My Sigma 10-20 mm for nikon is going past infinity

[sunilmendiratta]

<p>Hi All,</p>

<p>Few days back i purchased sigma 10-20 mm lens and i heard that sigma has quality control issues so to test it i compared shots with nikon 18-55 mm lens and at 100% crop sigma was sharper than nikon. so my lens produce sharp images.</p>

<p>Yesterday i noticed that when i try to focus at far objects my lens distance scale shows past infinity, Is this a problem? I never used lenses with distance scale so i am not sure.<br>

Addition - I use AF all the time, infinity mark is relevent at AF or only in case of manual focus.<br>

Regards,<br /> Sunil</p>

[Dieter Schaefer]

<blockquote>

<p>Is this a problem?</p>

</blockquote>

<p>Quite normal for a lot of AF lenses. But it can be a problem when focusing manually and being used to a hard stop at infinity.</p>

[sunilmendiratta]

<p>Can you please elaborate?</p>

[alex_zepeda]

<p>The long and the short of it is that the focus scale isn't calibrated. The camera's autofocus system can find AF just fine regardless of what the scale says, but you can't rely on the scale (or stop) if you're trying to manually focus on infinity. My Sigma 30 is the same way (actually so are all of my MF lenses, Nikon or not) — course the autofocus on my Sigma 30 still sucks rocks even after getting it back from Sigma.</p>

[Michael R Freeman]

<p>It is very common for autofocus zoom lenses, and some primes, to "focus" beyond the center position of the infinity index mark, particularly if the zoom lens in question is a varifocal design and not a "true zoom" parafocal lens (I have no idea if the Sigma is varifocal). Nevertheless, you should not rely on the physical stop at the end of focus travel with such a lens to set infinity focus. If it "focuses" beyond the infinity index, it is highly unlikely that it will be sharp at infinity if set to the stop. That's not really a quality control issue, but a design issue.<br>

-</p>

 

<blockquote>

<p>"<em>The long and the short of it is that the focus scale isn't calibrated."</em></p>

</blockquote>

<p>Depends on the lens. Some of the Nikon manual focus AiS/Ai primes have focusing scales that are very accurately marked, and can be easily adjusted so that the infinity stop is dead on accurate. But many autofocus lenses certainly have focusing scales that are so compressed they are all but useless.</p>

[sunilmendiratta]

<p>So what do you suggest should i return it and ask for another one, or just leave it and its not worth it?</p>

<p>Regards,<br>

Sunil</p>

[juanparmenides]

<p>"So what do you suggest should i return it and ask for another one, or just leave it and its not worth it?"<br>

Don´t worry about that, I have about 14 , maybe 15 lens at home and every AF lens I have has the same behaviour (it is not a problem) . Even my expensive lenses (Nikkor) do the same. Do not return your Sigma, it is ok. Ah, I forgot, I have the same lens and is sharp when well used.</p>

[kevin_chow1]

<p>To reinforce the above, it is <strong>designed</strong> to focus past infinity. This is normal behaviour - you will probably also find that it focuses slightly closer than the minimum focus distance as well. The AF system <strong>will </strong>correctly find both the infinity and minimum focus points.</p>

<p>If you want to focus manually and your lens doesn't have a printed focusing scale, you might want to "make your own one"; I've done this on my 35mm f/1.8 prime by sticking some address labels around the focus ring and marking on where minimum and maximum are.</p>

[eric_arnold]

<p>sunil, a hard infinity stop is only needed when manual-focusing. as others have noted, its quite normal behavior for an AF lens to not have this. if you were going to do a lot of MF tripod work, you could exchange the sigma for one of the tokina UWAs, like the 11-16 and 12-24, which do have calibrated focus scales and hard infinity stops (FWIW, my tokina 100 macro also has a hard infinity stop, but my sigma 15-30 which i use on FX doesn't). the 12-24 and 11-16 are both quite good, but neither goes to 10mm, which is a meaningful difference on DX.</p>

<p>otherwise, you can focus with AF or just dial up infinity on your lens in the event of manual focusing.</p>

