concise response, sorry I like thorough, I hope that is allowable
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I have, [ among others, check my profile if interested ] both the SMC Pentax-A 50mm F1.4 and SMC Pentax-DA 50mm F1.8
both are fine lenses and I recommend either of them
this article might be of interest:
" . . . Currently Pentax makes three different 50mm lenses: the SMC Pentax FA 50mm F1.4, D FA 50mm F2.8 Macro, and DA 50mm F1.8. All three can be used on digital cameras and the first two are considered full-frame lenses. Although the DA 50mm is marketed as an APS-C-only lens, some speculate that it may also work on full-frame (i.e. film) cameras. There is thread concerning this issue on our forum, but until the issue is finally put to rest we will have to take the position that the lens is to be used only on APS-C digital cameras and is not full-frame compatible. . . . "
Read more at:
Pentax 50mm Prime Lens Shootout Review - Introduction | PentaxForums.com Reviews
unfortunately for our purposes, neither the SMC Pentax-A 50mm F1.4 or the SMC Pentax-A 50mm 1.7 were included but here is the link to the " user reviews " of those lenses:
SMC Pentax-A 50mm F1.4 Reviews - A Prime Lenses - Pentax Lens Reviews & Lens Database SMC Pentax-A 50mm F1.7 Reviews - A Prime Lenses - Pentax Lens Reviews & Lens Database
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the biggest problem for me [ as always caused by " Operator Error " ] is nailing the focus on the 1.4 quickly
so in situations where I am concerned about fast focusing, I tend toward the 1.8
but I keep on trying to improve my focusing skills on the 1.4
the only other difference is the filter size, the 1.4 is 49mm and the 1.8 is 52mm
I have more lenses that use the 49mm than I have that use 52mm