JohnCollins Senior Member  539 posts Likes: 2 Joined Nov 2005 Location: Philadelphia area More info | Feb 25, 2014 20:11 | #1 Guide numbers confuse the dickens out of me because it depends on the zoom setting and not all flash makers use the same formula. It is said that strobes are many times more powerful than speedlites, but nobody gives strobe power in GN.
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TheLoftStudios Goldmember 1,072 posts Likes: 9 Joined Oct 2009 Location: Houston, Texas More info | Feb 25, 2014 20:36 | #2 You will get varying opinions on this ranging from 60ws-85ws... Also depends on what zoom the flash in on also! MARK
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FlashZebra This space available  4,427 posts Joined Mar 2006 Location: Northern Kentucky More info | Feb 25, 2014 20:40 | #3 Frequent and reliable forum member CurtisN has rated the 580EX II at 40Ws. The 580EX (no II designation) would be the same.
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JohnCollins THREAD STARTER Senior Member 539 posts Likes: 2 Joined Nov 2005 Location: Philadelphia area More info | Feb 25, 2014 20:51 | #4 Thanks!
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Wilt Reader's Digest Condensed version of War and Peace [POTN Vol 1]  More info | Mar 09, 2014 09:29 | #5 Be aware that studio flashes are all over the place in terms of efficiency of conversion of electricity to light. Reasons for this include:
Decades ago, softbox manufacturer Chimera published a catalog showing measured (meter) light output from many different brands of '1000 watt-second' studio flash units used in the Chimera softbox. This was a good comparison because the softbox neutralized differences in reflector spread and efficiency of light distribution. In the published results, Brand X might be -1EV less light than Brand A and -0.4EV less than Brand B, for example...ALL of them with '1000 watt-seconds' So if you compared the Canon 580EX to one of them, WHICH one do you equate it to, which 'standard of comparison'?! That is why comparisons are relatively meaningless unless you state which two units are being compared -- the standard of reference becomes some fixed result, not variable (depending upon brand/model chosen) results. Unfortunately, Chimera no longer publishes this catalog...I am sure Brand X complained to them after seeing their unit publicly proclaimed the weakest light output of the bunch!  You need to give me OK to edit your image and repost! Keep POTN alive and well with member support https://photography-on-the.net/forum/donate.php
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LeftHandedBrisket Combating camera shame since 1977...  More info | Here's a video that demonstrates what Wilt is saying. PSA: The above post may contain sarcasm, reply at your own risk | Not in gear database: Auto Sears 50mm 2.0 / 3x CL-360, Nikon SB-28, SunPak auto 322 D, Minolta 20
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