21st October 2003, 11:54 AM
External Flash with DSLR 1.6x multiplier
After reading henavs thread, http://forums.clubsnap.org/showthrea...threadid=48902, i was wondering how do an external flash determine the focal length of a DSLR with a 1.6x multiplier. Canon's 420ex covers 24-105mm range, so if the focal length is 18mm on an EF-S, will it be 18*1.6=28.8mm or 18mm? Will dark corners exist on the photos if i bounce the flash at the focal length?
21st October 2003, 12:05 PM
if i am correct,
if u set your lens to Xmm and rely on the flash units auto zoom head, it will zoom to Xmm for you. however if you manually set your flash head to (X x 1.6)mm, it will still expose as correct. setting it at auto X mm only wastes the light at the edges which are cropped out due to the 1.6 multiplier
not familiar with canno, but i guess that the 420 ex in ur case would adjust itself to its widest setting, ie 28mm.
Originally Posted by likefunyouare
21st October 2003, 12:21 PM
From my own experience, since most Digital SLRs is based on film SLRs, the zoom head in a flash responds to the "real" focal length of the lens.
This means that if you set your lens at 80mm, the zoom head will also set at 80mm (provided there is 80mm zoom setting in your flash). There will not be any dark corners since your lens' 80mm actually has smaller angle of view (around 120mm of normal lens, if the cropping factor is 1.5x). However, sometimes I take that as a disadvantage as I could get more GN if the flash's zoom head is set at 120mm.
The case will be different with the "built from scratch" digital camera. Take Minolta DiMage 7Hi, for instance, if you set the lens at 28mm equivalent, or true 7mm, the flash will set its zoom head at 24mm. Not 28mm because the flash was originally designed for film (Dynax) cameras that have 2:3 width-height image ratio, unline 7Hi's 3:4 ratio.
Hope this helps.
21st October 2003, 12:41 PM
you can always manually set the zoom setting on ur flash head.
Originally Posted by MrBram
21st October 2003, 01:24 PM
the 420ex do not have any manual controls and it will automatically adjust its zoom head according to the true focal length of the lens. thanks for confirming this, guys.
21st October 2003, 02:59 PM
because the frame is cropped, you can set zoom range to its equivalent (x1.5 multiplier). thus saving power on the flash batteries... but its troublesome...just allow the zoom head (if you have one) to do its thing... no problems...