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10-09-2007, 02:22 AM   #1
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Voigtlander SL lenses - Infinity focus question

Hello fellow Voigtlandarians... or however that goes. I have now had the chance to get used to my CV 125 and will receive my 180 tomorrow, but I've noticed something about the 125 that I wonder about.

With its infinity focus, I've discovered you must very slightly touch the focus back from fully retracted in order to gain proper infinity focus. I have samples of success with its (now) very crisp infinity focus, and of what happens if you just roll it back to the very end and try a shot.

Heres an unadjusted, fully retracted infinty shot -


And the exact same shot but just touching the focus out a tiny amount (really tiny, an almost imperceptible nudge) -


Its really a massive difference. To be honest, at first I thought my lens wasn't right, but once I discovered this, and shot these -





...then I was happy again.

So my question is - is this normal? If so, why? Should/can I send it in for an adjustment? Do all CV lenses exhibit this?

Thanks.

10-09-2007, 03:01 AM   #2
and
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I dont know about your question, I dont own this lens, but looking at the other pictures you posted here I feel even more like getting it. Too bad its discontinued because I dont want to go with this lens for my next purchase but I wish it would be available later on. It sure is sweeeeeet, fantastic sharpness and clarity in those mountain shots.
10-09-2007, 03:42 AM   #3
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It could be your camera too. Believe it or not, many modern cameras (applies to AF lenses too) are calibrated to focus slightly beyond infinity. Whether they were designed that way or loose QC I don't know. But as long as the focus screen agrees with the film plane (CCD in this case), the camera is considered fine. What this means is that one can never rely on the lens infinity mark anymore . But this is old news, isn't it?
10-09-2007, 05:02 AM   #4
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This is normal. It is done for two reasons, first becasse every lens will be ever so slightly different and each lens would have to be calibrated individually think of that slight turn that it takes to get your lens into focus now imagine having to do that for every lens that comes out of a factory and then having a precise enough stop so that the lens stops exactly there....not very efficient.

Now the first reason is simply a matter of manufacturing efficiency, but here's the thing even if you had a perfectly calibrated lens it wouldn't matter because it would only be perfect at the temperature at which it was calibrated because as the elements and body (particularly the metal found in older lenses) of the lens expand and contract the focus changes as well. This is the real reason that lenses focus beyond infinity.

Getting infinity focus is no more difficult than focusing on anything else be it autofocus or manual, except for one thing, as you have discovered once you overshoot infinity IQ drops very quickly.

If you're looking for something that you can set without looking through the viewfinder to make sure everything is sharp keep in mind the concept of hyperfocal distance.

10-09-2007, 06:30 AM   #5
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QuoteOriginally posted by thePiRaTE!! Quote
With its infinity focus, I've discovered you must very slightly touch the focus back from fully retracted in order to gain proper infinity focus.
I just want to add to the previous arguments the fact that many long focus and telephoto lenses are designed to focus a bit past infinity to allow for thermal expansion of the metal used for the lens barrel. But the barrel of 125/2.5 is hardly long enough to make thermal expansion an issue. And it doesn't seem that my copy of the lens exhibits this behavior either (cannot be 100% sure, because it's nighttime here and it's quite difficult to focus accurately in the dark), so maybe you'd better have the lens checked.

Cheers,
10-09-2007, 08:49 AM   #6
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The reasons explained for it all make perfect sense, thank you for your contributions, yet as Abbazz has explained, I haven't noted this characteristic with any of my other lenses, new or old. I am to receive the 180/4 today, I guess if it exhibits the trait also, I'll suspect it to be a factory setting rather than an error.

The lens still works great and I'm very pleased with the IQ, but I missed a few shots in the weekends batch at infinity which I hadn't had happen with other MF lenses I use, even after I had learned of the necessary adjustment. I'm still only using the standard focus screen of the K10 though, I'll research that topic next and perhaps resolve the issue this way.

Still, I'd be curious to hear of more owners experiences.
10-09-2007, 09:22 AM   #7
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Just curious on this issue -- are you saying the infinity mark on the barrel is wrong or just that when it's focused as far as it will go it isn't at infinity? I think that on almost all of my lenses they focus past infinity, and the focusing/distance guide shows that. If I point them properly at infinity it works great.

I'm worried I'm not being clear so I'll rephrase just in case. I could have a lens with markings for 1 m, 2 m, 10 m, 20 m, and infinity, for instance, and the barrel will twist past infinity, but the lens is properly marked to indicate that infinity is not at full extension.
10-09-2007, 09:49 AM   #8
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Hi Lunelson. You've just caused me to look over all my lenses and see how many focus past inifinity on their markings. Only my Sigma 15mm EX does. It has a distinct over-throw past inifinity by its markings. The Voigtlander, my 31mm LTD, Tele-Takumar 400/5.6 and several other older Takumars all line up the infinity mark with the end of the turn exactly. Now, with the Voigtlander, the adjustment of which I speak is so small that it is negligable whether its still lined up with the center of infinity or not, but it is definately lined up with it at full rotation.

