jimfoto Posted July 28, 2007 Share Posted July 28, 2007 I've read threads here regarding ettl issues with great interest. I've been battling the dreaded 2/3 stop underexposure issue when using my 580 ex's as the main light indoors with low ambient light levels. I'm going to try changing my custom flash function to average to see how it works. To date I've just been dialing in +2/3 flash compensation. Here's my question: I've noticed a great variation in exposure depending on my ZOOM level. I've read about the distance issue but nothing regarding zoom. My set up is a 20d body, 580 ex flash and 24-70l lens. When zoomed back (full body) I'm underexposed by 2/3 stop. When I zoom in I go through correct exposure to overexposed by 1/3 to 2/3 stop. Will changing the custom function setting help this? Changing flash compensation after zooming is a royal pain! Link to comment Share on other sites More sharing options...
randy_kurtz Posted July 28, 2007 Share Posted July 28, 2007 What mode are you shooting in TV, AV,P,or Manual? Whats your white balance set on? You can try runing a faster ISO or try manual exposure. If it was me I would shoot in raw and do fine tuning in photoshop to. randy Link to comment Share on other sites More sharing options...
jimfoto Posted July 28, 2007 Author Share Posted July 28, 2007 I shoot in M indoors, typically 1/80 - 1/125 @f3.5-4.5. White balance is typically flash when shooting at iso 100-400. I shoot events (600 images last night over 3 hours) and can't bear the thought of RAW workflow with that number of images. Link to comment Share on other sites More sharing options...
PuppyDigs Posted July 28, 2007 Share Posted July 28, 2007 With my 10D I need to dial in -2/3 FEC. My 20D needs +2/3. Oddly my 5D normally doesn't need any FEC. I haven't noticed any flash exposure variation at different zoom settings. Sometimes the light’s all shining on me. Other times I can barely see. - Robert Hunter Link to comment Share on other sites More sharing options...
randy_kurtz Posted July 28, 2007 Share Posted July 28, 2007 This is my 20D with 580EX and 24-70 2.8 ISO 800, 1/125 and f3.5 in manual and ETTL. Is this what you are seeing? http://s64.photobucket.com/albums/h175/RLKURTZ/?action=view¤t=IMG_9964.jpg http://s64.photobucket.com/albums/h175/RLKURTZ/?action=view¤t=IMG_9965.jpg Link to comment Share on other sites More sharing options...
randy_kurtz Posted July 28, 2007 Share Posted July 28, 2007 Try custom function 14. Link to comment Share on other sites More sharing options...
randy_kurtz Posted July 28, 2007 Share Posted July 28, 2007 Or try setting your 580 ot a manual zoom. Link to comment Share on other sites More sharing options...
jimfoto Posted July 28, 2007 Author Share Posted July 28, 2007 That's pretty much it, Randy, 'cept I'm seeing people, not fish. I plan on trying cf 14. Are you saying leave my flash set at say 50mm? I pull the difusser down which sticks the flash zoom at 14mm and it still does it. Thanks for the help Link to comment Share on other sites More sharing options...
randy_kurtz Posted July 28, 2007 Share Posted July 28, 2007 Jim sorry about the fish photo lol. Link to comment Share on other sites More sharing options...
colinsouthern Posted July 28, 2007 Share Posted July 28, 2007 See if partial metering gives you any improvement. You might also like to give FEL (Flash Exposure Lock) a go. Cheers, Colin Link to comment Share on other sites More sharing options...
doug_landrum Posted July 28, 2007 Share Posted July 28, 2007 You need to understand Canon flash. Here's the best Internet source to learn: http://photonotes.org/articles/eos-flash/ I always use average metering in Custom Function 14. That helps a lot. Link to comment Share on other sites More sharing options...
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