Sharpness issue on 18-55mm and DLSR lenses in 2025

[paperdigits (Mica)]

@europlatus

I assume it’s just a trust-based deal? Is there any way to guarantee you’re not dealing with a scammer?

They have some guards in place, but it isn’t like a business and you’re still dealing with a person. They seem to ban people pretty fast tho

[Tamas_Papp (Tamas K. Papp)]

@Vente

The thing is, it doesn’t always happen and I don’t know why.

Could be field curvature. The article describes how you can test it (eg shoot a field with grass and then see where the sharpness is).

[Vente]

Thanks, I’ll take a look and try the lens before I give up on it

[cedric (Ted Cousins)]

@Tamas_Papp

Could be field curvature . The article describes how you can test it (eg shoot a field with grass and then see where the sharpness is).

Good suggestion which is readily enhanced by Edge Detection combined with the Threshold function in the GIMP.

[Vente]

I haven’t tested my lens yet, but I found that I have more photos of this scene and one of them doesn’t have the sharpness issue, even though it’s the same focal length and aperture. It’s quite likely that I have focused much further.

I remember that I was trying to focus hyperfocal a lot that day, so I would avoid blurry foreground, but the field curvature probably doesn’t really allow for that…

[Vente]

@Vente

I’ll take a look and try the lens before I give up on it

So, uhhhh…

@Vente

I might get the Sigma 17-50 though, I’m not sure yet.

… I got it before trying the kit lens

@Donatzsky

Here’s the Sigma lens on MPB: https://www.mpb.com/en-eu/product/sigma-17-50mm-f-2-8-ex-dc-os-hsm-nikon-fit

Thank you, Nis, for pointing me to MPB! The lens came in a very nice package (the original wasn’t available, oh well). I can see that people at MPB know what they’re doing.

First impressions:

• I thought that the zoom ring is stuck until I noticed a literal “lock” switch on the lens
• The zoom ring is reversed compared to my kit lenses, so far it’s really throwing me off
• F2.8 is GORGEOUS, especially at 50mm close focus
• I’ll need to get used to AF/MF switch being “exclusive” (no manual override in AF mode)

Thanks y’all for tips!

[cedric (Ted Cousins)]

@Vente

Is there any tool that would make it easy to quantify sharpness on an image?

I use Laplace Edge Detection in the GIMP and observe the result. That method is also useful for determining the field of focus of a lens, as has been done by Roger Cicala of Lens Rentals.

Another way is to shoot a five degree Slanted Edge and measure it with e.g. QuickMTF.

Another popular target is the Siemens star …

… and there’s also Concentric Rings.

Yet another way but more complicated is to take a Fast Fourier Transform of the Region Of Interest but good luck assessing the result.

Please respond if there’s interest in any of the above.
Post an image if you would like me to quantify it’s “sharpness” …

[luator (Felix Kloss)]

@Vente

The zoom ring is reversed compared to my kit lenses, so far it’s really throwing me off

That drove me crazy as well when frequently switching between Sigma and Nikon lenses :D.

[cedric (Ted Cousins)]

Good old Nikon. Not to mention the backasswards rotation lens mount as opposed to many other cameras …

[Vente]

@cedric

the backasswards rotation lens mount

That’s at least not a problem for someone with only one camera

[Vente]

Well, what are the chances that two different lenses (kit 18-55 mm and Sigma 17-50 mm) seem to have almost the identical issue?

I found out that the Sigma seems to have the same sharpness problem at around 24 to 32 mm – noticeably softer on the right center side of the frame compared to the left side where most photos are shot at F/8. The center of the frame is always nice and sharp. While focal lengths up 32 mm are always less sharp from center (understandable), it’s the right side that’s often the worst.

It’s the long distance land a cityscape photos that suffer this issue, phots where distances are shorter seem ok.

It feels like the lenses (and especially the Sigma) perform their worst at middle focal lengths, which is the opposite of what I’ve been always told. Any ideas what could be wrong? Was I just unlucky again and got a lens with asymmetrical field curvature?

[Ofnuts]

Did you try after disabling the IS and if possible shooting with a tripod (or with the camera set on something stable)?

[fdw]

Do you get the same result if you focus using live view rather than the viewfinder?

Regards, Freddie.

[Vente]

@Ofnuts

Did you try after disabling the IS and if possible shooting with a tripod (or with the camera set on something stable)?

Yes, it’s not related to motion blur, it’s focus distance related.
See this thread, in some relies I explain what’s actually going on:

Sigma 17-50 mm on D3500 viewfinder AF - weird sharpness issue

I think the lens needs calibration, as nothing through phase-detect AF is properly sharp, no matter where I focus (I mean the cityscape scene). Viewfinder always focuses closer, even at close distances (less than 1 m) compared to live view, so I think calibration is the solution. My best sharpness is through live view (infinity focus in case of the city scape scene). needs calibration There’s a problem with that though. The lens doesn’t support docking and my camera doesn’t support calibrat…

Sigma 17-50 mm on D3500 viewfinder AF - weird sharpness issue

[IMG_20250526_160725] [IMG_20250526_160803] This is what my lens’ focus ring reads when I aim at the same spot in the distance

@fdw

Do you get the same result if you focus using live view rather than the viewfinder?

Regards, Freddie.

Check the link above, viewfinder differs from live view, which suggests a need for calibration.

[fdw]

It is possible that the issue is with the camera especially if two separate lenses are giving you issues. Having to manually focus beyond infinity is a giveaway here.

With that said if you’re shooting landscapes the slow focus speed of live view is unlikely to be a problem and it is almost always more accurate.

Regards, Freddie.

[cedric (Ted Cousins)]

@Vente

Check the link above, viewfinder differs from live view, which suggests a need for calibration.

I just looked up the D7000 in DPReview, it says:

“39 area (9 cross type) TTL phase detection with AF fine tuning”

But I don’t know if you can apply it to just the 17-50mm, not all lenses.

[Vente]

@fdw

t is possible that the issue is with the camera especially if two separate lenses are giving you issues.

Sigma 17-50 and Nikkor 18-55 give differences between live view AF and viewfinder AF, but not Sigma 105 or Nikkor 70-300… now what?

EDIT: in case of 70-300 the difference is extremely tiny, only proper pixel peeping shows a little something different…

To my current knowledge every lens might be off slightly though, so idk, I’d like to be proven wrong if my thinking is wrong.

[cedric (Ted Cousins)]

@cedric

I just looked up the D7000 in DPReview, it says:

“39 area (9 cross type) TTL phase detection with AF fine tuning”

But I don’t know if you can apply it to just the 17-50mm, not all lenses.

It is said that up to 20 individual lenses can be fine-tuned.

[Vente]

D7500 should be able to do that too. Although official website doesn’t mention it, there are tutorials and posts that show the feature…

[paperdigits (Mica)]

@cedric

AI tells me that up to 20 individual lenses can fine-tuned.

I thought we were not doing this anymore.