5D MKII - Your Live View Metering Experience and Thoughts ... meter changes with magnify box position?

Just wondering if anyone can explain to me how the live view metering works on the 5D MKII.

I am using it to focus exactly on a fairly close macro shot with a lot of depth of field, too much, so I am shooting 7 shots focused from close to furthest (with a 180mm macro lens), and then combining with Helicon Focus.

The close focus points and further focus points are all over the frame of the picture. So, I move the magnify box to cover the area where I want a particular focus point and magnify it to focus exactly. Then, I move the magnify box to the next further focus point, which may be on the other side of the picture frame, magnify it, and shoot that one, etc., until all shots are completed.

I want to be careful that the exposure level stays about the same as I'm doing this outdoors, in manual metering mode, so I note the level of the manual exposure scale, say, perhaps about 1 stop light for a light colored flower, and I want to keep that exposure level for all the frames shot.

But I find that when I move the magnify box to a different location in the picture, the metering level changes, even though the light did not actually change. Obviously, the position of the magnify box is what is influencing the meter, rather than the overall metering level of the entire frame.

Can anyone explain this behavior to me? How much does the meter read? If I'm not magnifying, it reads one setting, then at 5X, it reads another, then at 10X another? Like a spot meter?

I often have to wait for many long seconds to make sure the subject is motionless, all the while with the magnify box showing it close up, and i want to be able to see if the light may have changed a third of a stop, so I can change the shutter speed and keep the exposure constant for all the frames.

Is there a metering pattern that live view uses? Can it be changed? The histogram only works without the magnifying box, but I would like to use the actual 1/3 stop metering scale and just make sure it stays the same, which is quicker and easier when trying to shoot a lot of shots.

I find that shooting multiple macro shots for combining focus is very difficult. The slightest subject movement and all is for nothing. I want to simplify the metering as much as possible.

If anyone knows any resources like web pages or books that might be helpful in trying to use this multiple shot technique for depth of field, please let me know.

Thanks in advance for any help and suggestions.

Does this have anything to do with Exposure simulation being turned on or off?

In exposure simulation mode the displayed image in the LCD is exactly what the sensor will capture given the exposure settings effective. The reading in LV might be different from normal reading as the camera is using the image sensor to read exposure, this is more accurate than the standard light meter chip that is inside the prism housing.

Thank you for your comments. I'm still trying to figure it out.

It seems like there are three ways to figure out the best exposure:

One, which is probably the best, but doesn't work well if you're in a hurry, is to use the live view histogram, which gets it close, but often lets it over expose a bit.

Then I can use the meter through the viewfinder, the old fashioned way.

Then I can also use the meter reading that is visible in live view.

It seems like the live view meter reading (manual exposure, just reading from the + and - scale) and the meter reading through the viewfinder should be the same, but I often find that they are a bit different, even though the composition and lighting have not changed.

Also, since I am a fairly recent digital convert, I have trouble using the spot meter like I did with film. I know about how to manually control the tonality of a subject, knowing how it would look on Velvia or Provia film. But, now everything has to be "overexposed" some to "ETTR", expose to the right, to avoid noise and get the most photons to the pixels.

If I was shooting a picture of a light colored flower, with film, I would spot meter the flower and manually set exposure so the flower would be about 1 stop light. Now, it seems that it has to be about 1 2/3 stop light by the spot meter to maximize the histogram.

And it seems like effective ISO speed is not the same anymore, compared to film. Actually i haven't tried using the old "Sunny F16" rule. I should try it. I'll bet though that a better exposure from the histogram would be Sunny F11 1/3 or something which would equate to a lower ISO speed.

In live view, the camera seems to be reading the part of the image that fills the monitor, whether it is the full view or the 5X or 10X magnified view. I'm not sure that's what is really happening but it seems like it.