Coding error?

[rramesh]

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I coded a CV 21mm f/4 Color-Skopar as an Elmarit-M 21mm f/2.8 11134. When I took a picture at f/4 and reviewed the EXIF I see the aperture shown as f/2.8. This is clearly incorrect.

 

Any reasons? See image.

 

http://www.flickr.com/photos/11459470@N05/7031431549/meta/in/photostream/

[stunsworth]

If you are using an M8/9 the aperture is just a guesstimate made by the camera - there is no electrical connection between the body and the lens. Since it's a guess the recorded aperture isn't always accurate - as in this case.

[01af]

I coded a Voigtländer Color-Skopar 21 mm f/4 as an Elmarit-M 21 mm f/2.8 11134. When I took a picture at f/4 and reviewed the EXIF I see the aperture shown as f/2.8. This is clearly incorrect. Any reasons?

The aperture gets estimated by the difference in brightnesses perceived by the TTL metering cell in the camera's bottom and the blue eye at the camera's front. The blue eye has a fixed angle-of-view, the TTL cell's depends on the focal length of the lens.

 

The 21 mm lens has an unusually wide angle-of view ... so in this case, the TTL metering cell sees more than the blue eye. In the picture, the center is dark, and brighter areas are grouped around the center, particularly in the upper middle. I guess the TTL metering cell saw more of the bright parts than the blue eye, so the brightness difference (usually darker behind the lens) was under-estimated, so the aperture got estimated wider than it actually was.

[jaapv]

http://www.l-camera-forum.com/leica-forum/leica-m9-forum/130720-m9-faqs-frequently-asked-questions-answers-2.html#post1725880