A small aquatic tank for macro work

The idea came from the book "The Complete Guide to Close-Up & Macro Photography" by Paul Harcourt Davies. Among the many different techniques and methods he discusses for capturing macro subjects on film, he talks about placing micro-aquaria subjects between two sheets of glass, separated by a clear plastic sheet with a deep U cutout. The subject sits in the confined space created by the cutout between the glass.

I took this a step further, and created a very small aquatic tank out of sheets of clear acrylic, with a glass front. I did this for a couple of reasons:

1. It greatly restricts the movement of the subject. With the extremely short depth-of-field of macro work, holding focus on something that might be swimming in any direction is frustrating in the extreme.

2. Lighting can be accomplished from any angle, and any background can be produced. The tank can even be used outside for natural light macro with bushes or grass, out of focus, as a blotchy aquatic-looking background.

Addendum summer 2012: I've done a couple of other variations of this now, which have their own uses, pros, and cons. So you can also skip down to:

The [first] tank I made is 25mm x 65mm x 90mm inside dimensions, roughly the size of a deck of playing cards. You'll want to consider your size carefully, with your intended subjects and with the ability to clean it — mine's a little too tight to slide my hand inside to wipe down. However, if I were to do it again, I might not make a simple box shape, but rather have the back wall meet the front in a deep 'V'. Reflections from the back wall may be reduced (though this hasn't been a problem), but the deeper an aquatic animal goes in the tank, the more its movement is restricted. The bottommost portion will probably be filled with sand, and the depth of the sand can control how much maneuvering space remains for your subject.

I had scraps of clear acrylic handy, so that's what I used, but it can be tricky stuff to work with. However, since it marks and scratches very easily, I made the front wall, which I would be photographing through, out of glass. Plexiglas, Lexan, and clear acrylic all have slightly different properties, but are similar enough to be interchangeable for this project, so feel free to use whatever you can get your hands on.

You can see the sides are haphazard in shape, not making a nice clean box, but it's actually much easier this way, and allows you to use whatever scrap of glass you can get your hands on without worrying about perfect fits. Mine was obtained from a cheap 4x6 inch photo frame from the Dollar Store.

On the bottom is a T-Nut in 1/4-20 thread size, standard tripod mount. It's positioned to be flush with the bottom edge of the glass, so that not only can the tank be mounted on any tripod or head, it will stand upright on its own between the glass and T-Nut.

The various clear plastics are slightly difficult to work with, since they're tough and have a hard-to-detect 'grain' that affects how you cut them. The scraps I had were 1/8" thickness, but you can use thinner than that, and it will probably be easier on you. Be warned, though — the thinner it is, the less strength in the joints (smaller contact area) and the greater the chance of cracking. You can use the plastic from a CD case if you liked, but you should know how easy they are to crack.

You can 'cold-break' most plastics by scoring deeply with a sharp utility knife, then bending them over a straightedge like the edge of a table, but it doesn't always want to follow the scoring (note the bottom edge visible at my middle finger, where the break departed from the score line). Cold-breaks are easier on thinner stock. Or, use a fine-tooth modeling saw for your cuts. I've also used such things as 'cutoff' wheels on a motor tool (such as a Dremel,) but the high speed and friction melts the plastic to some degree and usually requires a lot of cleaning and sanding for a straight edge.

Now here's the nice thing about the design: very few edges have to be uniform, and getting them straight isn't hard.

As I said, acrylic can scratch easily, so I wouldn't recommend using it for the front. On the sides or bottom, any scratches or even gouges should be inconsequential, but on the back they make still show against your background, or reflect the light from your flash and produce a hot spot. Scratches can be sanded away using finer and finer grit sandpaper, working up to a wet-sand with 600 grit, which will produce a haze. Then, some serious polishing with a clean sponge, some toothpaste (not gel), and a small amount of water will buff this to almost perfect clarity. This takes a lot of effort, though, so you want to avoid scratches as much as possible.

Pick a size for your finished inside dimensions, and cut a back piece (directly opposite the glass you'll use to photograph through) a bit larger than this, by at least twice the thickness of your stock (to account for the sides) — a little more won't hurt, and you don't have to be exact. The only crucial edge is the bottom, you'll want that reasonably straight. We'll make it perfect shortly.

Next we cut two side pieces, and it works best if they are uniform width. Sand down the edges that will be going against the back piece on coarse sandpaper, like 100-150 grit, used against a smooth level surface. This will give the necessary straight edge. Then smooth those edges with 300 grit to get better joints. I joined my pieces with two-part clear epoxy, used in enough amounts to completely seal the edges. Clean the contact areas first with alcohol. Glue the side pieces the desired width apart, as flush as possible with what will be the bottom edge of the tank. Allow to set and dry thoroughly.

Now, sand the bottom edge of all three pieces on a flat surface, again with coarse grit, until they are all perfectly even, then finish with fine grit. Sand carefully so you don't flex the side pieces and break the glue joints.

Cut a bottom piece, overlapping the others by a small amount. Again, only one edge has to be reasonably straight, and that's the one to go against the front glass. Glue this to the bottoms of the other three assembled pieces, getting it flush with the front edges — this is easiest to do by setting them face ('front') down on a flat surface. Let dry thoroughly.

Now's the time to put on a mount of some kind, if you intend to use one. Just make sure it doesn't overlap the front edges where the glass will go.

Place the assembled unit face (open side) down on coarse sandpaper and sand it down vigorously until you're sure that all edges are straight and even, then smooth with fine grit. This is the side that goes against the glass, so all edges have to be perfectly even, but sanding them after assembly makes this far easier.

