Macro Focus Stick for 67mm Flat Port

[Davide DB]

I'm asking a question, maybe a dumb one, so don't shoot me 🤡
I remember back in the days of the Nikonos, extension tubes had a stick and frame to have a sure reference as to where the camera would focus and frame size. I don't even know the exact name for it, but it is a vintage item that has no reason to exist today except in very special cases.

 

 

 

Inon reworked this concept in part for its macro lenses for GoPro and even patented it.

 

 

Is there something similar for flat ports for use with add-on lenses?

Since I can't find anything on the net I got the doubt that my question is dumb. Yet there are use cases in my shooting where having an immediate visual reference if I have positioned the lens at the right distance from the subject would be very handy. And this fantasy object would be perfect.
Here where I usually dive, many of the subjects I try to film in macro are on steep, muddy rock slides. Being able to position the tripod is already a feat, and clouds of mud rise with every adjustment. Sometimes I give up even before I press the REC button. Sometimes corals close polyps if illuminated for too long. Even under ideal conditions, the depth often does not allow me to waste too much time.

In short, I see this as a likely DIY project. 

I imagine a 67mm ring with a mechanism similar to Inon's or simpler or even fixed, but where the stick is interchangeable. The size or references on it would change depending on the focus range of the additional lens used. The stick can also be a straw.
For starters, do you have any idea of the standard thread pitch of the 67mm ports and add-ons? I have only found those for photographic filters:

 

https://www.marumi-global.com/blogs/technology/faq-thread-pitch

 

 

 

 

[Isaac Szabo]

I believe the M67 thread pitch is 0.75mm.

[Davide DB]

15 minutes ago, Isaac Szabo said:

I believe the M67 thread pitch is 0.75mm.

 

Basically, from the Marumi table the same thread pitch as photography filters.

 

Thanks

[Elvandar]

For the inon lens, the system is a screw on solution, like this:

 

 

[Davide DB]

Thanks,

 

I guess it's impossibile to print that thread pitch at home. So I will buy a cheap 67-82mm step-up filter and I will print a ring that will fit inside.