optiphot-1: fine focus knob trouble

[iconoclastica]

In order to take exact meaurements of the fine focus knob size and tapering, I tried to take the left one off. According to the repair manual, I tried to do it the correct way:

DISASSEMBLY PROCEDURE
1. Coaxial Coarse and Fine Focus Unit (OPTOPHOT, LABOPHOT) (Fig. 110)
1) Releasing HS screw [142A], remove the right [101] and left [102] fine focus knobs.

However, the screw disappeared when (almost?) loose. I dutifully cursed, thinking having dropped it without even seeing it. Now to get the size of the screw to find a replacement, I tried to unscrew the right one too, taking great care not to drop the screw this time. This screw, too, disappeared when coming off. I hasn't dropped, so it must have gone into the knob somewhere. Both fine focus knobs now turn freely, without making any change to the actual focus. BUT: they won't come off. No movement except turning, whatever hard I pull. Could anyone explain me what's happening here?

[Jose Antonio Mena]

Must be inside, the knobs are hollow inside; look inside trougth the hole with a ligth, be sure the screw is out or loosened; the knobs must go out; see these pics in "microscop assembly">>"Labophot">> "Fine focus mechanism":

https://lavinia.as.arizona.edu/~mtuell/

Regards

JA

[apochronaut]

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I believe your focusing knobs may have been designed by the same person(s) that were responsible for the Toyota that requires partial disassembly of the front end in order to change all of the spark plugs and as well, possiby the Ford Aerostar that requires jacking the engine in order to remove the water pump. The latter may not be the case unless it was a burp out of the Mazda design lab, just one of many.

[Jose Antonio Mena]

More from colegues of the forum:

https://blekenbleu.github.io/microscope ... #FineFocus

https://www.photomacrography.net/forum/ ... s&start=30

[iconoclastica]

I think this photo of Bekenbleu's probably explains what happened to me:


Yet I still cannot remove either knob. There's some play (c. 1-2mm) along the fine focus axis, but then it stops completely.

Must be inside, the knobs are hollow inside; look inside trougth the hole with a ligth, be sure the screw is out or loosened; the knobs must go out; see these pics in "microscop assembly">>"Labophot">> "Fine focus mechanism":

[Jose Antonio Mena]

It must go out, if the screw is out or enough loosened...
Check the screw

[Hobbyst46]

There is a manual named:
Nikon OPTIPHOT BODY LABOPHOT REPAIR MANUAL
for the beginner and experienced technician alike (seriously!)
It has been downloadable from the University of Arizona site.
It provides exploded views and instructions for disassembly of the focusing gear.

[iconoclastica]

There is a manual named:
Nikon OPTIPHOT BODY LABOPHOT REPAIR MANUAL

Thank you, but see my first message in this topic. That manual is either incorrect, or I am misinterpreting it. It says to unscrew the screw (doesn't warn for loosening it too far) and then the knobs would come off, as I read it. Apparently, sometimes they do, but frequently they don't (see this message where the same thing happened, and could be solved only because the gear was broken already).

[blekenbleu]

Thank you, but see my first message in this topic. That manual is either incorrect, or I am misinterpreting it. It says to unscrew the screw (doesn't warn for loosening it too far) and then the knobs would come off, as I read it. Apparently, sometimes they do, but frequently they don't (see this message where the same thing happened, and could be solved only because the gear was broken already).

That photomacrography.net message is almost certainly wrong.
Breaking that polymer fine focus gear by twisting both ends of the fine focus shaft is highly unlikely.
However, twisting a fine focus knob while holding a coarse focus knob (which is tempting, because larger and easier to hold) will easily break the gear.

In the future, consider performing any maintenance involving tiny screws on a large white terry towel.
Tiny parts are less likely to bounce on the towel and escape, and are they more easily seen.

Meanwhile, those set screws raised burrs on the shaft, which cause the knobs' bushings to hang up.
Twisting and pulling one fine focus knob while holding the other fine focus knob will eventually work it free.
Then, one can grasp the exposed fine focus shaft with pliers to work the other knob loose.
Emery paper will remove burrs from the shaft, facilitating knob reinstallation.

One may break that polymer gear by pulling too hard on a knob,
since that gear is what stops the shaft from coming out of the coarse focus tube when one knob is removed.

[iconoclastica]

OK, some progress made.

At the left side there was just enough room to slit in the blade of a small flat screwdriver between the fine and coarse knob and then turning the blade a bit to force the knobs apart. Working round the knob, changing twice to a larger screwdriver, the fine focus know gradually came out. It took the axle with it, so eventually the right fine focus knob came off.

As it turned out, only the axial gear at the right side, the one that uses to break, was now the only thing that kept the axle from being pulled out entirely. The left FF knob still won't budge, but I do not care enough to try to change that.

Both screws were retrieved from the inside of the knobs indeed and could be reseated.

The infamous axial gear however is broken. It is a single, clean cleft; I am not beyond hope yet that a drop of super glue won't cure it.
And I've got to figure out how to replace the three cog wheels of the FF gear system. But that is for tomorrow.