stop." (end quote) I don't see how either of those two recommendations can affect the exposure. Surely the TTL sensor will quench the strobe after 'x' amount of light has been received by the film, regardless of strobe to subject distance, f-stop, and shutter speed? Hope that you can shed some light on this! Is the book just wrong, full-stop? TIA, TC |
#13
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TC wrote:
Hi Alan & bruce The book is "The New Guide to Sea & Sea" [cameras & strobes], Joe Liburdi & Cara Sherman, 1977, ISBN 0-9621111-3-9. (quote) p.82 "How to bracket" "When shooting with an external strobe in TTL mode:" "It's impossible to bracket in the same manner as when using the strobe in manual mode. No matter which f-stop you select, the TTL sensor will automatically compensate for the measured light refelecting off the film plane. Therefore, we must intentionally over or underexpose to create different exposures. Okay up to there. [NIT: Further, as the aperture gets smaller, you rapidly approach the max power of the flash.] 1. Bracket by altering strobe to subject distance. Take your first picture at the recommended f-stop & strobe to subject distance. Then remove your strobe from the base plate and handhold it. One foot Not in TTL ...TTL will always adjust as they say above. forward or backward will efectively change your exposure by one f-stop. Huh? if you are 10 feet away, with a manual flash: --you would need to approach to (SQRT(2)*10)/2 = 7.07 feet to get 1 more stop of light on target (or double the amount light). --To get 1 stop less you would need SQRT(2)*10 = 14.14 from target. Notice now that 7.07 is half of 14.14 feet ... they are two stops apart (4x the amount of light at 7.07 feet than at 14.14 feet. For a given distance from subject to flash, and change in that distance follows the inverse square law. The only way their example would hold would be if the orig. dist from strobe to subject was 3.4 feet away ... which for underwater photography might well be the case in many circumstances ... is that the context of the discussion in the book (eg, from about 3.5 feet away...)? 2. Bracket by changing shutter speed. Change it one speed faster and one speed slower than the recommended exposure. Do not change f-stop." Shutter speed has no effect the flash exposure (except when S is faster than the sync speed and you get a partially exposed frame). A flash photo is really a double exposure, one for ambient light, one for flash light. The ambient can be controlled with both shutter speed and aperture ... but the flash exposure can *only* be controled by the flash power output and the aperture ... shutter speed has nothing to do with it. (end quote) I don't see how either of those two recommendations can affect the exposure. Surely the TTL sensor will quench the strobe after 'x' amount of light has been received by the film, regardless of strobe to subject distance, f-stop, and shutter speed? Within its power limits, yes. The usual means of controlling TTL flash output is either flash compensation or rating the ISO to fool the flash (rate it higher to lower the flash power; raise the ISO to increase the flash). In an underwater shoot, rerating the ISO might be a bit tricky! Do this in Aperture priority, however, becasue if you do it in S-pri then the aperture will be determined in part by the ISO setting. Hope that you can shed some light on this! Is the book just wrong, full-stop? See above about the context of the example regarding 1 foot change of distance... Cheers, Alan -- -- rec.photo.equipment.35mm user resource: -- http://www.aliasimages.com/rpe35mmur.htm -- e-meil: there's no such thing as a FreeLunch.-- |
#14
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TC wrote:
Hi Alan & bruce The book is "The New Guide to Sea & Sea" [cameras & strobes], Joe Liburdi & Cara Sherman, 1977, ISBN 0-9621111-3-9. (quote) p.82 "How to bracket" "When shooting with an external strobe in TTL mode:" "It's impossible to bracket in the same manner as when using the strobe in manual mode. No matter which f-stop you select, the TTL sensor will automatically compensate for the measured light refelecting off the film plane. Therefore, we must intentionally over or underexpose to create different exposures. Okay up to there. [NIT: Further, as the aperture gets smaller, you rapidly approach the max power of the flash.] 1. Bracket by altering strobe to subject distance. Take your first picture at the recommended f-stop & strobe to subject distance. Then remove your strobe from the base plate and handhold it. One foot Not in TTL ...TTL will always adjust as they say above. forward or backward will efectively change your exposure by one f-stop. Huh? if you are 10 feet away, with a manual flash: --you would need to approach to (SQRT(2)*10)/2 = 7.07 feet to get 1 more stop of light on target (or double the amount light). --To get 1 stop less you would need SQRT(2)*10 = 14.14 from target. Notice now that 7.07 is half of 14.14 feet ... they are two stops apart (4x the amount of light at 7.07 feet than at 14.14 feet. For a given distance from subject to flash, and change in that distance follows the inverse square law. The only way their example would hold would be if the orig. dist from strobe to subject was 3.4 feet away ... which for underwater photography might well be the case in many circumstances ... is that the context of the discussion in the book (eg, from about 3.5 feet away...)? 