Using focusing rail manually with X4 objectives?

[len]

Hi,
I'm trying to build my first extreme macro setup. I'm planning to use a Canon APS-C CMOS sensor camera in a vertical position similar to Charles Krebs set-up http://www.photomacrography.net/forum/v ... f=8&t=9453. I'll use x4/0.10 finite objectives on different tube lengths to control my field of view. I don't know the exact math but I guess each step should be at least 0.1mm, according to tube length.

My question is, which manual focusing rail can work with such a setup? It should be accurate enough to be able to manually move by a few tenth mm at each step and not slide down alone due to the weight of the camera.

I read good reviews on https://www.aliexpress.com/item/4001176273693.html does anyone know if it can satisfy my needs?

[rjlittlefield]

At NA 0.1, the nominal DOF is 0.055 mm. You could go a little bigger than that, but at 0.1 mm you'll definitely see blurring at an actual-pixels view. Usually it's better to go a little smaller, say 0.040 mm.

The screw pitch on that rail is 1.25 mm, so the required movement would be about 1/30 of a turn. That is possible, though fiddly, by using a technique like I show at viewtopic.php?p=216901#216901 with the iShoot rail (1.0 mm/turn).

For manual focusing with a microscope objective, a better solution is to use a micrometer driven rail, such as shown by Krebs at http://www.photomacrography.net/forum/v ... php?t=6290 . The micrometer part has a finer screw thread (0.5 mm) and a dial with fine tick marks, both of which permit smaller movements. A gentle touch and close attention will still be required, however.

For regular use with microscope objectives, most people use either a motor-driven screw rail or a re-purposed microscope focus block. For a vertical setup, it can be simple to extend the stage of a microscope so as to utilize the focus block with no mods to the microscope itself. See for example http://www.photomacrography.net/forum/v ... 4797#94797 . I see a couple of Olympus CH scopes on eBay right now that would work fine, for about the same price as the aliexpress rail.

--Rik

[ray_parkhurst]

If you can move the subject rather than the camera+lens, I'd suggest using the relatively cheap Z-axis micrometer platforms. Their resolution is 10um per micrometer "tick" mark, with good repeatability and minimal backlash due to spring loading. I use these extensively for manual stacking up to 10x, and for general fine focusing and setting stack start/stops without having to make adjustments to the rail control software. Here is a seller that has sizes from 40x40mm up to 125x125mm:

https://www.ebay.com/itm/224643139599

[rjlittlefield]

I use these extensively for manual stacking up to 10x

That's an elegant approach. Do you have that documented somewhere, so I could add it to the list at viewtopic.php?p=55311#p55311 ?

From a standpoint of economics and flexibiility, I think it's worth pointing out that a microscope stage will comfortably make movements 10 times smaller, over a wider range, and includes XY controls, for about the same price as the platform if I fudge by selecting a used microscope and one of the larger platforms. Aside from new versus used, the major advantages I see for the micrometer platform are that it's tidy, compact, and no DIY required.

--Rik

[ray_parkhurst]

I use these extensively for manual stacking up to 10x

That's an elegant approach. Do you have that documented somewhere, so I could add it to the list at viewtopic.php?p=55311#p55311 ?

From a standpoint of economics and flexibiility, I think it's worth pointing out that a microscope stage will comfortably make movements 10 times smaller, over a wider range, and includes XY controls, for about the same price as the platform if I fudge by selecting a used microscope and one of the larger platforms. Aside from new versus used, the major advantages I see for the micrometer platform are that it's tidy, compact, and no DIY required.

--Rik

I have not documented the use of these stages at 10x manual stacking in any of my posts. I mainly use them for setting the start/stop of the stacks, and for fine-tuning the focus for single shots. For 10x I usually use the THK automated rail, but before I set that up I used the Z-stage as described. If you think it would be useful, I could do a stack at 10x with with the manual rail and show resuts. Indeed doing a 3D rendering would show the usefulness of this method, since 3D relies on accurate Z-steps.

For sure the Z-stage is a nice add-on to any existing vertical setup as it gives convenient, fine-step vertical adjustments. However, I do agree that if there is sufficient space in the system, a microscope stage can do the same, with even finer step size capability. In my own system, I have an XY table, with Z-stage on top, and a tip-tilt on top of that, so no room for a fine-step microscope stage even though I own a couple different ones. Ultimately, what you use depends on what you need, and what you have room for.

[rjlittlefield]

Ultimately, what you use depends on what you need, and what you have room for.

I agree totally. My only intent was to clarify for the OP what some of the tradeoffs are.

If you have time, it might be helpful to post some illustrations of your setup with the platform. The more relevant links I can get in the FAQ list, the better.

--Rik

[OioMik]

Before going with automated rail, i used an old Newport 421 rail, and pictures were perfect with my x4 microscope lens!

[len]

If you can move the subject rather than the camera+lens, I'd suggest using the relatively cheap Z-axis micrometer platforms. Their resolution is 10um per micrometer "tick" mark, with good repeatability and minimal backlash due to spring loading. I use these extensively for manual stacking up to 10x, and for general fine focusing and setting stack start/stops without having to make adjustments to the rail control software. Here is a seller that has sizes from 40x40mm up to 125x125mm:

https://www.ebay.com/itm/224643139599

This is an interesting option, can you clarify your comment about the spring backlash. does it actually spring? The reason I use a vertical rig is to avoid pinning the insect. I just lay it on the surface in a natural position and move the camera above. Does this stage move smoothly? my concert is that if it "jump" in each step the insect part like the antenna may move during the stacking.