Glue the glass plate to the front of it all. If you're doing like I did, then you have to be sure the glass sits even with the bottom of the T-Nut, and this is probably easiest by setting the glass face down on an empty bookshelf tight against the side, then gluing the assembly to it with the T-Nut also against the side. And that's all there is to it.

Despite my care with the epoxy, I still had a minor leak in a joint when done, so I went over all the joints with clear silicone caulk and that took care of it. If you lay out the joints like I outline above, all caulking can take place on the sides, where it won't show in the photos and you can be as messy as you like.

Now that it's done, add some water, a bottom surface of some sand (or whatever is appropriate) and perhaps some seaweed as 'environment'. Find a good place to photograph that allows you to control the light however you like, and some form of natural-looking background. As seen in this shot, I occasionally use a camouflage T-shirt. It's far enough away that it becomes well out-of-focus, and the mottled greens and browns work well.

My flash is shown on-camera here, but much more often I'll use it with an off-camera cord held off diagonally for better light and no chance of reflections. It was just impossible to get a pic of that on my own.

Also, be warned that a spill is very likely, so I would suggest doing this where such a thing won't bother you, like NOT over the hand-woven Persian rug.

The tank is supported by a Bogen/Manfrotto Long Lens Support, US #3252. It's essentially a clamp with an adjustable arm, topped by a mini-ballhead, and is intended to attach to the camera when using a long lens with its own tripod mount. Does a great job of reducing camera shake. But it also works well with the macro tank, allowing me to place it wherever I need to and get light from any angle. It isn't necessary, but if you're into nature photography it's a valuable addition to your equipment.

Once you're set up, pop in your subject and fire away! But, a few things to be aware of:

1. Clean the surfaces thoroughly each time you change your subject, or right before you start to photograph. Dust, lint, and hairs show up very well, and the flash can reveal a dribble trail of residue from water that's spilled down the sides. And if the water is still there, you'll definitely get hot spots from the flash.

2. Use the cleanest water you can manage, since the flash will show all sediment. This can be difficult to do, especially if your subject is active, but filtering the tank water and pre-rinsing the 'environment' that you put in there (such as the sand bottom) can get rid of a lot of the finer stuff that will float around.

3. You should always try several different angles with the flash. It's difficult to tell what angle might produce more highlight from the back of the tank and create an unnaturally bright background. And your subject might dictate several different light angles, as the shadows, or lack thereof, hide the details you're after.

4. As with any nature photography, be patient. Your subject is probably going to head straight against the sides or right to the bottom, keeping you from getting a good composition without having the tank seams themselves in the shot. Wait it out for a short while, let your subject relax or explore a little. But don't make it too long — the water in the tank isn't getting replenished with oxygen, and your subject may be using it up quickly. If you can't get the shot in a reasonable amount of time, switch your subject back into a circulated tank and replenish the water. You can always try again later.

And of course, this wouldn't be complete without a few examples of how it works. And if you look closely at some of the photos, you can see where some of the warnings above come from ;-)...



Variation Two, the mid-sized tank.

For this one, I had purchased from the local department store a small 'Betta' tank that was intended to house small boring fish, or serve as a temporary holding area for new ones to become acclimated — it cost five bucks and had a separating partition and a drain in the bottom; I tossed the partition, since I changed the interior shape slightly. A piece of glass from a 5x7" photo frame turned out to be a good fit for the front, kind of. My goal was to slope the front glass backwards slightly, since photographing through a glass-water interface at any angle introduces significant distortion, and I wanted to a) shoot slightly downwards to be able to use more of the bottom substrate as a background, and b) not have to get into ridiculously uncomfortable positions when shooting with the tank on a tabletop. But the pentagonal footprint of this particular tank meant that sloping the front glass by too much would produce an opening larger than the 7" wide glass, so the angle became limited. Something to consider when choosing either your tank or your glass.

I drew nice, straight, carefully-measured lines with a permanent marker, then cut the front off with a Dremel tool and cutoff wheel. This does not produce perfectly straight edges, so the whole tank was turned face down on a large sheet of sandpaper and sanded away until all three edges (left, right, and bottom) formed a flat plane for the glass. Then I simply glued the glass to the front with clear epoxy, after cleaning all edges with alcohol. It's hard to see here, but the curved surface of the tank was used for the back, which helps reduce reflections from your lighting even more.

The tank is still big enough for many subjects to move around too much, but it's also big enough to create a nice setting with a background if desired (like the second image here,) and to leave subjects in for a bit longer without worrying about them. It's still a small amount of water that can respond to temperature changes rapidly, though, so don't use for extended periods in the sun.

Variation Three, the tiny 'tank.'

Okay, these aren't tanks, they're glorified microscope slides, but they work very well for extreme macro work on those small aquatic subjects that refuse to hold still. I made two versions: the deep-well (left), which is the same thing as described by Paul Harcourt Davies at top, two microscope slides sandwiching a notched cutout of acrylic (used vertically); and a multi-well (below), which is several holes drilled in acrylic and glued to a single slide (used horizontally.) While I used epoxy for these two, which produced the yellowing, it might work better to use cyano-acrylate (Superglue, Crazy Glue, etc.) for a cleaner bond. Since the microscope slides are the only portions you'll be photographing through, the condition of the acrylic doesn't matter too much, but using something other than clear plastic may limit your lighting options by blocking light from the sides. Both of these work well for backlit and darkslide techniques, and require handling your subjects with an eye-dropper or pipette. You might have noted that I used a portion of the obscure (writeable) section of a slide for two of the wells, but this was an experiment that really didn't work, since the texture of the obscure section shows up too well in the photos — it's better to use some other diffusing material much further away from your subject where it will remain well out of focus.