|Posted: Fri Aug 21, 2020 4:36 pm Post subject:
|My cheap and cheery spanner wrench, actually it's cheap, but solid, will go to 12.5cm with the centre rail out.
. . .
Thank you. That's encouraging to know. I'll shop around and see what I can find.
|. . .
By the way, in your dismantlement, did you get to the aperture iris? The iris in mine is lazy and needs cleaning. I haven't tried reaching it yet. But if you have, maybe you can give me a heads-up about any sort of difficulty you had in reaching it?
No, I haven't reached the iris yet. It's below the group seen in my second photo.
As soon as I can, I'll have another go at dismantling the rear end. If I get to the iris, I'll let you know.
|Posted: Tue Sep 08, 2020 3:55 am Post subject:
I gave the lens (yet) another try, and this time I had a bit more success.
Regarding the deep elements seen in my first post: I tried but failed to get them out from the rear. So I modified my spanner to reach them from the front. Crude, but effective!
As for the rest of the lens, I was able to get most of it apart - and back together.
I've documented the process below.
This was a trial and error situation, and I learned as I went. My goal was to reach inner and rear elements for cleaning. And this guide is focused the on the disassembly needed to reach them. I haven't covered cleaning or lubrication, but if you have any questions or suggestions, let me know.
Regarding the elements, I'm going to refer to the different assemblies as groupings. There are 3 groupings in front of the iris and 2 behind. But the 2 rear groupings are screwed together.
Most groupings were easily removed. The only difficult one was the third which sits directly in front of the iris.
Tools used: Set of small, flat blade screwdrivers, lens spanner, dental pick, solvent and heat. And I used a large cake pan as a work area to help prevent small pieces from falling to the floor.
Before I get to the full disassembly, cooltouch asked about the reaching the iris. Because of the sequence in which I proceeded, the quickest route to the iris is different from the full procedure listed below.
For those who just want to get to the iris:
Turn the focus ring to closest focus distance, skip ahead to step 3 and proceed as far as needed.
To get the aperture ring off, the zoom ring needs to move forward. By turning the focus ring to its closest focus, there may be enough space for the zoom ring to move forward and uncover the aperture ring screws.
And if that isn't enough, loosen the focus ring stopper screw until the focus will go beyond its usual stop. You should then have enough space without having to remove the focus ring.
Okay, here's the full disassembly.
Starting at the front:
1) To remove the first elements grouping:
Around the rim, just above the silver trim ring, there are three screws. Loosen, but don't remove them. Now the front of the lens should unscrew and the name ring and first grouping will lift out. The name ring has spanner slots to access the elements.
Also, with the front assembly out, turn the zoom ring to 85mm and the slotted, second element grouping is easily reachable with a spanner.
2) To remove focus ring:
Remove the single, focus stopper screw. Turn the focus ring toward closest focus distance until it separates from the inner helicoid. Go slowly and, for reassembly, make sure to note the point at which the ring separates.
The built in hood is also part of this piece of the barrel. I would think there should be a way to remove it if needed, but I left mine in place.
3) To remove zoom ring:
Warm the textured grip with a hair dryer or some other (gentle) heat source. Pry up one end of the grip at its seam and peel it back until you've uncovered 4 screws (all at the upper end of the ring). Remove the 4 screws and the ring will slide forward / off.
Moving to the rear:
4) Remove the silver mount:
Remove one screw from the base and the mount will unscrew (left handed thread).
5) Remove silver, stop down / preview button from the lower barrel:
The button is held by a slotted nut. I was able to get it loose with a screwdriver.
6) Remove retaining collar below tripod mount ring:
The collar has spanner slots.
7) Remove tripod mount ring:
Don't forget to relax the thumbscrew first - and then the ring should just slide down / off.
8] Remove aperture ring:
Remove 4 screws and ring will slide down / off.
To remove rear barrel / gain access to auto stop down levers:
9) Remove security screw and unscrew threaded junction collar which connects the lower and upper barrels:
My screw loosened easily, but tolerances are so tight, it wouldn't come free from the barrel until the upper and lower barrels separated. But it caused no trouble. Just make sure it's fully unscrewed from its hole.
