I hate 13 month years!

That looks very unusual Normally there's a sort of inner
column that everything else attaches to. That looks like it's
built onto the external aperture and focusing rings. I would
expect it to wobble a bit on a worn lens. Early Tomioka's were
built in a similar fashion even to the point of not having to
remove the beauty/name ring.

Just need to wedge the pin up now

I suppose if you can get at the pin from the front and Dremel
it off it might work. EDIT::: DON'T KNOW WHY I SAID THAT!!!
It has to be pushed in and there's usually a spring
mechanism at the other end..... so you have to do all
the work at the other end otherwise there won't be
any give in the system.

The reason some of the Yashica's are impossible is that the pin
acts as a pivot for other items and you can't reassemble the
lens with the pin pushed in, which rules out using a piece
of plastic from and electric cable. The helicoid is also a
pig to get back together.

Fujinon lenses used to thrash Pentax lenses in tests

The top one looks like a guide to stop the other part of the
helicoid turning. The other looks to move radially. It could well
connect to the iris for some reason.

It's very unusual for a lens to be assembled just from the front?

You can glue the pin in, but I wouldn't risk bits of glue breaking
off inside the camera.

Fairly basic lens.

50mm is correct it's always f where f is the focal length.
The distance object to focal plane/sensor is 4f at 1:1

With a 50mm lens all the elements move back and forth via the
helicoid so it doesn't matter if its set to 0.45m or infinity
on a bellows performance will remain the same.

Just suppose I have a 100mm non IF focus Macro lens, but
I am too close to the bugs and frighten them off. Would spending
a lot of money buying a 180mm/200mm IF Macro lens be of any help.
What FL would the 180mm IF Macro be at 1:1?

I also have a 50mm f/1.7 standard lens..... what length of tubes
will I need to take 1:1 macros with it.

-

Took a bit of finding, but this is the supplier/thread.
link

You will see from the last post that Gareth bought one. I later
bought it off him from the PU Classifieds for £15 quite well made.

You need to do a Google search for this lens type to see
if conversion is possible. Some lenses such as Helios
are simple to do..... some Yashica's can't be done.

The easiest solution is to buy a M42 to K converter with the
flange that pushes the pin down. Someone on one of the MF forums
sells them.

The robin on the roof and the bunny for me.... great!