Opening Ed 111

[jpoyner]

Is it possible to open up the scope (re my misted lens). Can't seem to see how but guess there must be a way.
Just cannot get the moisture to shift and I need it badly.......

JP

[scampo]

I think - but don't know - that you'd be mad to. The optics are aligned to perfection and sealed / nitrogen filled. I'd post the scope to Nikon with a stiff complaint about the misting and I bet they'll fix it for next to nothing if the fault is a manufacturing one.

[jpoyner]

I think - but don't know - that you'd be mad to. The optics are aligned to perfection and sealed / nitrogen filled. I'd post the scope to Nikon with a stiff complaint about the misting and I bet they'll fix them for next to nothing if the fault is a manufacturing one.

Yes I suspected it wasn't a good idea, unless anybody had any other suggestions/comments?

JP

[kabsetz]

I also recommend against it, for all the reasons already quoted and then some. However, assuming that you are in an emergency and there are no other options, here's how it is done with an ED 78, which I have opended. In this scope, and very likely (but not certainly, as I haven't opened the F IIIs) the front end (the objective cell plus the objective tube, meaning the black part with the lenses and the lime-green tube) screw onto the midpart which has the focussing ring. So, if you take a very firm grip of the back end of the scope and twist the objective tube counterclockwise, it should thread out. However, to retain original collimation INDEX THE ALIGNMENT OF ALL PARTS THAT MIGHT BE TWISTED BEFORE DOING ANYTHING, AND ONCE THINGS BEGIN TO UNTHREAD, COUNT HOW MANY FULL ROTATIONS IT THREADS OUT. The latter is not so important, as it will be pretty obvious when you are at nearly fully tightened position, but use a marker or masking tape or something to tell you the PRECISE alignment at which things were before you started.

Supposing you got it apart, I would guess that the best way of drying it would be to first gently warm it with a hair-dryer on the exterior (taking care not to blow dust inside), and then enclosing the opened parts in an airtight plastic bag with liberal amounts of dry silica gel, such as is available at boating supply stores here in Finland and marketed as gizmos for keeping humidity out of your boat's interiors or damp closets at summer cottages etc. Then, if possible, get the re-assembly of the parts started without taking them out of the bag. This way, the air that you have inside the scope will be as dry as possible with home-made systems without nitrogen. Of course, if you do have access to nitrogen, then use that.

I have opened my ED 78 A once to dry it, and re-assembled it outside in -15 C. dry air, which at least in theory contains much less humidity than warm indoor air. That worked pretty well, but as I have since had the scope worked on, it had nitrogen inserted at that time. I cannot say how much of the nitrogen is still in it, but it does not mist up in cold weather these days.

The rotational orientation of the lens assembly to the optical axis of the rest of the system is critical, and at least in my scope even 5 degree changes in the orientation of the objective lens cell make a noticeable difference in the image quality. So, if you end up doing what I and everyone else recommend you not to do, at least be very careful.

Hope this never comes to be of any help to anyone.

Yours,

Kimmo