10-09-2007, 10:23 AM   #9
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After seeing these pictures I want one of those lenses thePiRaTE

They're beautiful.

That does it, LBA has struck again.
I'm about to go into town, and check out the pawn shops hoping for something as nice
10-09-2007, 05:32 PM   #10
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Thanks for the kind words And and LittleLaker, I'm just glad it can get the shots, I was worried at first. Laker, CameraQuest Home still has a few units left of the 125 and 180s. FWIW, even if this infinity things turns out to be unintentional, the lens has so much else going for it (including the price) its well worth the purchase, especially considering they're now discontinued.

Any other owners who can verify this infinity focus thing? I'm less concerned than I was, but I'm still curious...
10-10-2007, 09:08 PM   #11
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Just thought I'd mention to those who might be interested that after having received the 180/4 and testing the infinity focus on it, I can confirm it too has the same characteristic. While not nearly as pronounced as the 125, its still easy to notice the difference. The lenses are marked infinity at the full turn though, so its still a bit of a mystery whether this is intentional or not. At the very least, let it be known for the archives to all Voigtlander owners, make sure and touch back that focus!
10-16-2007, 01:44 AM   #12
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QuoteOriginally posted by rdc Quote
This is normal. It is done for two reasons, first because every lens will be ever so slightly different and each lens would have to be calibrated individually think of that slight turn that it takes to get your lens into focus now imagine having to do that for every lens that comes out of a factory and then having a precise enough stop so that the lens stops exactly there....not very efficient.

Now the first reason is simply a matter of manufacturing efficiency, but here's the thing even if you had a perfectly calibrated lens it wouldn't matter because it would only be perfect at the temperature at which it was calibrated because as the elements and body (particularly the metal found in older lenses) of the lens expand and contract the focus changes as well. This is the real reason that lenses focus beyond infinity.

Getting infinity focus is no more difficult than focusing on anything else be it autofocus or manual, except for one thing, as you have discovered once you overshoot infinity IQ drops very quickly.

If you're looking for something that you can set without looking through the viewfinder to make sure everything is sharp keep in mind the concept of hyperfocal distance.
With regards to your first point, I can assure you that you are incorrect. I don't see how this can be normal. Every lens that leaves the factory needs to be collimated to ensure the lens focuses at infinity. That's an integral aspect of lens assembly. Simple as that. This lens is not a super tele and even though the lens barrel can extend quite a bit, thermal expansion shouldn't be an issue so there is no reason for it to focus beyond infinity. Even my Sigma 400mm focuses exactly at infinity.

My Voightlander 125mm focuses exactly at infinity and not beyond.
This was in fact my second copy as the previous copy had a assembly fault that didn't allow the aperture to go wider than f/3.5. My local agent had the Cosina factory ship over the replacement copies within a few days. I can vouch that 2 people I know who own the same lens doesn't have this issue.

Last edited by creampuff; 10-16-2007 at 01:50 AM.
10-16-2007, 09:15 AM   #13
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huh. Thanks for that creampuff. You know, I would say that since I've grown accustomed to adjusting for the issue and can still get the result I want that its ok to leave it, but I still get a nagging feeling that "What if I didn't adjust it optimally?" I mean, its more by feel than by observation through the view finder. I could easily be selling myself (and the lens) short from time to time because the adjustment I tweak might be slightly off the mark of exact infinity. I wonder if I should have them calibrated? Perhaps I should check with CameraQuest...
10-16-2007, 05:47 PM   #14
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QuoteOriginally posted by wlachan Quote
It could be your camera too. Believe it or not, many modern cameras (applies to AF lenses too) are calibrated to focus slightly beyond infinity. Whether they were designed that way or loose QC I don't know. But as long as the focus screen agrees with the film plane (CCD in this case), the camera is considered fine. What this means is that one can never rely on the lens infinity mark anymore . But this is old news, isn't it?
Not to me! Though I'm a relative newbie. I spoke with Stephen at CameraQuest about the issue and he has asked me give the lenses a try on a film body and note the results before taking any action. Because both of the CV lenses I now possess (125 & 180) seem to exhibit the same focus trait, your comment seems more poignant to me now.

I'm just at work at the moment, but if anyone else has considered ways of verifying the accuracy of infinity on their K10 - or perhaps more importantly, how to correct it - and would care to mention it, I'd be glad for the head start.

As for testing the Lenses, I think I'll ask my contact at the Camera Store here in town if he wouldn't mind hooking me up with an older K body to test...

Thanks,


Kelly.
10-23-2007, 03:34 AM   #15
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Seems there is a "cure"

I found the following thread in 'another' forum. Checkout distudios response as well:


Re: Voigtlander 125/2.5 APO Macro: Pentax SLR Talk Forum: Digital Photography Review



I'm not suggesting you tinker with your lense - I certainly wouldn't dare to - but I thought it was interesting.
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