>OK, I did test whether or not an ST-E2 can affect a light meter. My >conclusion is, yes, it does. .....snip.... > >In summary, I conclude that an ST-E2 is equivalent to about a 3 GN (feet, >100 ISO) flash unit, up to about 9', with respect to influence on a light >meter. Now I know why an optical slave plugged into a flash unit will get >prematurely tripped when in the vicinity of an ST-E2. > >Best regards, > >Bill Neukranz
Thanks! So we must keep in mind that if the flash meter is set at very short shutter speed, the premature triggering caused by the trigger-preflash *may* cause the tail of the flash to be not measured. I think I have found this to happen with the measurement-preflash which happens much earlier than the trigger-preflash (if flash is in E-TTL auto mode) but perhaps the trigger-preflash is so close to the main flash that this is a non-issue in manual flash mode. Also, since/if the preflash(es) consists of several short pulses I'm not sure the flash meter measures it exactly correctly (or, why not?). 550EX has GN 180 (105mm, ISO100). I'm not at all sure if the reduced power reduces the GN the same amount but assuming so we could say the ST-E2 is equal to 550EX at 1/32-1/64 power setting (1/64 * GN180 = GN2.8)? This actually looks similar to what I found when I tested my 550EX in master switch on and off positions against a flash meter. At and above 1/8 level the difference between master switch positions was quite small but at 1/64 power level the flash meter gave one full stop higher reading when the master switch was 'on'. So, at small power levels the trigger-preflash from ST-E2 or 550EX may be significant and may make the flash meter useless. I just wish the older EOSes had the same manual flash metering capability as EOS-1D does and I have wished for my '3': set flash in M-mode, point at medium gray, press FEL button and look at the flash exposure scale in the viewfinder to adjust the aperture (or adjust the flash power). No flash meter needed. SOMEONE PLEASE: --------------- I hope someone of you could set the ST-E2 and 550EX side by side pointing at a flash meter and trigger the flash using ST-E2 and 550EX alternately, at different output powers and measure how much in f-stops is the effect of ST-E2 at let's say 3 or 6 feet in each case. THAT would tell what's the effect of ST-E2 in real life. Using umbrellas or softboxes or reflectors would make the situation even worse because in such cases the GN of the flash would be clearly smaller. Vesa _________________________________________________________________ Send and receive Hotmail on your mobile device: http://mobile.msn.com * **** ******* *********************************************************** * For list instructions, including unsubscribe, see: * http://www.a1.nl/phomepag/markerink/eos_list.htm ***********************************************************
