50mm Apo Summicron - Focus past infinity

[JTLeica]

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Hi guys,

I think this is two fold. I have a very well priced 50 Apo Summicron, its perfect condition so I am very happy with it. I used it for a week in Cornwall and will share some images soon with it...

I need a sounding board as always 🙏 

1 - At infinity on the scale (as in turning until it cannot turn anymore) the focal plane is a hair past infinity. It's extremely small and the scene is still acceptably sharp, certainly not blurry. I have had lenses like this before. At F2 though its sharp at infinity - Thoughts on this? 

2 - Further to the above, turning the focus maybe 0.5-1mm back the other way results in perfect focus.

3 - The rangefinder seems accurate with the lens, whilst I am still getting my eye in again with rangefinder focus, the calibration seems ok. I will test again tonight.

Thanks in advance

Edited September 15, 2023 by JTLeica

[spydrxx]

There are lots of posts on why lenses may focus on an infinity target slightly short of the infinity mark on the lens, assuming their rangefinder is properly calibrated. Many lenses focus shift slightly as you stop them down, others need a tiny amount of room for thermal expansion in hot weather or sunshine. If you're getting sharp shots, especially wide open, based on what your rangefinder tells you, don't worry about whether or not the focus scale reads infinity or you can actually move the lens focus past infinity.

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[lct]

Try again with an EVF instead of the RF. Are your findings the same then?

[Warton]

Can you educate me how to test the infinity focusing with range finder?

I move the focus ring to the farthest until it's stopped, so it's infinity. But how do I check via rangefinder the focus patch is overlayed perfectly on top of an infinite object?

what puzzles me even more is that you mentioned 0.5mm movement is perfectly focused. I can never do that especially I don't even know which object is infinite.

[Pyrogallol]

Step outside at night and focus on the moon. The further away an object is the less accurate the infinity setting needs to be. I have read that “infinity” can be regarded as 1000 times the focal length of the lens. You notice more any inaccuracy when focussing close up.

[JTLeica]

Cheers guys, I am going to try and test this again today or tomorrow. Possibly my 'infinity' before wasn't far enough away. I'll make sure its 500m plus away this time and report back.

[lekitr]

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On 9/15/2023 at 1:39 PM, Warton said:

Can you educate me how to test the infinity focusing with range finder?

I move the focus ring to the farthest until it's stopped, so it's infinity. But how do I check via rangefinder the focus patch is overlayed perfectly on top of an infinite object?

what puzzles me even more is that you mentioned 0.5mm movement is perfectly focused. I can never do that especially I don't even know which object is infinite.

Personally I use stars at night.  I consider the infinity stop on the lens to be perfect, so the stars to calibrate the rf and if the infinity on the file or negatives isn't perfect then it's the lens that need calibration.  If you have more than one lens that's the way.  My two cents.

[Derbyshire Man]

Can I bring this back up?

All of my lenses (Summilux 35mm ASPH, 35mm Nokton, 50mm Nokton 1.2 iii) actually focus just in front of infinity for infinity via rangefinder. On EVF they all focus exactly at infinity.

I suspect that means it's not quite calibrated correctly.

If I have a tendency to misfocus via rangefinder when I to attempt to focus on the front eye but end up focussing on the slightly distant eye. I can't confidently get my head around whether that is consistent but it feels the other way around. Leading me to wonder whether it's been factory set up to font focus to make up for non linearity in the rangefinder mechanism where infinity error is much less likely to be photographically evident that close focus?

[lct]

In RF or LV mode, all your M-mount lenses should focus accurately at all subject distances from MFD to infinity. If you notice the same focus error on all your lenses in RF mode only, the RF is probably the culprit.

[Derbyshire Man]

Thanks, that's what I suspected!