07-14-2013 05:50 PM
When I use my 580EX flash with my 18-135 STM, the flash only shows 28-105. Is this normal?
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07-15-2013 09:32 AM
07-15-2013 01:29 PM - edited 07-15-2013 01:31 PM
In this case, because you are using the 18-135 on a crop sensor camera, at the wider setting the flash is factoring in the crop and correctly using the 28mm setting. The flash is actually capable of setting slightly wider automatically, but the flash's 28mm setting is the correct setting for this lens zoomed to 18mm on that camera.
But, yes, there is the diffusion panel on the flash, too. That can be manually engaged and is designed to accomodate up to 16 or 17mm wide lens, if memory serves, on a full frame camera. That would be equivalent to a 10 or 11mm lens on your 7D.
At the tele setting, 105mm is simply the longest that the flash goes. You would still see that even if using 200mm, 300mm or even longer lenses on the camera. There are flash extenders available, if you ever need to accomodate a longer lens like these, but I wouldn't bother with 135mm on a 7D.