What's Up With This Lens? Advice Please!

justinitus

justinitus

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Name
Justin
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Hi All

I had a Sigma 18-50 f2.8 which I sold and regretted ever since :cuckoo: so I bought another copy (new) which arrived yesterday.

However, I think I've got a duffer. It's no where near as sharp as my previous copy at f2.8 (I've checked some images from the old lens, although the subjects were different). I showed it to a couple of the guys from the camera club last night and they agreed with me, I just wanted to guage some opinion on here before I ring the dealer again.

Table tripod, timer release, ISO200, 1/50sec, f2.8, centre focus point on M/A white letters (crop):
DSC_5167-Copy.jpg


All the following are centre focus point on the bottom of the pear stalk

Table tripod, timer release, ISO400, 1/40sec, f2.8:
DSC_5201.jpg

Crop of above:
DSC_5201-Copy.jpg


Table tripod, timer release, ISO400, 1/25sec, f4:
DSC_5202.jpg

Crop of above:
DSC_5202-Copy2.jpg


Any ideas? Am I doing something wrong or (as I am thinking) the lens ain't right? Thanks in advance :thumbs:
 
If I read these boards right, then Sigma's do have an issue sometimes. You either get a sharp as a tack copy, or one that is slightly soft

But I may be wrong
 
that really doesnt look right. Maybe rear focusing?:shrug:
 
Certainly doesn't look that sharp considering you've used a tripod, Sigma do have a history of bad quality control on some of there lenses, personally i think i would return it and try out another one in the shop ;)
 
Like pears some versions are softer than others.
Have you got any shots with the other one so we can compear them
If you had kept the other one you would have had a great pear of lenses one soft one hard.

sorry couldnt resist :D

I suppose you could send it back and tell them your not happy with the results

Dave :thumbs:
 
I would test it side by side with another lens of known quality. Identical settings and processing. Looking at single images in isolation is extremely difficult - too many factors at play.

Also, test at a more normal distance. Shooting that close is bringing in lots of other potential errors that may be confusing things.
 
Cameraman said:
Like pears some versions are softer than others.
Have you got any shots with the other one so we can compear them
If you had kept the other one you would have had a great pear of lenses one soft one hard.

sorry couldnt resist :D

Dave :thumbs:
Click to expand...

:lol: nice one!

Thanks for the responses guys.

The shots I have with my old lens are also on a different body (D90) and are not anywhere near the same setup, so I didn't think it was a fair comparison but you know when you get the feeling that the shots aren't top notch..? Never had that with my old lens, heck even at f5.6/50mm my 18-200VR Nikkor is MILES better!

I have tried the AF micro-adjustment on the Pear shot, changing the adjustment by 2 increments each time to as far as +20 and -20 and it gets worse with each step. If anything, the "0" setting is the best of the bunch, which is what you see here.
 
justinitus said:
:lol: nice one!

Thanks for the responses guys.

The shots I have with my old lens are also on a different body (D90) and are not anywhere near the same setup, so I didn't think it was a fair comparison but you know when you get the feeling that the shots aren't top notch..? Never had that with my old lens, heck even at f5.6/50mm my 18-200VR Nikkor is MILES better!

I have tried the AF micro-adjustment on the Pear shot, changing the adjustment by 2 increments each time to as far as +20 and -20 and it gets worse with each step. If anything, the "0" setting is the best of the bunch, which is what you see here.
Click to expand...

I'm guessing that the close distance is what may be pushing the lens outside its optimum design envelope.

Wide zooms are often a bit prone to that, especially f/2.8 versions. Even the legendary Canon 17-55 2.8 is nowhere near its best at that distance.
 
Thanks for that Richard, here's one of Mrs M taken outside handheld (me braced against a column) about 1m away, ISO200, 1/640sec, 50mm f2.8. Single focus point on the join of her lips:

DSC_5128.jpg


DSC_5128-Copy.jpg


I also took a few shots of a ruler @ about 45deg @ f2.8 focussing on the 25cm marking. All were blurry but the 25cm marking was the clearest. I deleted these though :cuckoo: This would rule out front/back focus though right?
 
It's just very hard to tell without a side by side comparison. For example, some sharpening in post processing could transform that image. Maybe.

Compare it against your 35 1.8, both at f/2.8 and then at f/5.6. Subject at least 2m away.

I'm not saying that you have or haven't got a problem, just that all we can do by looking at pics in isolation is guess TBH.
 
Thanks Richard, will try it at lunchtime :thumbs: Don't want to cause the dealer any hassle if it's user error as they have been brilliant in the past!

None of these images have been processed / sharpened - just converted from RAW-Jpeg. The lens/pear shots were from about 50cm away. The only cropping is on the second copy of each image to enlarge the focus point.

