The thing about aquarium photography is that it tends to be rather opportunistic—you are limited as to what angle you can take a picture from and typically need to wait until the critter you want to photograph moves into the right position. The other day I was cleaning my aquarium and noticed a couple of mating snails (family Lymnaeidae) crawling on a plant. So I grabbed my camera and took a couple of quick photos. Even slow moving animals like snails will quickly move out of position; so by the time I had checked the photos on the camera, the snails had crawled away and I went back to cleaning.
Once I was done with the aquarium I uploaded the photos to the computer to take a better look. The photo was OK, but not great (see below). In my first post on this blog (Close-up photography of a large yellow underwing) I referred to some “rules” I follow to get great close-up or macro photos. This picture meets all those rules: I got good and close to the subject; the critters are doing something interesting and are relaxed and comfortable [I assume that snails are relaxed and comfortable while mating! In any case, their behaviour was natural, and that’s what counts]. Lastly, I was at eye level (for the critters) and their eyes are in focus [you can partially see the eye of the rearmost snail just under the edge of its shell].
The problem with this photo is that the shells of these snails are wider than their body. This isn’t exactly a surprise given that they retract into the shell for protection. But that means that the front surface of the shells is closer to the viewer than their eyes [the snail’s eyes, not the viewer’s eyes]. When I took the photo, I automatically focused on the snails eyes—that’s usually the easiest way to make sure they are in focus. The problem is the shallow depth of field that results from the high magnification of macro photography. Depth of field in a photograph refers to the area in front of and behind the actual plane of focus that still looks acceptably sharp. In this case the depth of field wasn’t deep enough to include the eyes and the surface of the shells. In macro photography it is fine to have the background out of focus—in fact it is usually preferable. It also looks natural…if you take a small object and look at it up close, objects in the background will be out of focus. But if the front of your photographic subject is not in focus, you can’t help but notice. You can get away with it if the out of focus part is small and not significant to the main focus of the picture (like a leg or antenna). But in the case of my mating snails, the bulk of the animals are out of focus. Hence it isn’t a bad photo; it just isn’t a great one.
Contrast it with the photo below of another pond snail I photographed on the same day (and on the same plant). In this photo, the bulk of the shell is behind the eyes. And when I took it, I purposely focused not on the eyes, but on the edge of the shell slightly in front of the eyes. As a result, all the important bits are in focus. It isn’t perfect, but I really like this photo.
The technical stuff:
Camera: Olympus E-620 digital SLR
Lens: Zuiko 35mm macro
Settings: manual exposure (F14 @ 1/125 sec)
Lighting: On-camera flash (full power)