Guide / Tutorial Cheaper Macro/Coin Photography - Converting an existing camera+lens - Extension Tubes

[Charliemouse]

This guide is for people with an existing interchangeable lens camera and a lens with a focal length between about 30mm and 100mm.

With a relatively low (£50 or less) investment, you can convert your existing lens(es) to take macro photos.  In comparison, a true macro lens will cost you £200 to £600.

As I’ve stated in other guides, a 1:1 reproduction ratio is pretty much ideal for photographing coins.  If your existing lens is outside of the 30-100mm range, you may struggle to get close to 1:1, but you can still use extension tubes to get much closer than you would without.

What are extension tubes?

An extension tube fits between the camera and lens; it has a camera mount at one end and a lens mount at the other.  It looks like a lens, but is actually hollow and contains no glass.

Using extension tubes effectively adds distance between your camera and lens, and due to the magic of optics (beyond the scope of this guide), increases the reproduction ratio (magnification).

Which do I buy?

You typically buy a kit of 2 or 3 tubes, and you can stack them to get combinations.  Because there is no glass, you do not lose any image quality.

Important: Make sure you buy the right tubes to fit your camera.  Also, make sure you buy ones that are described as “auto focus”.  They will pass the electrical signals from the camera to the lens.

The price difference between sets is down to:

• Number of tubes in the kit: 1, 2 or 3.  I recommend you get three, giving you most flexibility to experiment with magnification, and is the best value.
• Metal tubes are more expensive than plastic, but are a bit more resilient.  This probably doesn’t matter for coin photography.
• Brand.  There really isn’t anything to be gained from buying more expensive name-brand tubes, since there are no optics.

What tube(s) to use with what lens?

Below I describe the mathematical way to get to the desired magnification, and the experimental way.

The maths

You can skip this section if you want, and go to the experimental section below.

Total reproduction ratio = Lens reproduction ratio + (Total tube length / Lens focal length)

So you need to know the focal length of your lens (right in the name of the lens) and the reproduction ratio.  The reproduction ratio is provided in the detail specification of the lens, and is easily Google-able.

Example: Say you have a classic 50mm lens for your camera.

• Lens: AF-S NIKKOR 50mm f/1.8G
• Lens focal length: 50mm
• Lens reproduction ratio: 0.15 or about 1:7 (get this from the spec sheet)
• Tubes: 12mm, 20mm, 36mm

Using a 36mm tube:  0.15 + 36/50 = 0.87 or about 1:1.2

That’s very close to the 1:1 ratio of a true macro lens.

Using 12mm+36mm tubes: 0.15 + 48/50 = 1.11 or about 1:0.9

That’s slightly more than the 1:1 ratio.

Experiment without the maths

As a first guess, you want to use tubes with a total length of about ¾ that of your lens.  So roughly:

Lens focal length	Attach these tubes
30mm	20mm
50mm	36mm
60mm	12+36mm
80mm	20+36mm
100mm	12+20+36mm

After you look at the subject through the camera, if you need more magnification then add more tube length.  If you need less, take it away.

The longer your original lens, the more tube length you need to make a difference to your reproduction ratio.

What if I use more tubes?  Can I make a microscope?

Sadly no.  Every time you increase the tube length, you bring the focus distance closer.  At some point, your focus distance will actually move to inside your lens, and you won’t be able to focus on anything.

What about zoom lenses?

What if your lens has a range of focal lengths, e.g. 24-70mm, i.e. a zoom lens.  You can absolutely use extension tubes with zoom lenses.  Zooming in and out will change the magnification ratio (see the maths above) and the possible focus distances.  When experimenting enthusiastically, just be careful not to move too far forward and bump the lens into the subject!

What are the drawbacks?

Why do people ever spend money on dedicated macro lenses when you can just use extension tubes on existing lenses?  As with everything, there are disadvantages.  Most of these disadvantages get worse as the tube length increases.

