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Marco
Rating: N/A
Votes: 0 (Vote!) | | Posted on Tuesday, June 20, 2006 - 08:31 am: | 
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I purchased a badly worn Nikkor 180mm 2.8 manual lens for a very small amount of cash...
The glass is perfect, but the focusing helical sometimes does not engage properly and focusing is fiddly at best...
Has any one taken on of these apart all the way to the focusing threads? And even if I reach the threads are there any adjustments that can be made to improve the situation?
Thanks
Marco |
Glenn Middleton
Rating: N/A
Votes: 0 (Vote!) | | Posted on Tuesday, June 20, 2006 - 09:09 am: |
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I am not familiar with this lens. If you are saying that the helical is so worn that the threads are riding over each other - then the lens is probably scrap.
However a more likely cause is that the screws holding the focus ring to the helical have worked loose, allowing the ring to slip. This can happen if the helical starts to become tight, due to the grease drying out.
Can you see any grub-screws around the circumference of the focus ring? If you can, try tightening them first.
Nikon manual lenses a very well engineered and will withstand enormous abuse. The only ones exhibiting focus problems that I have seen, had been dropped. In those two, the glass was also damaged. |
Marco
Rating: N/A
Votes: 0 (Vote!) | | Posted on Tuesday, June 20, 2006 - 11:36 am: |
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Glenn,
thanks for the info.... I did disassemble to the extent that i could see the screws you are talking about, I will try to tighten these tonight.
The helical on the lens is in good condition, as far as I could see. But I can't see the mating helical (is there one?) on the focus ring.
Marco |
Marco
Rating: N/A
Votes: 0 (Vote!) | | Posted on Tuesday, June 20, 2006 - 11:57 am: |
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Thanks for your quick reply.
I did clean the helical as best I could but I did not check for the tightness of the screws. I will try that tonight.
How do you remove the rubber focus ring to access the helical? I guess I am trying to understand how the focus ring couples with the helical..
Thanks
Marco |
Glenn Middleton
Rating: N/A
Votes: 0 (Vote!) | | Posted on Tuesday, June 20, 2006 - 07:50 pm: |
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The only way to get to the helical is to screw it out of the barrel. Generally the focus ring is just a plain tube, secured onto the rotating member of the helical by grub-screws. It is done this way so you can align the distance scale, when you have calibrated the infinity setting of the lens. In many cases the focus ring can be pulled off the barrel after the grub-screws have been loosened. Also there must be at least one male and corresponding female multi-start threaded component in any manual focus lens.
A very crude explanation of a common/typical helical set-up is as follows:- Imagine the lens mount/rear assembly as a large nut, threaded with a very fine single start female thread. Into this is screwed a short piece of tube, with a corresponding fine single start male thread. Once the tube is screwed in its arc of rotation, is limited by a stop, to the focus extremes. The inside of this tube is threaded with a female multi-start, square form thread. The lens assembly with a male multi-start thread is then screwed into the aforementioned tube. Once the optical unit is inserted, it is prevented from turning by a sliding 'keyway' that is secured to the mount/rear section of the lens.
Thus the only part that can rotate (over a limited arc) is the tube. It is to this tube that the focus ring/grip ring is fastened, usually by 3/4 grub-screws. However the focus grip and the tube can be machined as one piece, especially on non-telephoto lenses.
On some lenses you only have to remove the mount assembly and this will allow you to remove the slide/keyway stops. You can then unscrew the inner helix member out of the barrel, other lenses require a greater depth of stripdown.
As I said in my first post; I cannot help you with detailed repair instructions for the 180mm telephoto lenses, also you probably know the above already. |
Glenn Middleton
Rating: N/A
Votes: 0 (Vote!) | | Posted on Tuesday, June 20, 2006 - 08:36 pm: |
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Marco,
Contact me direct with your email address. Kevin (KP) has very kindly sent me a copy of his repair notes for this lens. I will forward same, once I know where you are.
Glenn. |
Marco
Rating: N/A
Votes: 0 (Vote!) | | Posted on Wednesday, June 21, 2006 - 07:32 am: |
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Thanks Glenn I will contact you offline.
I did tighten the screws attaching the focusing ring to the helical and this did "solve" my problem, but the focus is still slightly "tight"...but considering the number of dent repairs on the lens hood, I'm surprised it works at all! Proof that old nikon nikon lenses can be dropped (several times!) and still be made to work... |
