The Focusing Helicoid Disassembly of the Carl Zeiss Jena Flektogon 25mm f4 M42 Zebra Version

2026/7/5

One of the first issues I noticed after acquiring this lens was that the focusing ring was extremely stiff. At certain points, it required considerable force just to turn it. Considering that this is a 50-year-old lens, it's no surprise—the original helicoid grease inside the focusing mechanism has most likely dried out over the decades. Instead of providing smooth lubrication, it has become a source of resistance.

Following the previous article on rear-end disassembly, this installment covers the disassembly, cleaning, and re-lubrication of the focusing helicoid. The first step is to remove the entire optical assembly. Looking from the rear of the lens, once the aperture linkage, aperture ring, and related components have been removed, the retaining ring that secures the front optical assembly can be unscrewed. The complete optical unit—including the front lens group, aperture assembly, and rear lens group—can then be lifted out from the front of the lens, leaving only the focusing helicoid behind.

這顆鏡頭入手之後，令人困擾的問題之一是對焦環很緊，有些位置甚至需要非常用力才能轉過去，畢竟是50年的老鏡頭了，鏡筒內的潤滑油應該都乾掉了，原本潤滑的功能變成阻力。

接續上篇拆開後鏡筒之後，這次就來拆開對焦筒、清潔、重新潤滑。首先，要把整個鏡組取出，從後鏡筒觀察，光圈開閉連桿、光圈環等相關的零件拆除後，再將鏡頭前面的鏡組固定環卸下，即可將整個鏡組、光圈筒和後鏡組從前方取出，剩下的就是對焦筒了。

The retaining ring that secures the front optical assembly is the first ring adjacent to the lens barrel.
緊鄰鏡筒內的第一圈壓環就是用來固定整個鏡組


The focusing helicoid consists of three main components:
(A) The outer barrel, which supports the optical assembly and the aperture housing.
(B) The focusing ring, engraved with the focusing distance scale.
(C) The depth-of-field scale ring.

On the underside of Ring C, there are two metal tabs positioned 180 degrees apart. These tabs couple Ring C to Component A, and each tab is secured by two screws. After removing the four screws and lifting off the two metal tabs, Component A can be separated from the combined B + C assembly.

對焦筒由三個零件組成 (A) 固定鏡組和光圈筒的外筒 (B) 有對焦距離刻度的對焦環 (C) 有光圈景深刻度的環。C環的底部相對180度位置有兩個與A環連動的鐵片，每個鐵片有兩個螺絲固定，將這兩個鐵片卸下，即可將這Ａ環和B+C環分解。

Inside Ring B, you will find a set screw that secures the infinity focus position. After removing this screw, Ring B can be separated from Ring C. I first used WD-40 to dissolve and remove the hardened grease from the helicoid threads. Afterward, I cleaned away any remaining WD-40 with isopropyl alcohol. Once the threads were completely clean, I applied a thin, even layer of medium-damping helicoid grease before reassembling the three rings by reversing the disassembly steps. The focusing ring now turns exceptionally smoothly.

B環內部可以看到一顆無限遠刻度的固定螺絲，將這顆螺絲旋下，便可將B環和C環分解。我先使用WD-40清洗螺紋上已經乾掉的油脂，再用酒精將WD-40清除，最後在螺紋上一層中度組尼潤滑油，之後反向操作上述步驟便可將這三個環再組合起來，轉起來非常順手。









When threading Component A back into the combined B + C assembly, it is important to engage the helicoid at the correct starting position. After the two metal coupling tabs have been reinstalled, Component A should be able to travel all the way to the bottom of the B + C assembly, which corresponds to the infinity focus position. Finally, reinstall the optical assembly, the rear aperture control mechanism, the M42 mount, and the remaining components. With that, the restoration is complete.

當A環要重新旋入B+C環，須注意螺紋旋入的位置，當上述兩個鐵片固定後，A環需能夠到達B+C環的底部(也就是無窮遠的位置)。最後裝回鏡筒，以及後端的光圈控制機構相關零件、M42接環等，就大功告成了。

Rear Mount Disassembly of the Carl Zeiss Jena Flektogon 25mm f4 M42 Zebra Version

2026/6/4

Today, while cleaning the aperture blades of a Carl Zeiss Jena Flektogon 25mm f/4 M42 lens, I removed the front optical assembly and took out the aperture blades for cleaning. After carefully reinstalling the blades in their correct positions, I attempted to refit the aperture control cylinder, only to discover that it would not go back into place because it was being blocked by a small metal tab that actuates the aperture mechanism. It became apparent that the M42 mount at the rear of the lens had to be removed first so that this component could be detached before the aperture control cylinder could be reinstalled.

