Can Lens Scale Pass Infinity?

[BKimelb1]

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I noticed my 90mm APO Summicron lens scale passes infinity at the end.  Is this reasonable or does lens need an adjustment.  See photo below at f/2 I thought the "2" should line up with infinity (lazy eight).  Your advice would be appreciated. Lens works fine.

 

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[jdlaing]

I have several lenses that do the same and all are fine. A lens can focus past infinity.

[BKimelb1]

Much obliged for your quick answer.  I heard sending them out for service is a royal PITA. 

 

[jdlaing]

1 hour ago, BKimelb1 said:

Much obliged for your quick answer.  I heard sending them out for service is a royal PITA. 

 

If it ain’t broke don’t fix it.

[Michael Geschlecht]

Hello BKimelb1

Welcome to the Forum.

A simple test would be to put the camera/lens on a tripod (This is necessary.).

Then, on a reasonably clear nite, with a reasonably full Moon, with the lens set at f2.

Set the exposure in the camera for the surface of the the Moon to be 18% gray/Zone V. Daylight, of course.

Frame the the Moon in the center of the frame & then make:       

3 exposures with the lens focused back & forth & then set at the marked Infinity.

3 exposures with the lens focused back & forth & then set at the point where the lens stops turning past Infinity. 

3 exposure with the lens focused back & forth & then focus on the Moon using the range/viewfinder.

Then, look & see.

Please keep in mind, as JD wrote above, a number of Leitz/Leica lenses are deigned & manufactured to focus past Infinity for a variety of reasons.

Best Regards,

Michael

[spydrxx]

As long as your rangefinder image matches wha shows up on film or your sensor, yhis isn'y a problem. However if you zone focus it can be an issue. Most lenses have this ring aligned with the infinity symbol and held in place with 3 setscrews, which sometimes loosen causing the ring to shift. It doesn't change the actual focus of the lens, merely a shift of the visual scale. It is usually a quick and easy fix for a competent repairperson or amateur if one has the right tools and knowledge. As Michael ,mentions above, some lenses actually focus past infinity, often to take into account of thermal expansion  of the metal focusing components.

Edited August 4, 2021 by spydrxx
misspelling

[jaapv]

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2 hours ago, BKimelb1 said:

Much obliged for your quick answer.  I heard sending them out for service is a royal PITA. 

 

Depends where you send them.

[Danner]

IMHO, the hard stop should be at infinity.  So, it's a question of whether the distance printing on the lens barrel passes infinity, or the actual point of focus passes infinity.  I would not be happy if it passes the infinity focus point with any M lens.  Hard-stop should equal infinity focus.

Edited August 4, 2021 by Danner

[Michael Geschlecht]

Hell Danner,

A number of lenses, made by Leitz/Leica & other manufacturers, focus past Infinity for a variety of reasons. 

1 common reason is that it is sometimes necessary, with certain lenses, to be able to focus precisely at points that are NEAR Infinity. Focus travel beyond Infinity gives the photographer the focus travel back & forth necessary to more easily determine the correct point of focus in that situation.

That is NOT to write that this is, or is not, the situation here. We are still investigating here.

Best Regards,

Michael

[Danner]

I should mention that focusing past infinity is more common in long focal lengths, for thermal reasons is no others.  However, on a 50mm or shorter focal length, that would be a deal-breaker for me.

[adan]

A certain amount of bad information here.

NO correctly-adjusted M-Mount lens should ever have the focus ring turn past infinity.

Being able to scale-focus accurately when desired (including at infinity) is a necessary feature of the M rangefinder system.

There are certainly non-M lenses that focus past infinity. Including some Leica R-system lenses (and probably some S and SL/TL lenses, but I'm not that familiar with them), and lenses for other cameras that use through-the-lens focusing (SLR or mirrorless EVF).

As Danner says, this is to provide leeway for thermal expansion in longer lenses' metal lens barrels, which may not otherwise focus to infinity if too warm. Same reason Canon paints all their pro teles white - to absorb less solar heating during long hours in the sun (outdoor sporting events and similar).

Anyone who thinks they have seen a Leica M-system lens that focuses beyond infinity should double-check that observation - they are confused.

