Posts Made By: Roland Christen

The lens is actually contained, even though it can float loosely inside the aluminum cell. The glass is resting on cork pads in the back, and these may have compressed a bit with time. The front retainer cell is not actually in contact with the glass, and should not be. It is there primarily to prevent the lens from falling out when the scope is held upside down. The reason why the lens is not tightly held is because the glass contracts slower than the aluminum cell. If it were the same size as the inside diameter of the cell, and the temperature dropped by 20 degrees, the glass would be severely pinched.

In a normal airspaced lens, the front retainer must put some pressure on the glass to keep the airspaces from shifting. This 180 lens is oil spaced, and it cannot have any pressure on the glass, either from the side or from the front retainer. It must only rest on the cork pads on the back. In this respect it is quite the same as a Newtonian mirror, which also cannot have any pressure from side or from the clips in front. Pressure from the retainer ring will cause the lens to distort with resultant astigmatic images.

There is no worry that a shifting lens set will cause any kind of optical problem. The shift is very minute compared to the diameter, and consists of perhaps .01 to .02 inches at most. Under use in the sky the lens will settle nicely on the lowest diameter and the cork pads on the back. The three elements cannot move relative to each other since they are oiled together, and even a team of horses could not pull them apart. Air pressure at 14lb/sq inch sees to that.

When those lenses were made originally, we were content to let them float freely in their lens cells (same as your normal Newt mirror). Today a typical oiled lens is glued into the cell in several places with a very soft rubber cement. Can it be done with this 180 lens? Yes, but that will entail quite a bit of work and time for me, and I suspect quite a bit of money for you.

Roland Christen

Dang, that is a lot of detail. Amazing.

Roland Christen

The image is too dark to see the faint stuff. It looks like the histogram is clipped.

Rolando

That's almost what mine looks like right now. Normally we are 2-3 weeks ahead of Minnesota down here in Illinois. Have you had an unseasonably warm winter?

Rolando

These Jaegers Maks were made in Poland, assembled by high school kids. This was during the communist era.

They were ultra-sensitive to decollimation, and most if not all were miscollimated by the time they reached the final customer.
I tried to adjust a number of them for local amateurs, but the adjustments were incredibly crude. It took hours of trial and error to line one up. They were pretty horrible scopes even when properly aligned. Don't even think of buying one.

Rolando

>>Even when the RA locking knobs were fully in the "locked" position, you can move the scope "right to left" a couple of degrees. >>

All that the locking knobs do is to attach the axis fully to the worm wheel. Basically it tightens the clutch mechanism to the worm wheel. As you have seen, this does not eliminate the worm backlash (or "play" as you call it). Worm backlash is caused by the driving worm gear being somewhat out of mesh with the large worm wheel. What you must do is to put the worm back into mesh. It is an adjustment that every mount needs at some point in its life, and it is not a sign that something is wrong with the mounting. It's simply out of adjustment. Go back to your manual and look up the worm adjustment procedure.

RC

>>You can find the tutorial at:
http://www.petesastrophotography.com/tutorial/polaralignment.html
FLASH required. >>

Excellent discussion and graphics!

RC

Amazing detail for such a small aperture. Good work.

Rolando

To answer your question directly, it is typical to edge and center each individual lens element in a triplet apo to an accuracy of .0001" wedge tolerance (which is approximately 2.5 microns). I don't know any of the top apo makers that do not routinely achieve this minimum level of accuracy in their centering.

Each element is normally edged as a unit on the same machine in sets of three so that they come out with the same exact diameter. They don't need to be exact, but it makes final adjustment easier.

The elements are then placed into a cell where the edge positions are held by the cell wall. The spacers between the elements must be held to a thickness tolerance of approximately 1/2 tenth (.00005"). Even then the final adjustment of the spacing is usually tweaked by carefully polishing off an infitesmal amount of material until all signs of coma are gone. This is done during the final alignment process. It compensates for any wedge in the glass or the spacers and spacer positions. Another way to do it is to provide 3 screws around the periphery of one of the elements which allows the optician to move the element sideways to counteract coma. It is not a precise way to do it because it inevitably introduces a tiny bit of lateral color, but it is the easiest, fastest and cheapest way to do final alignment.

Roland Christen

Woah! It looks like you're in orbit around it!

Rolando