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Joshua Cadmium

Avoiding Helical Thread Wear on Vintage Zeiss When Using Wide Angle Adapters

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Posted (edited)

I have a Century Double Asphere and a bunch of other heavy wide angle adapters I want to use with a Zeiss 10-100 T1.8 MK II and a 12mm T1.3 MK II.

 

I know that due to the telescoping nature of the helical focusing threads, you shouldn't have anything heavy (or at all) attached to the front of the lens while focusing, like a clip on matte box.

 

I was wondering, though, if the threads would be okay if I prefocused the lens, then attached a wide angle adapter, and then did not focus the lens at all while the adapter was clamped on. (I know I would need to find the exact focus point for non-zoom through adapters, like the Double Asphere, but I'm not worried about that.)

 

With the 10-100, it also has the macro mode, where the focus wouldn't be extended at all and be at its starting point on the threads.

 

I'm also thinking about using an anamorphic adapter, plus a front variable diopter, which would be several pounds hanging off the front. If I went that route, I would have each part individually supported on rods and, again, would not touch the focus at all at that point, but I don't know how safe that would be.

 

Those two lenses currently have perfect focusing, especially for their time and I really don't want to wreck the threads.

Edited by Joshua Cadmium

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Anyone want to chime in one way or the other and offer some opinions? 🙂

 

Basically, would 1-3 lbs of unsupported weight damage the focusing threads if no focusing was actually being done?

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Well your theory is right - it’s focussing that introduces wear to the helical threads, and a heavy weight on the front will hasten that wear. I’m not sure pre-focussing before attaching an adapter is a very practical solution, but if it doesn’t interfere with your time schedule or throw off the focus then go for it. A support would work, if it can support the front weight while allowing the adapter to telescope.

The 10-100 should be ok though,  since the focus threads are large diameter and have many turns, which gives it a fair bit of stability. The worst position is very close focus, where the front is extended and so less threads are engaged, but even so I wouldn’t worry too much about the zoom.

The 12mm is more susceptible, but if you’re not doing heaps of focus pulls or using motors that drive the focus repeatedly from one end to the other during calibrations etc again I think you have to be practical about it. The main thing to avoid is grease that is old or contaminated, since then it becomes less a lubricant and more of a lapping compound. Depending on how much you use them, and in what environments (eg dusty deserts vs studio) you might want to regularly send your lenses to a reputable repair place like Duclos and have them cleaned and relubricated. That is the best way to keep them working well. 

If the threads do start to wear, it usually manifests as image shift, which is where the image moves a bit when you start to turn the focus ring or change the direction you’re turning it. I‘ve found it tends to be more noticeable on short focal lengths. Repair shops can fix it by building up the threads again with a spay-on hardening compound. 

With Zeiss Super Speeds, they should feel slightly firm to turn the focus. If the focus is very free it means there is some wear to the threads already.

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Thank you so much for the info! I was actually hoping to hear from you specifically, so that was super helpful.

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My local lens tech likes to relubricate the helicals with a high viscosity grease. Being thicker, it offers more protection to the threads, at the expensive of it being slightly harder to turn the barrel.

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