Thanks Godfrey, for going to all that work. I think I've just reached the point that either the A50, or my attitude, needs an overhaul. I am 100% certain that there is nothing wrong with the lens. Either my eyes, camera, attitude, or a combination of them is my problem. I have had good shots with this lens on the D, but they're more the exception than the rule. I went out after a rainstorm this morning with the D wearing an older (all metal) M50/2 I had just cleaned. 22 shots, all wide open, and not a single seriously mis-focused one. (Good bit of motion blur though!) ;-( Granted the smaller stop is a big help, but it's just strange that I can't do this with the brighter lens. Oh well, ya gotta use what works. ;-)
Thanks again for the tests. Don > -----Original Message----- > From: Godfrey DiGiorgi [mailto:[EMAIL PROTECTED] > Sent: Sunday, September 04, 2005 4:28 PM > To: pentax-discuss@pdml.net > Subject: Re: A50/1.4 versus M50/1.4, Comment Please > > > Don, > > Your tests with the 50mm lenses made me interested to do a little > testing, since I have F50/1.7, A50/1.4, A50/1.7, and A50/2 lenses at > present. I also have a K50/1.4 lens belonging to another PDMLer which > needed a quick test because the box it was shipped in was so crushed > in shipment to me (I'm handing this lens off to yet another PDMLer.. > yeah, complicated). > > I set up the tripod and DS body on my porch, used a set of U-Haul > moving boxes (for their printed matter) at about 10' distance as a > focusing target. My F50/1.7 has been the only "problematic" Pentax > lens on AF I've got ... it is the only one that regularly doesn't > focus smoothly and quickly ... so I started with that. I set aperture > wide open, set exposure via Av for the F and A series lenses, set the > same exposure manually for the K, and made two exposures each: one > focused manually by eye, one focused manually with the 2x magnifier. > I made an additional exposure with the F50 using AF. I wasn't looking > at OOF rendering or other characteristics in this test, just near- > center resolution/contrast and my ability to focus the lenses > accurately. > > The results: > - For all lenses, a noticeable change in focus was seen with the 2x > magnifier when making a focus ring change of less than 10 degrees. > The F50 ring has the shortest turn and is the most sensitive to > change. The focus indicator light is illuminated through 10-15 > degrees turn of the focus ring with all of these lenses, so for f/1.7 > and f/1.4 lenses, it simply cannot be trusted at wide open aperture. > > - F50/1.7 focused very poorly on AF with this target. Out of 5 tries > (set focus on my hand at 20 inches, let refocus on the target), four > were badly defocused, the fifth was passable only. Focused manually, > it produced the sharpest and clearest image. > > - Differences between the A50/1.4 and K50/1.4 are small but > noticeable. The A50 is sharper and more contrasty wide open, lead to > greater focusing accuracy with either eye or magnifier. Both require > some delicacy and patience in setting critical focus... even a tiny > movement of the focus ring can throw them off the best setting. > > - The A50/1.7 was almost the same as the F50, although *slightly* > less contrasty. Perhaps they improved the lens coatings between the A > and F versions at tiny bit? The difference is within my average focus > error, it seems. The A50/2 was also surprising close to the A50/1.7 > on center too, although corners and edges fell off more. > > - The use of the 2x magnifier helps, but it still requires patience > and care to set accurate focus with such a large lens opening at this > distance. Three out of the five sets showed no significant difference > in focusing by eye, vs with the magnifier, one was better and one > slightly worse. That says to me that it helps but only to a limited > degree, at least on this kind of target. > > I would certainly not refer to any of these lenses as "unusable" at > wide open aperture, however. More difficult to focus, yes; not as > desirable on certain types of subject matter, maybe. But all of them > turned a creditable quality image for wide open work, as long as you > make an effort to focus them accurately. > > http://homepage.mac.com/godders/50mm-focus-snips.jpg > > Godfrey > > > On Sep 3, 2005, at 3:13 PM, Don Sanderson wrote: > > > Thanks Rob, that's about what I found on these when on the ist-D. > > It's nice to have the bright finder but if it won't focus for me > > anyway it's no advantage. > > The thing is I never had a problem wide open with the M on film. > > The _good_ thing is the FA50/1.7 seems to really shine when used > > on the digital. > > Live and learn. I happy now and I'm sure someone will enjoy the A. > > > > Don > > > > > > > >> -----Original Message----- > >> From: Robert Whitehouse [mailto:[EMAIL PROTECTED] > >> Sent: Saturday, September 03, 2005 4:52 PM > >> To: pentax-discuss@pdml.net > >> Subject: RE: A50/1.4 versus M50/1.4, Comment Please > >> > >> > >> Don, > >> > >> I also own an "M" 50/1.4 and an "A" 50/1.4. > >> > >> I found that they are both just about un-usable at f1.4 and I > >> wouldn't try > >> unless I am desperate. > >> > >> However, by the time you get to f2.8 they are both fine and at > >> f4.0 they are > >> the sharpest lenses that I have - I know that I can get great > >> results with > >> portraits at f4.0 to f5.6 on both film and digital. > >> > >> Rob W > >> > >> > >> > >> -----Original Message----- > >> From: Don Sanderson [mailto:[EMAIL PROTECTED] > >> Sent: 03 September 2005 02:44 > >> To: PDML > >> Subject: A50/1.4 versus M50/1.4, Comment Please > >> > >> Here is a quick comparison of the "Wide Open" performance of my > >> like new SMCP-A50/1.4 and one of my rather dusty SMCP-M50/1.4 > >> lenses. > >> Both at 1.4, both focused on the mailbox using the in focus > >> indicator, > >> shots within a couple of minutes of each other. > >> Shot just before dusk in indirect light. On the ist-D. > >> JPEG straight from camera, no post processing. > >> Any idea what could be wrong with A? > >> It looks and acts perfect but the image quality below 5.6 hoovers! > >> By 5.6 they're about equal, at 8 and smaller the A wins. :-( > >> > >> http://www.donsauction.com/pdml/A_vs_M.htm > >> > >> Don > >> > >> > > > > >
