Originally posted by Class A On the one hand you have a point and at f/8 the Super Tak is even better than the HD D-FA* (provided the measurements have been done under the same conditions), but on the other hand there is
HUGE (as in "gianormous") difference in achieving a certain performance level at f/1.4 vs f/8 (the latter being the aperture the Super Tak needs to be stopped down to in order to reach the performance of the HD D-FA* wide open! It becomes non-linearly harder to achieve good performance the larger the aperture becomes. That's the reason why the HD D-FA* is so big and heavy.
I'm glad the Pentax engineers optimised the HD D-FA* for large apertures (it doesn't even stop down to f/22). In my usage so far, I don't think I ever stopped down beyond f/2.8.
Oh no, I'm doomed.
Technically you are 100% right. But think about practical use - if you are wanting the f1.4 stuff you know that only a small proportion of your image is going to be in the dof plane and it is likely the corners are not within the dof plane so the quality of the oof is more important there.
And apart from astro stuff you are not likely to have the need to be at the wide end for infinity work where drop off in the corners is more apparent.
I was really surprised at the Ephotozine results but also they totally reflect what we think of the 55 f2 vs the 50 1.4.
When I saw the charts I immediately knew why I always reached for the fast 50s in my arsenal.
Absolutely not trying to dis the FA* (just blimmin envious) so congratulations and don't waste post 10000 growling at me!.
EDIT Dang - missed it. Good on ya Tom and thank you for making this niche in PF. Pentax Forums has taken me from a greenhorn newbie to a know-it -all old git in 7 years. And without the Kiwi thread giving me confidence I would never had gotten so involved.