Voigtlander 50/2 APO Lanthar infinity stop question

alanwilder
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p.1 #1 · p.1 #1 · Voigtlander 50/2 APO Lanthar infinity stop question

I noticed on the Z or E mount versions of this lens that the hard stop intentionally goes a few mm past the infinity symbol. At optical infinity, exact spot-on focus occurs at the tic mark where the index line perfectly aligns at the center of the infinity symbol. It's a little bit of a nuisance since it requires you to use the cameras focusing aids to nail exact infinity focus rather than having it occur at the hard stop as in the Leica M version. Does anyone know why it was done this way? Is it a thermal shift issue from the five special dispersion glass elements if the lens heats up? The M version is optically different by substituting three conventional element without the special dispersion features compared to the Z or E versions.

Edited on Oct 01, 2023 at 03:34 AM · View previous versions

Sep 27, 2023 at 08:44 PM

akul
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p.1 #2 · p.1 #2 · Voigtlander 50/2 APO Lanthar infinity stop question

I have noticed that with ZF series too. I think the rational is that it is better that it passes infinity than it never reaches. I also found it annoying but got used to it. I think my 40mm /f1.2 also shows the same.

Luka

Sep 27, 2023 at 09:56 PM

philip_pj
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p.1 #3 · p.1 #3 · Voigtlander 50/2 APO Lanthar infinity stop question

1. Due to rangefinder issues (let's call them) the M lenses have to be set up properly for infinity, 'properly' in this instance meaning: at the hard stop. Not to offend but I'm not at all comprehending if there are other reasons why M users obsess over infinity/hard stop alignment - apart from not being able to see well what is happening. Maybe the MFD is affected for lenses that focus past infinity? Field curvature (FC) is a frequent concern for them as well. In an EVF camera, you can easily scan the entire composition to see whether you are losing the corners to rearwards FC.

2. For EVF cameras, it's easy to focus a 50mm exactly on 'infinity' (as commonly understood), and as you see, the index mark on the APOs is exact. It occurs in other CV lenses as well, you often need a smidgen less than the infinity mark.

3. For many MF lenses, it has long been a convention to afford infinity to be reached in all circumstances by permitting the ring to pass the infinity mark. It was dreadful on DSLRs as you never knew what exactly was going on - you simply could not see well enough with long lenses!

4. Should you actually want to focus the focal plane at infinity you will be be wasting precious depth of field (DOF) in so doing. Many experienced photographers place the focal plane somewhat closer than infinity to take advantage of the extra DOF in their fore/mid grounds, depending on the composition being discussed. Experience is the best teacher here. It's mildly controversial - estimates range from one half to one third of DOF lying beyond the focal plane. See:

https://vanillavideo.com/articles/how-depth-of-field-occurs-optics/

5. If you wish to disavow yourself of hyperfocal focusing forever, read this document for a thorough refutation of this bogus method:

http://www.trenholm.org/hmmerk/TIAOOFe.pdf
(avoid the formulae)

6. A further focusing issue is our old friend field curvature (FC), which adds to the futility of using the hyperfocal method. Few lenses possess perfectly flat fields; actually you have one in your CV APO (it shows up in MTF, taken by convention at infinity)..

https://www.cosina.co.jp/voigtlander/en/z-mount/apo-lanthar-50mm-f2-aspherical/ (flat 40 lpmm lines = no FC)

..and other makers are improving fast in this regard. FC varies by aperture and by focus distance - what an image killer! It is very disturbing to some, such as me. Like focus shift, it is an area for which reviews are almost uniformly inadequate - Fred's reviews being a major exception here. Fred's review of the 50/2 APO E is recommended as it is the same lens spec as your Z-mount one:

https://www.fredmiranda.com/forum/topic/1625777

More on FC from lensrentals - great graphics, rather intuitive:

https://www.lensrentals.com/blog/2014/09/field-curvature-and-stopping-down/
https://www.lensrentals.com/blog/2019/11/practical-use-of-field-curvature-graphs-the-50mm-primes/

Sep 27, 2023 at 10:20 PM

Ripolini
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p.1 #4 · p.1 #4 · Voigtlander 50/2 APO Lanthar infinity stop question

I think I have *never* taken a picture (with MILCs) by setting the focus on the basis of a mark on the lens barrel.

Sep 28, 2023 at 05:42 AM

alanwilder
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p.1 #5 · p.1 #5 · Voigtlander 50/2 APO Lanthar infinity stop question

My experience with Leica M was that properly calibrated M cameras using lenses between 50-135 were generally spot on agreement at infinity between image plane focus and RF alignment. If they weren't, I always investigated to find out the reason. Assuming the camera's rangefinder calibration was accurate with 50mm and longer, shorter focal length lenses from the late 70's would usually focus slightly past infinity at the hard stop but I didn't obsess because it was well within the DOF wide open. I never checked earlier M wide angle lenses from the 1950's to early 70's as they may have been calibrated more precisely. MF Nikon F lenses at 300 or shorter were usually in focus at infinity at the hard stop whether film or digital bodies. 3rd party lenses that have to be adapted to mirrorless cameras probably need some wiggle room due to the adapter. The APO Lanthar however is a MF lens specifically made in a Z mount so infinity focus calibration should be a known quantity. That said, with the exception of the Z 58/0.95 Noct which is MF, none of the Z mount lenses have a hard infinity stop since they are all AF lenses that focus a little past infinity.

Sep 28, 2023 at 09:57 AM

gyoung143
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p.1 #6 · p.1 #6 · Voigtlander 50/2 APO Lanthar infinity stop question

Ripolini wrote:
I think I have *never* taken a picture (with MILCs) by setting the focus on the basis of a mark on the lens barrel.
It was my practice 'normally' on my M6 and M3 to use the scales with lenses 28mm and wider for landscape etc. Even 35 and 50 occasionally. In fact, with the early Voigtlanders 15 and 25 there was no option.
I've carried this on with Sony and Fuji. Making sure adapters sre the 'correct' register.
I see no reason why native E, X and Z mount Voigtlanders should not have an accurate focus scale and hard infinity stop at infinity, the scales are pointless if not (reasonably) accurate, especiallyat infinity.

Gerry

Sep 29, 2023 at 05:00 AM

Ripolini
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p.1 #7 · p.1 #7 · Voigtlander 50/2 APO Lanthar infinity stop question

gyoung143 wrote:
I see no reason why native E, X and Z mount Voigtlanders should not have an accurate focus scale and hard infinity stop at infinity, the scales are pointless if not (reasonably) accurate, especiallyat infinity.
Gerry

I think the reason is that Sony, Fuji and Nikon Z cameras allow precise focusing with no rangefinder.
In my experience with digital cameras, I have never focused (manually) at infinity (I don't practice astrophotography). In landscape photography, I select the plane of focus, or make focus stacking.

During the film era, my Nikkor AI-S 28/2.8 did not have hard infinity stop, I mean, the infinity mark was either ahead of or behind infinity; don't remember exactly, it was around twenty-five years ago, I guess. However, I remember that the technician at the Nikon service in Rome fixed it in a couple of minutes.

Sep 29, 2023 at 05:45 AM


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