Quite simple...

If I turn the focus ring of the 200 by say, 4 x 1/2 degrees as shown on the protractor, the focus point of the 200 with the 50 attached will be 4 x 0.05 mm. further into the subject, for that given extension (only),
The more receding the subject plane, e.g.as in the side of a ball, the greater the number & the smaller the size of steps required for "continuous" focus around the contour in the stack.
Hope this helps,

Roger.

Leaps & bounds, Steve, leaps & bounds!

I remember seeing the light through the wrong way as a pointer on Photomacrography site a while ago.
Someone made up a small light unit that clipped onto the viewfinder slots & I was impressed with the elegance of it in use.
But I'd been asleep since then & forgotten all about it......
But i've just shone a torch in the viewfinder of the K5 & VOILA!! A spot on the coin!

I've also, by utilising a cheap micrometer I got from Banggood a while ago, related the degrees on the protractor to the linear advancement of the focus.
It works out that 0.5 of a degree on the protractor represents 0.05 movement of focus of the lens (at that extension) plus whatever more is gained by stopping down.
Below is my latest, 200 + rev. 50, 150 ext.on the bellows, stack of 7 in CZP.
No crop.
Heavily (paper) diffused AF200T flash, but highlights still a problem.....


https://www.flickr.com/photos/188519063@N07/50955820743/in/datetaken-ff/


Good here, isn't it!

Roger.

Just one question, Steve.
How on earth do you "measure" & move(!) your camera +300 f4, one twelfth of a millimetre at a time?






Roger.

Thanks, Steve.
I think for these purposes, the reversed lens' role is a passive one, but just as a carrier for the iris to stop down with.
I would have thought that, as long as the lens has a manual focus ring for the protractor to sit on, focal length is irrelevant.
You're simply focusing the "main" lens as you would in any other circumstances, it's just that it's that bit closer than normal!
Just pop an 18mm wide angle backwards on the front of a 300 & see what happens.....!

Go for it,

Roger.

O.K., David.

I'm using the 200 f4 to focus.

It was a case of finding a way to move/focus the assembly/lens by very small increments, smaller than is possible with the (rotary) focus ring alone or using the linear focus rail.
The protractor is fixed to the focus ring of the lens. The pointer is fixed to the bellows, which, after preliminary coarse focus, does not move. This fixed point could be anywhere, but not anywhere that will move in this final, fine focus stage.
As the lens is focused, the focus ring "revolves", taking the protractor with it. The pointer does not move. The degree markings move past the fixed pointer. Et voila!
(I have toyed with relating the rotary, degrees scale, which is entirely abstract to the normal function of the lens, to the depth of focus "steps" which Steve referred to, but this will be different throughout the focus range of the lens....& , as far as stacking is concerned, though interesting, would be entirely irrelevant.)

As I said, it's easier to do than describe & oh, by the way, it works!

Thanks for the continued interest shown,

Roger.

Don't know the diff between each shot, since that'not how I shoot it......
See images 1 & 2, showing the arc of degrees which is concentric with the 200mm f4 lens on which it is held, with a rubber band around the focus ring. Its position on the circumference of the ring is adjustable to suit the position of the focus ring for the particular image,
The pointer, an insect (black) needle taped to a double-wound garden wire is adjustable to suit. It is anchored by a couple of button magnets to the distance scale bar on either standard of the Auto Bellows M.
in this case the front one.
Focus is set by:
Coarse focus with the focus-rail assembly moved fore/aft on the SmallRig rails which are screwed to the 22mm oak base-board.
Secondary focus by moving the bellows on its built-in focus rail, having set the bellows standards to achieve the required magnification.
To set the focus range for the stack:
Using L/V, find the nearest point of out-of focus. Make a note of the degrees position of the pointer.
Focus through the subject until all becomes out of focus at the back end. Make a not of the pointer finishing degree position.
I then decide how many shots to take for that depth of image & at what f stop. I rarely, if ever, take more the 25, otherwise my computer begins to glow & consider spontaneously combusting.....
The finest step I can achieve with this set-up is 0.5 degrees, which when translated to axial focus movement of the lens is "pretty small".
This image of the "IRB" was 9 at 0.5 degrees., making a total of 4.5 degrees of focus, plus.










It certainly becomes easier to do, rather than describe!

Hope this helps & good luck!

Roger.

It appears that Elements "chose" to crop/trim the stacking artifacts off of that last (stack) image,
Sorry about that!

Roger.

...& here it is.





Stack of 9 in Combine ZP.
No crop.
Elements 11, Auto Levels only.

Roger.

Well.

I thought I was losing it to be honest!

Got it all set up last evening, popped-off a frame or two....

RUBBISH!

Cut a long srtory short, this morning re-checked every thing. Thought I had over-reached myself,TBH.

Questioned in my mind everything,.

Then it dawned. I'd been using my right-angle finder M, for the focus, checked on L/V.
I'd knocked the dioptre focus on the eyepiece of the finder out of thingy!
Come back all I said about that nice Mr. Pentax & his b****y M lenses!!!

Anyway here's mine, albeit on a new(ish) 2p piece:




Single frame, SOOC.
(Think I'll do a stack & see what happens.....)

Roger.

Steve,how about giving it the full PP works & see how it comes up?

Roger.