Go Back   Steve's Digicams Forums > Digital SLR and Interchangeable Lens Cameras > Canon Lenses

Reply
 
Thread Tools Search this Thread
Old May 7, 2006, 6:46 AM   #1
Member
 
Join Date: Dec 2004
Posts: 67
Default

Yesterday, I bought a Sigma 10-20 EX HSM for my EOS 350D (Digital Rebel XT). Today I walked around and sbot some pictures. By examining them on my PC I have noticed significant CA on the LEFT side of the picture but not so strong on the right side. On the other hand, the right side of the picture looks rather soft.

Does anyone have experience with this lense, is it common to show these kind of effects. If yes, how can I minimise it?

Thanks,

fisheye
Attached Images
 
Fisheye is offline   Reply With Quote
Sponsored Links
Old May 7, 2006, 11:58 AM   #2
Senior Member
 
VTphotog's Avatar
 
Join Date: Mar 2005
Location: Extreme Northeastern Vermont, USA
Posts: 4,214
Default

Your picture was apparently too large for posting here, and was truncated at around 600 pixels. You might want to crop the relevant parts and post just them.

From what I was able to see, it looks less like CA than the purple fringing that occurs in high contrast edges in a photo which is over-or-nearly-overexposed.

There is softness on both sides, but definitely worse on the right. Without Exif or shot data, I can only guess, but it appears to be motion blur, probably from torquing the camera while shooting. As to why more on the right than left, it is likely that your shutter travels from left to right, and the camera motion was greater at the end of the shot. This occurs quite often, due to the photographer pressing shutter and immediately moving on to the next picture.

Recommend trying again with camera on tripod. Meter on the sky to avoid blown highlights, and that will help the purple fringing. This may cause underexposure, so bracket, and if necessary, combine exposures with software for High Dynamic Range.

brian
VTphotog is offline   Reply With Quote
Old May 7, 2006, 1:10 PM   #3
Member
 
Join Date: Dec 2004
Posts: 67
Default

Brian,

thanks for your useful suggestion!

The picture is cropped in height to about 1/3 of the original size. The width is still intact. Concerning your idea with the motion blurr I don't think that's was has happened here because the camera settings are to fast (ISO 100, Av 6.3, Tv 1/400) to allow for a motion blurr (beside this I didn't move the camera for the next shot).

Interestingly, almost all of the pictures show the effect of a blurr on the right side. I include another picture, please compare the trees/bushes on the left with the trees/bushes on the right.

Somehow I'm disappointed. I would have expected Sigma to deliver a better quality for that amount of money.

Many thanks,

fisheye
Attached Images
 
Fisheye is offline   Reply With Quote
Old May 7, 2006, 1:12 PM   #4
Administrator
 
Join Date: Jun 2003
Location: Savannah, GA (USA)
Posts: 22,378
Default

What you attachedis 3454 x 601 pixels.

It looks like you tried to resize it without constraining proportions, unless this is a pano from multiple images stiched together.

I see some fringing. But, that's normal in those conditions, especially on the edge of a frame at wider apertures with many lenses. Stop down your aperture a bit (smaller f/stop numbers) and it would probably help some (I can't see what your camera settings were). Make sure to keep an eye on shutter speeds. Most lenses are sharper 2 or 3 stops down from wide open. Try shooting at around f/11 in the same conditions if lighting permits and see if it improves. Fringing is usually a bit worse at zoom extremes also (and I assume you were at 10mm with it).

As for softness, it's hard to judgefrom the resized version. But, it looks like you locked focus on something closer to the camera. Since the right side of the frame contains elements further away, they'd be more out of focus compared to the left side if that's the case.

Focus will also impact fringing.

JimC is offline   Reply With Quote
Old May 7, 2006, 1:19 PM   #5
Administrator
 
Join Date: Jun 2003
Location: Savannah, GA (USA)
Posts: 22,378
Default

P.S.

I see you posted another image while I was posting my comments. So, I didn't see your second image or comments until after I posted.

To check to make sure you don't have a lens problem (or misaligned sensor), use a tripod and shoot some newspaper, making sure the camera is absolutely square to it, using the Center Focus point. I wouldn't be surprised if you were using a different focus point for those photos.

