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Author Topic: Can I repair this lens's iris?  (Read 1646 times)

Offline Don_1

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Can I repair this lens's iris?
« on: 31/10/2015 12:25:43 »
Some time ago I acquired a monstrous lens with a problem. I would like to have a bash at dealing with the problem myself, since professional repair could prove very expensive.

So, here is the lens in question:



It is a Tele Athenar II 1200mm f6.8 manual focus T mount with a Nikon F mount adapter.

Made around the 1990ís in the USA by Century Precision Optics (now a part of Schneider Optics), it obviously does not couple to the cameraís AE or AF functions and, having no aperture pin, must be used in stop down mode. But herein lies the problem.

The aperture ring is a 22 blade construction but some of the blades have dislodged and can be seen to be out of place. There are also some which seem to have slipped out altogether and can be heard rattling around.

Now I must admit, it is unlikely that I will keep this lens, even if I do manage to sort out the aperture ring. At almost 1m long and requiring its purpose built cradle, which fixes to any tripod capable of taking its weight, it really is too big for my requirements (not to mention taking up a hell of a lot of storage room). But these lenses are said to be of exceptional quality. From what I can gather, the longer focal length Tele Athenar IIís were used by the US and Canadian air forces, while the Tele Athenar was used in the movie industry. So I would rather like to hook it up to my Nikon D300 or D800 to give it a whirl. My thoughts are that the crop frame sensor of the D300 might be better than the full frame sensor of the D800, where vignetting might be servere.

So my question is, is there anybody out there (perchance an ex-employee of Century) who has any knowledge of these lenses and their aperture construction, who can give me any pointers as to how I might be able to repair the iris, or just anyone with a tip or two, before I embark on opening up this monstrous beast of a lens?


 

Offline syhprum

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Re: Can I repair this lens's iris?
« Reply #1 on: 31/10/2015 14:39:09 »
To dismantle and repair anything requires special skills and often special equipment, special skills can be learnt go at it slowly but once you find special tools are needed stop !
 

Offline Don_1

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Re: Can I repair this lens's iris?
« Reply #2 on: 31/10/2015 15:52:15 »
I do have a micro tool kit & a basic knowledge of the aperture ring assembly, but not of this particular make.

I should also have pointed out that the ring seems to have been de-clicked. The square collar you can see around the aperture ring holds a motor for remote adjustment. This was a simple clamp-on affair which I have removed. I can only assume that the lens may have been used in an aircraft where access to the lens would not have been possible whilst in-flight.

The aperture ring only opens to just a fraction under f8. This may be because at the fully open f6.8 the depth of field would have been too narrow. On the other hand, it might be a dislodged blade jamming the ring, so I don't want to try to force the ring fully open for fear of doing more damage to the already dislodged blades. Having new blades made would, I think, put the lens beyond a reasonable cost of repair.
 

Offline RD

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Re: Can I repair this lens's iris?
« Reply #3 on: 31/10/2015 18:41:39 »
... any pointers as to how I might be able to repair the iris, or just anyone with a tip or two, before I embark on opening up this monstrous beast of a lens?

From personal experience with expendable Russian lenses, I know if you leave an oily fingerprint on the blades of the diaphragm it will impede their movement. [ that includes natural skin oil , as well as WD40 ].  So it's a fiddly tweezers-job to relocate the blades.
« Last Edit: 31/10/2015 18:51:11 by RD »
 

Offline Don_1

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Re: Can I repair this lens's iris?
« Reply #4 on: 31/10/2015 19:39:23 »
Absolutely so RD!

And with your comment in mind, I think it might be a good idea to ensure the tweezers are clean & oil free.

I must admit, I am find the thought of 22 blades rather daunting.
 

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Re: Can I repair this lens's iris?
« Reply #4 on: 31/10/2015 19:39:23 »

 

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