Most people don't care. However I recently acquired, a "new", at least
to me F 70-210 from KEH.com. So I thought I'd post the salient points
of the pros and cons of the two lenses.
First off I think I'll say I don't hate the Sigma, I just don't love it
either and life is too short to put up with things you don't love if no
one is paying you for too.
Physical comparison, the Pentax is about 1/2 inch, (~12mm), longer, only
slightly wider in diameter, and surprisingly not that much heavier than
the Sigma.
The Pentax is mostly metal, and the Sigma is mostly plastic, most of the
weight in both lenses seems to be the glass.
I've partially torn down a F 70-210 Pentax, (and also received back the
remnants of another used as a parts donor), so while looking at it from
the outside it appears to be a much more solid build, there are
decisions on interior construction that aren't quite so confidence
inspiring. I haven't torn down the Sigma but if it's anything like the
plastic Pentax lenses I've had apart, it is, other than in materials,
maybe better built. It would certainly be harder for things to get out
of alignment, (but once they do, in most cases, you might as well throw
the whole mess away).
The Pentax has a very long focus throw, the focus ring is very narrow,
manual focus dampening is relatively light, but not too unpleasant, and
can be very accurate due to the long focus throw. Auto-focus can be slow
if the camera decides to rack the lens from infinity to closest focus.
The Sigma has a much wider manual focus ring, slightly better dampening
and a much shorter focus throw, about 45° as opposed to almost 130° for
the Pentax, so focusing when the Camera decides to rack the lens from
closest focus to infinity is a bit faster. Manual focusing is still
pretty easy to be fairly accurate and one of the things I really like
about the Sigma is, it's, for an auto-focus lens, luxurious wide focus
ring. That said, the K-5II very seldom racked the whole focus length to
find proper focus, except under the dimmest of lighting conditions.
Optically the Pentax is just better, maybe not much, but enough that it
was noticeable. Pretty much at all focal lengths and apertures that I
normally use. I've owned three F 70-210mm lenses and the first was the
best, sharp at all focal lengths, the second was a little soft at around
210mm but still not too bad, the new one is probably somewhere between
the the first and second. The Sigma was never quite as sharp at any
focal length as the second Pentax. Not really bad it could be mostly
corrected in post processing, just not as quite as sharp.
The Pentax focuses closer, the Sigma claims a 1:4.7 reproduction ratio,
(it's written right there on the focusing scale), the Pentax according
to Boz' site has a 1:4 reproduction ratio, it doesn't seem like much of
a difference, but once again it feels noticeable, I was always
frustrated with the Sigma in that regard.
The Sigma is not as flare resistant as the Pentax, or maybe it is in
different ways. It seems to be more prone to veiling flare, so if a
bright light source is even close to being in frame there is a
noticeable loss of contrast and sharpness, the SMC coating on the Pentax
even though 15 years older is much more effective than the Sigma's.
Still it's hard to get actual flair artifacts with either lens at least
on a digital camera. I don't have the dedicated lens hood for the
Sigma, and an after market lens hood was one of those things I kept
putting off buying. I adopted an old Super Takumar lens hood for the
Pentax which works perfectly for the focal lengths on APS-C.
Bokeh is different, but a lot of that has to do with how busy the
background is neither of these lenses will ever be mistaken for being
fast, so that's kind of a non issue. There are lots of other minor
differences, most of which aren't important in the digital era, such as
color rendering more a matter of taste, and easily manipulated in photo
software.
I guess I could go on a lot longer. Let's get to the bottom line.
The Sigma is a real bargain, you can pick one up for less than $40. in
Ex to LN condition, (or as KEH.com would call it Bargain), or for free,
the way I did. Optical and mechanical quality is reasonable, you get a
lot more than your 40 bucks worth. It's so cheap that it's almost not
worth selling it. So I'm not going to. It will sit on the shelf
collecting dust, (as a backup for that inevitable day when something
comes loose in the F 70-210 and I have do decide to repair or replace),
next to my film cameras and actual great lenses I seldom seem to use
because they are inconvenient, (more convenient to use on a Pentax
Digital than if I was a Canon user with a collection of the same
vintage, but still)...
The Pentax is just better, slightly heavier, slightly bigger, mostly
metal with that cool feel of solidity that the K-5II has in the hand.
They don't look like they were made for each other, (in fact F lenses in
that greenish grey color are some of the silliest looking lenses in my
opinion), but they feel like they were made for each other. Sharper at
all focal lengths and f stops, than the Sigma, more flair resistant,
just all around, better, and you can find it /nearly/ as inexpensively
as the Sigma.
--
I don't want to achieve immortality through my work; I want to achieve
immortality through not dying.
-- Woody Allen
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