Then, check to make sure the print in all 4 cornersis equally soft. Note that it is normal to see some edge softness with most lenses, especially a lens as wide as this one, and especially at wide open apertures. But, all 4 corners should be equally soft using the center focus point when you're square toa flat target like a newspaper. If not, you've got probably got a lens issue or sensor alignment problem (and if the corners are not equally soft, try a different lens to narrow it down to the camera or lens).

I'm going to move this thread to our Canon Lenses Forum for now.


JimC is offline   Reply With Quote
Old May 7, 2006, 1:33 PM   #6
Member
 
Join Date: Dec 2004
Posts: 67
Default

Thanks everybody for the hints!

I'll try Jim's suggestion tomorrow and in the meantime I post another pictures which in my opinion shows the bias to the left in sharpness.

Thanks,

fisheye


Attached Images
 
Fisheye is offline   Reply With Quote
Old May 7, 2006, 1:46 PM   #7
Member
 
Join Date: Dec 2004
Posts: 67
Default

If anybody is intersted I post some comments I've just seen on some other forums concerning the Sigma 10-20:

"at 10mm right third of the image unacceptable( soft, blurred, defocused )"

"would have been a 10 rating if not that first copy had the common right defocussing issue"

"After shooting some landscape shots mostly stopped down, I noticed some obvious right sided softness/blur in the pictures. At first glance I thought it was an isolated thing. But as I took more pictures I saw a pattern emerging. This closely resembled a known issue with some copies of this lens - decentered lens elements."

"after he tested *3* other copies of the Sigma, they all manifested a simular behaviour which I had described - soft on the right side."


Fisheye is offline   Reply With Quote
Old May 8, 2006, 6:40 PM   #8
Senior Member
 
Join Date: Aug 2003
Posts: 166
Default

Fisheye

It looks like you are having troubles on the left and right sides of the image. The center looks sharp though. I currently have this lens on my 20D, and have no problems. It is sharp all the way across the image, and at all focucal lengths. Now for the F stops, I find that when wide open it is a bit soft. Once I stop it down betweenF8 and F11, it is really sharp and great depth of field. A good copy of this lens should be able to keep up with the highly followed Canon 17-40mm F4 L. Mine does, and I perfer it over the Canon.

What are your settings for these images? Have you tried to stop the lens down? Also, do you have a UV or Skylight filter on or any other filter? Are their any marks on the front element?

How does your camera work with any other lens?

I have read about others having problems with this lens, but it is a great little lens. Is it possible that you can take it back to the shop that you bought if from and test another before you leave? If that is not possible, contact Sigma and have them calibrate it for you. They are quick and fast about it.

Here is an image from my 20D and Sigma 10-20mm EXthat I took a few weeks ago on a trip. This is at 10mm and F10.
Attached Images
 
Speedie is offline   Reply With Quote
Old May 8, 2006, 10:56 PM   #9
Member
 
Join Date: Dec 2004
Posts: 67
Default

Speedie,

thanks for the picture, this is what I would have expected from a $400 lens!

Regarding your questions: the image was taken an F8 1/300 ISO 100 with no filter attached. The front element is perfectly okay as is the rest of the lens (at least from looking at it from outside). My camera works fine with all other lenses (18-55 kit lens and 70-300 sigma apo)

Yesterday, I brought it back to the dealer and he will get a new one for me on Thursday. Although he denied that Sigma 10-22 generally has problems he acknowledged that somethings could be wrong with my lens.

Before accepting the new lens on Thursday I will thorougly check it.

Thanks,

fisheye
Fisheye is offline   Reply With Quote
Old May 9, 2006, 1:31 PM   #10
NHL
Senior Member
 
NHL's Avatar
 
Join Date: Jun 2002
Location: 39.18776, -77.311353333333
Posts: 11,545
Default

Fisheye

The problem you're having with the 10-20 is typical of most superwide... (especially up close)

You're standing on the left side of the street, hence:
1. The distance to the left is less than the distance to the right
2. The camera is focusing on something way down the street
3. The superwide capture the right side way more OOF because of 1+2

Next time you do the test, try to be in the middle of the street, and focus on something closer (in the line of cars), the DOF will then cover you to infinity and then both the L+R will be equidistant (and in focus)
-> Closing down the aperture just buy you more DOF
NHL is offline   Reply With Quote
 
Reply


Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off



All times are GMT -5. The time now is 7:34 PM.