Disassembly Guide for Pentacon 135mm f2.8 (Preset) Lens [Part 1 of 2]

Pentacon 135mm f2.8 (Preset)

focal length: 135mm (medium telephoto prime)
aperture range: 2.8 - 32
aperture blades: 15
min. focus distance: 1.50 m / 5 feet
construction: 5 elements in 4 groups (lens schema)
weight: ~ 515 grams
filter size: 55mm
mount: m42 screwmount (interchangeable)
serial #: 84*****
purchase price: (???)
others: dedicated metal hood

the earliest incarnation of this lens is the zebra-styled body under the meyer-optik görlitz orestor brand name. this subsequently turns into the pentacon brand name due to mergers, with the earlier now pentacon-branded lens still retaining the zebra styling. later versions loses the black & white stripes for an all-black look, and even then, there are at least 3 different all-black body style produced that i'm aware of. the earlier ones have knurled metal focusing ring (i used to own this, but has since sold it), followed by the square-grid focusing ring style (it is metal although it may look like rubber from photos) - this version will be the subject of our study here. the latter ones still have the square-grid focusing ring, but the front-end of the body is now flush in a straight line with the dedicated lens hood where previous versions isn't.

subsequently, the preset lens was discontinued and replaced with the 'auto' version, which loses the beautiful 15-blade rounded aperture that this lens is now famous for.

disassembly, cleaning and aperture repair guides

this guide is based on the all-black version with square-grid focusing ring, likely the 2nd all-black version - although i believe this should also applies to the other all-black versions as well. the zebra-styled body may have slight differences though from what i've seen. my primary purpose for disassembly here is to repair the aperture which was damaged (oh well, at least i got a refund and gets to keep the damaged lens too) - and as this required a strip down of all major parts to access the aperture assembly, the guides here should be sufficient for general-purpose cleaning as well.

as a general guide, it is highly recommended to mark the positions of everything relative to other parts before removing them, either by marker pens or sharp objects for internal parts. also, taking a lot of photos along the way will be useful for reference later in case something goes wrong. and keep the cats away...

for starting, it is recommended to set the aperture to max/wide-open, and turn the focusing ring to infinity position. this will tuck the aperture blades aside and move the internals closer to the rear of the lens, from where we'll start the disassembly process. in my case, due to the aperture is damaged, it'll have to be left in the stuck position for now.

the rear lens mount [1(b)] is removable and is held in place by a retaining ring [1(a)]. unscrew this retaining ring (counterclockwise turn. from now on, unless specifically mentioned, all unscrewing turns should be CCW). besides this retaining ring, the mount is also held in place by a protruding screw (see [2(c)] below) that fixed the mount position and prevent it from rotating in place.

with the mount off, we can see three screws [2(a-c)] securing the next part to be removed. Note the position of screw [2(c)] for reassembly later, as this is different from the other 2 screws, but they fit into the same holes. remove these 3 screws, but do not lift up this ring yet.

pay attention to [3(a-b)] - these are 2 short pointed guide pins that ensure the lens assembly attached to the helicoid do not rotate during focusing, as well as preventing the focus ring from twisting off. note: the focus ring should probably be turned to minimum focus distance first before these 2 pins are directly visible. These 2 pins are pushed by springs against the inside of the ring that you're about to remove (see [4(a)] below), so be careful in removing this ring and ensure the 2 springs do not fly off when the tension is released. else, good luck searching for them... then again, considering the average age of these lenses, the springs are more likely to be held in place by hardened old grease instead, like on mine.

with [4(a)] lifted off, remove the 2 springs and pins in [3(a-b)]and store them away. next, the focus ring [4(b)] can be removed by unscrewing it further in clockwise direction. now do this slowly, and mark the exact position that the focus ring comes free from the helicoid to make it easy for reassembly later. otherwise, you'll need to do the reassembly of this part by trial-and-error a few times later.

note for [4(b)], the upper portion which holds the 2 guide pins should be turned all the way to the left for reassembly later, if you've moved it around during cleanings. this will be the infinity position of the focus ring, or to be correct, is slightly past infinity.

