Canon 40D exposure issue...

I'd appreciate help or advice with these two images...not the images themselves, but the exposure. Both were taken with a 40D, aperture priority at f4, 24-70L at 24mm, no flash, evaluative metering, auto ISO at 400, RAW, etc. The second was taken 2 seconds after the first. The exposure for the first was 1/1600 s, the second was 1/5000 s. This happened more than once during the day, but this is the most obvious because the scenes are nearly identical and the time between exposures was so short. It was literally click, click and this is what happened. Any ideas? Thanks a lot.
1
http://tnicol.net/potn​/sally_alex_556.jpg

2
http://tnicol.net/potn​/sally_alex_557.jpg

I'm totally lost on subject of exposure when it comes to metering, but that's one tough scene for proper metering. black tux/suits + white dress. Wedding photographers must have one heck of a time post-processing exposures with 40D... I know my 40D exposure is inconsistent like yours, but over a span of at least 4 to 5 shots.

Seems like a drastic difference for evaluative metering.
It would not be surprising if you are using spot or even center weighted metering.

Welcome to photography, bub. You can fiddle with highlight priority mode or all that crap, but the easiest way to fix that exposure is to shoot RAW and adjust it in post processing.

I'd Meter the exposure for the white dress (just barely blow it out) and then bring the detail in the dark suits back out with a RAW processor (In Adobe Camera RAW, the slider would be called 'fill light').

I'm sure more people will chime in.

P.S. I don't set ISO to auto because I don't trust my camera.... its so dumb that it didn't even finish high school!

Was the point of focus the same in both shots

arkphotos - I agree, but I checked and both were metered the same and it was evaluative.

tarzanman - Thanks to you too. I know all that, but the question remains - why, given that scene and identical camera settings, two seconds apart, did I get 1/1600 on the first and 1/5000 on the second? Mysterious...

I can't swear the focus point was the same, but it's close because both are about equally focused.

White dress and black suits on a sunny day are a nightmare, even in evaluative. A slight shift in position can cause the camera to meter more black, or more white and really through off your exposure. The best thing to do in this situation is lock exposure on the grass, or shoot manual.

I dislike Evaluative simply because you do not know what algorithm the meter was following! The only difference I could see was that the overexposed shot had just a bit of a groom's party member at the edge of the frame, and that might have caused Evaluative to bias exposure for those zones.

I use Spot mode simply because both I CHOOSE the target to use for metering, and I CHOOSE how to bias the exposure for that target (when the target is not 18% tonality!) and then I set the camera on Manual so that I absolutely remain in exposure control regardless of what targets enter or leave my frame.

Not to get this into a discussion of relative merits of different metering modes... ah, hell...I will.....

I use evaluative virtually exclusively...why...be​cause I have used it for tens of thousands of shots and I know it well and I also know when and how to use exposure compensation, depending on the scene. I also sometimes will frame the scene differently and lock the meter (1/2 press).

Spot, evaluative etc.... learn how to use one mode, well, as opposed to all 3, more or less.

Exposure is one thing I usually nail every time.

Ok... why the different exposures. How you did it, no idea other than you did not frame the shots even remotely the same when the 2 shots were metered. No real need to explain it further than that.

Those are also a tough combination of subject colors in the same shot, black and white and sky etc. If there was no danger of missng the moment (often one doesn't have time to screw around to make a deliberate exposure) and depending on the lens, I would have filled the frame with the white dress by zooming in or getting close, camera on Manual, Spot, metered, compensated with + EC, reframed by zooming out or walking back and taken the shot.