Extreme Underwater Macro with a dSLR

Guido Zsilavecz

Cape Town, January 2014

Bobtail in sand using 60 mm lens and Inon add-on lens - frame is 15 mm wide.

What I call "scary stuff amphipod" using 60mm lens and Inon add-on lens - frame is 15 mm wide.

Another bobtail, using 60mm lens and 12 mm extension tube - frame is 16.5 mm wide.

"Dance of the caprella" using 100 mm lens and 25 mm extension tube - frame is 16 mm wide.

Fiery nudibranch on egg case using 100 mm lens and 25 mm extension tube - frame is 16 mm wide.

"Dance of the caprella" part 2 using 60 mm lens and both 12 and 25 mm extension tubes - frame is 11.5 mm wide.

Caprella with prey using 60 mm lens and both 12 and 25 mm extension tubes - frame is 11.5 mm wide.

Strawberry anemone using 60 mm lens and both 12 and 25 mm extension tubes - frame is 11.5 mm wide.

Soft coral polyps using reversed 28-80 mm lens - frame is 7.5 mm wide.

The face of a platanna klipfish using reversed 28-80 mm lens - frame is 7.5 mm wide.

Detail of a starfish using reversed 18-55 mm lens - frame is 5 mm wide.

Hunchback amphipod using reversed 18-55 mm lens - frame is 5 mm wide.Note that the aperture was mistakingly fully open, resulting in very little depth of field.

Another hunchback amphipod using reversed 18-55 mm lens - frame is 5 mm wide. Note that the aperture was mistakingly fully open, resulting in very little depth of field.

A different amphipod using reversed 18-55 mm lens - frame is 5 mm wide. Note that the aperture was mistakingly fully open, resulting in very little depth of field.

Reverse 18-55mm lens - frame is 5 mm wide, this time with aperture set properly - depth of field may be narrow, but it makes a difference!

Reverse 18-55mm lens - frame is 5 mm wide, also with aperture set properly - depth of field may be narrow, but it makes a difference!

Left: the threaded ring which matched the lens thread. Right: a standard Canon body-cap. Middle: same type body cap with centre removed. The ring on the left was glued to this.

The 18-55 mm lens mounted in reverse. Note that the front of the lens (the actual back) is now fully exposed - in the housing that's ok, but be careful on land not to bump the lens!

Introduction

Cape Town's often murky waters do not lend themselves often to wide-angle photography. Thankfully the vibrant invertebrate life on the reefs make macro a very attractive alternative - there really is much to look at, and in a fractal way the closer you get, the more you see. From my initial forays into underwater photography using the great Nikonos V macro has been a personal favourite for those very reasons. Using extension tubes and their framers it was also relatively easy to take macro photos of sessile subjects. With standard framers and tubes allowing for 3-to-1, 2-to-1 and 1-to-1. I use the convention that the first figure is the subject, the second the film or sensor - so if film is 36 mm wide, then 3-to-1 means a subject of 108 mm wide is possible. Stacking tubes allowed going beyond 1-to-1 - with framers for 1-to-2 being available - I never had on of those, so my maximum was a subject 36 mm wide, in a 1-to-1 framer.

With dSLR's giving the ability to see your subject through the viewfinder the need for framers was no longer there. This also meant that different methods could easily be used. In this article I'll explore most of those.

