up until IF lens designs came out all lenses were optimized for a given reproduction ratio. This was usually near infinity as most photos were taken that way. As you focus these lenses closer, the performance drops. That why many early lenses dont focus very close as it was the MFGRs way of keeping the performance high even though they could have easily designed the barrel to focus closer.
Most MACRO lenses are optimized for 1:10 or greater repro rations and thus arent as good at infinity as their regular lenses are. Once floating element IF designs started it was possible for the first time to have ideal performance at any distance. Most, if not all the Pentax dedicated macro lenses are not IF designs however.... JCO > -----Original Message----- > From: Fred [mailto:[EMAIL PROTECTED]] > Sent: Tuesday, September 10, 2002 4:04 PM > To: [EMAIL PROTECTED] > Subject: Re: Favourite K mount normal lens poll > > > > A50 2.8 MACRO IS NOT A "NORMAL" LENS. > > > IT WILL NOT PERFORM AT INFINITY AS > > WELL AS THE OTHERS LISTED WILL. IT'S > > COMPROMISED AT INFINITY FOR BETTER > > CLOSEUP PERFORMANCE. > > I haven't found that to be true, JCO. My A 50/2.8 seems to do quite > well at infinity (at least up to a 5 x 7 - 13cm x 18cm - sized > print, which is the biggest photo taken near infinity with the > 50/2.8 that I can lay my hands on here right now). > > I do know that older macro lenses may have favored macro over > infinity, but I have not myself noticed this with the A 50/2.8, F > 50/2.8, A 100/4, A 100/2.8, or A* 200/4 macros, all of which I have > (or my wife has) used at one time or another at or near infinity. > > (Note that I am not saying this is not true, JCO - I am merely > saying that I have never noticed it.) > > Since I often pack the A 50/2.8 Macro (since it's so nice and > compact, even though I prefer the bulkier A 100/2.8 Macro when I > know I am going to do some macro shooting), and sometimes do have to > press it into service as "the only 50mm lens in the bag", I will > have to look more carefully at infinity focus images taken with it - > as I've said, though, I haven't noticed any "crummy" shots yet > (judging for sharpness, not for composition - <g>). > > Fred > >