At NA 0.1, the nominal DOF is 0.055 mm. You could go a little bigger than that, but at 0.1 mm you'll definitely see blurring at an actual-pixels view. Usually it's better to go a little smaller, say 0.040 mm.

How do you calculate the step size? For my purpose, I'll work with lower magnification of 2x-4x using 4x objective with different size tubes to control the magnification. How can I know how does it affect the step size? I'll probably need to open another thread on the subject

The screw pitch on that rail is 1.25 mm, so the required movement would be about 1/30 of a turn. That is possible, though fiddly, by using a technique like I show at viewtopic.php?p=216901#216901 with the iShoot rail (1.0 mm/turn).

Does the iShoot rail consider as good as the Niki in my link?

For manual focusing with a microscope objective, a better solution is to use a micrometer driven rail, such as shown by Krebs at http://www.photomacrography.net/forum/v ... php?t=6290 . The micrometer part has a finer screw thread (0.5 mm) and a dial with fine tick marks, both of which permit smaller movements. A gentle touch and close attention will still be required, however.

Sound a good option but will is held in vertical position? I assume the delicate screw of micrometer could bend when holding the weight of a camera with equipment.

Thanks for you all the information.
Does the forum has any FAQ on manual focusing?

[Adalbert]

Hello Rik,

Which one is more precise?

- Newport M-426 linear stage
or
- Olympus CH microscope focus block

Best, ADi

[ray_parkhurst]

This is an interesting option, can you clarify your comment about the spring backlash. does it actually spring? The reason I use a vertical rig is to avoid pinning the insect. I just lay it on the surface in a natural position and move the camera above. Does this stage move smoothly? my concert is that if it "jump" in each step the insect part like the antenna may move during the stacking.

The micrometer Z-stages have springs that hold the stage surface "down", to keep a bit of pressure on the micrometer, so that no backlash can occur. They are very smooth in operation, with no jumps as long as they are working properly. I've had some where the bearings were a bit tight, but even with these the operation was smooth due to the spring loading. This is similar to many micrometer-based stage designs, including the Newport M-426 you are asking about. The quote below is from the M-426 description:

"Springs provide preload against the actuator tip to eliminate backlash"

[JKT]

How do you calculate the step size? For my purpose, I'll work with lower magnification of 2x-4x using 4x objective with different size tubes to control the magnification. How can I know how does it affect the step size? I'll probably need to open another thread on the subject

When you go to lower magnification with the same finite objective, you could increase the step size, but you don't have to. If you want the formula for how much - then a new thread might indeed be in order.

[rjlittlefield]

Which one is more precise?

- Newport M-426 linear stage
or
- Olympus CH microscope focus block

The focus block is more precise.

To explain...

Newport M-426 is just the sliding stage (https://www.newport.com/p/M-426). To control its motion, Newport recommends an SM-25 vernier micrometer (https://www.newport.com/p/SM-25). This micrometer moves 500 microns/turn (thread pitch 0.5 mm), and it has a small diameter knob. Using this knob, it is possible to make movements of 1 micro, but such movements are difficult to make accurately and repeatably.

The Olympus CH microscope focus block moves only 200 microns/turn, and it has a large diameter knob. Using this knob, it is trivial to make accurate and repeatable movements of 1 micron. Movements of 0.5 micron are not difficult.

On a related issue...

I assume the delicate screw of micrometer could bend when holding the weight of a camera with equipment.

The micrometer shafts are hardened and short. I have never heard of one bending.

Newport rates their SM-25 as having a 23 lb load capacity (https://www.newport.com/p/SM-25).

But it would be madness to hang 23 pounds on a CH focus block. Horses for courses...

--Rik

[Adalbert]

Hello Rik,

Thank you very much for the detailed answer!

The most important feature for me is the move/turn,
as I want to connect a stepper motor to it.
The difference between 200 vs. 500 is already big, so Oly is a clear winner.

Now just one question, if I want to go to 0.1 μm,
should I put a gearbox 10:1 or a belt pulley in between
or solve this issue with the micro-steps of the stepper motor?

Best,
ADi

[lothman]

Now just one question, if I want to go to 0.1 μm,
should I put a gearbox 10:1 or a belt pulley in between
or solve this issue with the micro-steps of the stepper motor?

Microstepping works quite well. But: If you mean with 0,1µ a consitant step width between 90nm and 110nm than it is no longer a question of dividing pitch by transmission ratio. For such small steps you probably need a piezo stepper , because with mechanics your step width might change over several steps. It is a question about friction, stick slip, tolerances, elasticity.... of all parts involved.

[ray_parkhurst]

Microstepping works quite well. But: If you mean with 0,1µ a consitant step width between 90nm and 110nm than it is no longer a question of dividing pitch by transmission ratio. For such small steps you probably need a piezo stepper , because with mechanics your step width might change over several steps. It is a question about friction, stick slip, tolerances, elasticity.... of all parts involved.

Another option for moving the subject in small increments is a VCM. The typical voice coil I use has 1mm throw at max current from the controller (1A I believe), and with 2055 steps this gives a ~487nm step size. This can be reduced by adjusting the reference current. Going to 125mA would result in ~61nm steps. The VCM is fairly weak, so is not good for moving the camera, and the overall adjustment range is small, but the same would be said regarding a piezo transducer.