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

Carl Zeiss Jena Flektogon 35mm f2.8 and Sony A7C

2026/3/22

I own three Carl Zeiss Jena lenses: the Tessar 50mm f/4, Biotar 58mm f/2, and the Flektogon 35mm f/2.8 featured in this test. The Flektogon 35mm wide-angle lens was produced in several versions. The one I have is the so-called “zebra” version, recognizable by its striped focusing ring. It has a remarkably short minimum focusing distance of 18 cm, which reportedly provides a reproduction ratio approaching 1:2. A later multi-coated (MC) version was also produced, featuring a faster f/2.4 maximum aperture and a 20 cm minimum focusing distance.

The principle behind most macro lenses is to move the optical assembly farther away from the film plane. However, this increased distance reduces the amount of light reaching the film. In other words, when shooting at a 1:2 reproduction ratio, the amount of light reaching the film is only about half of what it is when focused at infinity. Although the lens is mechanically marked as f/2.8, the effective light transmission is closer to f/4. This lens incorporates a thoughtful design feature. When shooting wide open at f/2.8, the aperture scale gradually shifts from f/2.8 toward f/4 as the focusing distance becomes shorter. In the era before TTL metering, this served as a useful reminder to photographers that they needed to compensate for the light loss by slowing the shutter speed by one stop.

Mounted on a Sony A7C and shot using Auto White Balance, the Carl Zeiss Jena Flektogon 35mm f/2.8 produces fresh, clean colors under bright morning sunlight. It faithfully renders the pale blue sky, the yellow-brown tones of bare tree branches, the vivid green grass, and the soft pink of azaleas. I suppose that is part of the enduring charm of classic lenses.


我收集的 Carl Zeiss Jena 的鏡頭有三顆，Tessar 50/4、Biotar 58/2 和這次測試的 Flektogon 35/2.8。Flektogon 35mm 廣角鏡頭有許多版本，手上這顆的外觀是俗稱的斑馬鏡，最近對焦距離是 18cm，據說是接近 1:2 的放大率，後期還有光圈 f2.4 、最近對焦距離是 20cm 的 MC 版本。大部分微距鏡的原理，就是將鏡組遠離底片平面，但較長的距離會使得到達底片光量減少，換言之，當微距攝影達 1:2 放大率時，底片的感光量只有對焦無窮遠時的一半，雖然機械光圈標示為 f2.8，但實際的感光量為 f4。這顆鏡頭在設計上有個小巧思，一開始以光圈f2.8拍攝時，隨著對焦距離越來越近，機械光圈標示會從 f2.8 移動到 f4，這在相機沒有TTL測光的年代，算是一項對攝影者的善意提醒，需要使用慢一檔快門來補償失光量。

Carl Zeiss Jena Flektogon 35/2.8 接上 Sony A7C，以自動白平衡拍攝，在上午的大太陽底下，色彩清新乾淨、忠實呈現出天空的淡藍、枯樹枝的焦黃、草地的鮮綠和杜鵑花的淡粉紅，我想這就是老鏡的特色吧。

Carl Zeiss Jena Flektogon 35mm f2.8


Carl Zeiss Jena Flektogon 35mm f2.8

Carl Zeiss Jena Flektogon 35mm f2.8

Carl Zeiss Jena Flektogon 35mm f2.8

Carl Zeiss Jena Flektogon 35mm f2.8

Carl Zeiss Jena Flektogon 35mm f2.8

Lens Comparison: Carl Zeiss Jena Sonar 85/2 T vs Jupiter-9 85/2 MC

2026/5/16

After taking the Soviet Jupiter-9 85mm f/2 MC (M42) out for a photo walk last time, I thought it would be interesting to compare it directly with the West German Zeiss-Opton Sonnar 85mm f/2 T (Contax RF), which led to this test record.　I mounted both lenses on Sony E-mount adapters for the comparison. In terms of physical size, the Jupiter-9 is about 1–2 mm taller. When stopped down to f/4, the Jupiter-9 maintains an almost perfectly circular aperture shape, while the Zeiss-Opton produces a more polygonal, star-like diaphragm opening. As for weight and handling, the two lenses feel fairly similar in hand.

