May 6, 2025

Repairing my Zeiss 7x42B T*P

The problem is that the focus has become extremely stiff. And I know why. The 35 year old grease in the focus mechanism has "dried out". It might be more accurate to say it has "petrified". The thing to do is to take the binoculars apart, clean out the old grease and replace it with new.

I'll stop here to say that this is not something the average person should do themselves. The general advice is to leave repair work to Zeiss. Get in touch with the Zeiss repair experts or someone with experience working on high end binoculars and have them do this. In theory at least Zeiss offers to take care of these forever. I have not (did not) attempt to contact them.

That said, for the handful of people with experienc and ability doing this kind of work, here we go.

It was not obvious to me how to take these apart. Clearly I needed to get at whatever was under the cap with the red T*P markings. I tried various things, being extremely cautious, but got nowhere.

The following video showed me how the game was to be played.

The guy in the above video is clearly not working on a pair of Zeiss binoculars. It turns out though that the focus mechanism is almost entirely the same.

Removing the cap

It just needs to be pryed up. It does not unscrew. It is not glued on (as in the video) -- it just snaps on and off. I used a handy wood chisel because it provided a thin edge that I could put right where it needed to go. Careful work ensures no scratches or gouges.

Removing the screw

Under the cap is a "screw" (threaded bolt actually) that you will need a spanner wrench to turn. If you can afford a pair of these binoculars, you can go on Amnazon or wherever and buy the tool if you don't already have one. I needed one with bent tips to get the spanner pins close enough to engage the holes. The bolt ("screw") then comes off easily with no undue force and can be removed.

Remove the eyepieces

You might be smart at this point and move the focus to one extreme or the other and then take some measurements. I did not do this and had to do some trial and error during reassembly to get the proper range of focus.

The eyepieces just lift straight up, but you will need to rotate the silver colored "rod" with two flat sides to the right orientation. This is already set up for you with the first eyepiece, but the lower one requires you to rotate the rod. Note that the flats need to be parallel to the line from the rod to the eyepiece.

The focus mechanism

Things are easy now. You do not need to remove the focus wheel, so leave those 3 tiny screws alone. The wheel does not just spin, as it might seem to on first examination, but it works with a very fine pitch thread. And the thread is reverse from the usual. So if you rotate it counterclockwise, it will go down and deeper into the binoculars and eventually bottom out. So rotate it clockwise and keep turning until it comes out!

Now you are at the heart of the matter. I got some Xylene and using paper towels and Q-tips, I cleaned out all of the old grease. I cleaned up rather quickly using Xylene. Do this with the binoculars on their sides and pay very very special care to not get any grease or solvent into the eyepiece holes and thus on the prisms!! Keep using new Q-tips and towels until the come up clean and stop removing grease.

Now new grease. Don't be stupid and use too much. I have some fancy grease for focus helicoids on camera lenses, so I used that. My second choice would have been Tri-flow synthetic grease as is recommended for sewing machines. I'm not sure what the third choice might be, but you could contemplate using vaseline or even some quality white lithium grease.

Grease on the eyepieces

I did all this once, then found the action to be sticky after final assembly. So I took it all apart and examined the eyepieces. You will see a red rubber O-ring like line that provides the weather seal. I used a toothpick and applied a small bit of pure silicone grease to the part of each eyepiece that slides on this red seal. This made a big difference. You should only use pure silicone, as other greases can attack the rubber O-ring. I am sure Zeiss has something special if they don't use pure silicone themselves. Don't use too much! You don't want this stuff migrating and getting on prisms and optical components.

Reassembly

You took it all apart, so nobody should need to tell you how to put it all back together.

The only potentially tricky part is where to set the two screws when you attach the eyepieces. What I did was to screw to top screw (that actually engages the eyepieces) all the way in. Then the main screw I put in all the way, then turned 2.5 turns out. Then on go the eyepieces. Some rotation of the rod will be needed to line up the flat sides of the rod.

Lastly the "bolt" goes in using the spanner wrench. I made a trial assembly, checked the focus range, then removed the bolt and applied some blue threadlocker (Locktite 242). This was not present in the original assembly, but I feel it is wise and harmless. Do not use red (permanent) threadlocker.

I will use them for a few days before replacing the T*P cap. Note that there is a locator pin on this cap.

Feedback? Questions? Drop me a line!

Tom's Bird Info / tom@mmto.org