HOWTO: Homemade Reversing Variable-Length Extension Tube Macro

Here I will explain super cheap homemade variable length (like a bellows, sorta) reversing extension tube.

First, the technologies involved:

Reverse Lens

Lens reversing has been used as a technique for macro photography for quite a while. Decen’t close ups can be achieved by mounting the lens reverse directly on the camera, and really high magnification can be achieved by mounting the lens reverse on another (front mounted) lens. A reversed 50mm lens is basically a +10 diopter. The reason this works (I’m not a physicist, so this is a stupid explanation) is, while a lens is designed to take a large image and make it small (on your sensor), reversing it will take a small image and make it bigger.

Extension

Moving the lens farther away from the film plane increases magnification. Obviously. There are two commercial implementations of this. Extension tubes, some of which preserve the electronic connection to the lens, and bellows, which are variable length (you can contract or expand the bellows to focus and increase magnification). These are both often used with a reverse lens for added effect.

So I decided I would just make my own extension tube, and it just so happened that it ended up variable-length. I had some old diopters that were really bad so I never used them, and I had a dremel. I decided that it was possible to design a reversing extension tube with a drilled out body cap and a bunch of busted-out filters as spacers.

So what you need is:

A body cap

Some old filters that you don’t want (stackable). How much magnification you get depends on how many you use. I used 7 total, but find that 4 is the best to get good shots with. Should all be the same size and should fit the lens that you want to use.
Lens. It would probably be best to use a prime, and it can’t have an electronic aperture. You must be able to change the aperture with the ring on the lens, without it being connected to the camera. I use Nikkor 50mm/1.8D. Your lens will just attach to this mount, so you’ll still be able to use it for normal purposes after this project.

I thought of this project looking at the clearance table at Wolf, and bought 2 circular polarizers, 2 UV filters, and a body cap for a total of $12. I had a set of diopters that I never used too.

First thing to do is break all the glass out of the filters.

Do this inside a ziplock bag and one quick whack with the hammer should do it. Once the lens is fully busted shake all the broken glass down into the bottom of the ziplock bag. Dispose of the broken glass properly, make sure you don’t leave broken glass shards laying around. Do this to all the filters that you want to use. Afterwards, run water over them and clean them thoroughly with a rag. There are little tiny pieces of glass dust all in them (especially two-part rings like polarizers) and your sensor will be exposed to this if you do not clean them. This is going directly on your camera with no lens between it and the sensor, so be careful.

For turning filters, like polarizers, you don’t want to have your extension tube body turning all the time, so a dab of superglue where the two parts connect (in three or four places around the circle) should stop that problem.

Now get the lens cap and dremel out the center of it. Be sure to keep the mount in tact:

The dremel will likely melt the plastic, a bit that’s ok! makes it smoother. Sand it down. Wash all the little bits of plastic off.
Now onto the front of the body cap (that faces away from the camera), glue a filter ring, with the male side facing out. This is the side that’s going to interface with your lens. Mine wouldn’t fit on the no-name body cap that I was using so what I did was glued one male side in, and then glued another one female-female (giggidy giggidy) on top of that. So it ended up with the male side out, just using two filters. This is ok!

Now, you can either reverse mount your lens directly on the body adapter, or you can add your extra spaces to extend. This will increase magnification.

Here’s my finished extension tube and my first subject:

And here’s my first shot with it:

This picture is taken with 4 rings worth of extension.

Full manual mode only. The lens is not electronically attached so there is no metering. It’s pretty easy to get good shots with flash and the power dialed way down on it. You won’t be able to see through the viewfinder with the aperture stopped down, so what I do is open the aperture to compose, then stop it down and shoot.
Total investment: $12 + a bit of super glue. Oh and somewhere in the process I got my sensor dirty and had to clean it. So I used a little bit of compressed air too.