上次帶著蘇聯 Jupiter-9 85/2 MC (M42) 外拍後，想到應該要與西德 Zeiss-Opton Sonnar 85/2 T (Contax RF) 比較一下，所以就做了這次的測試記錄。我將兩顆鏡頭都裝上了Sony E轉接環，就高度而言，Jupiter-9 約高了1~2mm，縮光圈至 f4 時，Jupiter-9呈現近乎圓形，Zeiss-Opton則是多角星芒狀，重量手感則是差不多。

These test shots were taken indoors under mixed lighting conditions, combining tungsten bulb lighting with daylight coming through a window. Comparing both lenses wide open at f/2, I personally find the Jupiter-9’s background rendering more pleasing, with stronger subject separation and a greater sense of three-dimensionality. The Zeiss-Opton Sonnar, on the other hand, stands out for its superior sharpness and contrast. When stopped down to f/4, it becomes even clearer that the horizontal lines behind the text are actually composed of dotted segments. I’ve also included both full-frame images and enlarged crops for reference.

All test photos below were taken with a Sony A7C with in-body image stabilization enabled (85mm setting).

這次的測試照片是在室內燈泡光源和窗戶室外光源混和的條件下拍攝的，以光圈f2來比較，我覺得 Jupiter-9 對背景虛化的處理比較令人討喜，也較有立體感，而Zeiss-Opton Sonnar 則是勝在銳利度和反差，縮光圈到 f4 時更可以清晰地看到文字後的橫線是點狀虛線所組成。同時附上全幅和放大裁切後的相片給大家參考。

以下測試照片均以 Sony A7C + 防手震啟動(85mm) 拍攝


Jupiter-9 85/2 MC at f2, 1/250, ISO400


Jupiter-9 85/2 MC at f4, 1/60, ISO400


Zeiss-Opton Sonnar 85/2 T at f2, 1/250, ISO400


Zeiss-Opton Sonnar 85/2 T at f4, 1/60, ISO400

Center crop at 100% magnification:

擷取影像中間，100%放大後：


Jupiter-9 85/2 MC at f2, 1/250, ISO400


Jupiter-9 85/2 MC at f4, 1/60, ISO400


Zeiss-Opton Sonnar 85/2 T at f2, 1/250, ISO400


Zeiss-Opton Sonnar 85/2 T at f4, 1/60, ISO400

MC Jupiter-9 85mm f2 and Sony A7C

2026/3/22






My third collectible Soviet lens is the Jupiter-9 85mm f/2 MC, a lens with a strong lineage tracing back to the pre-war Carl Zeiss Jena Sonnar 85mm f/2 made for Contax RF cameras. This particular copy was manufactured in the late 1980s and features MC multi-coating. Although the exterior shows heavy signs of wear, the optics themselves are actually quite clean. When I first received the lens, the aperture scale and index mark did not line up correctly. I spent quite a bit of time disassembling the entire optical block and aperture ring, then recalibrated and reassembled it so that each aperture marking now aligns perfectly with the indicator.

The most distinctive characteristic of this lens is its rendering wide open: contrast is very low and the image appears soft and dreamy, but once stopped down, the contrast improves significantly. In the first photo, the background blur behind the uBike bicycle seems to “melt away” into the distance, while the highlights carry a slightly creamy texture with a hint of swirl, producing an exceptionally smooth bokeh.

