3D Print Your Macro Photography (part #3) the Coupled Reverse Lens Adaptor

The series

This Instructable is the third in a series of four. If you are already familiar with both macro photography and 3D printing, you can jump right in. To learn more about macro photography and this series, go here.

I will not go into as much detail in this part, as I covered the basics in Part #1 and then detailed the processes in Part #2. You should review these if you get stuck

This lesson - Coupled Reverse Lens Adaptor

After this lesson, you will be able to:

Explain the advantage of reverse coupled lenses
Print an adaptor that will allow us to fit a coupled reverse lens.
Set the reversed couple system up on our camera
Take macro images using this system
compare and contrast the outcome to a single reversed lens setup

Step 1: Coupled Reversed Lenses

With the Reversed Lens Adaptor (Lesson #2), we could mount a lens back to front and use it as a Macro lens. However, we can improve this design by mounting a long lens on the camera and use the Coupled Reverse Adaptor to reverse mount a shorter focal length lens to it (See Diagram above.). Why do this?

Control is better. The 'rear lens' is connected to the camera's electronics which means we can control it.
The quality is better. (A single reversed lens can be soft in the corners)
The magnification is higher. The non reversed lens is acting as a tube extender

You can get a rough idea of the magnification by dividing the long focal length by the shorter one. In my case, I used the 250mm end of one zoom and the 18mm end of the other, giving me an astounding 14:1, though this is likely to be less in reality

More details about reversed lenses and their application are available here and here.

Please note how I refer to each specific lens in the diagram above, as I'll use these terms in this lesson.

The 'rear' lens is the one closest to the camera
The 'front' lens is furthest from the camera.

If you just want to look at the files they are available here

Step 2: What Can You Expect With This Adaptor?

	No adaptor Lens: 18-55mm zoom Focal length: 55mm Content approximately 24mm height This is the kit lens zoomed in as much as I could. While not promoted as a macro lens it performs well closeup.
	Single reversed lens Lens: 18-55mm zoom Focal length: 18mm Content approximately 4mm height This image is from the last lesson. It's about a 3:1 magnification
	Coupled reverse lens (50mm) Lens: 50mm prime + 18-55mm zoom Focal length: 18 and 55mm Approximately 3.5mm in height There is only slight enlargement (3:1) compared to the single reverse. Notice that it is sharper
	Coupled reverse lens 55mm Lens: 18-55mm and 55:250 zooms Focal length: 18 and 250mm Approximately 1mm height By using the 18mm end of one zoom with the 250mm end of the other, I get about 12:1 enlargement. However, as you can see, the image is beginning to lose some clarity. An AI sharpening algorithm may be able to claw a little back.

Step 3: Files for Printing

The files are hosted here on Thingiverse. You can get to them directly with the links below. Please note that these adaptors are Canon RF and EFs mount only.

	One Colour Files
	Reverse lens coupler 52 to 58mm.stl	Use this file if one lens has a 52mm thread and the other 58mm. This diameter will be written on the inside front of your lens like this ∅58mm.
	Reverse lens coupler 58 to 58mm.stl	Use this file if you have two lenses with 58mm threads. The manufacturer will have written the diameter on the inside front of your lens like this ∅58mm.
	Reverse lens hood.stl	This file prints a lens hood that fits over the rear element of the front lens. It protects it, stops stray light from entering and allows you to add filters and the diffuser.
	Reverse Adaptor locking knob.stl	This thread dives a locking bolt for the lens hood, should you wish to use it. Full instructions are in Lesson #2.
	Reverse mounted diffuser.stl	If you have a clear filament, you can create a diffuser for your lens. See lesson #2 for details
	Two Colour Files
	Reverse lens coupler 58 to 58mm - MMU.stl	Use this file if one lens has a 52mm thread and the other 58mm. This diameter will be written on the inside front of your lens like this ∅58mm.
	Reverse lens coupler 52 to 58mm-MMU.stl	Use this file if you have two lenses with 58mm threads. This diameter will be written on the inside front of your lens like this ∅58mm.
	Reverse lens hood - MMU.stl	If you have a clear filament, you can create a diffuser for your lens. See lesson #2 for details. Use the single colour files for the knob and diffuser.

Step 4: 3D Printing

Settings

Filament: PLA, but PETG, if you have, might wear better.
Layer height: Set to 0.2mm. 0.1mm is preferable if it is available to you as it will help define the threads.
Support: No. Print in the orientation the file comes.
Brim: Yes. All items have a thin edge on the build plate. A brim 5 to 7mm brim will help to secure these.

Post-processing

You must clean up the threads carefully. Fit and check the adaptors before you shoot. Do this carefully, as the first fittings will help 'cut' the threads. If the adaptor doesn't go on easily, check the threads for any stray filament and make sure the adaptor is parallel to the front of the lens.

Screw the adaptor on and off a few times till it easily screws on.

Step 5: Controlling Your Lens

Set your camera to manual mode now

Aperture

Use the front, i.e. reversed lens, to control your aperture. The rear lens should be left fully open. Stopping down the rear lens will cause aberrations.

In lesson #2 I explain the trick in how to set the aperture on a reversed lens.

Vignetting

Vignetting is when you see the inside of your lens cutting off the corners of your image. This can happen with this technique and will depend on your unique combination of lenses. If it does, then Read more here and here.

Example above

Shutter speed

There is nothing particular to shutter speed for this method. However, like all macro photography, the faster, the better.

Focus

Focus the rear lens to infinite. Move your camera back or forward, or use the font lens locus ring to focus on your object.

Step 6: Putting It All Together

Step by Step

Mount the long focal length lens directly to the camera
Screw the appropriate adaptor into the front. (You can screw it onto an existing filter, but the lens itself has more thread, so it’s better to remove ‘the filter and screw it directly into the lens.
Screw the reversed short focal length lens onto the mounted long focal length lens
Add the rear-mounted lens hood from lesson #2
Add the diffuser from lesson #2 if you desire

Support Your Lens

You must support the lens for two reasons. The lens mount is not designed to carry that much weight. The lens will shake, making focus more difficult. Supporting your lens on a tripod will be difficult unless you have a rail system designed for the purpose. On the other hand, the answer is straightforward: use a small beanbag when off the tripod. Google "camera beanbag" to see what I mean. They start at about $15 on eBay, but it can't be difficult to make

Step 7: That's All for Coupled Reverse Lenses

My thoughts

I've achieved the best quality with this method but not at the highest magnifications. I haven't experimented with all the possible combinations of factors and haven't done a 'thorough' literature search. It may be possible to improve quality further, but I think it will always drop off as magnification increases

As a rule, I've found that the smaller the subject, the more problems you have and the greater the restrictions. In this case, I found:

The framing was difficult; the smallest movement I could make was too much
Even when the lens and camera were secure, the image would shake whatever focus method I used
I was limited to flat subjects, though this would be solved by focus stacking
I needed a lot of light. My flash was very close to the subject and set at 1/4 power

Let me know how you go with your experiments.

The next Part Coming soon.

Part #4 is on Macro tubes. I'll discuss how they compare with reversed and coupled reversed adaptors. You'll be able to print camera adaptors, lens adaptors, a set of tubes and even reverse mounts so that you can reverse mount lenses on tubes.

Not only that, I'll give you a way to produce tubes of any length you want, and if that's not enough, there is a surprise item that will bring your whole collection together.

Hope to see you there.