Last night, I tried to clean the TN5's lens... but, it is stuck in its cell (I think I know why).
Since this is the main thread for this weird RFT, here are some Specifications...
LENS CELL Diameter = 148mm [outer]
LENS CELL Length = 54mm
LENS CELL Weight = 6.8 lbs
LENS Diameter = 134mm
LENS Clear Aperture = 128mm (5.04")
LENS Focal Length = 680mm (26.77")
LENS Focal Ratio = 5.3
The Cell was machined from a single piece of aluminum. It is anodized black. Where it's been rubbed, this black is shiny. A previous owner painted the front & back with flat black, which has worn off in some spots. The cell sides have streaks from being slid in & out of the tube.
The Lens has 3 elements -- E1 / E2 / E3 (from sky to eye). E2 is the thinnest, and has that large clam on the front face that extends 3mm into the light path, and is 28mm wide at its base. Flat black paint was used on the exterior faces of E1 & E3 to mask the clam. Why isn't the clam itself painted? Glad you asked! This lens has no spacers. E2 has a bead of glue between it and the other 2 elements. Under the microscope, this bead has a uniform width & thickness around the circumference -- except where the impact that clammed E2 occurred. IOW: The lens was made this way, then damaged. I see no / zero / nada dust between the elements. What I thought was mold / debris are tiny flaws in E3's coatings (eye side of this glass). I don't know what this glue is, but it's a translucent white. It hasn't yellowed the way Canadian Balsam has on some old lenses I've owned. Here's my best guess on the lens elements (not to scale, & curves exaggerated):
This large clam makes for some interesting star tests:
What I try to show is that as the rings get closer to the clam, they widen on that side. Then, the first couple that intersect the clam deform around the shadow. Finally, the outermost rings disappear at the clam edge, and reappear on the other side.
I suspect that whoever painted the lens to shadow-out the clam used the same flat black paint on the "lens compartment" of the cell, rather than blackening the lens edge. I did that with both my Mogey 3 and JaegerMeister 4 cells. I think that over the years, the lens pressed into this paint, and is now stuck to it. This paint resists Zeiss Lens Cleaner. Can't recall if I've tried alcohol on it. So, all I could clean were the two exterior faces -- that's when I saw the pin-sized flaws in the coatings.
Edited by Bomber Bob, 05 March 2020 - 07:11 PM.