我收藏的第三顆蘇聯鏡頭是Jupiter-9 85mm f2 MC，與戰前的CONTAC RF相機接環的Carl Zeiss Jena Sonnar 85mm f2有著濃濃的血緣關係。這顆鏡頭是上個世紀80年代後期製造的，有冠上MC鍍膜，雖然外觀磨損的很厲害，鏡片倒是蠻乾淨的。這顆鏡頭剛到手時，光圈環的數字和指標位置有些差異，我費了一些功夫拆下整個鏡組和光圈環，將光圈環重新鎖定在正確的位置，讓每個光圈環的數字和指標都能對得上。

這鏡頭最大的特色是在光圈全開時，反差很低、很柔和，但縮光圈後反差也就好很多。第一張照片uBike腳踏車背後，散景一路往後「化開」，高光邊緣帶一點奶油感與旋轉感，非常滑順。

Industar-61-L/Z MC 50mm f2.8 and Sony A7C

2026/3/22





My very first Soviet lens collection piece, the Industar-61 L/Z MC 50mm f/2.8, is back in action. I took it for a walk around the National Taiwan University campus to soak up some sunshine. Under bright sunlight, using the sparkling highlights filtering through the leaves as the background, this lens can produce its signature “star-shaped bokeh” effect.

Over the past few years, NTU has been undergoing constant redevelopment. Old buildings have been demolished one after another, while new buildings funded by alumni donations continue to rise. Even NTU Xiao-Fu, where I used to bring my kids on weekends, has been torn down. Over these past two decades, my photos of the NTU campus have gradually evolved from Fujifilm slide film and peel-apart film to digital photography and Instax film.

我收藏的第一顆蘇聯鏡頭 Industar-61-L/Z MC 50mm f2.8 又出動了，帶它來台灣大學校園走走，曬曬太陽。在大太陽下，以樹葉的點狀反光作為背景，就可拍出這顆鏡頭特有的「星狀散景」效果。

這幾年台大持續大興土木，老舊建築一棟一棟的拆，校友捐贈的新大樓一棟一棟的蓋，以前週末溜小孩的台大小福也拆掉了。這二十幾年來，我拍台大校景的照片也從富士正片、撕拉片，漸漸得變成數位相片、Instax底片。不變的就是手上的四十幾棵手動對焦老鏡頭，拜各種轉接環之賜，得以在數位相機和拍立得相機上復活，使得一些傳統優質老鏡的價格也水漲船高。


Industar-61-L/Z MC 50mm f2.8


Industar-61-L/Z MC 50mm f2.8


Star-shaped bokeh, Industar-61-L/Z MC 50mm f2.8


Industar-61-L/Z MC 50mm f2.8

Zeiss-Opton Biogon 35mm f2.8 T and Sony A7C

2026/3/22

This Zeiss-Opton Biogon 35mm f/2.8 T (Contax RF mount) is a lens I added to my collection over twenty years ago, back when I was still actively shooting film. Its defining feature is the highly protruding rear element, which comes very close to the film plane. This design was intended to achieve near-zero distortion, resulting in images with virtually no geometric deformation and extremely high resolution. However, what was an advantage in the film era becomes a limitation in the digital age. Because the rear element sits extremely close to the image sensor—and digital sensors are less capable of capturing oblique light rays—this leads to noticeable vignetting around the edges of the image. The effect is especially pronounced at f/2.8, but improves significantly when stopping down to around f/5.6–f/8.

這顆 Zeiss-Opton Biogon 35mm f2.8 T (Contax RF接環) 是我在二十幾年前還常在拍底片時收藏的鏡頭。它的特點就是後鏡組很突出，就快要頂到底片平面了，據悉這樣的設計是追求零畸變，成像幾乎沒有變形，且解析度極高。但這項在傳統底片時代的優勢，在數位攝影時代，因為後鏡組極度靠近感光元件，且因感光元件無法取樣斜進光線的特性，導致成像周邊有很明顯的失光現象，在光圈f2.8時非常明顯，光圈縮小至f5.6-8之後可獲得大幅度改善。


Zeiss-Opton Biogon 35mm f2.8 T (f2.8)


Zeiss-Opton Biogon 35mm f2.8 T (f5.6 or smaller)


