Harvesting and adapting an Olympus CHT focus block

[rjlittlefield]

In an earlier thread, I was seen first complaining that the design of an Olympus CHT focus block makes it hard to harvest, then muttering that "However, I'm gradually coming to feel better about the scheme of using a filler block, no need to cut anything off, and in fact those stage mounting tabs could come in handy. That needs to sit in my head for a while."

In this thread, I'll illustrate that I came to rather like the idea of a filler block. Bottom line, I was able to harvest and adapt the block essentially using just a drill, a hacksaw, a file, and a hardware store, with no risk to the block and no chance of device failure down the road.

To begin at the end, here's the block being used in a vertical setup. It's hard to say where the weak spot is in this arrangement. To get the thing apart, you'd have to either snap two 1/4" bolts near the base, or a single 1/4" bolt near the camera, or shear and snap two 4 mm screws and four 3mm screws in the middle.



Here's the block by itself, from three different viewpoints.







The camera side consists of a plywood filler block to which is bolted an Arca Swiss clamp. I've used here a very inexpensive clamp -- you can get these things for about $6 on eBay. I've chosen here to fasten it with a single bolt, partly to avoid modifying the clamp and partly to simplify aligning the clamp on this side with the Arca Swiss plate on the other side.



Beneath the clamp is a hole that's been drilled to accommodate a T-nut pressed into the back side.



Here is the collection of all parts that were added to the focus block.



And here's the focus block itself, modified only by drilling two holes in the metal, two holes in the plastic back plate, and cutting off the head mount. I anticipated questions about cutting off the head mount, so I paid particular attention to that operation. It took just under 5 minutes of slow but steady work with a hacksaw, using a new blade. The material appears to be an aluminum alloy, not magnetic, and soft enough to shave easily with a sharp knife.





Here again is the block as fully assembled.



Both of the Olympus arms and the one Amscope arm that I've looked at would be amenable to the same trick of drilling two holes from front to back and just sticking a couple of long bolts through them. Probably there are other arms that are not, but this is a technique that's worth considering.

I hope this information is useful to somebody else. Although in the end the machining was simple, I will happily confess that it took a long time for me to figure out how to do this easily. If I can save somebody else the trouble, that's great.

--Rik

[Olympusman]

I harvested an Olympus focus block a few years ago and gave up on using it vertically -- way too much focus creep.

Mike

[TheLostVertex]

It's hard to say where the weak spot is in this arrangement.

I harvested an Olympus focus block a few years ago and gave up on using it vertically -- way too much focus creep.

Focus creep crept into my mind when reading that myself. I imagine it slowly sagging with a lot of weight like that, or possible stressing the focus shaft a lot from having the tension set high. Have you felt like either of these things would be a problem?

Also, what is your method for aligning the clamp? It would seem the better aligned this piece(and any 'tilt') in the set up, the less boundary pixels you would have to throw away when stacking.

Edit: Also, I assume the rubber band is for when the focus block is used horizontally. Is there any reason you have it tight while it is vertical?

[JGVilla]

Hallo Rik,

I haven't been active for a long on the photomacrography.net.
At the end of last year I started thinking of "bratcamming" my focusing block (still going strong).
At the moment the focusing block is at my manufacturer but I will try to stop that program,
because I found a way how anybody with some basic DIY skills can "bratcam" a focusing block/microscope for him/herself.

The program is in its final prototyping phase and it will take a couple more weeks before I can show the final results,
but the pictures you posted here look remarkably like my set-up so I will post a picture of my prototype here to give you some idea.
As you can see against the back plate (your bottom plate) I mounted an Item 5 profile 40x20
(see their catalog at http://catalog.item24us.com/en/index.ph ... ories.html or google "item profile").
I just ordered the black anodized version of that profile plus all required connectors and sliding nuts.

In my prototype I drilled two M5 holes in the Olympus bottom case, similar like you did with your L-profile to hold the quick-release plate.
Through the slots and nuts in the profile I placed two M4 setting screws against the back of the Olympus CHC.
Bolting down the profile to the bottom case and then adjusting the setting screws, affectively takes care of the slightly rounded back of the Olympus CHC.
(see the space between the Item profile and the back of the Olympus CHC).
Finally I made an M4 u-bolt. Construction is as tight as a house.



To the side of the profile I mounted two stubs of the same profile.
The one extending is 40mm and the one perpendicular to that one is 58mm.
To the bottom of the last one I will bolt a Nema17 mounting bracket (on order).
The (cognisys) stepper motor can then slide left/right, up/down and forward/backwards.
The pulley on the fine turning axle of the Olympus CHC is already in place, although I will probably place a 90-teeth pulley here.
The 32-teeth pulley for the stepper motor with a bore of 5 mm is on order.