• Maximum focus distance is reduced.  When you use an extension tube, you will no longer be able to focus out to infinity.  In fact, you probably won’t be able to focus beyond a couple of metres away.  In order to use your camera for anything other than macro, you will have to take out the extension tube(s).
• You will lose some light.  I won’t go into the reasoning or the maths for this, but the longer the tube length, the less light will reach the sensor.  Since you are generally on a tripod and/or have control of the light, this shouldn’t matter.
• It’s a bit more cumbersome and lengthens the amount of ‘stuff’ hanging off the front of the camera.  This is usually fine, as the tubes themselves weigh very little.  Taken to extremes, if you used multiple sets of tubes, you might need a sturdier tripod.
• You are going to get very close to the subject.  If you are using some kind of lighting rig, you may need to shorten the tube length.
• You are definitely going to need a tripod, to hold still for longer exposures.  If you don’t want to use a tripod, shorten the tube length.

The following aren’t exactly drawbacks, but there are advantages that dedicated macro lenses give you, specifically beneficial to macro photography, which you won’t get when using extension tubes with other lenses:

• Fine focusing.  Most macro lenses allow very smooth adjustment of focus, for the tiny distances.  Remember, you will almost certainly be manually focusing.
• Nice out-of-focus backgrounds (bokeh).  Macro lenses generally have lots of diaphragm elements and curved elements, to smooth out the background.
• Smaller apertures.  Most macro lenses can be set to very small apertures (above f/22), increasing the depth of field when needed.

Alternatives to extension tubes

There are other ways to adapt an existing lens to work as a macro lens.  I am not going to give the full ins and outs, but I will list them here for completeness.  I may write guides later, if there is interest.

• Reversing ring.  The very cheapest (<£10) option.  Believe it or not, it actually involves mounting your lens backwards, using a hollow metal ring that joins the front of your lens to the camera, instead of the back.  Yes, it actually works.
• Macro conversion lens.  This is like a reading glass for your camera.  It screws onto the filter thread at the front of the lens, and varies the magnification of the lens in a similar way to tubes.  Can be a bit more convenient, as it doesn’t significantly lengthen the lens.  Also may be able to use on a fixed lens camera, if it allows attachment of filters.
• Bellows.  These are effectively flexible extension tubes, where you can vary the distance between the lens and the camera precisely.  Of course they are cumbersome, but they do give you a very cool retro-looking camera.

Summary

If you already have a camera with a medium(ish) lens, buy a set of three “auto focus” extension tubes and have a go at photographing coins close up.  You should get some amazing results.

I intend to do some experiments with different lenses,  covering the top, middle and bottom of my suggested range of focal lengths.

Edited December 19, 2023 by Charliemouse

[Charliemouse]

Experiment I - Wide angle

Here are my experiments using a wide angle lens, a Sigma 35mm F1.4 DG HSM.  This is definitely not useful as a macro lens on its own, having a reproduction ratio of only about 1:5.

• Focal length: 35mm
• Reproduction ratio: 1:5.2 or 0.19x

The photos are not the prettiest, but I tried to keep the angle of the coins and camera the same, just moving the camera closer as I added tubes.  Images are uncropped.

No tubes: 1:5 - minimum distance

Shot at minimum focus distance (as close as I could get).

12mm tube:  0.54x or close to 1:2 - minimum distance

What a difference with just the smallest tube!  We are only at half macro here, but already the image of the coins is so much better.

(The reason it is framed like this is that I needed to be so close to coins that the lens was resting on the platform, and to keep the angle the same I didn't want to raise the camera and tilt down.  In reality, you would find a better angle, or just back off a little.  But for the sake of the experiment, I wanted minimum distance.)

12+20mm tubes:  1.1x or about 1:0.9 - minimum distance

At minimum distance, the lens is touching the coin capsule and blocking almost all of the light.  I had to place a light directly above, shining down into the gap.  This is getting impractical, but if you wanted to highlight a specific detail of a coin, this could work well.

12+20mm tubes:  0.19 + 32/35 = 1.1 or about 1:0.9 - maximum distance

And this is the maximum distance, only about 2 cm away.

