[SOLVED] disassembly of 105mm f/2.5 AIS / access inside of rear element

[whatdoido]

Hi
I’ve been re-acquainted with my MF Nikkors recently and I really have forgotten the fun – and image quality – to be had.

Unfortunately, I’ve discovered my 105mm f/2.5 AIS lens seems to have some small spots of fungus on the rear element.  I found this guide that lets give me instructions to disassemble the lens (surprisingly easy).

http://forum.mflenses.com/tutorial-how-to-open-and-clean-a-nikkor-105-2-5-ais-t33023.html

However I am not able to unscrew the rear element block as per the image from the above link:



The next question is how to take apart the rear lens block to access the inside of the rear element for cleaning.  The rear element looks to be sandwiched in … perhaps with a retention ring?



Do we have any members who have been able to disassemble this lens and can help?  I’d hate to have this lens ruined by fungus spreading.

Thanks in advance

[Erik Lund]

Start here:


http://nikongear.net/revival/index.php/topic,5826.msg94491.html#msg94491

[whatdoido]

Thanks Eric,
I'd already seen that forum post and also Richard Haw's site - I then noticed that he was also a member here!

However, Richard's link seems to be specific for 105mm Auto-Nikkor-P and not the 105mm 2.5 AIS;  looking at the images on his site compared to the components of the 105mm AIS, they are different.  I've already taken apart my 105mm AIS to compare.

[Erik Lund]

Almost at the end you see him removing the 'glue' covering a small hole, underneath is a small set screw you have to untighten/remove.

[longzoom]

This way or that, you will open it. So be sure the fungus is on the surface of the any element, so you are able to remove it, not a big deal. Be sure to disinfect even the metal parts, with alcohol pads - it is contagious. But, if that fungy inside the clued elements, what is in most cases, unfortunately - there is nothing what you can do. Yes, it is possible to destroy the adhesive and separate the elements, and kill mushrooms, but how to put the elements back,  together?  Ah, there is nothing to loss, anyway...  Good luck!   LZ

[whatdoido]

Ok, I finally managed to solve this.

The rear element block is simply screwed in; there are no grub screws but the screw thread is simply glued/thread locked. I hadn't realised that the blob on the picture (2nd picture in the original post - http://forum.mflenses.com/userpix/201010/big_2108__DSC5893_1.jpg) was glue / threadlock.  When I applied nail polish remover to this (via a cotton bud / q-tip) the rear block unscrewed easily.

With the rear block out, there is a retaining ring holding one of the elements in place - a lens spanner let me remove the ring and the element could be popped out; I had to let gravity plus a few bumps help, although I guess a lens sucker would have been helpful.  I found the fungus to be on the inside of this element and cleaned it with white vinegar, followed by soap and then eclipse.  It was luck that the fungus was not on the inside of the rear element as I could see no way to remove the rear element from the casing.

Hopefully this lens can last another 30+ years before I have to do any more surgery on it again!

Thanks for the input and the motivation held in the forum

EDIT:
---
Adding instructions just incase the internet loses the original pages.

Access to lens groups:

• extend the lens hood to uncover 3x small set screws - remove these screws
• grab the exposed barell hidden by the hood and the silver grab ring and unscrew - this gives access to the lens assembly which is a single block
• hold the lens so the rear element points down and set focus to closest focus and aperture ring to wide open - you can lift the entire optical assembly out; this includes front group, aperture mechansim and rear lens group
• front group - you can unscrew, there are no apparent thread locking/glue on threads
• rear group - to unscrew, locate the hole on the rear group - there are 2; locate the one closesr to the rear element (the other one is semi buried near the aperture mechansim;  add solvent/nail polish remover to the hole via a qtip/cotton bud and shortly this group can be unscrewed

The instructions for rear lens group differs slightly to the external link in the OP as he removes more than is needed which allows access to the aperture system - I need access to the rear elements so be aware.

Rear element group:
Be very careful with this group - the rear element is convex - CURVES OUT - so if you need to set this down, have the rear element face UPWARDS

• hold the lens group, rear element facing down
• use a lens spanner to remove the inner retention ring to gain access to the first of the 2 elements
• pop element out with gravity or lens sucker
• access to inside of rear element unknown - not known how to remove rear element from rear group casing

Re-assembly:

• Rescrew the lens groups to give the single piece optical unit
• notice the large silver screw on the side - this guides the optical unit into the lens barrel assembly, v similar to this image from Richard Haw's 105mm 105 2.5k https://richardhaw.files.wordpress.com/2017/10/img_2303.jpg?w=535 (disassembly is different to the 105mm f/2.5 AIS)
  
  
• ensure that the aperture blades are wide open, if not move the flat aperture level - if not, you will have problems with aperture or focus ring catching after re-inserting
• ensure the lens barrel is set of closest focus and apeture is wide open
• gently slide the optical group into the lens barrel
• check the focus ring can turn from rear to INF and aperture ring opens/closing - if either catches, see the note #3 above
• screw on the lens hood assembly and attach 3x the grub screws and we're done