The junction collar needed several doses of solvent and heat before it would budge.
10) With the lower barrel separated, now the rear elements module can be removed. It contains the fourth and fifth element groupings which are screwed together:
Use a spanner to unscrew the large, black, slotted retaining ring. The module will lift out (note the small slot which slides onto a pin to locate the module).
Now the iris assembly will be exposed, but it's still fastened in place.
To remove the iris assembly from the barrel:
11) The (inner) zoom ring has openings to allow access to 3 screws beneath it. The screws hold the iris in place. Rotate the zoom ring as needed and remove the 3 screws (blue arrow).
12) Lift off the brassy C clip (blue arrow) and the iris assembly will fall out. (A dental pick is useful for lifting C clips.)
Luckily, my iris had no problems. Here it is:
13) To remove the (inner) aperture ring:
The junction collar rotates and has holes to access 3 screws underneath. Loosen the screws a couple turns, but don't remove them (see green arrow in photo #5).
Now the collar's slotted, silver retaining ring can be unscrewed with a spanner and the collar will come off (see green arrows in photo #6).
[This retainer was difficult to reach. It's not deep, but the gap between the collar and inner barrel is narrow, so I had to file down the shafts of my spanner in order to fit it in.]
The aperture ring will now slide off. Removing and replacing will probably be easier if you loosen the brassy strip on the right side [see photo #5]. It's pushing a ball bearing against the barrel to give the aperture ring its click stops. I removed this strip and my bearing stayed attached to it. But be careful - such ball bearings are easy to lose.
14) To remove focus helicoid barrel:
Remove 4 screws around the top of the helicoid. The barrel will slide off.
(The velour / felt strip around the base of the barrel is for damping the [external] zoom ring's movement. My velour is tattered because I removed it when looking for hidden screws. There aren't any screws there. Just leave the strip alone.)
15) To remove (inner) zoom ring barrel (see blue arrows in photo #8 above):
Remove 2 side by side zoom ring stopper screws.
Next, remove 4 zoom cam screws and bushings (I believe "cam" is the correct term..?). They're the ones in the eccentric channels.
Then, remove the C clip from the upper barrel and the barrel will lift off.
The cams weren't as difficult to deal with as I'd feared. I don't know if there's a best way to disassemble them, but I rotated the zoom to the 300mm end so the two different element carriages were near each other at the lower end of the barrel. Tolerances were tight, but the cams came out and went back in without a lot of effort.
Before removing the cams, I suggest you study how the different pieces are positioned and how they move. And, as always, take notes and photos for reference.
16) Accessing the third element grouping:
After the cams/screws are out, the carriage for the second element grouping will slide forward and out - along with its elements if you haven't already removed them. [See it in photo #2.]
And this is what I had left - externally and internally:
As you can see in the view from above (middle picture), the third element grouping has spanner slots. But even at its highest position, it's still 11cm deep inside the barrel. And there are no spanner slots on the bottom side.
I thought certainly the lower barrel would separate and allow me to get the carriage and grouping out from the rear, but I couldn't get it apart.
And on the lower, outer barrel there are holes to access screws holding the zoom guides. I removed one guide and I briefly tried to get the second one out. But it didn't appear that removing them would have any effect so I left the second one in place.
(That single screw at the bottom of the barrel is the locating pin for the rear elements module. Leave it in place.)
I was able to clean the bottom surface of the grouping from below, but I wanted to actually get the grouping out for a thorough cleaning. So I modified my spanner to give it a longer reach and was able to remove the grouping and clean it (see spanner in photo #1).
And . . . that's The End. Good luck getting everything back together!
Also, I must say how impressed I was with the build quality of this lens. It's already around 50 years old, and with proper care it should still be functioning 50 years from now. Well done, Canon!
Finally, if you need to disassemble your 85-300, I think by studying my steps you'll be able find a more coherent path than I did.
Knowing what I know now, if I were going to do it again, I'd start at the rear and work forward.