D80 metering comparision DX vs Sigma

Started Apr 12, 2007 | Discussions thread
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kuma37 Regular Member • Posts: 130
D80 metering comparision DX vs Sigma

I had been straging with the unstable D80 matrix metering for more than
3 months. And noticed that with DX lense (VR18-200), the
over exposure is not excessive compared to Sigma 17-70 MACRO.

To confirm my observation, I did a simple test.
What I did is to take a same scene using 2 lenses varing the
diaphragm. It was completely sunny day, and I carefully
placed the camera to take almost same scene, and all the shots
are taken within 2 minuts.

As I expected SIGMA images were alywas obviously ove exposed
and brighter than Nikkor, and the EXIF data were as follows.

F SS (SIGMA) SS (Nikkor)
4.5 1/200 1/250
5.0 1/160 1/200
5.6 1/125 1/160
6.3 1/100 1/125
7.1 1/80 1/100
8.0 1/60 1/80
9.0 1/50 1/60
10.0 1/40 1/50
11.0 1/30 1/40

As you can see, SIGMA alwasy over exposes around 1/4 steps.

I am not sure why this big diffenrece happens.

Is this because 3D metering system uses differenet
algorythms for the dirrenet lense type?

Or is this because the real speed of the lense is not
fully described by "F-value" but "T-value"??

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