21mm on m9 more light

[stump4545]

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just starting shooting with a 21mm for the m9 and i know this might sound crazy, but does a wide angle like a 21mm gather more light per frame then a 50mm would?

 

in the same scene, my 50mm would be at say 1/125 and for the scene but with the 21mm attached at the same fstop i would get a 1/360 shutter speed.

 

why would this be?

[adan]

Are you talking about what the meter reads? And is so, how do the two exposures actually look?

 

A 21 takes in a lot more scenery because of its wide field of view. Outdoors, this may mean the meter "sees" a lot of bright sky. Indoors it may mean spot light sources not "seen" by the narrow view of the 50mm lens are visible to, and affect the metering with, a 21mm..

 

In other words, the M9 has a variable metering area proportional to the wideness of the scene. And you have to be conscious of where you are pointing the camera, metering with different lenses.

 

I note that Leica no longer explains this with diagrams in the M9 instruction manual, although they do so for the film cameras. Here are the diagrams for the M7 - the M9 may be slightly different but the relative metering areas from one lens to the next will be similar.

[stump4545]

thanks for the explanation.

 

i guess the m9 uses more center weight metering with a 21mm and less of a spot metering camera like when using a 50mm/90mm.

 

thanks.

[adan]

i guess the m9 uses more center weight metering with a 21mm and less of a spot metering camera like when using a 50mm/90mm.

 

Well, sort of, yet not exactly.

 

Set an SLR to full-frame metering. Put on a 400mm lens, and while the camera meters the whole finder area, it is only metering a tiny piece of the world (that deer over there in the meadow, that fills the frame with a 400mm lens). Put on a 20mm lens, and the same SLR with the same meter pattern meters the meadow, the sky, the trees - and the deer is only a tiny part of the metering.

 

Changing the lens changes the metering area (even if you don't change the camera's metering pattern). That SLR is metering a "spot" with a 400mm - and a "wide area" with a 20mm.

 

The M9 is no different. It always meters the same part of every picture you will take (roughly a circle, roughly half the height of a horizontal frame). But the picture you will take is NOT "the whole finder" (unless you happen to be using a 28mm lens) - it is only the area surrounded by the framelines for the lens you are using.

 

Basically, using any lens other than a 28mm, you must ignore the finder as a whole, for either composition or metering, and only pay attention to the area marked off by the framelines for your current lens. With a 21, that means the lines in an accesory 21mm viewfinder.

 

Within those lines, the M9 will always be a consistent center-weighted area.

[jaapv]

If you have a scene with highlights in it, the exposure meter will see more of those highlights with a wide-angle lens, tricking the camera into underexposing.