I like to use manual exposure because I find it easier for backeting etc. However, I sometimes find myself confused when using 16 point evaluative metering. Once the meter is active and I am framing a subject, I push the shutter halfway ready to take the shot and the exposure reading changes by as much as 1 1/3 stops on occasions. If I reset the exposure then it appears I am a stop or so out until I am ready to take the shot again. Why such a large discrepancy between readings. What is the meter reading when active, what is the meter reading when shutter halfway and ready to take the shot? I usually select Auto focusing point selection. I have noticed in Tv mode for example with the same shutter speed, there doesn't seem to anything like the same discrepancy. Any comments much appreciated.

-- Andreas Rubin (arubin@iname.com), October 07, 2000

Answers

On page 38 of the EOS 1n owner's manual it states, "...In manual focusing mode, evaluative metering is based on the central focusing point...when the subject is lit by strong backlighting or a narrow beam of light such as a spotlight, we recommend using partial metering or fine spot metering..."

If you place the camera on a tripod, point it at a subject, lock the head down in that position, and then press the shutter half-way, the exposure value should not change on subsequent "half presses" of the shutter button, so long as the lighting and scene doesn't change. One potential source of error can occasionally come from stray light entering the viewfinder when one's eye is away from the camera; using the viewfinder shutter solves this problem.

On the other hand, if you're changing the composition between successive meter readings, then the exposure values may of course change accordingly. Depending on the type of subject, manual shooting mode may be better suited to partial or spot metering.

-- kurt heintzelman (heintzelman.1@osu.edu), October 07, 2000.

For relatively stationary subjects, the use of automatic focusing point selection (AFPS) is often not advisable or necessary. In general, I find AFPS to be useful ONLY when shooting *certain" moving subjects in AI-Servo AF mode. In one shot AF mode, I NEVER use AFPS.

-- kurt heintzelman (heintzelman.1@osu.edu), October 07, 2000.

Thanks for the response. I was refering to Manual exposure mode not manual focusing. However, perhaps the exposure difference between half presses could be linked to AFPS. Perhaps depending on the AFPS the camera has selected it has determined the main subject is something other than a general average exposure over the whole 16 points. I do prefer to use spot metering in general, but on occasions it is useful to get a average reading overall. I used AFPS because quite often the main subject is not right in the centre of the frame. So if I choose a central focusing point only, how much of the exposure determination is based on the central area, and how much on the other 15 points?

-- Andreas Rubin (arubin@iname.com), October 08, 2000.

I screwed up in my quote of the manual--it should say manual "shooting" mode--sorry for the confusion.

-- kurt heintzelman (heintzelman.1@osu.edu), October 08, 2000.