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Promaster 100-400 4.5-6.7 w/ Elan IIe

Tim Robison , Aug 20, 1999; 08:56 p.m.

I recently purchased a used Promaster 100-400 4.5-6.7 lens used at a great price. When on the Elan IIe, at 400 the aperture reading is 5.6. My question is, is the lens actually at 6.7 when I get the 5.6 reading, or should I manually select the 6.7 aperture? This lens is the same as the Vivitar 100-400 and the Phoenix, anybody with experience with this lens would be appreciated if they would share their knowledge...

T. Robison


Jim Strutz , Aug 20, 1999; 10:57 p.m.


This is fairly common with small aperture zooms. They report f:5.6 because most Canon EOS cameras (and others as well) are designed to NOT allow auto focus with smaller apertures. Canon builds them to reliably AF down to f:5.6 and doesn't want people to complain about erratic performance with slower lenses.

In actual practice most EOS bodies will AF as low as f:8, but only if there is sufficient light and contrast. I wouldn't worry about it. AF performance will not be the greatest but the exposure will still be accurate even with the wrong f:stop being reported.

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