How to extend the back-focus a little longer / バックフォーカス、もうちょっと・・・

You must have stamped your feet in frustration for the scarce lack of the back-focus in focusing on the target,once or more. ” If a few millimeter more back-focus!”
I will show you a wise trick now.

Remove the end adapter and check if the draw-tube will plunge into the focuser to the minus profile. If you are happy to find your draw-tube will plunge a bit into the outer tube as the movie below, you can get some more back-focus by lathing the end adapter.

ほんの数ミリのバックフォーカスの不足で地団駄を踏んだことはありませんか? 長年のマニアであれば、一度や二度はそんな経験があったはずです。^^ 私は奥の手をたくさん知っていますが、今回は、末端アダプターの裏側をほんの少し加工するだけで数ミリバックフォーカスを稼ぐ裏技をご紹介します。



Here is the answer.(above movie)
It’s just “Columbus’ egg”.