AE of M7 ?

A

alexz

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Usually we know that AE mode utilizes in its fundamentals some kind of center-weighted approach, which means breaking the entire frame area as visilble through VF into segments, metering per each segment, then calculating the average while biased (weighted) more towards the middle frame sections. (say, 60% for center, the rest for other sections).
All that sounds fair when camera imploys metering throughout the entire frame. However, M7 apparently has focusing spot similar to that of M6, i.e. about 25-30% of the frame area and in the middle of such, while the rest is beyond its metering pattern.
So, bearing that in mind, how AE is implemented there ?
 
AFAIK the metering area is the same between M6 TTL and M7. The M7 selects the shutter speed for AE.

Is this what you are asking?
 
Yes, metering area (large spot) is similar to that of M6.
So, if I understood you correctly, M7 just selects shutter speed according to its metering off that large spot, but no any center-weighted consideration or alike ?
 
Yes, it meters off the white area; but that area is what I would call 'center weighted.' It's not matrix metering, segmented, spot, etc. I'd describe it as simply center weighted.
 
I understand.
However, in my assessment I wouldn't call it center-weighted, because there is no weighting involved. In order to be such, the camera would be expecetd to take into account surround areas but in its exposure calculation just give more importance to more centered metering zones.
In our case I'd probaly call it center-metering, but not center-weighted one...
 
OK Alex, if this makes you feel better: the meters on the M6TTL and M7 are remarkably accurate. I tested the meters in both my M7s against my M6TTL and they gave virtually identical readings. IMO the meters in these cameras are excellent. I do carry an incident light meter but I don't use it that often.
 
Thanks Peter.
In fact, I was not questioning M7 meter reliability in AE mode, I'm aware people are quite rave about it. I was wondering just frmo technical point of view.
I used to trust my M6 meter as well - when it was "new" in my hands, I compared it with incident meter in various situations and gained my confidence in its precision.
I used to trust one even for slides.
 
Alexz - If you're shooting slides, then, IMO, you should go to an incident meter rather than use the reflective meter in the M7.

In the M7, set your shutter speed - - then, using the incident meter, compute the f stop for the lens and set it.

You'd be surprised about the number of "Keepers" this will provide, as the M7 shutter, in this mode, is right on. I'm not saying that your keepers will be well-composed, etc.., but that the slide,s per se, will be properly exposed.

George, The Old Fud
 
alexz said:
Yes, metering area (large spot) is similar to that of M6.
So, if I understood you correctly, M7 just selects shutter speed according to its metering off that large spot, but no any center-weighted consideration or alike ?
Click to expand...
Yes, the meter reads the light reflected by the large white spot on the shutter curtain. Due to the laws of optics, the meter probably has a somewhat higher responsiveness to changes at the center of that circle than at the edge. This happens with cameras that read more or all of the shutter curtain, and since the sensitivity is higher at the center of the field, this is termed "center weighted".

I went out looking for a 3-D meter sensitivity map for the M7, as other makers publish, but did not find one. But Leica's M7 manual has a discussion about meter sentivity areas starting about page 100 where it says:
"The metering field covers approx. 23% of the
viewfinder image for the lens being used.
However, the following reference value applies to
all lens focal lengths:
The diameter of the circular metering field is
approx. 2/3 of the short side of the applicable
bright-line frame. This also applies to lenses with
viewfinder attachments, such as the LEICA
ELMARIT-M 135mm f/2.8."
To download a .pdf of the manual go to http://www.leica-camera.us/photography/m_system/m7/

For some interesting discussion about the M7 including metering issues, see http://www.nemeng.com/leica/002bb.shtml

Have fun!
 
Thanks guys.
George, in fact I do shoot slides occasionally and for that used both, my M6 meter and my handheld incident one. The meter in my M6 proved to be very precise and reliable, I had no troubles using it for slides (of course, coupled to my manual adjustment to achiev a proper exposure based on my zone system evaluation). But I more use one (M6 in-camera meter) in kidn of large "spot-meter", just measuring off the uniformly illuminated surface (yields reference exposure) and adjusting manually to obtain a proper exposure.

Doug, yes, I remember the circle in diameter is about 2/3 of side fraem line at any given focal length, I remember it learning thruogh my M6 manual.
 
I've been shooting the M7 for almost 2 years, and have only rarely gotten poor exposures in AE, and then only off by a little. Once you know what to point at, and what is getting metered you are all set.

An easy test is a grey card on a black or white wall- get close enough so the grey card is filling the frame. Back up untill the shutter speed changes- this will give an easy demo of what the metered area is.

I shoot 90% in AE with the M7's, when shooting with the M5 I'm just as accurate, only slower.
 
sepiareverb said:
I've been shooting the M7 for almost 2 years, and have only rarely gotten poor exposures in AE, and then only off by a little. Once you know what to point at, and what is getting metered you are all set.

An easy test is a grey card on a black or white wall- get close enough so the grey card is filling the frame. Back up untill the shutter speed changes- this will give an easy demo of what the metered area is.

I shoot 90% in AE with the M7's, when shooting with the M5 I'm just as accurate, only slower.
Click to expand...

I just tried the gray card test. With a 50mm lens attached the shutter speed changed when the card filled the 75mm frame lines.
 
alexz said:
I understand.
However, in my assessment I wouldn't call it center-weighted, because there is no weighting involved.
Click to expand...
There is no weighting (in technical sense) involved with most any other center-weighted meter. The term refers to uneven readout from metered area, with bias to center zone. In older designs, it is a natural effect of meter's photodiode angle of view, rather than some tricky calculation involving weights. Modern cameras however, possessing a multitude of sensors, might emulate that.
 
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