2. Bracket by changing shutter speed. Change it one speed faster and one speed slower than the recommended exposure. Do not change f-stop." Shutter speed has no effect the flash exposure (except when S is faster than the sync speed and you get a partially exposed frame). A flash photo is really a double exposure, one for ambient light, one for flash light. The ambient can be controlled with both shutter speed and aperture ... but the flash exposure can *only* be controled by the flash power output and the aperture ... shutter speed has nothing to do with it. (end quote) I don't see how either of those two recommendations can affect the exposure. Surely the TTL sensor will quench the strobe after 'x' amount of light has been received by the film, regardless of strobe to subject distance, f-stop, and shutter speed? Within its power limits, yes. The usual means of controlling TTL flash output is either flash compensation or rating the ISO to fool the flash (rate it higher to lower the flash power; raise the ISO to increase the flash). In an underwater shoot, rerating the ISO might be a bit tricky! Do this in Aperture priority, however, becasue if you do it in S-pri then the aperture will be determined in part by the ISO setting. Hope that you can shed some light on this! Is the book just wrong, full-stop? See above about the context of the example regarding 1 foot change of distance... Cheers, Alan -- -- rec.photo.equipment.35mm user resource: -- http://www.aliasimages.com/rpe35mmur.htm -- e-meil: there's no such thing as a FreeLunch.-- |
#15
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Alan
Thank you very much for your detailed & informative answers. I've answered nearly 6000 questions on usenet myself (about a particular software product), & it's nice to get an answer to one of my own questions, for a change! It's clear that the book is incorrect. I'll follow this up with Sea & Sea (the camera manufacturers), or the author, if I can contact him. If I get a result, I'll take the liberty of CC'ing it to you, unless you ask me not to do that. As for the 3.4 foot question - yes, it is commonly recommended that underwater pictures be taken from a max distance of about 4 feet (for the obvious reasons). But it seems that his information is still all wrong, in any case. Thanks again for your answers. I'll print them off & digest them carefully. Yea for newsgroups :-) Regards, TC Alan Browne wrote in message ... TC wrote: Hi Alan & bruce The book is "The New Guide to Sea & Sea" [cameras & strobes], Joe Liburdi & Cara Sherman, 1977, ISBN 0-9621111-3-9. (quote) p.82 "How to bracket" "When shooting with an external strobe in TTL mode:" "It's impossible to bracket in the same manner as when using the strobe in manual mode. No matter which f-stop you select, the TTL sensor will automatically compensate for the measured light refelecting off the film plane. Therefore, we must intentionally over or underexpose to create different exposures. Okay up to there. [NIT: Further, as the aperture gets smaller, you rapidly approach the max power of the flash.] 1. Bracket by altering strobe to subject distance. Take your first picture at the recommended f-stop & strobe to subject distance. Then remove your strobe from the base plate and handhold it. One foot Not in TTL ...TTL will always adjust as they say above. forward or backward will efectively change your exposure by one f-stop. Huh? if you are 10 feet away, with a manual flash: --you would need to approach to (SQRT(2)*10)/2 = 7.07 feet to get 1 more stop of light on target (or double the amount light). --To get 1 stop less you would need SQRT(2)*10 = 14.14 from target. Notice now that 7.07 is half of 14.14 feet ... they are two stops apart (4x the amount of light at 7.07 feet than at 14.14 feet. For a given distance from subject to flash, and change in that distance follows the inverse square law. The only way their example would hold would be if the orig. dist from strobe to subject was 3.4 feet away ... which for underwater photography might well be the case in many circumstances ... is that the context of the discussion in the book (eg, from about 3.5 feet away...)? 2. Bracket by changing shutter speed. Change it one speed faster and one speed slower than the recommended exposure. Do not change f-stop." Shutter speed has no effect the flash exposure (except when S is faster than the sync speed and you get a partially exposed frame). A flash photo is really a double exposure, one for ambient light, one for flash light. The ambient can be controlled with both shutter speed and aperture ... but the flash exposure can *only* be controled by the flash power output and the aperture ... shutter speed has nothing to do with it. (end quote) I don't see how either of those two recommendations can affect the exposure. Surely the TTL sensor will quench the strobe after 'x' amount of light has been received by the film, regardless of strobe to subject distance, f-stop, and shutter speed? Within its power limits, yes. The usual means of controlling TTL flash output is either flash compensation or rating the ISO to fool the flash (rate it higher to lower the flash power; raise the ISO to increase the flash). In an underwater shoot, rerating the ISO might be a bit tricky! Do this in Aperture priority, however, becasue if you do it in S-pri then the aperture will be determined in part by the ISO setting. Hope that you can shed some light on this! Is the book just wrong, full-stop? See above about the context of the example regarding 1 foot change of distance... Cheers, Alan |
#16
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Alan