tuck [4(a)] & [4(b)] away - clean them if necessary - and we'll proceed further with [4(c)].

the rear lens assembly [5(a-b)] contains the 4th and 5th lens elements and screws into the helicoid. There are 2 small notches on opposite edges of the housing's rear end to facilitate removals of this assembly unit. with a suitable tool (i used a cheap pair of drawing compass with the sharp ends clipped off and flattened), unscrew this assembly from the helicoid [5(c)]. be extra careful here if you're not using a specialized tool for this - you don't want to slip up and scratch the lens elements now...

note: you can actually do this step much earlier as the rear lens assembly is accesible from the start without needing to remove anything else.

in this rear lens assembly [5(b)], there appears to be an inner housing with another set of notches to allow for removal of the rearmost lens from this assembly. unfortunately, on mine, i'm not able to make this inner housing turn for releasing even with considerable forces applied. there may be some adhesive/loctite applied? not sure here - i guess i'll have to leave the dust inside... better than ending up with a scratched lens later.

from [5(c)], we'll proceed with removing the next outer ring [6(b)] from the remaining assembly. this is part of the outer lens body and only has a red dot on it which points to the current aperture value. this is secured by a small grub screw [6(a)] near the helicoid. remove this grub screw and then unscrew this ring.

for re-assembly later, note that you should turn the aperture ring to the wide open position and align the red-dot on [6(b)] with the '2.8' value. if you just screw [6(b)] back on all the way without paying attention, it'll most likely points slightly past '2.8'... well, that's fine if you intend to confuse others :)

with [6(b)] off, another 2 screws are revealed. one is attached from the inner side and serves as the minimum aperture stop point for when turning the aperture ring (i think?), in order to prevent potential damage to the aperture blades - this can be left in place. the other screw [7(a)] sits inside a notch and couples the aperture ring to the actual aperture mechanism inside. remove this screw followed by the ring [7(b)] which has all the aperture values marked around it.

Note: there is a metal spring under the aperture ring (see [8(b)] below) that tensions it as well as this [7(b)] ring upwards. thus you'll need to push the ring down while removing the [7(a)] screw.

with [7(b)] removed, we can see that there is a long slot with a small hole which actuates the aperture assembly when moved. near this slot is yet another screw (see [8(a)] below) that needs to be removed.

unscrew and remove [8(a)], followed by the aperture ring [8(b)]. remember that there is a metal spring [8(d)] underneath that pushes upwards, so you'll need to counter this force when removing the [8(a)] screw. observe how the metal spring [8(d)] is attached in place [8(c)] before removing it. anyway, [8(d)] is shown in the correct orientation for re-attaching this spring later.

from [8(c)], there is yet another tiny grub screw [9(a)] that secures the helicoid/aperture combo [9(b)] to the front optical block [9(c)]. with this grub screw off, the helicoid/aperture combo can now be detached by unscrewing it off. note: there are considerable number of turns needed before the 2 parts will separate.

[9(d)] is a conical cone that locks the housing for the group of 2nd and 3rd lens elements in place. by right this can be unscrewed off as well in order to take out the lens assembly inside. once again, mine proves uncooperative by refusing to budge. note the there is no slots on this cone to help with unscrewing, so you'll need some sort of friction tools to get a good grip. oh well... anyway, there is really no need to remove this, as the 2nd and 3rd elements are supposed to be a cemented group anyway. if you want to clean off the dust between this group and the front element, fret not - we can still enter from the front side...

moving on to the front side, detach the metal hood if it is not already so. the front element is held in place by a retaining ring [10(a)] that screws directly into the filter thread. there are 2 notches on opposite sides of this ring as well that allow a suitable tool to latch onto and twists this ring off. so there, take off the front element (handle with care!) and clean it up nicely as needed, and clean off the dust and whatever junks there are in the space inside. then replace back the front element and lock the retaining ring back in place...

here is the end of part 1. head on to part 2 of this guide, where we'll take a look at the aperture assembly, as well as some further tips for re-assembly later...

>> continue to part 2...