Zerstorer said:That's precisely what is intended, the ambient exposure should be AE-locked on the background.
Let's see this in 2 parts. Camera is metered for background (shutter/aperture is set for correct exposure of background).
Point of focus is however on a person and this subject fills a considerable portion of the frame.(more than a 1/3). The camera then attempts to allocated a greater weightage of flash output control to the TTL sensor that is near the object at point of focus.
When the flash fires, the flash exposure is adjusted only for light that is reflected from the film plane onto the TTL sensor and typically, the one that receives the most light will be given highest priority to avoid blowout. Distance of subject to background is not an issue here, the more important thing is distance of subject to camera.
Under these circumstances, bearing in mind that shutter speeds are already rather high and that FPsync(greatly reduces usable guide number) is being used, there is very little chance of overexposure.
In any case, a normal camera with an autoflash works perfectly using the above method for daylight fill flash(-1ev). So I think there isn't much chance for a TTL based system to misbehave too badly.
I'm pretty confused...........
U mean to say that our camera's TTL sensors are tied to the focus sensor? I always thought it was tied to the exposure settings... in my understanding, if u use evaluative/weighted average metering and the background is substantially brighter than the subject (which is often the case in bright sunlight), then the camera will expose for the background and the TTL sensors will fire at a lower power due to the high ambient light condition..... this leads to correctly exposed background but a dark/black subject.....
But u seem to be saying that in the scenario I painted, the camera meters the background due to higher ambient light from the bright background (as before) while the TTL sensor will meter for the area that the focus is locked on using whichever focus sensor.... is this right? Cos it does not seem to happen for me...... could u read through what i do and point out where it might have gone wrong?
I dun know if I understood u correctly but this is what happens when I shoot under the same condition that I described: There are 2 different ways with 2 very different results..... perhaps u can explain to me what is happening in light of the discussion u had with forbytes..... all shooting done with a TTL Minolta flash without HSS (basically a 3500xi on a Dynax 7)
(1) If I want to shoot a subject to the left of my viewfinder with flash on, I use the left focus spot on the subject and then depress the shutter button halfway... the camera focuses and meters. In this case, I nearly always end up with a underexposed subject cos the camera's evaluative metering system or weighted average metering system (which ever mode I choose) gets fooled by the bright background light........
(2) But if I choose to spot meter the same subject to the left of the same frame, with the flash on, I use the centre focus spot (no choice) then recompose and then shoot.... this of course forces the camera into slow sync mode. Now if the shutter speed drops to a value that is withn the 1/125 limit (no HSS remember), I get a correctly exposed subject with a slightly overblown background (about 1 stop in my guesstimation). If the shutter speed is above the 1/125 limit, my subject is underexposed but not as badly as in the (1) (about 1/2-2/3 stop in my guesstimation). Basically only part of my flash burst (if any at all) gets caught in the film but the lower shutter speed (compared to without slow sync) I think helps with a more decent exposure.....
I understand also that u can compensate by dialing some overexposure..... but as my lens have limited f/stops (like f/5.6 at 135mm on Tamron zoom), if I want a bokeh look, I might be at the limit of my f/stops and ading +3EV is not going help...... cos u can't open up the aperture beyond f/5.6....... so I spot meter to get around the problem........
I hope u understand me and I am coherent......... kekeke......... I'm trying very hard to understand flash photography......... I'm very bad at getting good exposures when the ambient light from the background and subject are very different............
Thanks a lot!