Olympus H.Zuiko Auto-S 42mm f/1.2 Disassembly – Repairing Balsam Separation

The Olympus H.Zuiko Auto-S 42mm f/1.2 is the fast standard lens made for the Olympus Pen F series of half-frame SLR cameras. This one came to me with heavy balsam separation and a sticky aperture lever, and I worked on it in November 2024. This post walks through the disassembly and repair, step by step.

Some lens elements are made of two pieces of glass glued together with a clear optical cement, often called balsam. With age the cement can start to let go, and you may see haze or frosty patterns inside the glass. Cleaning the outside surfaces will not help, because the problem is between the two glasses.

The Olympus H.Zuiko Auto-S 42mm f/1.2 held in a gloved hand, with a speckled pattern visible inside the glass — The H.Zuiko 42mm f/1.2 on the bench, before the repair

1. Looking into the lens

Looking into the front of the lens, a dense, speckled pattern fills the middle of the glass. It is not on the surface: it sits inside the lens.

Looking into the front of the lens, with a speckled pattern deep inside — The pattern sits inside the lens, not on the front surface

2. Taking out the front group

The front lens group unscrews from the barrel as one unit. With it out, the aperture mechanism behind it can be seen.

The front lens group partly unscrewed from the barrel — Unscrewing the front group

The barrel with the front group removed, showing the aperture mechanism — The barrel with the front group out

3. Opening the front group

Here is the front group out of the lens, from both sides.

The front lens group seen from its threaded side — The front group, threaded side

The front lens group seen from the rear — From the rear

The front element comes out first, which opens the way to the element behind it.

The front element lifted out of the front group cell — The front element lifted out

4. The balsam separation

With the front element out, the problem is plain to see: a white, feathery pattern spreading across the cemented element inside the front group.

Inside the front group cell, a white feathery pattern of balsam separation on the cemented element — A white, feathery pattern on the cemented element

5. Taking the cemented element out

The cemented element sits in its cell with the metal rim crimped over the edge of the glass to hold it in. To get it out, I lifted the crimped rim with a hobby knife.

A hobby knife blade at the crimped rim of the lens cell — Lifting the crimped rim with a knife blade

The cemented element coming out of its cell — The element coming out of its cell

The cemented element seen from the edge, showing the two pieces of glass — From the edge: two pieces of glass, cemented together

Held up to a light, the separation shows clearly. The frosty pattern runs right across the glass.

The cemented element held to a light, showing the frosty pattern of balsam separation — Against the light

The same element from another angle, with the white separation pattern — From another angle

6. The aperture lever, from the mount side

This lens had a second problem: the aperture did not move cleanly. Its lever was sluggish and caught as it moved. To reach it, I took the lens apart from the mount side. The mount is held by small screws, and with it off, the aperture linkage can be reached from the rear.

Removing the screws that hold the mount — Taking out the mount screws

The mount, marked Lens Made in Japan, lifted off the lens — The mount lifted off

With the mount off, I worked on the aperture linkage with a wooden toothpick and a needle oiler until the lever moved smoothly again.

The rear of the lens with the mount removed, and a wooden toothpick — The rear of the lens, mount removed

A wooden toothpick at the aperture linkage inside the barrel — A toothpick at the aperture linkage

A needle oiler held over the lens mount on the work bench — A needle oiler at the mount

7. Re-cementing

To separate the two pieces of glass, I boiled the pair in a pot of water on the kitchen stove. The heat softens the old balsam, and the two glasses came apart.

Two separated pieces of lens glass on a towel next to the kitchen stove, with a small bag labeled CL133 in Japanese — The pair, now apart. The bag says “CL133, balsam separation” in Japanese

Before cementing them again, the old balsam has to be cleaned off both glasses.

For the new cement I used xylol balsam, the same balsam I always use for this repair. Then the lens went back together.

8. After

The Olympus H.Zuiko Auto-S 42mm f/1.2 after the repair, front view at an angle with clear glass — After the repair: the glass is clear again

The H.Zuiko 42mm f/1.2 from the side, showing the focusing ring — From the side

The H.Zuiko 42mm f/1.2 from the mount side, showing the depth-of-field scale — From the mount side

About six weeks after the repair, in December 2024, the lens found a new owner in the United States through our eBay shop.

Balsam separation looks serious, but it can often be repaired by taking the pair apart and cementing it again.
Thank you very much for reading.

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日本語

オリンパス H.Zuiko Auto-S 42mm F1.2 は、ハーフサイズの一眼レフ「オリンパスペンF」シリーズ用の、明るい標準レンズです。この個体にはひどいバルサム切れと、絞りのレバーの動きの悪さがあったので、2024年11月に作業しました。分解と修理の流れを順に紹介します。

レンズの中には、2枚のガラスを透明な光学用の接着剤（バルサム）で貼り合わせたものがあります。年月がたつとこの接着が剥がれてきて、ガラスの中に曇りやザラッとした模様が見えることがあります。原因は2枚のガラスの間にあるので、表面を拭いても直りません。

1. レンズを覗く

前から覗くと、ガラスの真ん中に細かい点々の模様がびっしり見えます。表面ではなく、レンズの中にあります。

2. 前群を外す

前のレンズ群は、ひとまとまりで鏡胴からねじって外れます。外すと、その奥の絞りの仕組みが見えます。

3. 前群を開ける

外した前群を両側から撮りました。まず前玉を取り出すと、その奥の玉に手が届きます。

4. バルサム切れ

前玉を抜くと、原因がはっきり見えます。前群の中の貼り合わせの玉に、白い羽根のような模様が広がっています。

5. 貼り合わせの玉を取り出す

この玉は、金属の枠の縁を内側に折り曲げて（かしめて）ガラスを押さえてあります。取り出すため、デザインナイフで、かしめた縁を起こしました。

取り出した玉を横から見ると、2枚のガラスが貼り合わせてあるのが分かります。

光にかざすと、ザラッとした模様がガラス全体に走っているのがよく分かります。

6. マウント側から絞りのレバーを直す

このレンズにはもう1つ不具合がありました。絞りの動きに引っかかりがあり、レバーの動きが悪かったのです。そこへ手を届かせるため、マウント側から分解しました。マウントは小さなネジで留まっていて、外すと後ろから絞りの仕組みに手が届きます。

マウントを外したあと、爪楊枝と注油器で絞りの仕組みを手入れし、レバーがなめらかに動くように直しました。

7. 貼り直し

2枚のガラスを剥がすため、台所のコンロで、お湯を入れた鍋で煮ました。熱で古いバルサムがゆるみ、2枚が外れました。袋には「CL133 バル切れ」と書いてあります。

貼り直す前に、両方のガラスから古いバルサムを落とします。

貼り直しには、いつも使っているキシロールバルサムを使いました。そのあと、レンズを組み立てました。

8. 仕上がり

修理からおよそ6週間後の2024年12月、このレンズはアメリカの新しい持ち主のもとへ渡りました。

バルサム切れは見た目が深刻ですが、貼り合わせを剥がして貼り直すことで直せることが多いです。
最後まで読んでいただき、ありがとうございました。

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この記事のような分解清掃を、国内のお客さまのレンズでもお受けしています。静岡県富士市の工房で、カビ・くもり・絞りの油染み・バルサム切れの清掃を、1本ずつ作業します。

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