MTF data
Posted 23/05/2008 - 11:47
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I understand the Pentax 16-45mm F4 is really an F2.8-4 lens, but with a cam mechanism to stop it down to provide the constant F4 max ap.
It is therefore not extraordinary that Photozone find its peak resolution is F5.6 at 16mm, and F8 at 45mm. (Center & border averaged).
this is how all constant and near constant aperture zooms work. Since f/ number is the ratio between focal length and aperture, both have to change in concert to keep constant f/4 (or 2.8 or whatever).I understand the Pentax 16-45mm F4 is really an F2.8-4 lens, but with a cam mechanism to stop it down to provide the constant F4 max ap.
It is therefore not extraordinary that Photozone find its peak resolution is F5.6 at 16mm, and F8 at 45mm. (Center & border averaged).
IIRC even the modest FA28-80 3.5-5.6 stops itself down at the wide end when "wide open".
If it didn't, a lens which is f/5.6 at 80mm would of necessity have to be f/2 at 28mm.
you don't have to be mad to post here
but it does help
but it does help
Posted 24/05/2008 - 17:48
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each Pentax lens from the F series onwards contains a ROM chip which has (among other things) the MTF data stored on it. The camera acceses this data via the digital data contact on the lens mount.
this way, the camera doesn't have to be updated every time a new lens comes out, it simply asks the lens.
Thank you, that makes sense!
each Pentax lens from the F series onwards contains a ROM chip which has (among other things) the MTF data stored on it. The camera acceses this data via the digital data contact on the lens mount.
this way, the camera doesn't have to be updated every time a new lens comes out, it simply asks the lens.
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