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Nikkor 300 f4.5 AI-S ED IF cleaning attempt
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PostPosted: Tue Nov 03, 2020 11:43 am    Post subject: Nikkor 300 f4.5 AI-S ED IF cleaning attempt Reply with quote

The main goal is what looks like the spatter on the rear group, between the iris assembly and the glass, circled in the first image. I can get as far as pulling the middle group from the focusing tube (I think) but that doesn't let me get to the back side of the rear group. Ideally I would like to do a full clean/re lube. I can feel a slip in the focus going from closest to infinity at around the 4m mark though it doesn't seem to affect anything while looking through the lens.

here's what I've been able to figure out so far

image 2
screw 1, 3x around the focus ring. holds the markings to the focus ring I think.
screw 2a, 3x around the tube body, set screws I think
screw 2b, just 1
screw 3, 2x holds aperture key to aperature control ring.

image 3
under the focus rubber grip.
screw 7, 3x as marked, no idea what they might do
screw 8, under focus ring, Focus stop screw
screw 9, under focus ring, 6x, holes inner focus tube to focusing mechanism. inner focus tube holds middle optics group.

image 4
screw 10, only 1 under focus ring, accessible at ~2.8m focus, doesn't appear to move. looks like a set screw but doesn't allow anything else to unscrew when removed.
screw 11, 2x under focus ring, upper and lower, moves fwd/back as focus ring rotates, both accessible at ~2.8m focus. these have some sort of roller on them, metal or polymer, hard to tell for sure.

deeper in... surprisingly simple lens

Image 5: the pieces I've been able to disassemble. Main tube with focus ring, front group shroud, iris and rear group, 1 element, still inside. Front group top center, 3 elements. Mid group top right, 3 elements, focusing group moves forward/backward. Aperture key center, stop-down lever to the right of it under Mid group. bottom center is lens hood assembly. Lens mount is out of the shot, but nothing special there, 5 screws and a simple flocked tube that reaches the back side of aperture assembly.

Image 6: looking down the front with Front and Mid groups out. Rear group is fixed, and too deep in for me to reach as it is right now. first tube out from the center carries Mid group, attached to focusing mechanism by screw 9, six of them. anodized tube with slots is the main tube body it looks like. The grove that focusing ring rides on seem to be machined to the inside of the focusing ring. Outter most is front group shroud.

Image 7: looking down the back, nothing really complex. at the top is where stop-down lever attach. directly opposite, bottom of the shot around 6'o clock is tab for Aperture key. that's all the moving bits there is.

taking out screws 2a and 2b doesn't allow anything to unscrew as far as I can tell. Neither does screw 10, I thought that would allow me to unscrew the front group shroud but doesn't seem to be the case. Screw 8 is the focus limiter.

I'm pretty much stuck here. Some large piece must still come off the main tube, either the front group shroud or rear section where lens collar wraps around is a sleeve. Just don't know what. Put considerable pressure on the front shroud to no avail. still can't figure out what Screw 7 do... they seem to hold some steel or bare aluminum piece to the inside of focus ring but can't see where that might link to. Looking through the slots there doesn't seem to be a helicoid. the focusing group ride on groves machined to the inner wall of the focusing ring, the entire focus travel from closest to infinity is just maybe 5/8th of a full turn.

any ideas/suggestions on how to disassemble further would be much appreciated, on this particular lens, or another that's mechanically similar. So far I've looked at various disassemblies on Richard Haw's blog and videos on mikeno62's channel but haven't not see anything close.