Originally posted by climbertrev Wow!
Is this where Pentax is going?
O.K. Albeit at a loss of 1 fstop, does every APS-C lens become FF? i.e. does the 15mm f4 become 15mm f5.6 on FF?
Originally posted by ElJamoquio Conceptually, yes. A T/C "spreads" the light by a factor of, say, 1.4, very close to the 1.55ish required.
So the lens would be a 21mm f/5.6, with some bad vignetting wide open.
Practically, the T/C could be shrouded , or physically incompatible (glass hits glass). Generally T/C's are optimized for the relatively telecentric long focal length lenses... so performance on ultra wide angles usually isnt good.
The first thing I did when my Pentax 1.4x Teleconverter arrived was to attach it to a Pentax Z-1p film camera. Then I attached various lenses (below) that might be expected to hard-vignette.
None of them showed signs of vignetting,
looking through the viewfinder at a well-lit surface.
This isn't a test of image quality in the corners, just a test of whether there is any image in the corners.
The lenses I tested that apparently didn't hard-vignette at any focal length , showing image right to the corners, were:
DA 10-17mm Fisheye. (Not on the Pentax list of supported lenses!). This hard-vignettes on the Z-1p at 10mm and 12mm without a Teleconverter.
DA 12-24mm. This hard-vignettes badly on the Z-1p at wide angles without a Teleconverter.
DA 17-70mm. This hard-vignettes at all focal lengths on the Z-1p without a Teleconverter.
DA* 60-250mm.
I haven't yet tested any other lenses on the Z-1p with this Teleconverter. I may shoot my last roll of film with a range of lenses using this Teleconverter on the Z-1p to complete
my previous tests of lenses on the Z-1p. That will test image quality in the corners.