This 135mm f/2.8 AI-S is a direct upgrade to the AI version with no change in optical formula and outwardly looks very similar to its older sibling. The AI version was painful to service but how does the AI-S compare?
I didn't enjoy opening this lens. There are a few little surprises, too many small grub screws, and things not where you'd expect but heres some notes. If this reads familiar its exactly what how I felt about the AI version and whilst they are similar they are also changes that will potentially trip you up.
Optics
Having the same optical 5/4 formula as the AI version - which it itself inherrited from the new-K - we can refer to the AI lens structure:
The bulk of the elements can be seperated from the rest of the lens by unsecuring the grub screw and unscrewing.
- Remove the front retaining ring
Extract - don't just loosen - the 2x grub screws which sit in a quadrant
I've found the ring very difficult to remove using rubber pads/cone tools - I had to punch 2 points for a lens spanner to unscrew.
- Remove the front element retaining ring
The second element can also come out. Note the spacer between first and second element has the ridges facing front and the flat edge sits on the front element.
- Remove the front optical housing
Extend the barrel to MFD and loosen the grub screw - unscrew the front block
- The 3rd group can be accessed in place
- Rear element can be freed with lens spanner
Do note the orientation of the rear element as its very flat
This is further complicated if you think the rear element is flipped given its very similar profile for what should be facing in vs out. Annoying until you mount the lens and take an image its not apparent - calibrating for infinity also works although you will see that infinity is well short from your original reference points.
L: flipped/incorrect orientated rear element
Helicoids
- Remove the mount and take note of the how the optical block sits
The entire optical assembly - front, back and aperture mechanism - comes out. The optical block is secured by 3x deep lying cross head JIS screws: using a magnetised driver is key.
- Seperate the barrel and optical block
There are some key landmarks that need to be observed for reassembly. The iris is coupled to a notch on a cylinder with the aperture pin.
At infinity the helicoid keys sit quite high - mark this position for assembly reference.
This is how the aperture ring hooks onto the aperture pin.
- Remove the aperture ring, chrome grab ring and rubber grip
Remove the 2x screws on the aperture ring and lift off the aperture ring.
Mark infinity positions on the rear and center helicoid before you remove the ident spring and the chrome ring- notice the tape? That's from the factory and thats how the infinity and MFD positions are enforced. The mark under the tape is another infinity reference mark made at the factory.
- Prepare to seperate helicoids
Remove the helicoid keys, noting which is which - I mark the one to the left of the infinity position with an L. Collapse the rear helicoid and mark a different (angled) position to give another reference point for reassembly. Remove the tape that secures the focus distance scale - this ring provides the hard stop coupled to the chrome grab ring
- Separate the outer helicoid
Mark the separation point - the arrow on the outer helicoid lines up to the infinity reference mark made on the central helicoid
- Separate the inner helicoid
This helicoid can be separated through the front and the back. However this helicoid has zero lip top or bottom so you need to mark the helicoid on the black paint on the edge. This helicoid has multipe multiple starting positions so you have to be careful but its clear if the reassembly is incorrect as the keys only sit in one place to get back to the original positions that were marked earlier.
- Clean the helicoids with lighter fluid, kitchen degreaser, kitchen dish soap and then final clean with IPA. Wipe down/away most of the grease first, perhaps with lighter fluid applied to a thick kitchen tissue
- Apply a very thin layer of NLGI #00 grease to the inner helicoid and remate. On the central helicoid apply a thin layer of the same grease but adjust to taste as this will have the most impact on the lens's focus feel when fully assembled.
Remember to lightly grease the helicoid keys and its slots.
Check the position of the helicoid key screws when positions lined up for infinity - if the position is not correct seperate the inner helicoid from the front and retry.
Reassembling
The inner helicoid is painful to remate so patience is required. I find it easiest to sit the inner helicoid facing up on a desk and dropping the central helicoid on top to try to catch the mating point.When reassembling the objective and the barrel you need to ensure that the apeture notch sits on the iris mechanism and also the orientation is correct for the 3x deep lying screws.
To adjust for infinity, reassemble the lens fully except for the rubber focus grip and the tape on the distance scale - focus at a far far object and when happy secure the dinstance scale with tape and then reinsert the rubber grip.
Conclusion
This is a non-trivial lens to fully service - the lens elements are relatively simply but the helicoids are picky as well as the reassembly - front retaining ring is stiff and you can scar the lens with the punched notches for the lens spanner. It's probably easier than the 135mm f/2.8 AI as theres less small screws but the iris notch and the inner helicoid are painful.
No comments:
Post a Comment