Sigma 18-50 f2.8 problems

tarsus · 03-12-2008, 06:59 PM

I recently got the K10D with a Tamron 18-250 and the Sigma 18-50 f2.8 EX DC Marco. No matter what I do, and I have tried every mode and setting the K10D has, the 18-50 comes out fuzzy in some part of or all of the picture in low light. I had high hopes for this lens to shoot theater in low light. Tried it at recent show and not ONE came out. Fuzzy and out of focus. Finally put on the 18-250 and got a few decent shots. Did a test between the 18-50 and my Fuji F30 in low light around my house. The Fuji wiped the floor with the 18-50. That's just not right. Has anyone else had this problem? Any suggestions would be appreciated.

zorobabel · 03-12-2008, 07:56 PM

Is it focusing right? Try to manual focus and see how that goes.

aleonx3 · 03-12-2008, 08:30 PM

I have the same lens bought last year - I don't have the same problem as you described; in fact I am quite happy with it. I use this lens mainly with flash for night shots. See sample picture taken with this lens recently.

IMGP0374 on Flickr - Photo Sharing!

Before I bought this lens last year, I also read some review about quality problems but mostly it is something to do with luck.

blende8 · 03-13-2008, 02:35 AM

Probably the AF of the lens needs to be re-calibrated.
Send it in.

roscot · 03-13-2008, 05:21 AM

Originally Posted by blende8

Probably the AF of the lens needs to be re-calibrated.
Send it in.

Either that or it has decentering or BF/FF issues. How about posting some examples with the exif intact, so we can help you a little better in analyzing the problem.

wavecurrent · 03-13-2008, 05:47 AM

I also have the same lens, but my copy is working with no problems. Only one negative aspect of this lens, the coating of the lenses are not as good as the SMC coating on Pentax lenses!
I have a picture at the bottom of this thread regarding the reflection issues.

Surprising lens flare with Sigma 18-50mm f2.8

Mike

egordon99 · 03-13-2008, 08:00 AM

Samples! We need samples

Depending on how low the light is (and if you're not using flash), you still might not be able to get very fast shutter speeds even at f/2.8 and high ISO. So if you are trying to shoot someone running around on stage at 1/20s, you'll get fuzzy shots.

tarsus · 03-13-2008, 02:06 PM

Thanks for the replies folks. It just might be enough for stage shots, but even around the house it's just not working. Before I send it in, I'm getting together with a guy who is an expert photographer to see if it's just me or I'm pushing it too far. I'll let you know. I've been around the web and found confusing information on back and front focusing and still don'e quite understand what it is. Thanks again.

Gadget_Guy · 03-13-2008, 03:07 PM

I have the same lens and what I find works for me is to use the K10D in P mode and with the rear dial force the camera to F5.6

I also bump up the exposure to a +2

I get nice shots that way.

(I am no pro and am a newbie... this is just me playing around)

D.

tarsus · 03-13-2008, 09:18 PM

Here's an example of what I am getting with 100 percent crop.

Gadget_Guy · 03-13-2008, 09:51 PM

It looks like a depth of field issue.

D.

Talisman39 · 03-13-2008, 10:57 PM

I have this same lens and have not experienced any problems, but it's possible there's an issue with it.

Can you post jpegs with less compression (say, 70% quality setting)? There's so much compression in these it's hard to tell what's going on. Also, since this jpeg has no EXIF data we can't tell what the aperture is and therefore what the likely depth of field is. So we need some more info before we can really diagnose the situation...

However, if the common denominator is that the problem is only coming up in low light situations and is otherwise fine, as you seem to be saying, then it's 99% sure it's plain old camera shake or shallow DOF caused by shooting wide open at slow shutter speeds that's to blame, and the lens is fine. Lenses don't get more or less blurry depending on the amount of light. Do some testing on a sunny day and see if you have the same problem.

I've been really happy with this lens so far, I find that it's very sharp and has great bokeh. Some samples here: Zenfolio | Adam Richardson | Sigma 18-50 Macro

Hope this helps, Adam

tarsus · 03-14-2008, 06:20 AM

Here's the EXIF.

K10D
Aperture Priority
Center Weighted
1/30 Second
Ev Bias None
F 2.8
50mm
ISO 800
Contrast High
Saturation Normal
Sharp High

egordon99 · 03-14-2008, 06:30 AM

Awful JPG compression aside, 1/30s is a little on the slow side with regard to subject motion.

What I think is happening is the camera focused on the spider plant, so that would be sharp, but the woman would be out of focus at f/2.8. Did you have "Auto focus point selection" enabled? Or did you pick the focus point?

Gadget_Guy · 03-14-2008, 06:45 AM

Originally Posted by egordon99

Awful JPG compression aside, 1/30s is a little on the slow side with regard to subject motion.

What I think is happening is the camera focused on the spider plant, so that would be sharp, but the woman would be out of focus at f/2.8. Did you have "Auto focus point selection" enabled? Or did you pick the focus point?

This is why I suggested a DOF issue. The plant is in focus and the woman is not.

Try changing the camera to an F5.6 and try the same shot.

D.