Hope you get an idea of this prototype and as you can see it would not be too much of a problem to update your design.
I already tested the "fit" (including place of the stepper motor) and there are no problems here.
I hope I could give you an idea of the design and when my set-up is finished I will post an extensive description with photos here.

[rjlittlefield]

It's hard to say where the weak spot is in this arrangement.

I harvested an Olympus focus block a few years ago and gave up on using it vertically -- way too much focus creep.

Focus creep crept into my mind when reading that myself. I imagine it slowly sagging with a lot of weight like that, or possible stressing the focus shaft a lot from having the tension set high. Have you felt like either of these things would be a problem?

First, it's important to realize how these things work. There's a very low friction slider and gear train, combined with high friction washers on the knobs to provide "tension" that prevents focus creep. The gears feel whatever load is put on the slider, but if the tension is set higher than that, the shafts and gears don't feel the extra tension unless the slider runs into an end stop while being advanced under control of the fine focus knob.

Initially the tension setting on this block was not nearly enough to stop focus creep when loaded with camera and lens.

After adjustment, creep is no problem. As a "first-light" test case, I shot a stack at 2.5 microns using a 20X NA 0.28 objective. Since then, I've also checked that the rig does not creep even with an additional two pounds of beanbags added to the load.

Also, what is your method for aligning the clamp? It would seem the better aligned this piece(and any 'tilt') in the set up, the less boundary pixels you would have to throw away when stacking.

I stick a long plate in the clamp and use a construction level to make sure the clamped plate is vertical at the same time the focus block is. It turns out that the plate has a 3/8" hole in it that can provide access to the mounting screw, so I can hold everything in place while making the screw very tight.

Edit: Also, I assume the rubber band is for when the focus block is used horizontally. Is there any reason you have it tight while it is vertical?

Sheer laziness. Certainly there's no need for it in this orientation. Given the weight of the camera and lens, it might actually make more sense to flip the block over and let the stretchy band serve as a counterweight.

--Rik

[Chris S.]

Great post, Rik!

Although in the end the machining was simple, I will happily confess that it took a long time for me to figure out how to do this easily.

No doubt. It’s evident that a key design consideration was to come up with an approach that most people can emulate with simple, common tools and skills. That’s a tough requirement—as well as an elegant solution.

The use of through bolts is undoubtedly sturdy, and for this block and the others you referenced, apparently straightforward. For anyone wishing to alter a Nikon Labophot or Labophot 2 block, be aware that it would not be so straightforward. These blocks also have a plastic back plate, but they also have a very thin front cover, which is not structurally solid. Below this, there may or may not be room for through bolting, but that’s another conversation.

I anticipated questions about cutting off the head mount, so I paid particular attention to that operation. It took just under 5 minutes of slow but steady work with a hacksaw, using a new blade.

An excellent data point to have on record. I’m sure lots of people will happily file this tidbit away.

I’m curious why you chose to leave as much of the shoulder (right word?) of the stand in place. It’s not causing you any problems at present, but I could imagine its getting in the way for certain configurations. On the other hand, it’s a sturdy place to mount something, and you could loop your surgical tubing over it, if you wanted it to pull the other way. And if it ever does cause a problem, removing it is just another five-minute cut—or maybe a tad more, as the shoulder seems to get a bit thicker. Did I miss anything?

It's hard to say where the weak spot is in this arrangement.

In my imagination, the weakest point would be the potential for human error in adjusting the double clamp, double rail height adjuster—unless you’ve rigged some safety stops? Not sure my imagination is being rational, here. But I’m surely not the only person who sometimes keeps working when tired and mistake-prone.

I’d be tempted to add a second—redundant—double clamp below the existing one. Then adopt a protocol as follows: At least one clamp set is fastened at all times; before raising the block assembly, lock the lower clamp up tight against the upper clamp, such that the assembly can’t slide below the original position; before lowering the assembly, lock the lower clamp at distance below the upper clamp, but high enough to safely stop the camera if it slides.


Jan, I’m eager to see more of your “bratcamming” project. When you're ready, I hope you’ll give us a thread with lots of pictures and description. In the meantime, I’m wondering if it would be best to move your current post to a thread of its own, both to help people find your work easily, and to keep Rik’s thread centered on his CHT modification?

