Is my Sigma 50 f/1.4 focusing ok? EDIT: Lens is back from repairs!

996GT2

Diamond Member
Jun 23, 2005
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I just got my Sigmalux in the mail today! Needless to say, I was very excited and immediately got my 5D out for some test shots. Initially, it seemed like my copy was front focusing. However, after shooting some more test shots, I got the following results which seem to indicate that the lens is ok?

I'm confused. Can anyone help interpret these results for me? I'm not really sure whether it would be useful to send this copy back to Sigma for calibration.

These were taken at ~1.75 ft focusing distance:

First, the shot that made me suspect a bit of backfocusing. This was taken at f/1.4. To me, it seems like the handgrip on the camera is sharper than the point I focused on (the word "Leica").
TestShot.jpg


I took some test charts after that, but I'm not really sure what to make of the results...

f/1.4:
f1_4.jpg


f/1.6:
f1_6.jpg


f/1.8:
f1_8.jpg


f/2:
f2_0.jpg


f/2.2:
f2_2.jpg


f/2.5:
f2_5.jpg


f/2.8:

f2_8.jpg


And a shot of the basic setup for the test charts. I used one off-camera speedlight through a 45" umbrella to light the chart.
P1030952.jpg


As a side note, Sigma finally decided to get rid of their crinkle coating that was formerly applied to all EX series lenses! Here's how mine looks:
SigmaLensFinish.jpg
 
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PurdueRy

Lifer
Nov 12, 2004
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I believe what you are seeing here is the focus shift problem known to exist in these lenses. Overall though the focus looks good to me. A couple slightly front focused and a couple slight back focused but the center focus spot is always pretty acceptable in sharpness.
 

Aharami

Lifer
Aug 31, 2001
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i think your's is ok. I recently got one too. Mine front focused slightly (using the same exact method as you). I actually drove mine in to the Sigma repair center in Long Island, NY (about 2 hrs away from me). The guy there was extremely nice and not only did he adjust my 50mm f/1.4, but also adjusted my 10-20mm f/4-5.6. Both lenses are tack sharp now, even at wide open, but now I'm noticing a slight creaking noise coming from the focus ring of the 50mm. Not sure if I should send it back in case the focus gets shifted again
 

996GT2

Diamond Member
Jun 23, 2005
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i think your's is ok. I recently got one too. Mine front focused slightly (using the same exact method as you). I actually drove mine in to the Sigma repair center in Long Island, NY (about 2 hrs away from me). The guy there was extremely nice and not only did he adjust my 50mm f/1.4, but also adjusted my 10-20mm f/4-5.6. Both lenses are tack sharp now, even at wide open, but now I'm noticing a slight creaking noise coming from the focus ring of the 50mm. Not sure if I should send it back in case the focus gets shifted again

The strange thing is that many of my shots at f/1.4 come out kinda soft, which would indicate a focus problem that the chart doesn't reveal. For example, in the first picture of the point and shoot camera, the word Leica is softer than other parts of the picture, which leads me to suspect a slight focusing issue.
 

jpeyton

Moderator in SFF, Notebooks, Pre-Built/Barebones
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Aug 23, 2003
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Go out into the real world and shoot some pictures wide-open. If it's still soft, send it in for calibration.
 

996GT2

Diamond Member
Jun 23, 2005
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Go out into the real world and shoot some pictures wide-open. If it's still soft, send it in for calibration.

Did that yesterday, but it was at night so it was harder to judge sharpness. Will take it out for a shoot when I get off work today.
 

Aharami

Lifer
Aug 31, 2001
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i think that's just the way the lens is. at 1.4, hard edges are kinda soft, which sharpens up considerably at 1.8. I think this is called the 'dreamy look' most were using to describe this lens and the canon 50 1.4 at wide open. Although calibration got rid of this somewhat, I still have this issue at 1.4. doesn't bother me too much

I will post some before and after calibration pics tonight
 

Maximus96

Diamond Member
Nov 9, 2000
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the new coating looks nice. i never liked their old EX series coating but looks like its still there on the focus ring, no?
 

Aharami

Lifer
Aug 31, 2001
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btw, did you get that desk from Ikea? I think it's actually a TV stand. I think I have the same exact thing. I had to do a double take since my 'testing setup' looks exactly the same
 

jpeyton

Moderator in SFF, Notebooks, Pre-Built/Barebones
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Aug 23, 2003
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I remember when I bought mine, I went crazy with focus charts as well.

But when I took it out to actually take some shots, it was great.

The HSM focusing is very fast, but also very twitchy; keep that in mind. Listen to the lens and make sure it's locked on focus before squeezing the shutter.
 
Feb 19, 2001
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Ok. I'm a focus Nazi.

I think your lens is front focused at f/1.4, but you also see the focus shift phenomenon where focus is done at f/1.4 but when your lens stops down to take the shot, the focus shifts. I thought the Sigmalux lens was not as prone to focus shift issues as say the 50/1.2 which has blatant focus shift issues.

I would get it calibrated.

When I got my Tokina 11-16 and I posted this on POTN, people were like don't worry. I can see why.

a) It's not much of a backfocus
b) It's a UWA so you're not gonna have extreme DOF issues like shooting a 85/1.2 and not having the eyes in focus.

841280401_th6yG-X2.jpg

You can compare the far and near numbers. Compare the -20mm with the 20mm. Or even -20mm with the +40mm. Interesting. Even if you use a DOF calculator and you see that usually front focus and back focus different, but never an insane like 50 percent difference. Well here you have it. My lens was like 10mm backfocused IMO or something like that.

