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Sigma highlights another problem with plastics, thermal change



 
 
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  #41  
Old July 4th 12, 01:20 PM posted to rec.photo.digital.slr-systems
Chris Malcolm[_2_]
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Posts: 3,142
Default Sigma highlights another problem with plastics, thermal change

nospam wrote:
In article , Chris Malcolm
wrote:


If as was claimed more than half Sigma's lenses are bad, then a random
sample (e.g. me and friends) of 8 Sigma lenses which are ok is
probabilistically better than 8 heads in a row when spinning a
coin. That's enough to make one wonder whether there is some trickery
going on, enough to make one question whether the original claim about
Sigma unreliability and inconsistency was correct. Not enough to
refute it of course. It's possible to spin 8 heads in a row by lucky
chance. Just pretty unlikely.


how did you test them?


Wide angle lenses, so I did my usual specific tests of gravel beaches,
grass lawns with tape measures laid out on them, gravel beaches, brick
walls, and examined the results carefully with side to side, top to
bottom, edge to centre pixel peeping comparisons. I was surprised how
good they were at f8, I'd have been happy at the price if they'd been
worse. Especially the 8-16mm, which was noticeably sharper at f5.6
than at f8, one of the signs of a rather good lens.

One thing I quickly discovered is that wide angle lenses for various
technical reasons I don't fully understand autofocus poorly with at
least some cameras, including mine, which has given some of these
lenses an undeservedly poor reputation. I always manually focus
them. Which for most shots simply means carefully finding a good
hyperfocal setting and leaving it there.

And I always examine the results of any good shot carefully at pixel
level in difficult or critical areas. That sometimes gives me clues
about new aspects of lens or camera performance. It also sometimes
alerts me to unsuspected damage such as slight decentering.

--
Chris Malcolm

  #42  
Old July 4th 12, 01:34 PM posted to rec.photo.digital.slr-systems
Chris Malcolm[_2_]
external usenet poster
 
Posts: 3,142
Default Sigma highlights another problem with plastics, thermal change

nospam wrote:
In article , Chris Malcolm
wrote:


If Sigma lenses are as bad as they say, I'm surprised that none of the
Sigma lenses I have or are owned and much appreciated by several of my
local photographer friends have given us any problems. That good luck
should have stretched so far if most Sigmas are crap seems stretching
luck and probability rather far. I note when reading lens reviews that
some Sigma lenses seem to have been notoriously troublesome, while
some others seem to be well regarded for build, optical quality, and
consistency.

I wonder, could it possibly be the case that some Sigma lenses are
good and some are bad, and you can find out which are which by
checking reviews etc? Could it possibly be that lensrentals have
fallen out with Sigma over some service issues and are trying to get
their own back? What other lens rental agencies report similar
problems?


sometimes you can get a decent sigma lens but it's a crap shoot.


the reality is that most people don't care. they buy sigma because it's
cheap and they're happy.


very, very few people pixel peep or take pictures of test charts to see
if their lens is functioning properly. if their photos look reasonably
good, then as far as they're concerned, the lens works fine.


True, but I'm not one of those people, nor are my serious photographer
friends. That's why I'm surprised none of us have had these notorious
Sigma problems. Mind you, none of us were foolish enough to buy one of
the kinds of Sigma lenses which do have well documented problems with
our particular camera, e.g. in my case the stronger autofocus motors
in newer DSLRs quickly wearing out the gears in a couple of old Sigma
models which were obviously designed to cope only with the earlier
slower autofocus motors.

While we're on this topic of specific lens models rather than good or
bad manufacturers, there are some really bad cheap Samyang lenses out
there. And there are also some extraordinarily good ones.

--
Chris Malcolm
  #43  
Old July 6th 12, 05:09 PM posted to rec.photo.digital.slr-systems
nospam
external usenet poster
 
Posts: 24,165
Default Sigma highlights another problem with plastics, thermal change

In article , Chris Malcolm
wrote:

the reality is that most people don't care. they buy sigma because it's
cheap and they're happy.


very, very few people pixel peep or take pictures of test charts to see
if their lens is functioning properly. if their photos look reasonably
good, then as far as they're concerned, the lens works fine.


True, but I'm not one of those people, nor are my serious photographer
friends. That's why I'm surprised none of us have had these notorious
Sigma problems. Mind you, none of us were foolish enough to buy one of
the kinds of Sigma lenses which do have well documented problems with
our particular camera, e.g. in my case the stronger autofocus motors
in newer DSLRs quickly wearing out the gears in a couple of old Sigma
models which were obviously designed to cope only with the earlier
slower autofocus motors.


a problem that pretty much only happened to sigma. how often do you
hear of stripped gears with nikon or canon lenses, even with older
lenses that predate the high power focus motors?
 




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