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...

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

<< back to part 1...

this is a continuation of the previous part of the disassembly guide for the pentacon 135mm f2.8 (preset) lens. with most of the major sections now apart, we'll take a look at fixing the damaged aperture mechanism...

from the photo above, we can see that one of the aperture blades has dislodged and is now stuck between other blades at around the 2 o'clock position. note also the smudges on the blades, which are actually oils that most likely is what leads to the aperture damage. there is too much oils on the blades' surfaces which caused them to stick to each other and i guess is what eventually caused one of the blades to pop out from its slot due to the tensions induced when the aperture blades moves and drags against each others.

there is a 'C'-shaped plastic retaining ring [10(a)] that keeps the aperture assembly in place. one end of this retaining ring has a small slot, where one can hook a small screwdriver and pull the ring inwards to release it. from here, the slotted guide ring [12(a)] can be lifted up for removal, followed by the aperture blades [12(b-c)].

as there is so much oils on the aperture blades, the whole bunch of blades pops out in on piece [12(b)], and i had to pry them off from one another. [12(c)] shows a single blade which is the one that originally popped out of place. thankfully, there is no visible permanent damage on the blades.

[13(a)]: here, i made it easy for you to count the number of aperture blades present (15x total). the darker parts on the blades are oils, which is a lot... a commonly recommended cleaning agent for this is naphtha or lighter fluid. for me, i just wiped each blades one-by-one with a piece of tissue, and finishing by dabbing with cotton swabs moistened with alcohols.

there are additional 3 screws [14(a)] that attach the aperture mounting ring to the helicoid portion. i don't see a need to remove these though... there are 15 small holes here where one end of each aperture blades attaches to. after cleaning the aperture blades, it's time to reinstall them...

note that both ends of the aperture blades differs from each other: one end has a stud aligned at the middle [14(b)] - this stud goes into the holes in [14(a)] and pivots there. the other end has the stud offset to the edge of one side [14(c)] - this part should face upwards/to the front and goes between the slotted guide rings that we removed in [12(a)].

i forgot to take more detailed photos showing the assembly process of the blades here (oh well... i don't want to dismantle everything again just to take more photos!). anyway, the blades should be assembled as how they will be when wide-open, i.e. the entire blade should sits on the mounting ring, away from the opening hole. insert each blades by latching the stud on the correct ends into the holes in a clockwise fashion, i.e. the next blade should be inserted into the next hole in the clockwise direction (viewed from the front), overlapping the previous blade. this should be fairly straightforward for the first ten blades.

for the last 5 remaining blades, things may be a little more fiddly here as the remaining holes for attaching the blades are now covered by the previously inserted blades. here we'll need to slide these blades underneath the existing blades into position, and in the process one may accidentally dislodge the previously inserted blades from the holes. one tips here is that the other end of the blades has the studs on the edge of the blade, facing up. the inner wall right beside these studs is actually a little recessed (except at the opening slot for the aperture ring coupling mechanism), just enough to allow a tiny portion of the studs to slide under and 'lock' it in place against vertical movements. so the trick here is to push all the blades that are already inserted into this 'locked' position, and release just enough of them (should be less than 5 at the max - for the last blade) to allow you to slide the next remaining blades underneath - then push these unlocked end of the blades out just enough so that you can see the next hole to attach to underneath.

once all 15 blades have been successfully inserted, push all blades into the previous 'locked' position, and insert back the slotted guide ring [12(a)]. note that there is a hole at the side of the slotted ring where the screw from [7(a)] attaches to that couples the aperture mechanism to the aperture ring outside. the correct position of this hole, at wide-open position (when viewed from the side, with the aperture/front facing upwards, is at the far left of the slot openings (see [16(b)] further below for the slot opening/hole referenced here). make sure this is the last position at the far left before the hole disappears from view. if this hole is not visible at all, you're doing it wrong! :p

replace back the 'C'-ring from [11(a)] to secure the aperture mechanism in place. use a pin/small screwdriver to move the hole referenced above to test that the aperture is opening closing correctly. so there, we have a nice circular aperture opening again, with clean aperture blades to boot!

view of the aperture openings from the rear side [15(a)], and also the front side [15(b)] which is more commonly seen in product shots of this lens.

well, we can now proceed to reassemble the whole lens again. clean up whichever parts that may be deemed necessary, and re-grease all parts that should have grease added, if you've cleaned away the old grease (with a suitable grease of course - if you're not sure what to use, better leave the old greases alone even if they're full of dirts. it's still better than using a wrong grease that eventually seeps into the internals of the lens and coats everything, glass included). as for which parts should have grease and which part should not, well, generally i'd say if it appear to be greased previously prior to cleaning, you know what to do. but use your common sense - the aperture blades previously have greases/oils on them, but don't go and add them back after cleaning!!

the various parts should go back on in the reverse order that we've taken them off previously - just trace back the parts numberings here in reverse order. below are some additional guides at how some of the parts should align together, as a must.

to make things easy, we'll reassemble the aperture ring/control portions using the wide-open (f2.8) position as guideline. set the aperture mechanism to the wide-open position if it is not already there. the screw at [16(a)] should rest in the small slot closer to red dot at [16(e)]. meanwhile, the ring with the aperture index markings should have the small notch at [16(c)] aligned to the hole at [16(b)] such that the hole is visible through the notch with the ring fully in place. similarly, the '2.8' marking at [16(d)] should align with the red dot at [16(e)].

additionally, when reassembling the focus ring, if you did not mark the exact position for the insertion point w.r.t the helicoid during removal (which you should have done), you may find that the infinity mark do not align correctly with the red triangle [17(b)](distance indicator) at maximum focus ring turn, as well as the aperture red dot indicator [17(a)]. installed correctly, all these markings should line up together at infinity position. in this case, you can first make an estimate of the distance that the infinity mark is offset from the red triangle indicator. then slowly unscrew the focusing ring off again until the exact point it detached from the helicoid, and stop - from here turn the focusing ring just enough to compensate for the difference in the infinity mark position estimated earlier. screw the focus ring back in and check the infinity mark position again. if it is still off, repeat the previous sequence of steps again to correct the difference here. this may take a few tries before you managed to get the correct alignment.

the remaining parts should go back on without much issues. so there, all successfully assembled back together again. not that hard now right?