Since I was unable to find any videos or photographs online showing how to remove the M42 mount on this particular lens, I decided to document the entire disassembly process myself. I hope this record will serve as a useful reference for anyone attempting a similar repair in the future.

今天為了清理Carl Zeiss Jena Flektogon 25mm f4 M42 的光圈葉片，我拆了前鏡組，取出光圈葉片清理後，重新擺好葉片，再裝回葉片控制圓筒，發現裝不回去，因為有一個控制光圈葉片的金屬突起阻擋。看起來必須先拆鏡頭M42接環，才能將該零件移除才能安裝。由於網路上找不到相關的Ｍ42接環拆除影片或照片可參考，所以我就拍下整個過程，做個記錄與分享。


Carl Zeiss Jena Flektogon 25mm f4 M42 Zebra Version


This is the lens base after the front optical assembly and aperture blades have been removed. Once the aperture blades are correctly repositioned, the aperture-control cylinder can be reinstalled. However, at approximately the 8 o’clock position, there is a small metal protrusion that engages and rotates the aperture-control cylinder. This protrusion prevents the cylinder from being inserted back into place, so it must be removed first before reassembly can proceed.

這是前鏡組和光圈葉片取出後的底座，重新擺好光圈葉片，就可以放入葉片控制的圓筒零件，但在8點鐘位置有一個轉動葉片控制圓筒的金屬突起導致無法放入圓筒，必須先移除才行。



The rear of the lens features the common M42 screw mount, and at first glance there appear to be no visible screws for disassembly. In fact, the black base beneath the mount is an aluminum outer housing. To remove it, firmly hold the lens body and rotate the black housing counterclockwise. The housing will then unscrew and can be lifted off, revealing the internal mechanism underneath.

鏡頭底部是很常見的M42接環，外觀看不到任何可拆卸的螺絲。其實接環下方的黑色底座是一個金屬鋁外殼，先握緊鏡身，再將黑色的外殼以反時針方向旋轉，即可取下。



After removing the black outer housing, you will see a ring-shaped component. This part connects the aperture actuator pin on the M42 mount to the depth-of-field preview switch on the lens body, forming the mechanism that controls whether the aperture remains fully open or stops down. Once the single spring attached to this mechanism is carefully removed, the ring-shaped component can be lifted out, allowing access to the parts beneath it.

取下黑色外殼後，可以看到一個環形的零件，它連接了接環上的光圈頂針和鏡身的景深預觀鈕，是用來控制光圈「開/縮」的機構，將機構上唯一的彈簧拿下來後，即可移除這個零件。



After removing the ring-shaped component, you will see four screws located beneath the mount. Once these screws are removed, the M42 mount can be detached easily, providing access to the internal aperture mechanism and other components inside the lens.

取下環形零件後，就可以看到接換下方有四個螺絲，將這些螺絲旋起後，M42接環就可以順利拿下來。



Next, the metal linkage that directly controls the opening and closing of the aperture blades becomes visible. Attached to it is another spring, whose purpose is to keep the aperture blades positioned at the f-stop selected on the aperture ring. This spring provides the necessary tension to ensure that the aperture mechanism follows the setting of the aperture ring accurately and remains fixed at the chosen aperture value during operation.

接下來，真正控制光圈葉片「開/縮」的金屬連桿出現了，上面有另一只彈簧，是用來將光圈葉片固定在光圈環所選定的光圈值。



One end of the linkage extends into the lens barrel and connects directly to the aperture blade control mechanism. The other end features an L-shaped metal tab, which interfaces with the ring-shaped component removed earlier. Together, these parts form the complete aperture actuation system. Through the interaction of the M42 aperture pin and the depth-of-field preview switch, the mechanism ultimately controls the opening and closing of the aperture blades, allowing the lens to switch between full-aperture viewing and the selected working aperture.

連桿的一端是深入鏡筒內的光圈葉片控制機構，連桿另一端L形鐵片則是與先前拆下的環形零件連動，最終透過光圈頂針和景深預觀鈕完成「開/縮」光圈的動作。



By removing these two screws, the component that controls the opening and closing of the aperture blades can be detached. Once this part is out of the way, the aperture blade assembly and its control cylinder inside the lens barrel can be reinstalled without obstruction, making reassembly much easier.

拆下這兩顆螺絲，可以把控制光圈葉片「開/縮」的零件取下來，這樣鏡筒內的光圈葉片零件就可以順利安裝了。

I referred to mikeno62's video, Carl Zeiss Jena Flektogon 4/20 for Exakta, as a guide during the disassembly/reassembly process.

我參考了 mikeno62 的影片 Carl Zeiss Jena Flektogon 4/20 for Exakta

https://youtu.be/XkzOlicu1bo?si=cEWQ1F8tx5XDYN_p