120度レンズ系についてドイツからのコメント

　ある天文の本に、かって、ドイツのU-ボートに見掛け視界120°の望遠鏡が搭載されてあったとの記事が書かれてありました。120°とは随分と魅力ある視界だと思い、それを参考にして脇本先生（別項目参照）に設計を依頼し、ひとまずデータだけは確保してあるのですが、本当にドイツではそれを実際に作り上げたのか、なにがしかの疑問は持っていました。
　更に、ジョドレルバンク電波天文台にあった超広角双眼鏡が、その120°を利用した双眼鏡だ、と断言する天文台係員の言葉に、双眼鏡ではそのレンズの大きさから絶対に製作は不可能だと思ったのですが、意思疎通の問題もあり以後は納得はしないまま現在に至っていました。（ジョドレルバンク電波天文台についても別項目を参照下さい。）

　過日、双眼鏡について大論文を書いたHans. T. Seeger氏に（その論文についても別項目を参照して下さい。）この件について問い合わせたところ、やはり、こちらの認識が間違っていない事が分かりました。
　120°の望遠鏡は本に書いてあるようなU-ボートに搭載された機種ではない事。海上用ではなく対空用に考案された機種である事がまずはっきりしました。更に、双眼鏡として作る事は不可能である事もはっきりしました。当たり前と言えば当たり前ですが、明確になった点だけでも収穫であったと思っています。

　下記が届いた全文です。下手に訳すと勘違いもあるかと思い原文のまま載せてあります。ドイツ人が書いた英文なので平易です。興味のある方に一読をお薦め致します。

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Thank you for your fax message,dated April. 3 .2001(I have not been able to open your e-mail from 30. March 01 completely). It was interessting to learn about your long experience with optics. I want to comment your letter and give my opinion.

You tell me that you saw in England a U-boat periscope with a 120°field of view and the designation 15X75.U-boat periscopes indeed have a high field of vew(see publication of Prof.Kohler); German [ U-Boot-Periskope ] , however, had to my knowledge 2 magnifications: 1.5x or 2x as the lower and about 4x or 6x as the lower and about 4x or 6x as the higher.

You attach two drawings showing the optical construction of-as you write-[ U boat periscope with 15x magnification ] and you write also that these drawings have been published by a japanese author. For me, the latter statement seems to be incorrect.
These drawings were copied from a publication of Prof. Dr.Horst Kohler, the head of the Zeiss Oberkochen optical construction in the time from about 1950 to 1980. He died in 1999.

Prof. Kohler designed a 15x monocular telescope with a 120゜field of view, see his attached publication( Optik 17, 1960, page 500-509 ). The purpose of this monocular was to locate approaching aircraft. You will dedect easily that the Japanese author got his illustrations from this Kohler publication-and that these drawings have no connection to U-boat periscopes at all. Kohler, however, states that previously only for these periscopes extremely wide fields of view(f.o.w.) have been realized, and he describes the type of construction of one of these periscopes( see Abb.1 in his publication) and he gives the patent number in question. Abb.2 from Kohler-identical to the upper illustration of the Japanese author-describes a 15x75 telescope ( not a U-boat periscope) and is depicted to illustrate the unpractical huge ocular construction ( 18 cm diameter of the first ocular lens ) and to demonstrate that this optical construction cannot lead to a usable telescope.

Following this introduction , Prof.Kohler tells us that one has to develop another construction to realize a practical 15x75 telescope.Then he describes his new construction, Abb.3, 7, and 8. To my knowledge, only 2 of the Kohler 15x75 telescopes have been built. If you are interested, I can try to find out the location of one of these- it is on a test area of the German Bundeswehr.

Because of the large ocular lenses employed, telescopes with such a high f.o.w. cannot be construction in binocular form.

I want to add a comment and to correct an erroneous statement which you will find in my book (which you bought in Nurnberg ) on page 256.There was never a German binocular 18x105 with a 110°f.o.w. I have been able to find out something about the history of the so called 18x105- a glass which was acutually a 15x105 and had a f.o.w. of only 72°.In the next edition of my book I will add a comment to the chapter of Kevin Kuhne and I correct the statement given there. The statement in the lette of Dr. Tronnier ( cited in my book also ) is incorrect - nobody will ever know the reasons for his report about a binocular with 18x magnification and f.o.w. of 110°. I have discussed these questions with Mr.Leinhos, the right hand man of Prof.Kohler and also optical construction in the Zeiss company. He confirms my assumption: There was never a German binocular 18x 105 with a f.o.w. of 110°.

I do hope that my remarks can contribute a little bit to your knowledge about wide angle telescopes and their history.

With my best regards

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Hans .T. Seeger氏の手紙には、120°に関する資料が同封されてありました。レンズ構成図が何種類か、それらの各収差図、イラスト、データを並べた数字表、その他 もろもろ。ギッシリ書いてあるのですが、残念ながらドイツ語であるのと、余りにも細かすぎて到底読めるものではありません。表紙と、15x75の写真とイラストのみ載せておきます。