Nikon Alphaphot eyepiece focus ring problem

[J_WISC]

Hello.

Can someone advise how to properly lubricate a Nikon Alphaphot eyepiece focus ring? And please feel free to correct my terminology here.

I can turn the ring, but there's a lot of resistance. And I don't want to add something to loosen it if there a chance of it slowly working its way down to the mirror or prism in there. Is there a path for lubricant to reach the mirror or prism?

Thank you.

adjustsble eyepiece.jpg (169.57 KiB) Viewed 858 times

[apochronaut]

The mechanism works by moving up and down on a helical slide external to the eyepiece tube. I have not had that one apart but there are three principal designs.
One screws the knurled adjustment ring to a small sliding block that goes down and up to a stop in the helical slideway. Basically a worm and nut.
Two , has a female helicoid slideway and a knurled ring with an integrated male slideway. A screw is inserted that hits a stop at the top. Basically a bolt and nut.
Three has a helicoid female slideway with an intermediate piece as a nut and the knurled ring tightened to that with usually 2 or 3 set screws.

For all designs, removal or sometimes just backing off of the one , two or three screws allows you to bypass the stop and unthread the diopter grip ring right off vertically. Once off, you can clean the hardened grease off and relube it, with a grease of your choice.

[FredH]

On mine, the knurled focus ring has three small slotted set screws and what appears to be a socket-head set screw. If you loosen all three slotted set screws (not the socket-head screw), you can pull off the knurled focus ring.

Nikon_Alphaphot_diopter.JPG (171.22 KiB) Viewed 815 times

You will then see the focus tube as shown in the image above. Down near the bottom of the tube there is a helical slot with a pin poking radially into the slot such that as you rotate the tube, the tube moves axially to change the focus. If you rotate the tube to its maximum extension, you can clean any dried grease from the outside top section of the focus tube and apply a little fresh grease; you could also carefully apply some grease in the slot. If there is inaccessible dried grease that must be removed, I guess further disassembly (e.g. removing the pin somehow so you can pull the focus tube out) is required, but I haven't tried that.

When you put the knurled focus ring back on, the socket-head set screw sits in the rectangular slot at the top of the focus tube, but the width of the slot allows some angular slop. The three slotted set screws have pointed tips that tighten against a vee groove in the focus tube and lock the knurled knob to the focus tube, eliminating this angular slop and holding the knurled focus ring in place. I imagine you are first supposed to rotate the knurled ring so that the two eyepieces have the same focus (no diopter correction) when the two dots shown in your photo are aligned, then tighten the three slotted set screws.