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02-27-2008, 09:04 PM   #1
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Surprising lens flare with Sigma 18-50mm f2.8

I just picked up a Sigma 18-50mm f2.8 to replace my kit lens. Nice lens -- sharp and fast, and solidly built. But it has the oddest lens flare.

The shot was a six-second exposure, f8, no UV filter, with the lens hood on to boot. The surface of the lens was clean.

The kit lens didn't do this, and in fact had almost no flare under similar circumstances. Anyone else experience this with Sigmas?



02-27-2008, 10:08 PM   #2
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Very weird. I've been giving that lens some serious consideration, so I'd be interested to know what others have found.
02-27-2008, 10:32 PM   #3
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One would usually see a star pattern with as many spokes as the aperture has blades. At f/8, what's the shape of the aperture opening? Is it irregular in shape which could explain this pattern?
02-27-2008, 10:40 PM   #4
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I've been thinking of getting one of them myself, although in the Sigma mount for my event cam.

Personally I like the picture from an artistic viewpoint, but I wouldn't accept it from my lens

Ole's most likely right about the aperture opening being an irregular shape

02-27-2008, 11:35 PM   #5
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Nice shot. Not normal flare. Try again with different apertures.
If it's not abnormal aperture shape, please let us know what other things you've noticed with this lens.
02-28-2008, 01:29 AM   #6
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Is this the older non-macro version? I've never seen quite that kind of flare on my copy. Also, did you have a filter on the lens?
02-28-2008, 04:43 AM   #7
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Thanks for taking an interest, guys.

To your questions:

The aperture opening is somewhat irregularly-shaped, especially when stopped down. However, the flare exists pretty much to the same degree at f2.8 as at f22.

I haven't noticed anything else odd with the lens. It is a pleasure to use otherwise. For portraits in low light, it is decently sharp. See an example: Flickr

The lens is the older non-macro version, which I got at a significant discount as it was already discontinued. I've no idea if there are differences between the versions that could affect this kind of behaviour.
02-28-2008, 10:56 AM   #8
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is the rear element clean? i'd say give front and rear elements a good cleaning to make sure there's no oil on them.. if it persists, i'd say there might be an issue

02-28-2008, 12:58 PM   #9
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QuoteOriginally posted by Jim Royal Quote
Thanks for taking an interest, guys.

To your questions:

The aperture opening is somewhat irregularly-shaped, especially when stopped down. However, the flare exists pretty much to the same degree at f2.8 as at f22.

I haven't noticed anything else odd with the lens. It is a pleasure to use otherwise. For portraits in low light, it is decently sharp. See an example: Flickr

The lens is the older non-macro version, which I got at a significant discount as it was already discontinued. I've no idea if there are differences between the versions that could affect this kind of behaviour.
Jim,

I just noticed that your Canadian,
If you got this lens New through a Canadian Retailer Gentec would bring it in and at least examine it for you. If they found a problem they'd try their best to either fix it or replace it for you. However being an older model means that there might not be any more available to replace it with.

They're really good, even if they don't answer your e-mail or return your phone call right away.
02-28-2008, 01:15 PM   #10
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Jim,

I believe that Sigma makes at least THREE different 18-50 f/2.8 lenses; may be four different ones, now that they've come out with an HSM version. I have the EX DC MACRO. Which specific one were you shooting with? I've never seen this problem, indeed, it's a pretty decent lens all in all.

Will
02-28-2008, 02:16 PM   #11
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QuoteOriginally posted by WMBP Quote
it's a pretty decent lens all in all.

Will
Thanks for saying that Will, now I won't hesitate ordering one.
I just want it for some close range studio work, and possibly the odd event.
02-28-2008, 02:18 PM   #12
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OniFactor, the lens is spotless. The rear element is so clean it's hard to make out its surface.

Hey, Stu -- nice to run into a fellow Canuk. Unfortunately, I got the lens from Cameta Camera in New York, by mail. So bringing it in for a check will be difficult. I'm not even sure if this is a defect as such.

Will, I believe I have the first edition of this lens -- the 18-50mm EX DC. No macro. You can check to see if your copy of the lens does this by pointing it at a pinpoint light source, such as a halogen lamp, in a relatively dim room.


On reflection, the flare reminds me a lot of the flare generated by certain movie camera lenses. Except that when I see this type of flare in movies, it is always horizontal with respect to the frame.


Last edited by Jim Royal; 03-14-2008 at 04:54 AM.
02-28-2008, 03:31 PM   #13
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I have the I have the EX DC MACRO version of the lens, and the weak spot of it is the reflections as the picture shows, no SMC here like my FA 28-80 F4. It's much better in that respect.

Picture with the sigma, no filter, only lens with hood:

Last edited by wavecurrent; 07-07-2008 at 09:42 AM.
02-29-2008, 11:06 AM   #14
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I managed to get a support person at Sigma to look at my sample photo above, and he believes that there is a manufacturing defect with my copy of the lens. He provided some contact info for me for Gentec, and that's where I'll go next.

Thanks for the feedback, guys.
02-29-2008, 11:22 AM   #15
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That's pretty quick service from them, and good to hear Jim
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