Zeiss-Opton Biogon 35mm f2.8 T


Zeiss-Opton Biogon 35mm f2.8 T


Zeiss-Opton Biogon 35mm f2.8 T


Zeiss-Opton Biogon 35mm f2.8 T on Sony A7C

Zeiss 35mm f2.8 Lens Collection : Biogon, Distagon, Flektogon and Sonnar

2026/3/21

Previously, I was already using three cameras — the Zeiss Ikon CONTAX RF, Kyocera CONTAX SLR, and Sony A7III — and I also owned three 35mm f/2.8 wide-angle lenses, namely the Biogon, Distagon, and Sonnar, each representing different optical designs. On a whim, I started wondering whether there were any other 35mm f/2.8 lenses within the Zeiss lineup that featured different optical designs. The answer turned out to be Flektogon and Biometar. The former comes in M42 and Exakta mount versions, while the latter is available in the CONTAX RF mount. The Flektogon 35mm f/2.8 M42 is relatively easy to find on the second-hand market, so I also picked up a Pentacon Praktica L camera to pair with it, adding another set to my Zeiss 35mm f/2.8 lens collection. As for the Carl Zeiss Jena Biometar 35mm f/2.8, not only is it quite expensive, but it also overlaps in focal length with my existing Zeiss-Opton 35mm f/2.8, so I decided to put that idea on hold for now. Below is a description of these lenses quoted from ChatGPT:

先前因為已經使用 Zeiss Ikon CONTAX RF、Kyocera CONTAX SLR、SONY A7III 這三台相機，也同時擁有了三顆 35mm f2.8 的廣角鏡頭，依序是 Biogon、Distagon、Sonnar 這三種光學設計。 一時心血來潮，想說看看 Zeiss 鏡頭群中是不是還有其他不同光學設計的 35mm f2.8 鏡頭，答案是 Flektogon 和 Biometar，前者有 M42 和 Exakta 兩種相機接環版本，後者則是 CONTAX RF　相機接環版本。 Flektogon 35mm f2.8 M42 在二手市場上相對比較好取得，我也同時找了一台Pentacon Praktica L 相機來搭配，讓我的 Zeiss 35mm f2.8 鏡頭收集又多了一組。至於 Carl Zeiss Jena biometar 35mm f2.8 這顆鏡頭，除了價格不便宜，同時也和手上的 Zeiss-Opton 35mm f2.8　焦段重複，就暫時先打消收集的念頭了。以下引用 ChatGPT 對這些鏡頭的介紹：


These four 35mm f/2.8 lenses represent the optical pinnacle of Zeiss across different eras and camera systems. Although they share the same maximum aperture, their internal constructions and rendering characteristics are completely distinct:

這四款 35mm f/2.8 鏡頭代表了蔡司（Zeiss）在不同時代與相機系統上的光學巔峰。雖然光圈相同，但其內部構造與成像個性截然不同：

Zeiss 35mm f2.8 Lens Collection


(1) Biogon 35mm f/2.8: The Distortion Killer of the Rangefinder World

Optical Design: Highly symmetrical construction.
Key Strength: Near-zero distortion. Because the rear element sits extremely close to the film plane, the light path is very direct, resulting in minimal distortion and exceptionally high resolution.
Best Suited For: Street photographers and architectural photography enthusiasts.
Representative Model: Post-war Zeiss Ikon Contax RF.

(1) Biogon 35mm f/2.8：旁軸界的畸變剋星

光學結構： 高度對稱設計（Symmetrical Design）。
核心優勢： 零畸變。因為後鏡組極度靠近感光元件，光線路徑直，幾乎沒有變形，且解析度極高。
適合誰： 街頭攝影師、建築攝影愛好者。
代表作： Zeiss Ikon Contax RF 戰後版。

 



(2) Distagon 35mm f/2.8: A Stable Foundation for SLR Cameras

Optical Design: Retrofocus construction.
Key Strength: Excellent edge-to-edge image quality. The design deliberately extends the back focus distance to clear the SLR mirror, which also results in favorable light incidence angles on digital sensors.
Best Suited For: Photographers who appreciate classic Zeiss rendering with strong tonal depth and balanced performance across the frame.
Representative Model: Contax Zeiss 35mm f/2.8 T* (C/Y mount).

