In particular, @Lou Jost and others have praised the usefulness of microscope focus blocks for high power work. As it turns out, I had an Optiphot focus block that I have been trying to sell for more than a year, and it seems I could not give it away, so I decided to see if Lou and others were right. I had no doubt, of course, but had never put a system together with one of these. It was about time.
The focus block has a 100um/turn fine focus knob. It came to me with the plastic fine focus gear stripped, and I re-built the block as a beta tester for Lothar's offering of the fine focus gears for sale. You can see the beta test results here:
viewtopic.php?f=25&t=30067&start=30
During the rebuild, I didn't clean up the grease effectively, so had to do so for this recent system build. It was quite a chore, so I can perhaps understand why no one was interested in purchasing this block. After the cleanup, it operates as expected, with no backlash as long as the block is in its normal, vertical orientation.
The build consisted of the following processes:
1. Mount the focus block to a base. I chose a laminated bamboo cutting board, since bamboo is easy to work with, and the cutting board had nice rubber feet.
2. Add a top cap to mount the vertical column. I bought a 3"x3"x1/4" aluminum piece from eBay for this. I try to build everything from pre-cut aluminum bar stock or extrusions these days.
3. Mount the vertical column. I chose a 12" 8020 40-series extrusion, so drilled a 1/4" hole in the top cap and mounted the column with a long threaded rod. I do this with all my systems now and have done so for several years. It's the most rigid and simplest method I've found for attaching columns, etc.
4. Mount the 3x3 top cap to the focus block. 4 holes and countersinking the top cap, plus drilling and tapping the focus block.
5. Remove the non-graduated fine focus knob and replace with universal coupler. The shaft is 3mm, while my selected stepper shaft is 5mm, so I used the appropriate 3mm/5mm coupler. Took some care to ensure proper pressure on the bearing surfaces, similar to installing the knob.
6. Put motor mount in place, and place motor for marking the mount. I used the long side of an Arca L-bracket for this. Mark the screw holes, and extent of the center hole. Drill the screw holes and route/file the center hole.
7. Hard-mount the motor to the motor mount, the mount to the base, and the motor to the coupler. Test to ensure alignment and adjust as needed.
8. Install Arca plate to the column. I used a cut piece of a 480mm plate, approx 50% of the length, but any Arca plate will do.
9. Cut the mounting bracket from the front of a Vivitar bellows, and attach small Arca clamps to the lens and camera standards.
10. Install Vivitar bellows to the Arca plate
11. Plug motor cable into a stepper controller. I've used Peter Lin's @mjkzz controllers exclusively for years, and this is what I built with.
12. Install a stage mount to the focus block. I used the standard stage mount.
13. Install an XY platform to the stage mount. I did not have a Nikon platform, so installed a SuperEyes XY stage using double-stick tape. I plan to replace this stage with a Nikon XY, but the compactness of the SuperEyes is compelling and nearly overcomes its significant backlash issues, so I'm still living with it for now.
14. Install the lens. I tested the system with the 50x Mitty, and 20x Nikon MM. The Nikon is shown in the image below.
The system is more rock solid than any I've built to date. Just a pleasure to use. Settling time to small external shock is a couple hundred microseconds, and much faster for stepper movements or shutter actuations, so I can shoot at 50x with minimal time delays.
This is now my dedicated system for doing phono stylus contact surface imaging, and for any other work at 20x or higher. It has given my old HRT2i a new lease on life! I expected to use the HRT2i until it died, but ended up replacing it with the A7Rm4. Now the HRT2i can continue being productive.
The motor I chose for the build was a single-shaft NEMA-14 with 400-steps. A 400-step motor has 100-step hard detents when powered. These work nicely with the 100um/turn fine focus knob. Manual operation of the graduated knob gives 1um per detent step. Automated operation of the 400-step motor gives 250nm per full step, plenty small enough for almost any requirement.
My first automated setup kept the camera fixed and moved the subject stage. I subsequently have built 3 generations of setups where I move the camera while keeping the subject fixed. This setup goes back to the fixed camera / moving stage approach. I think this approach makes a lot of sense at higher power, since moving the camera involves moving a lot of mass, and a lot of precision. Moving the stage is easier, whether it be with a microscope focus block, or other method, and moves far less mass, so settling times can be much faster. I am not giving up my current stack and stitch setup for this one for general use, but for high power this new setup is far superior.
Here is a pic and description of the setup:
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