Manual lens infinity stop - what is the factory spec?

[Ian R]

I have quite a few manual Nikkor lenses from the 1960's up until this year - a brand new 50mm f/1.2. One thing I have noted is that many focus a hair past infinity - in fact many lenses go just the same amount past as if it was 'designed in'. I have placed a tiny silver mark on many to give me the true infinity so I can set it by eye for landscape, low light etc. But the thing is not all lenses behave the same as some have a very precise infinity stop.

Is there a 'correct' setting for this or does it depend on the lens? I have a 135mm f/3.5 that goes past infinity a bit and so before adding the silver dot to this, thought I would ask.

The 50mm f/1.2 performs much better when set at a true infinity, not just using the stop - and the same applies to many other lenses too.

I am thinking about sending them for calibration, however if going a bit past infinity is a correct setting then I am likely to get the lens back just the same and be charged for the pleasure.

Thanks for any thoughts.

[richardHaw]

I fix mine. I read that canon does this to compensate of expanding elements under the heat of the sun. 

Manual Zooms can even be trickier in this regard, trust me. As getting ine end will result in the other being a bit off.

[Bjørn Rørslett]

Haven't noticed any issues so far with my manual Nikkors regarding infinity focus.

One should realise that 'infinity' covers a vast ground.  Stars are probably what you should test infinity  focus for. When Erik lived on the water front in Copenhagen, we used street light from Malmö, the nearest Swedish city on the other side of Øresund straits, as targets. These corresponded to 16-17 km distance. Do take Earth's curvature into consideration as this will prevent really remote objects from being captured unless you are on a high mountain top.

All these manual lenses can have their infinity stop rearranged if so required.

[Ian R]

Thank you for the input. Quite often it is only about 0.5mm of extra rotation past the infinity stop, but even that is enough to see the image soften again. I do wonder whether it is a quick way of covering all the camera lens mount tolerances - and a bit more - so that there are less returns for lenses not reaching infinity.

Richard - are they easy to adjust? I would like to try on my 135mm f/3.5 Ai-S if possible if it is just set screw or similar.

[Akira]

I fix mine. I read that canon does this to compensate of expanding elements under the heat of the sun. 

Not only Canon, but any lens with ED (SD, LD or whatever meaning "extra-low dispersion") or fluoride glasses are made to focus past infinity to compensate for the focal length fluctuations.

[richardHaw]

Thank you for the input. Quite often it is only about 0.5mm of extra rotation past the infinity stop, but even that is enough to see the image soften again. I do wonder whether it is a quick way of covering all the camera lens mount tolerances - and a bit more - so that there are less returns for lenses not reaching infinity.

Richard - are they easy to adjust? I would like to try on my 135mm f/3.5 Ai-S if possible if it is just set screw or similar.

not sure on the Ai-S but it can be adjusted for sure
never opened the Ai-S version of that lens, only the C and cm.

i am going to show several samples, all of which involves opening up the lens.

the pic shows a 135mm f/2.8K, you adjust the stop by moving the brass part left or right after loosening the screws.

[richardHaw]

the 105mm f/2.5 Ai-S is a lot simpler, you remove the rubber grip and scotch tape then simply adjust the scale to your liking

[richardHaw]

on the 85mm f/2 Ai-S, it is adjusted by loosening this brass ring

[richardHaw]

on the 200mm f/2 Ai, you loosen the brass part and move it left and right as well 

i hope that this will give you an idea on how this is achieved. some lenses use brass shims/washers instead to calibrate focus. older lenses might not have any focusing adjustments at all plenty of times. they are built to exact standards. I was once sold a bad 135mm f/3.5 Nikkor-Q wherein infinity focus was never achieved irregardless of what I do. the only conclusion was somebody did a swap  the cu*t did not even bothered seeing if it focuses to infinity or not so I ended up shaving and repositioning screws   

[BW]

Richard, you are a pandoras box of wisdom

[richardHaw]

Richard, you are a pandoras box of wisdom

pandoras box, yes. but not of wisdom 

[Ian R]

Thank you kindly Richard - I now have some confidence to set my lens (or at least see whether or not I can).

[richardHaw]

Thank you kindly Richard - I now have some confidence to set my lens (or at least see whether or not I can).

Cheers, Ian. This is just to give you an idea. if you are not comfortable with this then I suggest that you don't try to DIY it. check on the net first to see how that lens should be calibrated. cannot find anything from the net now

[Alaun]

Better a bit beyond infinity than the opposite.

I have a little 180mm Lanthar, that is missing just the last bit to infinity (it goes 100m or so but the real far is not sharp).
I am not yet confident enough to open it, as in most situation it is ok.

 

[Øivind Tøien]

Before starting to adjust infinity stop of lenses, it should be considered whether the register distance of  the body is correct. I have seen some variation over the years here, including two bodies that I had replaced because register distance was too short and deviating too much. It is difficult to determine if a body is correct except by comparison other bodies or if one has a lens that has a confirmed stable calibrated infinity stop. (Could may be be a theme to check at an NG gathering with lots of bodies and lenses present).

That said, high resolution sensors (24Mpix Dx) may show some smaller deviations in infinity stop of lenses (non-ED) that were previously not detected at lower resolution (e.g. 16 MPix), but when I went back to the lower resolution body I was able to confirm it there. As these tests were performed wide open on stars at low temperature in winter I have not confirmed yet if it applies at higher temperature too. While the optical elements may be stable, the metal of the lens and in this case poly-carbonate mirror boxes of the bodies could have been affected slightly by temperature. We are talking about very small deviations here though that would not have practical consequences if a lens was stopped down for landscape use.