What is "macro" anyway

Look at many lenses, or screens of compact cameras, and often a little flower symbol is used to denote macro. What this generally means is that this is where the maximum magnification of the lens can be found, but the interpretation of what "macro" is tends to be happily ignored. Traditionally true "macro" meant lifesize magnification - that is, the image size and the sensor (previously a frame on film) are the same. Given the dilution of the term macro, lens manufacturers generally label only their true macro lenses as such, but even then they sometimes cheat. The only way to actually find out is by reading the manufacturer's specification of the lens. Canon makes several: the "old" ef 100mm f/2.8 macro, the new ef 100mm f/2.8 L macro, the ef-s 60mm f/2.8 macro and so on. The problem is, in the past SLR's used 36 mm film, so if we saw that this photo was taken using standard macro, we knew it was a 1-to-1 representation of a 36 mm subject, and if we saw it was taken using a 1-to-2 extension tube, we knew it was half that. But, on dSLR's there are many different sensor sizes - from the "full frame" as found on the EOS 5D, to the APS-C on the 50D which is about 22mm wide, to the four-thirds Olympus cameras, micro-four-thirds, etc. So, while a true macro lens would still provide life-size representation, what it represents depends on the sensor size - in other words, the magnification changes. To give an example, on the EOS 5D a macro lens still provides a subject size of 36 mm, while the same lens on a Canon EOS 50D it can now capture something only 22 mm wide. That means that, when displayed on the same computer screen, the EOS 50D magnifies more already. This is the well-known "crop factor", for Canon APS-C sensors this is 1.6. So the 50D natively already magnifies by 1.6x.

Why do I mention this? Because macro is all about magnification, and simply saying that this is "1-to-1" is meaningless unless you know what sensor was used. This is why throughout the rest of this article I'll be using the term "frame width" to describe the magnification - that is, what you see on your screen represents a real-life frame of x mm across. The term extreme macro is simply used to denote going beyond 1-to-1, that is, beyond what your true macro lens can reproduce on your sensor. The techniques can be applied to any sensor size, the magnification will vary of course. Note that all sample images shown in this article are un-cropped - this is to give an accurate rendition of the magnification achieved.

The different options for going extreme macro.

Add-on lenses - outside the housing

A number of manufacturers provide add-on lenses which can be mounted on the camera housing. Inon is such a manufacturer, making not only a variety of stackable lenses, but also adaptors for a whole range of housings, most of them housings for compact cameras. The manufacturer of my housing, the now-defunct SeaTool, also made an adaptor which fitted on to the front of a flat port, and had a thread allowing an Inon lens to added when necessary. This added great versatility, in that one could use the lens normally until one needed that extra magnification. Unfortunately, using it with my 60 mm macro lens resulted in a very short distance between front of lens and subject, for only marginal magnification - other methods give better magnification at greater distances. For this reason I don't use this setup for extreme macro, but rather with a kit 18-55 mm lens to achieve better close-up results.

Add-on lenses - inside the housing

It is possible to buy what is essentially a magnifying lens which screws on to the front of your lens. Given I have other alternatives, I've never explored this option, but it is certainly possible.

Tele-extenders

Tele-extenders are magnifying lenses put between camera body and lens - generally used for extending the reach of tele-lenses (Canon makes them in 1.4x and 2.0x magnifications), they can be used with other lenses as well. That is, in a non-Canon world, such as Nikon and Olympus. As a Canon user, I could thus not try this underwater, but the results I've seen are good. Generally tele-extenders have an impact on image quality, although the newer ones tend to impact much less than older ones.

Extension tubes

Yes, extension tubes still exist! And they come in different lengths too, just like in the Nikonos days. I have 12 mm and 25 mm ones, and, just as before, they can be stacked. By moving the lens away from the camera body the magnification increases. Move it further, and it increases more. Of course, there is a downside: your lens-to-subject distance decreases as well. If it was possible to use bellows underwater, you could really go wild, but I've yet to see a housing that could house it! Further down is a table which shows what magnifications one can get with the different tubes, combined with different macro lenses.

Reversing lenses

Another age-old technique, here you simply take a lens and mount in the wrong way around. Now of course no dSLR allows that natively, so you need to get a coupling ring. These can be bought, but are neither readily available in South Africa, nor cheap. There is a simple solution however, given to me by a fellow photographer: you take a body cap (like a lens cap, the plastic thing that closes the camera body if there is no lens on it), make a hole, and then glue onto it a threaded ring, where the thread matches that of the filter ring for that lens. I happened to have one lying around, but what can be used is the ring of UV filters - speak to your local photography repair place, and they probably have some lying around with broken glass. Take that out, and you can use it.

