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Hi all,
Just picked up a deal ($30!) on eBay for what superficially seems like a working Newport 481-A. I plan to use as a rotator for a half wave plate. However, it’s not at all clear to me whether it’s damaged or I just can’t figure out how to use it properly. The outer stage (the obvious one on top) rotates manually 360 degrees so it does what I need it to do regardless. However, if I understand the Newport description correctly, the micrometer on the side is allegedly supposed to allow an additional fine adjustment of about 5 degrees after the main rotator is adjusted manually. The only thing that seems to happen on this unit is that the part of the stage holding the fine adjustment micrometer is pushed away from the unit- which is only obvious after I loosen the setscrew holding the micrometer in place andvit snaps back. If anyone here has used one of these units, can you please describe to me what’s supposed to happen when the micrometer is turned? I see no indication at all of additional rotation. See attached Newport literature.
Thanks!

The micrometer will only do a couple of degrees of adjustment. The rotational stage is roughly adjusted by loosening the thumbscrew and rotating the insert bushing. I’m thinking this is a bit of overkill for that last few degrees of adjustment needed for a polarizer?

No argument there. I adjust using a light meter & calibrated polarizer & it’s pretty clear where the optimum points are. Interestingly though, at $30, this 481-A is cheaper than most used eBay Thorlabs RSP1 & Newport RM25a rotators. Just frustrated that the micrometer seems to do nothing on this unit. Made me think I must be doing something wrong since i’ve never had one to actually fool with before. There are still a couple of things I can try without taking it completely apart (which I won’t do). There’s a hex screw at the other end of the micrometer housing and when I take the micrometer off, it looks like there’s a tiny set screw inside. I’m thinking maybe the tiny internal set screw is too tight...? Don’t know if I really want to fool with it though without knowing since it is fundamentally working well as a manual rotator. You know how it is though when your curiosity about something gets the better of you! I’ve got a call into Newport so maybe i’ll hear back on Monday...

On most micrometers the entire head can be remove in its entirely , once removed soak it in penetrating oil ....

The micrometer itself is working fine. Already took it out and checked it. Seems to be the “tangentially driven high resolution outerstage” controlled by the micrometer, that’s not doing it’s job.

Soak it in PB blaster, or penetrating oil for a while ...

What is PB blaster?!

PB = Peanut Butter Blaster... best lubricant ever... (LOL).
(Joy here). Ive used those, I have similar, and I can double check one when I get into work today.
The general idea is to loosen the knob to use the manual spin, but you must tighten it to use the fine micro. The issue is that is not quite intuitive, and people break them (did you wonder why it was cheap?) Often they just snap the positioning springs, with the effect that the fine adjust only goes in one direction and the other direction pushes loose. If they are frustrated (or curious like you) they try to take it open and yes, undo one of the set screws that hold the stage together. If you're only using it for a waveplate, dont worry about it - you got a real hefty piece for a deal.
Incidentally, if you're shopping for used opto-mechanno, I recommend http://www.lightglassoptics.com/

Thanks Joy.
Yes, it does seem counterintuitive! Just tried it with the knob tightened & nada. The fine adjustment must be broken as you speculated. I can push the whole lower micrometer & knob portion a few degrees with my fingers and it snaps back to the right - it’s feels like a very tight spring. I assumed it was cheap because it was sold minus the micrometer & the knob. The knob is a 10-32 screw which I had & I had a spare AJS micrometer which slides right in so I didn’t see it as an issue. Still a good deal for its purpose although a little clunky.
Thanks again.

I've used these before. The knob isn't just a 10-32 screw. It has a shaped tip with a smaller diameter, if I remember correctly.