Cheers,

--Chris

[ChrisR]

Jan, I’m eager to see more of your “bratcamming” project. When you're ready, I hope you’ll give us a thread with lots of pictures and description. In the meantime, I’m wondering if it would be best to move your current post to a thread of its own, both to help people find your work easily, and to keep Rik’s thread centered on his CHT modification?

Jan - I think that would be better; CH2s and CHTs are probably different enough to be addressed separely. If you could start a new post we can add links.

[JGVilla]

Hallo Chris R & S,

That would be perfectly OK with me.

Actually I'm ready to publish. Point is, publishing takes -now- much more time than "bradcamming" a microscope (block).
My microscope block is ready and in the (mechanical) testing phase. Right now I'm also bradcamming my Olympus CHC micrsocope.
Made by all readily available off-the-shelf products. Probably ready tomorrow.

Are you interested in text and pictures or also in measurements, like lengths of profiles, length of bolts, etc.
and for the non-Item parts where I purchased them (all in Europe so that needs updating for US-members).
That might be of interest to anybody who likes to create his own DIY package.
Let me know what you're interests are (probably everything ':D').

The reason I reacted here is that I wanted to give some pre-information,
so that if wanted Rik could incorporate some of the "design" features into his project.
Also -out of necessity- he designed his "stage" around the fixed riser block of the CHL,
but I think it would be very valid to use something like that for all CH microscopes. I made a stage using Item profile 5 "building blocks":



Just a quick picture. Hope the construction is clear.

[rjlittlefield]

Although in the end the machining was simple, I will happily confess that it took a long time for me to figure out how to do this easily.

No doubt. It’s evident that a key design consideration was to come up with an approach that most people can emulate with simple, common tools and skills. That’s a tough requirement—as well as an elegant solution.

Thanks. Yes, that was a deliberate choice. Recall that the reason I started the related thread "How can I harvest and adapt a focus block?" was that I had recently received two emails asking close to that exact question. Those came to me from people who seemed to know about basic handheld DIY tools, so that was what I chose as a target for my endeavors.

The use of through bolts is undoubtedly sturdy, and for this block and the others you referenced, apparently straightforward.

Yes, that worked out well. Another "requirement" I imposed on myself was that there be no adhesives involved in supporting load. Clearly a properly chosen and well applied epoxy could do this job very well. But my goal here was explicitly to produce reusable information, not just to make a working unit for myself. As a matter of personal policy I'm not going to recommend a process that I know can fail unpredictably if the materials are not used properly. There's also the issue that especially when they are used properly, adhesives are pretty much a one-shot deal. If you mess something up even a little, you're basically stuck with it (pun intended).

For anyone wishing to alter a Nikon Labophot or Labophot 2 block, be aware that it would not be so straightforward. These blocks also have a plastic back plate, but they also have a very thin front cover, which is not structurally solid. Below this, there may or may not be room for through bolting, but that’s another conversation.

Thanks for the heads-up. Perhaps a simple clamping plate to span the front would address this issue; perhaps not.

I’m curious why you chose to leave as much of the shoulder (right word?) of the stand in place. It’s not causing you any problems at present, but I could imagine its getting in the way for certain configurations. On the other hand, it’s a sturdy place to mount something, and you could loop your surgical tubing over it, if you wanted it to pull the other way. And if it ever does cause a problem, removing it is just another five-minute cut—or maybe a tad more, as the shoulder seems to get a bit thicker. Did I miss anything?

I think you pretty much covered everything. My personal preference is to keep options open unless there's a good reason to close them. Clearly the dovetail and objectives mount would interfere with using the block as intended, and equally clearly some of the shoulder might be useful down the road, so I whacked off the head at the most conservative place that would do the job. It's relevant here that I had already decided to place the camera mount on top of the condenser block, because the design of the CHT frame made it impossible to do anything else without machining in close proximity to the slider bearings. If the camera mount were placed low, say bolted directly to the slider of a CHA, replacing the condenser block, then I would have whacked off more of the shoulder to match.

It's hard to say where the weak spot is in this arrangement.

In my imagination, the weakest point would be the potential for human error

I agree completely. When I spoke of "weak spot", I was thinking of things breaking. Vertical setups in general strike me as being dangerously vulnerable to operator error in changing lenses. That's one of the reasons I usually go horizontal. On the other hand I wanted to illustrate this beast in a vertical setup so as to emphasize the robustness issue, so for "first light" I chose a subject that was simple to manage by gravity in a vertical setup but would have been more challenging to mount for use with a horizontal setup.

--Rik