Originally posted by Asahiflex Well, I have a 5D and a K20D, and I can assure you that almost all of my old FF lenses (and I own quite a few lenses, like SMC Takumars (24 up to 200mm), Carl Zeiss Jenas) are doing quite well on FF. I have not noticed weak corners on any of my pictures. But maybe that's because of my shooting style, as I almost never take photos at infinity, and never choose architecture as a subject, so maybe that's why I didn't notice it.
Would I say someting stupid if I say that I'm under the impression that the FF lenses I own work better on the 5D than on the K20D (yes, I know the 5D has less resolution than the K20D).
Don't be too harsh on yourself, you just probably have a failling eyesight, it's normal after a certain age... I must be experiencing similar problems...
No amount of actual experience of using Pentax 24x36 lenses on FF will do... the Truth has been spoken: Pentax lenses aren't up to the task.
Better get along with it, even if you have countless shots that you find quite OK... it's just a question of you having low standards.
Anyway, did you spend enough time measurbating your gear?... didn't think so!
If you're not able to produce a complete set of brick wall tests shots (preferably with direct comparisons with corresponding DA lenses on K-7), what value does your experience carry...?
Anyway, your 5D is now obsolete and that's probably the reason it's performing acceptably with old glass: better drop it all in the trashbin as I just did.