parker@uiucdcs.UUCP (10/31/84)
I have been having problems with the performance of one of my camera
lenses. I have a Sigma 28-80mm zoom lens for a Pentax ME Super. I have
noticed that it consistently yields "dingier" pictures than my other
lenses (Pentax 50mm or Kiron 70-210mm zoom). By "dingier", I mean that
the overall picture is darker and certain colors do not reproduce well.
For example, a yellow-gold color comes out gold-brown.
I was wondering whether this is a characteristic of the lens (Sigma
brand). Or could it be that, because of the optics involved, wide
angle zooms respond in that manner? I have a friend who has a
Vivitar wide angle zoom that yields similar results.
Are there any lenses that do not exhibit this type of problem?
Any info would be appreciated...thanks
Paul Parker
parker@uiucdcsherbie@watdcsu.UUCP (Herb Chong, Computing Services) (11/01/84)
Knowing that Sigma is a reasonably reputable manufacturer, I would tend
to discount the lens as the source of you colour-balance problem directly.
It is possible that flare and other minor aberations in your lens is causing
colors to get muddled together, leading to a muddy appearing image. Zoom
lenses are more prone to this because they have more elements in them.
You do not state whether this has occured with any other lens you own.
It is possible that the film you used was improperly stored and caused
colour shifts. It is also possible that the lab processing your film had
a bad day. Muddy colours also can occur with badly underexposed film, but
this is easily diagnosed by almost pure orange negative and lots of grain
in the print. If colours appear to have mixed in from other parts of the
picture (most noticeable in light colours), it is possible that you are just
getting reflected light that is coloured. Without actually examining
your negatives and prints, it is very difficult to do more than speculate.
It is slightly possible that the aperture coupling to your camera is not
accurate and you are consistently underexposing every picture you take
with that lens.
Herb...
I'm user-friendly -- I don't byte, I nybble....
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BITNET: herbie at watdcs,herbie at watdcsujlg@lanl.ARPA (11/02/84)
> I have been having problems with the performance of one of my camera > lenses. I have a Sigma 28-80mm zoom lens for a Pentax ME Super. I have > noticed that it consistently yields "dingier" pictures than my other > lenses (Pentax 50mm or Kiron 70-210mm zoom). By "dingier", I mean that > the overall picture is darker and certain colors do not reproduce well. > For example, a yellow-gold color comes out gold-brown. Have the aperature linkage in the lense mount checked. This sounds like consistant underexposure to me. Actually a simple check for this would be to purposely overexpose with this lense. Try several different exposures from (say) one to for stops overexposed and see which come out best. If this is the problem, tell your camera repair shop that the lense is consistantly underexposing by 'n' stops. He should be able to work from there. I can't offhand think of anything else that would cause this problem. I guess it could be an obstruction in the lense, or a flaw in the optics not caught be quality control. Any optics experts out there think of other causes?
hartley@uvm-cs.UUCP (Stephen J. Hartley) (11/04/84)
I have a Vivitar 28-80mm f2.8 wide-angle zoom (not the new Series I) and I am pretty disappointed with it. My camera is a Pentax ME Super. First of all, it is not as crisp and sharp as the 50mm f1.7 that came with the camera. But that is to be expected. Overexposing a tad, say one third f-stop, helps brighten up the slide (I shoot Kodachrome 64 and 25 exclusively). The most frustrating and exasperating thing is the performance of the lens at near-to- fully wide open. The corners of the slides are noticably darker that the rest. A lot of the time this is downright ugly, although there are some situations where this effect is useful. I believe this effect comes from the length of the barrel causing the corners of the lense to block light at wide-open apertures. Because of this I will never again buy a wide-angle zoom lens without thoroughly checking the performance of the lens in all kinds of situations. This was the first lens I bought for my camera (other than the standard 50mm), and it was upon the recommendation of a friend who had one. I bought it through the mail sight unseen. Live and learn, I guess. -- "If that's true, then I'm the Pope!" Stephen J. Hartley USENET: decvax!dartvax!uvm-gen!uvm-cs!hartley The University of Vermont CSNET: hartley%uvm@csnet-relay (802) 656-3330
parker@uiucdcs.UUCP (11/07/84)
I tend to doubt that it was lighting conditions...Two of my friends
were taking the same shots (we were doing comparison tests) with
the same film. Each of us had different lenses and two of us got
the "muddy" results.
I will try experimenting with the exposures...A coupling problem
sounds more probable. I have taken shot in which I used three
lenses on the same subject with similar settings. Specifically,
I have taken a number of shot using a 70-210mm Kiron (set at 70mm),
a Pentax 50mm normal, and the Sigma. The first two produce similar
results.
Thanks to all for the responses.
Paul Parker
parker@uiucdcswagner@uw-june (Dave Wagner) (11/13/84)
It was interesting to read that someone else has had problems with vignetting with Vivitar wide angle zooms. I have a Vivitar 28-50 f2.8/3.5 which is a real dog. On the other hand, I now have a Tokina AT28-85 which really gives outstanding performance, considering that it is a zoom (and not a pricey name brand, like Pentax, Olympus, Nikon, etc.). Maybe the guys at Vivitar ought to get their act together? Any comments about this? Dave Wagner U. of Washington Dept. of Comp Sci (wagner@washington)