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: [email protected]
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
