On Apr 10, 2006, at 10:16 AM, Shel Belinkoff wrote:
My apologies if this appears twice on the list. The original
hasn't shown
up yet, and subsequent posts by others have and are already in the
archive.
First I've seen of it. PDML message traffic has been unusually
irregular for several days. For instance, I don't know if the PAW
message I posted four days ago has even been seen by anyone ...
Your questions are a bit more general than I feel comfortable
answering ... I've owned six or seven Pentax AF lenses and they are
much of a sameness to me overall. But I'll comment as I feel
appropriate.
* Are there any AF lenses (FA or otherwise) that definitely focus
faster
than other lenses?
Longer focal lengths generally take more time to focus than shorter
because there's more travel to deal with in the focusing mount.
Internal focusing lenses focus more swiftly than displacement
focusing lenses, front element focusing lenses often focus faster
than internal, etc. It's a matter with several dimensions: the
available power at the focus servo drive, the individual lens'
particular focus throw and friction in its drive mechanism, and the
AF discriminator's interaction with a particular lens' contrast and
resolution when wide open.
* What's the best and the worst autofocus lens you've used (wrt
focusing
speed and accuracy)?
I find focusing performance on my Pentax lenses runs like this from
best to worst:
FA 20-35/4 AL
FA 35/2 AL
FA 135/2.8 IF
FA 50/1.4
F 35-70/3.5-4.5 macro
FA 28-105/3.2-4.5 AL [IF] (now sold)
DA 14/2.8
F 100-300/4.5-5.6
The DA14 and FA28-105 rank relatively poorly not because they are not
quick but because on the DS body they are the two that seemed the
most likely to get close then fail to make AF lock. The F100-300 is
predictably the slowest focusing as it has the longest focal length
and one of the poorest performances optically when wide open. The
other five lenses are extremely close together in performance and
could easily be ordered slightly differently.
* Do lighter weight plastic-bodied lenses focus faster than the
heavier-bodied metal lenses?
I had the FA31/1.8 Ltd and didn't notice anything particularly
special or unusual about its focusing compared to the FA35/2.
* In general, do the DA lenses focus faster or more accurately than FA
lenses?
Can't say as I've noticed a huge difference between the DA14 and
DA16-45 vs the other lenses above. The DA14 like the FA28-105 seems
to get into an ambiguous state more often than others, the 16-45 and
20-35 seem about the same. One of the nice things about the DA lenses
is that they all have the QuickShift focusing feature, which I find
very helpful.
* Which autofocus lenses do you prefer for manual focusing, and why?
I've sold all my manual focus Pentax lenses and upgraded to the AF
versions except for the A50/2.8 macro. I prefer having the AF option
most of the time, even if I focus manually quite a bit anyway. The
reason I kept the A50/2.8 rather than upgrade is that I don't see the
need for AF with a Macro lens. The only AF lens that I find the
manual focusing to be poor with is the FA135/2.8 IF ... its internal
focusing mechanism always feels too loose and is short throw, hard to
be precise with when near infinity setting.
* Are there any things that can be done to improve focusing speed and
accuracy with a given lens?
AF: some folks say they get better focusing by locking to the center
AF sensor or using the manually selected multipoint sensor array. I
find I get just as good performance with fully automatic pattern
focusing and just flip to MF when it's not locking in on what I want
reliably.
MF: Practice. Ignore the focus indicator, turn off the 'hot point'
overlay, use a 2x Magnifier FB when really critical stuff is necessary.
Godfrey
