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I was convinced by this 1 article that there was some complicated Teflon roller system inside the lens that had malfunctioned.
The author was describing a fantasy world that doesn't exist. There could well be a good reason for that; perhaps Zeiss completely changed the design of the focus mechanism at some stage during production. Although it seems highly unlikely.
With reference to the correct information that this 2 article and hmzimelka have kindly explained I would like to clarify some points..
Pictures are copyright Yukosteel Photo Equipment Blog.
If i've got anything wrong with the following description please correct me.
The outermost focus ring that we hold and rotate in order to focus the image before taking a picture is secured to the main focus ring by 3 black coloured screws. The lens has been disassembled some way in order to access these screws.
In the picture below you can see that the author has removed the 3 black coloured screws and the outermost focus ring and has set it down next to the helicoid mechanism.
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https://yukosteel.files.wordpress.com/2021/06/sxt1z7726.jpg |
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In the picture above, at approx. 4 o'clock we can see what the author calls the "focus ring transmission". The bronze coloured piece secured to the main focusing ring by 2 black screws.
This "focus ring transmission" transmits your focus input to the helicoid mechanism.
As you rotate the focus ring back and fourth before taking a picture, any tiny gap in the contact points between this bronze coloured part of the focus ring transmission and the slot that it rides in will be detectable as play; free movement of the focus ring where no movement of the optical assembly and therefore focusing of the image is taking place.
If we look closely again at picture above. This time at the 9 o'clock and 3'oclock positions we can just see 2 more bronze coloured parts. What author refers to as "brass helicoid guiders". Each secured to opposite sides of the outer helicoid by 2 screws (invisible in this picture).
The picture below shows one of them removed.
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https://yukosteel.files.wordpress.com/2021/06/sxt1z7638.jpg |
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Each one of these 2 parts looks slightly different, one has an "open middle grove" cut into it.
The author explains: "In my sample guider with open middle groove is located at opposite side, and it required slight deformation to make it just a tiny wider to eliminate focusing “lag”, but still narrow enough to easily slide inside its socket without noticeable friction."
So these parts are adjustable and can be tweaked or adjusted to eliminate focusing play or lag.
hmzimelka wrote:
Unfortunately I haven't used the 35/1.4, and it's also the only ZM lens with a more complex helicoid focus system.
An uneven focus feel doesn't necessarily mean the lubrication isn't even or that the helicoid is at fault. It can be as simple as a guide with a minor imperfection. I've experienced a Planar 50mm that had the above discussed cut out, for the brass guide, slightly unevenly cut. It was slightly narrower at the top (infinity) than at the bottom (close focus) therefore focus feel was looser at close focus. This cut out had no visible issue, and it took some good quality vernier calibers to determine that it had differences in width. I presume the ring it's cut in was/is aluminium, it would be possible for the front of the ring to be deformed ever so slightly because the ring is open at the front by the cut out. The bottom of the ring still has sufficient support because the cut out terminates just over half way down the ring. It only takes a small fraction of a millimetre for the cut out width to influence the resistance of the tab moving up and down it and therefore influence the focus feel.
But the ZM Distagon 35/1.4 might be a different beast all together... I've not seen a repair guide for it yet.
But I doubt its any more complicated than the Ais Nikkor 55/2.8 Micro or the Ais Nikkor 85/1.4 which both have a CRC system, but aren't too complicated to disassemble... they just take longer due to having more parts....Show more →
So if there is inconsistent focus pressure, rather than backlash/play, then the "brass helicoid guiders" system may require repair, unless the 35mm f1.4 Distagon ZM has a different mechanism altogether rather than just the same design shown above but with extra helicoids for the floating element system. I'm wondering if the cut out in the focus guider acts like a spring so that the lens can still be focused even if it starts to tighten up at some point along it's travel?
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