They will find that either it was an SLR/mirrorless lens, or that it was not correctly adjusted or manufactured.

[luigi bertolotti]

I agree that for a 90, expecially if f2, APO and RF coupled, there ought to be no reason to focus beyond infinity... it's even a bit annoying... I'd suggest to perform the test cleverly explained by Michael and decide accordingly.

(I have the MR-Telyt 500, which is one of the lenses which is declared to go beyond infinity by design - my Summicron 90 un-apo does not : stops exactly in the middle of the infinity symbol)

 

Edited August 4, 2021 by luigi bertolotti

[Vlad Soare]

I never use the rangefinder to focus at infinity. To me, focusing at infinity means simply turning the lens as far as it will go. Thus, if one of my lenses went beyond infinity I would be very upset.

 

[jaeger]

I'm extremely surprised to see someone say it is alright to pass infinity. 

[Gobert]

4 minutes ago, jaeger said:

I'm extremely surprised to see someone say it is alright to pass infinity. 

Why? Beyond the horizon you’ll find paradise.

[Ko.Fe.]

Scale focus comments here are puzzling.  Why on Earth you won't RF focus at F2 and such long lens? 

Do you know what infinity means focus has to be on the moon, not on the next to your window light pole?

It means with this long lens you have to pay attention where you are focusing at all distances @f2. It means - use of RF.

And if it is more normal f5.6 and smaller at infinity use, I doubt here is any issues due to DOF at infinity @f5.6 and smaller with scale focus.  

If OP has this lens, why not to test it to see if here is any real issues in use? If no real use issues, it is just non practical perfectionism, which is PITA indeed. 

Some RF lenses are just build this way. Some are very critical. And for those type of RF lenses, infinity mark off indicates wrong multi-thread focus helicoid assembly. This will be visible at all apertures and all distances right away I have done it wrong with Elmarit-M 28 2.8 III once. No images in focus, at all.

[adan]

3 hours ago, Ko.Fe. said:

Do you know what infinity means focus has to be on the moon, not on the next to your window light pole?

Do you know what exaggeration means?

A 90mm lens set to infinity, at f/2.0 will render everything beyond 125m equally sharp. That's Leica's own figure from the 90 APO-Summicron DoF tables.

Even allowing for a large (1m x 1.5m print), and thus a circle of confusion 1/4 the "standard" size, anything at or beyond 600m is indistinguishable from infinity. The residual lens aberrations will blur things before "focus" does.

But in either case, "photographic infinity" will begin at 0.0000028 the distance to the Moon.

[Ko.Fe.]

3 hours ago, adan said:

Do you know what exaggeration means?

A 90mm lens set to infinity, at f/2.0 will render everything beyond 125m equally sharp. That's Leica's own figure from the 90 APO-Summicron DoF tables.

Even allowing for a large (1m x 1.5m print), and thus a circle of confusion 1/4 the "standard" size, anything at or beyond 600m is indistinguishable from infinity. The residual lens aberrations will blur things before "focus" does.

But in either case, "photographic infinity" will begin at 0.0000028 the distance to the Moon.

I'm not sure what are you trying to exercise here.  I was told by technician about checking infinity at the moon, if no specialized equipment is available. Not by something at 125 meters.

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Hallo,

Look here: Leica M

[spydrxx]

The moon is a good choice for true infinity, but optical infinity is usually defined as 1000 x lens focal length.

[BKimelb1]

On 8/3/2021 at 5:47 PM, BKimelb1 said:

I noticed my 90mm APO Summicron lens scale passes infinity at the end.  Is this reasonable or does lens need an adjustment.  See photo below at f/2 I thought the "2" should line up with infinity (lazy eight).  Your advice would be appreciated. Lens works fine.

 

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Sorry folks but this is still bothering me. 

I understand points made about longer lenses maybe having need for expansion and checking  focus on the moon. That being said let me ask it this way.  Does anyone have  an apo- 90mm Summicron lens and if so does the end of the focusing range=infinity after the middle of the lazy eight sign??? Please post a photo of such a lens. 

For mine you can turn the focusing ring a few mm further.  It seems like it needs an adjustment. No lens I ever owned ever went past infinity.