I have had dodgy copies of Sigma in the past (10-20mm) but got there in the end. Unfortunately there isn't a dealer in Northern Ireland that stocks the 18-50, so I'm stuck with online :(
 
Gordon Scott said:
It does look a bit soft to me and if it's not as good as you experienced before then I would reject it... where did you buy it from?
Click to expand...

I got it from RGB, who have been brilliant each time I have used them before. Don't want to give them a hard time unless I'm 100% sure, so I'm gonna try Richards idea before I call them.
 
justinitus said:
I got it from RGB, who have been brilliant each time I have used them before. Don't want to give them a hard time unless I'm 100% sure, so I'm gonna try Richards idea before I call them.
Click to expand...

Sure... remember there is only a 7 day window after purchase when they have to take it back for any reason.
 
Mr 18-50 shots seems a lot sharper than this, with a D300s. I have to dial in +8, but they're generally very sharp.
 
Chaz Photos said:
you taking RAW or JPG ? if RAW are you sharping it?
Click to expand...

The lens photo and the photo of the wife were RAW with a straight conversion to Jpeg - no sharpening or anything.

The pear shot was Jpeg in Neutral setting and again no sharpening or anything changed in camera or processing.
 
Kanine said:
Mr 18-50 shots seems a lot sharper than this, with a D300s. I have to dial in +8, but they're generally very sharp.
Click to expand...

These are reputed to be a great lens, if you get a good one! I tried +8 (and all other variations) and it just got worse. Thanks though
 
Gordon Scott said:
Sure... remember there is only a 7 day window after purchase when they have to take it back for any reason.
Click to expand...

Cheers Gordon, although RGB have indeed been great when I need them before - swapped out my D300s for a new one 3 weeks after purchase after I found a slight issue. Even collected it to save me the carriage cost!
 
I have this lens and the image quality is excellent. Looking at your shots compared to a silimar shot I would be able to produce, I would definitely say its faulty. This lens is able to focus quite close, so I don't think the distance to the subject is an issue.
 
justinitus said:
Thanks Richard, will try it at lunchtime :thumbs: Don't want to cause the dealer any hassle if it's user error as they have been brilliant in the past!

None of these images have been processed / sharpened - just converted from RAW-Jpeg. The lens/pear shots were from about 50cm away. The only cropping is on the second copy of each image to enlarge the focus point.

I have had dodgy copies of Sigma in the past (10-20mm) but got there in the end. Unfortunately there isn't a dealer in Northern Ireland that stocks the 18-50, so I'm stuck with online :(
Click to expand...

I don't think it's user error from what you've posted, but you need to be sure before you send it back. Sigma get some bad rep re dodgy copies but I'm not sure it's always justified. Sometimes it is though, and it is always possible that this is a poor copy that has already been returned once...

There are two points here, the first one being is this a good copy, and the second one being, if it is, then is it good enough for you.

I think both questions will be answered by shooting side by side with another lens of known quality, at a more representative distance and both at f/2.8 and f/5.6.

If it then sharpens up to an acceptable level, you might then want to repeat the side by side test again at a much closer distance, to see what difference that makes (if any). I think it might, and this may be entirely typical of even the best copies of this lens. However, if you like to shoot close ups from time to time, and who doesn't, then maybe that's another question.

However, that's all just musing though. First shoot some comparison pics and take a look.
 
justinitus said:
The lens photo and the photo of the wife were RAW with a straight conversion to Jpeg - no sharpening or anything.

The pear shot was Jpeg in Neutral setting and again no sharpening or anything changed in camera or processing.
Click to expand...
All RAW images NEED to be sharpened this is a fact, your JPG will sharpen to what you have the camera set to, what sharping is set?
 
Chaz Photos said:
All RAW images NEED to be sharpened this is a fact, your JPG will sharpen to what you have the camera set to, what sharping is set?
Click to expand...

Yes RAW needs sharpening, but they are not as soft as the OP images... sharpening will help, but that's not the point in this case I think.
 
Give Sigma support a call - I think they are usually very helpful and accommodating, based on what other folk have told me.

Andy
 
Thank you all for you help and advice on this.

I did some comparison tests (propably not really scientific enough though :lol:) against my other lenses but enough to satisfiy myself that this lens is indeed a pants copy.

Have spoken with the dealer again and as before, they were most helpful and the lens is on it's way back for a refund. They did actually offer to take out another new lens, take some shots with it with a D300s and email me the images to ensure I was happy before they sent it which I thought was pretty good, but I think I'll weigh up my options against Sigma/Tamron/Nikon once agan and wait until I'm in England, when I can visit a shop and test one to satisfy myself personally.

Have a good weekend all :thumbs:
 
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