Proof of concept: NiSi NM-200 manual focus rail (plus Post Update)

The following focus stacked composite image was created using a Fujifilm X-T3 mirrorless digital camera and Laowa 25mm Ultra Macro lens mounted on a NiSi NM-200 manual focus rail.

Toy dinosaur at 2.5x magnification.

The Laowa lens was set for 2.5x magnification and an aperture of f/4, the “sweet spot” for that lens.

The subject is a small toy dinosaur, viewed from above the anterior end of the dino. The toy is approximately 3.2 cm long (~32 mm).

The carriage of the focus rail was moved 200 µm (micrometers, also known as microns) per step, equal to 20 increments on the NiSi NM-200. A total of 28 photos were taken. A little back of the envelope math shows the carriage moved a total of 5.6 mm from beginning to end.

200 microns x 28 = 5,600 microns

5,600 microns x 1 mm/1,000 microns = 5.6 mm

The camera was set to record JPG plus RAF files. For simplicity the composite image was focus stacked in Adobe Photoshop using the JPG files straight out of the camera. The final output was slightly cropped and sharpened.

Look closely at the full size version of the composite image. I don’t see any glaring “focus banding” so the 200 micron step size seems to have worked. [See Post Update, at the end of this blog post.] As always, a sample size of one proves nothing. That said, I feel confident the NiSi NM-200 works as expected and will be a useful aid for creating macro focus stacked composite images.

Tech Tips

i used a step size of 200 microns — much larger than the 10 micron precision limit of the NiSi NM-200. My goal was to choose the largest step size that wouldn’t show “focus banding.” I’m not sure what the maximum “safe step size” is, given the settings for my photo gear, but it appears 200 microns doesn’t exceed that value.

Related Resource: “Toy dinosaur” includes a photo (shown below) that shows the entire toy. 2.5x magnification is more than it seems!

08 DEC 2020 |  BoG Photo Studio | toy dinosaur

Post Update

In the preceding post I wrote “Look closely at the full size version of the composite image. I don’t see any glaring “focus banding” so the 200 micron step size seems to have worked.”

Well, someone with more experience than me in creating focus stacked composite images actually looked closely at my image, and here’s what he saw.

Annotated image used with permission from Rik Littlefield.

Rik Littlefield, creator of Zerene Stacker, noticed there is in fact a problem with focus banding in my composite image. Rik highlighted the focus bands with a series of black dots.

My decision to use a “safe step size” of 200 microns was based upon the output from a depth of field – step size calculator that I now realize is fatally flawed. Honestly I can’t remember which calculator I used, but I can tell you this — after using Rik Littlefield’s DOF Calculator to determine the safe step size for the same macro rig is 58.038 microns, I knew 200 microns must not have worked as well as I thought. And as you can see in Rik’s annotated image, a step size of 200 microns is too big. Sincere thanks to Rik for his feedback!

Copyright © 2023 Walter Sanford. All rights reserved.

Manual focus rails: Useful or useless?

For the purpose of this blog post, let’s establish there are two types of focus rails: manual; and automatic. This blog post will focus on manual focus rails only.

Manual focus rails are useful for positioning your camera more easily when it’s mounted on a tripod. But most manual focus rails are essentially useless as an aid for creating macro focus stacked composite images. The issue is lack of precision. More about that later in this post. For now, let’s review a brief history of manual focus rails that I own and have tested.

Neewer

The Neewer Pro 4-Way Macro Focusing Focus Rail is the first focus rail that I bought and is still available for $39.99 from Amazon. Trust me when I tell you this focus rail is anything but “Pro” but the price was right (given what I was willing spend for a focus rail at the time) and turned out to be a relatively inexpensive way to gain experience using a focus rail.

The rulers on each rail are marked in centimeters; the finest increments are in millimeters.

Photo Credit: Amazon.

Novoflex

My next focus rail — the Novoflex Castel-L Focusing Rack — was a significant step up in price. The same model is still available for $279.00 from B&H Photo — overpriced like all products made by Novoflex, in the opinion of this author. This is one of only a few pieces of photography gear that I really regret buying.

Although the focus rail is beautifully engineered and operates smoothly it is no more precise than the much less expensive Neewer focus rail: the ruler on the rail is marked in centimeters; the finest increments are in millimeters.

Photo Credit: B&H Photo.

NiSi

I recently bought a NiSi Macro Focusing Rail NM-200 for $199.95 from B&H Photo. At that price point, the NiSi focus rail is five times more expensive than the Neewer focus rail, and nearly $80 less than the Novoflex focus rail.

Notice the ruler on the rail is still marked in centimeters and millimeters. So why would I waste more money on another focus rail that is no more precise than the other two? Because it turns out it is more precise than the other two!

Photo Credit: B&H Photo.

Look closely at the larger adjustment knob shown below. One full rotation of the knob moves the carriage one millimeter, or 1,000 micrometers (microns). The knob is marked in 100 increments, so each increment on the knob is 10 microns. Now we’re getting somewhere!

Photo Credit: B&H Photo.

Thanks to Andy Astbury for verifying the math using a digital caliper. (As part of my due diligence, I watched Andy’s video before deciding to buy the NiSi NM-200.)

Screen capture from YouTube video by Andy Astbury.

Do you need a focus rail with 10 micron precision?

In a word, yes!

According to Allan Walls, macro photography guru extraordinaire, the following list shows the “safe step sizes” for different macro lenses. Remember, the goal is to move the camera with 30% overlap between steps.

• 1x:1 = 0.7 mm (700 micrometers, a.k.a., microns) ← 70 increments on NiSi NM-200
• 2x:1 = 0.25 mm (250 microns) ← 25 increments on NM-200
• 4x = 0.1 mm (100 microns) ← 10 increments on NM-200

It’s somewhat unclear whether the preceding step sizes include the recommended 30% overlap. In Macro Talk #18, Allan said a step size of 60-70 microns would be better at 4x magnification (6-7 increments on the NiSi NM-200). Another macro photographer recommends a step size of 50 microns at 4x (5 increments on the NM-200). Regardless of which advice you follow, the NiSi NM-200 is capable of getting the job done.

As you can see, even at 1:1 magnification the recommended step size is less than a millimeter. The same idea expressed another way: It’s impossible to use a focus rail marked in one millimeter increments to do macro focus bracketing with right size step between images consistently. That is, unless you find a manual focus rail like the NiSi NM-200 that enables fine adjustments.

Testing 1, 2, 3 …

I just set up my new NiSi focus rail and need to do some testing. I am encouraged by the results achieved by other photographers using the same rail. Stay tuned for a follow-up blog post in the near future.

Related Resources

• Neewer Pro 4-Way Macro Focusing Focus Rail
• Novoflex Castel-L Focusing Rack – with MiniConnect Quick Release
• NiSi Macro Focusing Rail NM-200 with 360° Rotating Clamp (7.9″ Length)
• NiSi NM 200 Macro Focus Stacking Rail Review – Budget Friendly Macro Focus Stacking Accuracy, by Andy Astbury (49:55)
• Nisi NM-200: Best Manual Macro Focusing Rail!? – First Impression, Testing & Tips, by peterviragphoto (8:50)

Copyright © 2023 Walter Sanford. All rights reserved.