点分Screw thread 係 0.5 / 0.75 pitch

lc7535

手头上一些老镜同filters. 有D 拎落去好似唔係好顺。
请教大家、有無好方法去分辨？
小弟对Engineering 係白痴一名、其实点解要搅出两個standard.

承蒙赐教、感谢万分。

khw

In general, if you can make more than one turn, the pitch is correct.

Usually, old lenses has fine pitch (0.5mm). For modern lenses, small diameter thread still use 0.5mm (like 40.5mm) but other would be 0.75mm.

edwardyung

Pitch愈大，齒愈厚，所能受的力就愈大。固不同需要就有不同的設計。

例如 M42 mount 的 pitch 就要1mm，因為鏡頭較重。

edwardyung

基本上說，0.5 和 0.75 所引起來的問題不大。
更麻煩的是公制和英制的差異，引至"初夜矛盾"、就是「入好還是不入好」的問題。

edwardyung

Pitch 就是指相鄰兩個齒頂的距離，例如十一個齒頂相距5mm，即每個pitch是0.5 mm了。
當然要量度就要合適的工具，總不能拿阿女的膠尺吧。

lc7535

khw 發表於 2013-10-5 08:29
In general, if you can make more than one turn, the pitch is correct.

Usually, old lenses has fine ...

My question come from a Nikkor 135 3.5 LTM, after I put on a 43 mm B+W UV, the hood can't screw onto the filter. May be i need to try out my Walz filter for Nikkor to double check.

lc7535

edwardyung 發表於 2013-10-5 08:39
基本上說，0.5 和 0.75 所引起來的問題不大。
更麻煩的是公制和英制的差異，引至"初夜矛盾"、就是「入好還 ...

原来thread pitch 同承受力度有关、我可唔可以咁样去推理: Leica 当年先出来E36 to E41, 所以用0.5 就够、后来去到E46 就顶唔顺、要用0.75 。至得。

edwardyung

唔知呀？
你肯定支鏡是用43mm x 0.75 嗎？

如果支hood 之前可以上落支鏡，當上好filter之後........ 支hood 又上唔返落Filter.......
那麼好大可能支鏡就不是公制43 x 0.75 了。
之所以filter可以落到lens 是因為寛差吧了。（鏡大+filter小）
例如：1.75" x 36tpi  ...... 我亂估㗎咋

edwardyung

一粒10mm x 1 nut 可以落一支3/8" x 26tpi screw，但相反一粒3/8" x 26tpi 的nut 就不夠大落10mm x1 的screw 了。

同理

lc7535

edwardyung 發表於 2013-10-5 11:13
一粒10mm x 1 nut 可以落一支3/8" x 26tpi screw，但相反一粒3/8" x 26tpi 的nut 就不夠大落10mm x1 的scre ...

10mm > 3/8" 啊.

edwardyung

lc7535 發表於 2013-10-5 11:18
10mm > 3/8" 啊.

再用更淺的比喻，
我穿十號鞋、你穿十號半，我穿得落你對鞋，你穿不下我對鞋。

khw

lc7535 發表於 2013-10-5 08:59
My question come from a Nikkor 135 3.5 LTM, after I put on a 43 mm B+W UV, the hood can't screw on ...

Modern B+W should be 0.75mm. Walz is vintage and which may work. Alternatively is to use a Series 7 inside the hood. Walz should be a good choice as it is low-profile.