[jbensen8191]

Hi all, new here though been reading the lens reviews for a long time, very helpful info.

I've recently acquired a P645 A* 300mm F4 ED-IF and it is every bit amazing as the reviews indicate. Price was good, glass is clean and all the function is good. The only issue is the main barrel highlighted in green have a bit of play that I'm a little worried about. It doesn't appear to affect the image but if it increases I expect it might in the future.


I've gone in part way from the front and back. From the front there are 3 screws holding the front section to the middle section with the focusing barrel, didn't go in any further. From the back I can see the seam where the aft part of the barrel wiggles but I don't see anything holding it in place.Around the body I can access 2 set screws under the lens hood, these hold the front lens group in place. three set screws around the distance mark section of the focusing ring, looks like part of focus adjustment. 4 screws under the focus ring accessible when focus ring is at infinity, don't appear to affect the aft section of the barrel as they are all thread locked and very snug already.

Any ideas where on the lens body I need to get at so I can snug it up? or any disassembly info on pentax telephotos?

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My guess is the helicoid grease is drying out so you are not getting the dampening effect on such movement. If you can access the screws that hold the outer barrel with the rubber ring to the inner focus barrel removing those should allow you to remove the outer barrel. After that you should be able to unscrew the two barrels of the helicoid so you can clean and regrease the threads.

Most * lenses are usually valuable enough that you may consider having it professionally serviced rather than DIY.

[jbensen8191]

Turns out much simpler than I expected. There's no mucking about around any glass elements so very simple and low risk work with a set of small JIS screwdrivers.

Roll up the focusing ring grip to reveal 4 screws accessible with focus at infinity, there are another set of screw holes just to the left of these but these are the correct ones for proper focus after assembly. Marked A in first image.

After removing the A-screws you can pull away the aft section of the lens, this includes the diaphram and rear lens group etc. The 4 screws holding the aft section to the diaphram section have all worked themselves loose. marked B in second image. Simply tighten them up with a tiny dab of nail laquer should keep things snug for a while.

reassemble in reverse order align everything along infinity mark.

[bratzmahn]

Right!
I had the same issue with my A*600 f5.6

[kayakfari]

Turns out much simpler than I expected. There's no mucking about around any glass elements so very simple and low risk work with a set of small JIS screwdrivers.

Roll up the focusing ring grip to reveal 4 screws accessible with focus at infinity, there are another set of screw holes just to the left of these but these are the correct ones for proper focus after assembly. Marked A in first image.

After removing the A-screws you can pull away the aft section of the lens, this includes the diaphram and rear lens group etc. The 4 screws holding the aft section to the diaphram section have all worked themselves loose. marked B in second image. Simply tighten them up with a tiny dab of nail laquer should keep things snug for a while.

reassemble in reverse order align everything along infinity mark.

Interesting discovery! After separating into two sections, is the IF mechanism accessible for re/greasing?
Do you have any more pics of the process?

[scc]

Interesting.
I guess the same disassembly process was needed on my A*300 f/2.8 with jammed focus ring (see the related thread).

[jbensen8191]

Interesting discovery! After separating into two sections, is the IF mechanism accessible for re/greasing?
Do you have any more pics of the process?

Interesting discovery! After separating into two sections, is the IF mechanism accessible for re/greasing?
Do you have any more pics of the process?

I don't know if focusing mechanism is easily accessible, I didn't try to get that far. I don't have pictures but I'll try describe as best as I can.

From the front: 2 set screws accessed by pulling lens hood out to full. Removing these allows front lens group to unscrew from the barrel. Lens hood can be removed along with front lens group. 3 screws hold the front barrel section to the middle section. Setting focus to hard stop past infinity moves the focusing group up flush with the top of middle section. After removing the focusing group the focusing mechanism is partly visible through guide slots in the barrel. After the focusing lens group there is a single fixed element, then the aperature blades, after that the rear group and lens mount. There's no obvious way to get to the focusing mechanism from inside the barrel.

There are two holes in the upper part of focusing ring under the rubber grip, a polymer roller and a screw can be accessed from each when focus is set to around 5.5m. These I think ride the guides machined on the inside of the focusing ring. my guess is the focusing ring could be backed out by rotating past infinity after the rear barrel section is removed. I'm hesitant to remove these screws because they probably move and hold the inner focusing barrel in place.

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Last edited by jbensen8191; 07-29-2021 at 05:23 PM.