Summary

You can see that just using the small tubes with a wide-angle (short) lens, you get a lot of magnification very quickly, but the working distance shrinks so much that some shots will be impractical.  However, just being able to get half macro with the 12mm tube, makes a huge difference to the quality of a coin photo.

Edited May 25, 2023 by Charliemouse

[Charliemouse]

Experiment II - Telephoto

Next, I tried my portrait lens, a Sigma 85mm F1.4 DG HSM.  Again, this is definitely not useful as a macro lens on its own, having a reproduction ratio of 1:8.

• Focal length: 85mm
• Reproduction ratio: 1:8.3 or 0.12x

Again, I tried to keep the angle of the coins and camera the same, just moving the camera closer as I added tubes.  Images are uncropped and all at the closest distance I could focus.

No tubes - 1:8

12mm tube - 1:4

20mm tube - 1:3

12+20mm tubes - 1:2

12+36mm tubes - 1:1.5

12+20+36 tubes - 1:1.1

Summary

Again, impressive results coming from a lens that is nowhere near able to take macro shots without the extension tubes.  Without the tubes, the working distance was about 1 metre.

Even with all three tubes, I was still about 20cm from the coins.  This could be good news if you have room to work, but bad news if you are trying to shoot down onto a table with limited space.  The other downside was that even with all three tubes, I could not quite reach 1:1 ratio; this could be solved by buying another set of tubes.

So really, as expected, the opposite set of problems to the 35mm above.  Instead of everything being too close and too magnified, here we have plenty of space to move, but maybe not quite as much magnification as we'd hope for the really small coins.

Edited May 25, 2023 by Charliemouse

[Charliemouse]

Experiment III - Standard

Finally, I tried my standard lens, a Sigma 50mm F1.4 DG HSM.  'Standard' lenses, generally 50mm, are the cheapest and most common focal length lenses available.

• Focal length: 50mm
• Reproduction ratio: 1:5.6 or 0.18x

No tubes - 1:6

12mm tube - 1:2.4

20mm tube - 1:1.7

12+20mm tube - 1:1.2

12+36mm tube - 1:0.9 or 1.1x

20+36mm tube - 1:0.8 or 1.3x

Summary

This lens with extension tubes gives a really good working range of magnifications.  The 20mm tube alone, or coupled with the 12mm, gives a nice ratio, with the 1oz coin filling the frame.

However, you can go too far- above 1:1 magnification, the lens was so close it became difficult to light the coin.  I'm sure it's possible, and would be great for zooming into a specific detail, or filling the frame with a small coin.

 

Edited May 26, 2023 by Charliemouse

[Silverlocks]

21 minutes ago, Charliemouse said:

[ . . . ]

However, you can go too far- above 1:1 magnification, the lens was so close it became difficult to light the coin.  I'm sure it's possible, and would be great for zooming into a specific detail, or filling the frame with a small coin.

This was the major problem I had with using a smart phone - the 'macro' lens, which just clipped over the main lens on the camera, only allowed focusing out to a few cm distant from the subject.  This made it very difficult to light the coins in a way that was conducive to getting decent pictures.  Really, the axial lighting box was the only lighting that really worked.  With a macro lens I can get the camera 10 or 15cm away from the subject, which is far enough to use ring, panel and spot lights.  That made life a great deal easier.

[Charliemouse]

29 minutes ago, Silverlocks said:

This was the major problem I had with using a smart phone - the 'macro' lens, which just clipped over the main lens on the camera, only allowed focusing out to a few cm distant from the subject.  This made it very difficult to light the coins in a way that was conducive to getting decent pictures.  Really, the axial lighting box was the only lighting that really worked.  With a macro lens I can get the camera 10 or 15cm away from the subject, which is far enough to use ring, panel and spot lights.  That made life a great deal easier.

Yes.  Number one drawback of extension tubes (and other lens adaptations) is lack of focal range.  In order to focus closer, you have to sacrifice being able to focus farther.  The big advantage of macro lenses is their ability to focus from a few centimetres to infinity (and sometimes beyond 😉).