I have used two different kit lenses for this technique: an old 28-80 mm lens, and a newer 18-55 mm lens. You use them on the widest setting, and you'll need to play with the focusing to get the maximum magnification. Lenses by themselves have the aperture fully open - meaning you'll get minimal depth of field - to increase it somewhat you have to close the aperture down. This can be done very easily on at least Canon cameras: mount the lens normally, and in manual mode set the apperture to the one you desire (f/8 or f/11 is good), press the depth-of-field preview button, and while holding it remove the lens. Do not switch the camera off before doing this, as that lets the aperture open again! I made that mistake, with a subsequent serious loss of depth of field. There has been a report of this damaging the lens, but the lens had a problem already, so it is more likely because of that - that said, do so at your own risk! I have not had any problems.

Why does this work? Well, simple: on the wide end of a lens it is "compressing" a wide field of view into a narrow sensor-sized space - reverse it, and you do the opposite - take a narrow subject and "expanding" it to the width of the sensor!

Issues to think about

Distance to subject

In general, the higher the magnification, the closer you need to get to your subject. This becomes a serious problem when your subject matter is very small compared to the size of the port on your housing. In my most extreme case, using the 18-55 mm lens reversed, a subject matter of 5mm is dwarfed by a 95 mm diameter port! Trying to find your subject is thus very hard, but also because you are so close you need the subject to either be on something that sticks out, of on a fully flat surface, as otherwise the port will block you from getting close enough. Add to this the problem of getting strobe light in, given the strobes can, at best, be in-line with the port! All this also casts a nice shadow, so you'll need a focusing light that can shine into the narrow gap between port and subject, in order to at least see what you are doing. Remember that with the reversed lens technique your aperture is stopped down, so you will definitely need some external light, as otherwise it is all rather dark!

Depth of field

The closer, the lesser the depth of field. It's a pain, but there is little you can do about that underwater. With APS-C cameras use f/8 or f/11, not higher, as then diffraction will start kicking in and ruin your image that way. With a lack of depth of field keeping things in focus is a major exercise in patience if there is any surge around - it is amazing how things move with the slightest water movement. Add to this your inability to stay quite fixed yourself, and many shots will be ruining due to being out of focus. I find it easiest to tackle subjects on vertical walls next to sandy areas: there I can lie down and keep myself as steady as possible without damaging marine life.

Comparing techniques, showing magnification and distance to subject

LensDistance to subjectFrame widthMagnification
100 mm150 mm22 mm1.0x
100 mm with 12 mm ext tube138 mm18 mm1.2x
100 mm with 25 mm ext tube135 mm16 mm1.4x
100 mm with 12 and 25 mm ext tube125 mm15 mm1.5x
60 mm88 mm22 mm1.0x
60 mm with 12 mm ext tube82 mm16.5 mm1.3x
60 mm with 25 mm ext tube71 mm13.5 mm1.6x
60 mm with 12 and 25 mm ext tube69 mm11.5 mm2.0x
28-80 mm reversed at 28 mm47 mm7.5 mm3.0x
18-55 mm reversed at 18 mm38 mm5 mm4.5x
60 mm with Inon33 mm15 mm1.5x
Note here that the distance to subject given is generally from front of lens to subject, with the camera outside of the housing - that is, the distance from port to subject is smaller, and depends on the "fit" of the lens in the port. The last entry, with the Inon lens, is from Inon lens as mounted on the port, with the camera inside. The distance here can thus not be compared directly, but it does show that the distance is small, and for a magnification of about 1.5x using the 60 mm with 12 and 25 mm tubes is the better solution. I have not used all the above combinations, simply due to not having ports long enough to house all of them - the sample photos represent the options I have used.
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