Thank you very much for your detailed & informative answers. I've answered nearly 6000 questions on usenet myself (about a particular software product), & it's nice to get an answer to one of my own questions, for a change! It's clear that the book is incorrect. I'll follow this up with Sea & Sea (the camera manufacturers), or the author, if I can contact him. If I get a result, I'll take the liberty of CC'ing it to you, unless you ask me not to do that. As for the 3.4 foot question - yes, it is commonly recommended that underwater pictures be taken from a max distance of about 4 feet (for the obvious reasons). But it seems that his information is still all wrong, in any case. Thanks again for your answers. I'll print them off & digest them carefully. Yea for newsgroups :-) Regards, TC Alan Browne wrote in message ... TC wrote: Hi Alan & bruce The book is "The New Guide to Sea & Sea" [cameras & strobes], Joe Liburdi & Cara Sherman, 1977, ISBN 0-9621111-3-9. (quote) p.82 "How to bracket" "When shooting with an external strobe in TTL mode:" "It's impossible to bracket in the same manner as when using the strobe in manual mode. No matter which f-stop you select, the TTL sensor will automatically compensate for the measured light refelecting off the film plane. Therefore, we must intentionally over or underexpose to create different exposures. Okay up to there. [NIT: Further, as the aperture gets smaller, you rapidly approach the max power of the flash.] 1. Bracket by altering strobe to subject distance. Take your first picture at the recommended f-stop & strobe to subject distance. Then remove your strobe from the base plate and handhold it. One foot Not in TTL ...TTL will always adjust as they say above. forward or backward will efectively change your exposure by one f-stop. Huh? if you are 10 feet away, with a manual flash: --you would need to approach to (SQRT(2)*10)/2 = 7.07 feet to get 1 more stop of light on target (or double the amount light). --To get 1 stop less you would need SQRT(2)*10 = 14.14 from target. Notice now that 7.07 is half of 14.14 feet ... they are two stops apart (4x the amount of light at 7.07 feet than at 14.14 feet. For a given distance from subject to flash, and change in that distance follows the inverse square law. The only way their example would hold would be if the orig. dist from strobe to subject was 3.4 feet away ... which for underwater photography might well be the case in many circumstances ... is that the context of the discussion in the book (eg, from about 3.5 feet away...)? 2. Bracket by changing shutter speed. Change it one speed faster and one speed slower than the recommended exposure. Do not change f-stop." Shutter speed has no effect the flash exposure (except when S is faster than the sync speed and you get a partially exposed frame). A flash photo is really a double exposure, one for ambient light, one for flash light. The ambient can be controlled with both shutter speed and aperture ... but the flash exposure can *only* be controled by the flash power output and the aperture ... shutter speed has nothing to do with it. (end quote) I don't see how either of those two recommendations can affect the exposure. Surely the TTL sensor will quench the strobe after 'x' amount of light has been received by the film, regardless of strobe to subject distance, f-stop, and shutter speed? Within its power limits, yes. The usual means of controlling TTL flash output is either flash compensation or rating the ISO to fool the flash (rate it higher to lower the flash power; raise the ISO to increase the flash). In an underwater shoot, rerating the ISO might be a bit tricky! Do this in Aperture priority, however, becasue if you do it in S-pri then the aperture will be determined in part by the ISO setting. Hope that you can shed some light on this! Is the book just wrong, full-stop? See above about the context of the example regarding 1 foot change of distance... Cheers, Alan |
#17
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TC wrote:
Alan Thank you very much for your detailed & informative answers. I've answered nearly 6000 questions on usenet myself (about a particular software product), & it's nice to get an answer to one of my own questions, for a change! It's clear that the book is incorrect. I'll follow this up with Sea & Sea (the camera manufacturers), or the author, if I can contact him. If I get a result, I'll take the liberty of CC'ing it to you, unless you ask me not to do that. Sure. Nastier the better (g). As for the 3.4 foot question - yes, it is commonly recommended that underwater pictures be taken from a max distance of about 4 feet (for the obvious reasons). But it seems that his information is still all wrong, in any case. In the context of UW photography, the 1 foot/1 stop sounds like a rule of thumb that is likely reasonable/workable at that distance. But if it is TTL it will have no effect at all on the exposure. For a manual flash it is perfectly sensible. Thanks again for your answers. I'll print them off & digest them carefully. My pleasure. Cheers, Alan. -- -- rec.photo.equipment.35mm user resource: -- http://www.aliasimages.com/rpe35mmur.htm -- e-meil: there's no such thing as a FreeLunch.-- |
#18
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One thing I noticed while doing flash-exposure studies on slide film
is that you *can* bracket, but only under-bracket, as follows: Wait many seconds for full flash recharge, take a picture. As soon as the red "ready" light comes on, take another picture. The batteries don't have enough time to fully recharge the capacitor, so the second picture is a bit underexposed. This is not precise, and probably depends on your equipment, especially the speedlight and design of the Ready light. |
#19
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One thing I noticed while doing flash-exposure studies on slide film
is that you *can* bracket, but only under-bracket, as follows: Wait many seconds for full flash recharge, take a picture. As soon as the red "ready" light comes on, take another picture. The batteries don't have enough time to fully recharge the capacitor, so the second picture is a bit underexposed. This is not precise, and probably depends on your equipment, especially the speedlight and design of the Ready light. |
#20
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As soon as the red "ready" light comes on, take another picture. The batteries don't have enough time to fully recharge the capacitor, so the second picture is a bit underexposed. This is not precise, and probably depends on your equipment, especially the speedlight and design of the Ready light. The old rule of thumb was: the ready lite came on @ 75-80% of full charge. Bob Hickey |
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