theoldman Posted December 16, 2003 Share Posted December 16, 2003 Trying to choose a decent flash unit for Elan-7 without going too seriously broke, since my photography is just a hobby. What does it mean when the descriptive info on a flash unit says, among other things: "(Guide No. 139'/42m at 50mm)"? Does it mean the flash is good to 42meters with a 50mm lens? Doesn't sound probable, since it would be difficult for even a good flashlight to illuminate a target at 139-ft... Link to comment Share on other sites More sharing options...
moli_luo Posted December 16, 2003 Share Posted December 16, 2003 The 50mm stands for the zoom on teh flash, since flash heads zoom in and out to maximize flash usage. The guide number is used to calculate distance in conjuction with your aperture. For example, a GN of 42m used at f/2 would give you a max distance of 21m. Divide the GN by aperture to find the coverage. Link to comment Share on other sites More sharing options...
antony_bichon Posted December 16, 2003 Share Posted December 16, 2003 This is a basic flash question that has been answered many times.<BR> Please refer to the below link for some excellent Canon EOS flash documentation.<BR> http://photonotes.org/articles/eos-flash/<BR> <BR> Link to comment Share on other sites More sharing options...
theoldman Posted December 16, 2003 Author Share Posted December 16, 2003 Oh, OK, that's simple enough to understand. Thanks for the response, that seems to be a flash that would be adequate for all my needs. Link to comment Share on other sites More sharing options...
mark u Posted December 16, 2003 Share Posted December 16, 2003 Not sure exactly which flash you are contemplating acquiring,but be sure it doesn't work out more expensive than you expect. Canon specify a trigger voltage of no more than 6 volts. Too high a voltage can fry your body's electronics. I'd recommend you go for the Canon 420 EX Speedlite,which was designed to match an Elan 7 body. Link to comment Share on other sites More sharing options...
jbq Posted December 16, 2003 Share Posted December 16, 2003 K.G. : as surprising as it seems, yes, the flash is powerful enough to give you proper light on a target 42 meters away with a 50mm f/1.0 lens (which happens to be discontinued and very expensive). That's at ISO 100. With ISO 1600 you'd get 4 times the range, 168 meters (550 ft). As somebody said, the guide number needs to be divided by the aperture in order to get the working distance. With the more realistic case of a 50mm f/1.8 lens, with ISO 100 film, the maximum range is 23m. Stop down to f/4 for better sharpness and depth of field and the range falls to 10m. Link to comment Share on other sites More sharing options...
medina photography cherry Posted December 17, 2003 Share Posted December 17, 2003 I had the EOS Elan 7E (until I got my EOS 10D)I used the 420EX (Canon) with that camera and it worked flawlessly. I Then purchased the Sigma EF 500 Super DG to use for wireless setup. The Sigma worked so well and had more manual features that I stopped using the 420EX. As a matter of fact, I sold the Elan 7E and the 420EX and now only have the Sigma. I, of course, would be just as happy with the 550EX, but for the price the Sigma has been more than I could have hoped for. Bottom line....Sigma is a great unit for the EOS system. Link to comment Share on other sites More sharing options...
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