But I was never satisfied. I sent it back after comparing to my 17-55 which I deem to be perfect. I got my new 11-16 and it was picture perfect ON THE DOT.

You can fix the calibration at f/1.4 which I would do by sending it back, but focus shift? I dunno about that.

Also the MFD is like 17" for this lens right? I read that under 2 ft or was it 5 ft that this lens suffers from a lot of focus issues. Between 5-20feet where you will be shooting with this lens, it should work flawlessly.
 
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Aharami

Lifer
Aug 31, 2001
21,294
148
106
Ok. I'm a focus Nazi.

I think your lens is front focused at f/1.4, but you also see the focus shift phenomenon where focus is done at f/1.4 but when your lens stops down to take the shot, the focus shifts. I thought the Sigmalux lens was not as prone to focus shift issues as say the 50/1.2 which has blatant focus shift issues.

I would get it calibrated.

When I got my Tokina 11-16 and I posted this on POTN, people were like don't worry. I can see why.

a) It's not much of a backfocus
b) It's a UWA so you're not gonna have extreme DOF issues like shooting a 85/1.2 and not having the eyes in focus.

841280401_th6yG-X2.jpg

You can compare the far and near numbers. Compare the -20mm with the 20mm. Or even -20mm with the +40mm. Interesting. Even if you use a DOF calculator and you see that usually front focus and back focus different, but never an insane like 50 percent difference. Well here you have it. My lens was like 10mm backfocused IMO or something like that.

But I was never satisfied. I sent it back after comparing to my 17-55 which I deem to be perfect. I got my new 11-16 and it was picture perfect ON THE DOT.

You can fix the calibration at f/1.4 which I would do by sending it back, but focus shift? I dunno about that.

Also the MFD is like 17" for this lens right? I read that under 2 ft or was it 5 ft that this lens suffers from a lot of focus issues. Between 5-20feet where you will be shooting with this lens, it should work flawlessly.

My Tokina 11-16 front focuses a little bit too. But I never see it in real world shots because, like you said, an UWA is not gonna have extreme DoF. Also I shoot mainly in f/8-11 with my Tokina anyways.

But maybe I should send it in just in case. How was your experience with Tokina's service?
 

slashbinslashbash

Golden Member
Feb 29, 2004
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IMO it is damn hard to tell. f/1.6 and f/2 look great but f/1.8 looks worse. At these distances, focal length, and apertures, we should have close to 50/50 front/back from the focal plane. I.e. if 2mm is in focus forward, 2mm should be in focus backward. Up through f/2.8 it is like 49% back 51% forward, which is small enough difference that it should look the exact same front and back. DOF calculator.

Did you use the same focus for each of these photos? I.e., AF for the first shot, then turn the lens to manual focusing for all the other shots? Because it looks like your focus is shifting a bit, and that could be due to AF moving slightly back or forward, i.e. to the front edge or the back edge of the thick black bar.

BTW, just so we have the terminology down. Front focusing is when it focuses in front of the subject, i.e. closer to you/the camera/the lens. Back focusing is when it focuses behind the subject, farther from the camera/lens/you.
 

jpeyton

Moderator in SFF, Notebooks, Pre-Built/Barebones
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Aug 23, 2003
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The Sigma does have focus shift, but that wasn't a problem for me because I set my aperture first before focusing.

BTW, are you focusing using Live View contrast detect or using phase detect? Contrast Detect AF should ALWAYS be dead on, since it doesn't use your AF sensors.
 

996GT2

Diamond Member
Jun 23, 2005
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He's got a 5D, so no Live View.

Yep. I took more test shots indoors and outdoors, and it seems decidedly soft at the larger apertures. Since I bought this lens to use it wide-open, I sent it back to Sigma today along with a description of the issue and some sample images. Hopefully they'll be able to correct the focusing at f/1.4 without causing it to misfocus at the smaller apertures (f/2 and smaller).

What's Sigma's turnaround time usually like for calibrations? I'm located in Baltimore, which is not too far from their NY service center.
 

996GT2

Diamond Member
Jun 23, 2005
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btw, did you get that desk from Ikea? I think it's actually a TV stand. I think I have the same exact thing. I had to do a double take since my 'testing setup' looks exactly the same

Haha I got it for free when some people moved off campus. I think it is from IKEA though, since I got it in a batch along with some other IKEA stuff. I use it as a small table to put random stuff on (or do lens tests with)
 
Feb 19, 2001
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My Tokina 11-16 front focuses a little bit too. But I never see it in real world shots because, like you said, an UWA is not gonna have extreme DoF. Also I shoot mainly in f/8-11 with my Tokina anyways.

But maybe I should send it in just in case. How was your experience with Tokina's service?

I didn't send it into Tokina unfortunately. I sent it into the retailer who returned me a new lens in 1 week. I tested it and as a super anal retentive focus tester, I found it to be spot on the dot... I almost creamed my pants... haha.

How much difference would it have made? probably none in real world shooting :D

I asked about Tokina on POTN forums but no one seems to have provided any feedback about their warranty service.
 

996GT2

Diamond Member
Jun 23, 2005
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Sigmalux got back from repair today. Very quick turnaround...exactly 7 days from the day that I sent it in.

They adjusted the AF, and it seems to be focusing accurately now. Here's a recent shot I took at f/1.4 for a a newsletter article:

IMG_4740.jpg


100% crop:
IMG_4740Crop.jpg


Pretty sharp for f/1.4, no?