Motorized focus rail - my "Franken-rail" (warning: long post)

So here's the low down. I had been stacking for a while with the manual Nisi NM180 rail. Great quality, precision engineered but...totally manual and therefore subject to movement and above all, quite tedious when doing 20+ shots.

I found the WeMacro a bit too pricey to my taste and they are still not shipping from DE which means customs duties, VAT and handling come on top at import. So I went and purchased a relatively unknown el-cheapo domestic solution, the MVE rail which at €135 came in at a reasonable price.

Turns out the thing is cobbled together by an enthusiast, using some aluminium profiles, 3D printed plastic parts, an off-the-shelf stepper motor and a home made electronic controller. That last bit actually is the only part of the kit which works as it should. It allows you to set start, end and step size in microns and then goes to work moving the camera along and sending a shutter trigger signal through the remote cable supplied.

The rail itself is quite wobbly, with other words I can see the image move from side to side in liveview on the LCD screen as the rail progresses and I have narrowed it down to the 3D-printed plastic bits. It also lacks a bit of stability due to the fact it needs to be mounted to a tripod quick-release with an adaptor plate and takes the camera on a Manfrotto-type quick-release adapter. The Nisi is itself machined to fit Arca-Swiss quick releases (without needing an extra screw-in piece) and has a great rotating (with click-stops at 90 degree intervals) Arca-Swiss adapter for the camera on top.

So...I TOOK BOTH APART!

Of course with the idea to combine the stepper motor and controller of the MVE with the precision machining of the Nisi. I cut off the last end of the threaded shaft of the Nisi in order to fit it into the flexible 5-8mm coupler that came with the MVE. I am assuming the torque will not be very bad so two-sided tape and a tight fit on the end of the Nisi rail will do the rest. Currently, the only issue seems to be the flexible shaft coupler which is just a mm to wide to fit into the Nisi rail and still turn freely. So I ordered a couple of the 5-8mm flexible shaft couplers with a smaller diameter on Amazon. When they get here, I; ll follow up with part 2.

This is what the MVE looks like when purchased (this is the only image I did not shoot myself BTW):

Slightly disassembled::

The 3D printed carriage which holds the quick-release adapter for the camera

The various bits and pieces

The 3D-printed attachment which secures the cradle to the threaded shaft

The Nisi rail with its end cut off

This is how the coupler will link the motor shaft to the Nisi thread

I needed a flexible coupling with a slightly smaller diameter than the one I found on the MVE as it scraped the inside of the Nisi rail. To my surprise, these are pretty easy and cheap to come by. I got a bag full for only €12 (including postage) on Amazon. Turns out they are the exact type used in Prusa 3D printers and can be found as "Flexible couplings 5mm to 8mm for CR-10 CR-10S S4 S5 Makerbot RepRap Prusa i3 3D Printer or CNC Machine". Here's a few quick shots of the new next to the old from a few angles. The difference in diameter is only 1 mm (19 instead of 20) but that is precisely enough to clear the inside of the Nisi. The 5mm side fits onto the stepper motor and the 8mm side happens to be the exact size of the shaft of the Nisi.

Here is that new coupling in its place linking up in the inside of the Nisi rail. The Nisi has a bearing on the outside of the rail but just to minimize friction, I added two small metal o-rings on the inside before sliding on the flexible coupling.

So, fitting everything together, I set up my tripod with the geared Benro GD3WH head which has a standard Arca Swiss quick mount. The Nisi itself is shaped to fit AS mounts directly without the need for additional mounting plates.

And on the Arca Swiss mount of the Nisi, I can either mount the tripod collar of my Irix 150mm/f2.8 macro directly (yes, an extremely handy feature of that particular lens collar):

Or I can use any other lens (here the Tamron 90mm macro) by securing a wide adapter plate width-wise on the bottom of the camera (for added stability) and twisting the top plate of the Nisi through it's click-stopped 90 degrees position:

My initial tests show (as expected) a huge improvement in directional stability. When the wormgear is advanced by the stepper controller, the liveview image no longer wobbles and there are is lot less artefarcting in the final image such as banding, hot spots or edge defects.

All in all, I'll start using this combo and will be posting some examples once I get my sealegs and get to terms with the controller. That will be somewhat of a learning process as the diameter and pitch of the MVE shaft are of course slightly different from the ones on the Nisi gear such that the micrometer settings will no longer precisely match. I think that can be overcome by learning what the "translation" should be and applying that when setting up.

For now, chapter closed but the book continues!

Would it not have been just as easy to "grind down" the outer diameter of the existing connectors, to the desired dimensions?

As with many things nowadays, the time and effort involved in grinding down the outer diameter (and the equipment required) would far outstrip the extremely low cost of just getting a few new ones in the right size.

I'd also suspect that if the result of the grinding would be even slightly uneven, you'd introduce an inbalance which would cause wear on both the stepper motor as well as the rail.

Leswick II wrote:

… this type of rail can be bought...even with a motor.

Here's one I bought, but haven't had time to do anything with.

My plan is, rather than make a slider, to make an electrically-adjustable bellows.

I have a hunk of stainless plate I'm going to mount to the end. It will be the stationary lens mount. I'll put another upright on the moving part. It will have a horizontal tilt capability, and a camera mount. I'll put a bellows between the two.

You can find donor-bellows, from which to rob the actual bellows mechanism, dirt cheap on evilBay or Your Local Photo Swap Meet. Nobody want these things any more. Be sure carefully check it for light-leaks if the bellows material looks old.