<p>the bottom line here is that your lens produces sharp images and apparently has accurate AF. so there's really no problem and thus no need to over-obsess with imagined shortcomings.</p>

<p>if i were you, i would just continue to use the 10-20 as you have been, because it seems to be fine. one other thing: if you bought the sigma new, because its in their EX line, if you register it on the website you get additional warranty coverage should any actual issues with it develop.</p>

<p> </p>

[alex_zepeda]

<p>Michael: That was actually in reference to the Sigma (altho I expect most modern AF lenses are the same). My MF lenses are closer, but even my CV 58 focuses a bit past infinity. If the OP needs a hard infinity stop, a non USM/HSM/AF-S lens is needed.</p>

[eric_arnold]

<blockquote>

<p>If the OP needs a hard infinity stop, a non USM/HSM/AF-S lens is needed.</p>

</blockquote>

<p>right. well, that would be one of the tokinas. but it's not necessary unless you're shooting in MF a lot.</p>

[sunilmendiratta]

<p>So exchange for another Sigma 10-20 mm will not solve the problem(which may not be a problem at all).<br /> So if i have to manually focus at infinity then how to rely on distance scale, because my lens is not just going 2-3 mm but more than that.</p>

<p>Sunil</p>

[Michael R Freeman]

<blockquote>

<p><em>"... a non USM/HSM/AF-S lens is needed."</em></p>

</blockquote>

<p>That's not necessarily going to help either, since the hard stop on a "screwdriver focus lens" is frequently set "beyond infinity".</p>

<p>The important thing for Sunil to get from this discussion is that there is absolutely nothing wrong with his lens, and the focusing characteristics he is seeing with respect to the distance scale is completely normal. Exchanging the lens for another is not going to solve the problem, because no problem really exists.<br /> -<em> </em></p>

<blockquote>

<p><em>"So if i have to manually focus at infinity then how...</em>"</p>

</blockquote>

<p>When manually focusing, use the focusing screen to determine sharp focus at infinity. That's why DSLRs have an optical viewing system with focusing aids. To assist in focusing a lens manually. You can use the focusing confirmation signal (green dot) to help, or live view if that option is available.</p>

[sunilmendiratta]

<p>Thank you very much all of you for your help. I got the point that distance scale is not (very) reliable for this lens and better to confirm in viewfinder.</p>

<p>Regards,<br /> Sunil</p>

[alex_zepeda]

<p>IMO the viewfinder won't be too much help either (at least not on a DX camera). A split prism helps a bit, but on an ultra-wide lens objects at infinity are going to be very small and discerning proper focus will be difficult. My best advice is to practice a bit and learn where infinity lies (it /may/ be temperature dependent). With an autofocus lens, you can see where the distance scale lands when you focus on infinity and start from there.</p>

[eric_arnold]

<p>doing landscape work on a tripod, as sunil does, is an excellent opportunity to use Live View if precise manual focus is called for.</p>

[Peter_in_PA]

<p>As has been the case for decades, this is mostly a feature of ED (or whatever Sigma calls it) glass in the lens. It can change (as can the lens barrel, according to something I read) it's shape a bit depending on temperature. Therefore, they leave enough "play" in the infinity stop (and I would presume the whole focus scale) to allow for the lens to focus all the way to infinity in any temperature conditions. I believe that you will find that lenses with ED glass focus past infinity and those without often have a hard infinity stop.</p>

[juanparmenides]

<p>I want to add another question: Isn´t easier to hear the AF beep or see the green spot lighted into the viewfinder? All the modern AF will focus a lot better than us, except in very close macro, maybe, but this not the case. Why it matters if infinity mark is aligned or not in a landscape? Don´t you think we all are turning around the same circle? AF works for you, not against you.</p>

[brian_winshell]

<p>{Insert Buzz Lightyear quote here}<br>

I noticed the same thing with my Sigma 10-20mm. It still produced sharp pictures with the autofocus so I got used to it.</p>

 

[alex_zepeda]

<p>Juan: Well this /is/ a Sigma lens we're talking about…</p>