(2) Distagon 35mm f/2.8：單眼相機的穩定基石
光學結構： 反望遠結構（Retrofocus）。
核心優勢： 邊角畫質優異。為了避開單眼相機的反光鏡，設計上刻意拉長後焦距，這讓它在數位機身上也有很好的光線入射角。
適合誰： 喜歡德系層次感、追求全畫面平衡的攝影師。
代表作： Contax Zeiss 35/2.8 T* (C/Y 卡口)。

 



(3) Flektogon 35mm f/2.8: The Close-Focus Legend of East German Zeiss
Optical Design: Early retrofocus design (from Carl Zeiss Jena, East Germany).
Key Strength: Exceptional close-focus capability. The minimum focusing distance is typically around 18–19 cm, allowing for wide-angle shots with a macro-like perspective.
Best Suited For: Photographers who enjoy vintage lens character, especially for still life and flower photography.
Representative Model: Carl Zeiss Jena 35mm f/2.8 (M42 mount, commonly known as the “zebra version”).

(3) Flektogon 35mm f/2.8：東蔡的近攝傳奇
光學結構： 早期反望遠設計（來自東德 Carl Zeiss Jena）。
核心優勢： 超強近攝能力。最短對焦距離通常僅 18-19cm，能拍出具備廣角透視感的微距效果。
適合誰： 喜歡老鏡氛圍、拍攝靜物或花卉的玩家。
代表作： Carl Zeiss Jena 35/2.8 (M42卡口，俗稱「斑馬版」)。

 



(4) Sonnar 35mm f/2.8: A Modern Benchmark for Compactness
Optical Design: An asymmetric evolution of the Gauss-type design.
Key Strength: Exceptional compactness and high contrast. Despite its relatively simple construction, it is highly efficient, producing rich colors and the clear, modern Zeiss rendering.
Best Suited For: Photographers who prioritize portability and a “carry-everywhere” setup, especially Sony E-mount users.
Representative Model: Sony Zeiss FE 35mm f/2.8 ZA (pancake lens).

(4) Sonnar 35mm f/2.8：現代輕量化代名詞
光學結構： 非對稱的高斯演進版。
核心優勢： 極致輕便與高對比。結構簡單但效率極高，成像色彩濃郁且帶有現代蔡司的通透感。
適合誰： 追求「隨身機」手感、Sony E 接環用戶。
代表作： Sony Zeiss FE 35mm f/2.8 ZA (餅乾鏡)。

 




If you prioritize maximum resolution and near-zero distortion, choose the Biogon
→ e.g. ZEISS Biogon T* 35mm f/2.8 ZM
If you want close-up or macro-like wide-angle shots, choose the Flektogon
→ e.g. Carl Zeiss Jena Flektogon 35mm f/2.8 M42
If you want the most compact autofocus lens, choose the Sonnar (FE version)
→ e.g. Sony Zeiss FE 35mm f/2.8 ZA
If you’re on a budget but want classic Zeiss T* color rendering, choose the Distagon
→ e.g. Carl Zeiss Distagon 35mm f/2.8 (C/Y mount)

快速選購指南
如果你追求最高解像力與無變形 選 Biogon。
如果你想拍微距或特寫 選 Flektogon。
如果你想要最輕便的自動對焦鏡 選 Sonnar (FE版)。
如果你預算有限但想要經典 T* 色彩 選 Distagon。


The minimum focusing distances of these four lenses differ quite significantly. I’ve included uncropped sample photos taken with them adapted to the Sony A7 III for your reference.

這四顆鏡頭的最近對焦距離差異還蠻大的，附上專接到 Sony A7 III 拍攝的未裁切相片給讀者們參考。

Carl Zeiss Jena Flektogon 35mm f2.8


Carl Zeiss Distagon 35mm f2.8 T*


Carl Zeiss Sonnar FE 35mm f2.8 ZA T*


Zeiss-Opton Biogon 35mm f2.8 T