Perception Of Scale In Macro Photography; Why You Should Take Macro Pictures Of Large Things

f22 1/60s ISO 100, with SB-800 directly above and SB-600 to the left

Macro photography can have a massive visual impact by granting access to an alien world where things are perceived very differently than our natural vision.

f36 1/160 ISO 100 SB-800 flash

As things get smaller, problems like depth of field and diffraction get bigger, decreasing the image quality (all else held equal). However, if you can take a picture of an object that is larger than average, you can often increase the impact of the image because the viewpoint is very different from the viewer's normal experience. Likewise, taking a picture of a smaller than assumed object can reduce the impact of the image, because it looks closer to what the viewer perceives as normal.

When looking at photos, viewers subconsciously make assumptions about the scale of the subject. At normal magnification, the viewer's assumptions are usually quite accurate, but at high magnification people have less reference and tend to assume that the object they're looking at is the size they're used to. For example, the image on the right gives away very little information about the size of the whole leaf, so while a very knowledgable viewer might be able to guess the species and therefore guess the size, most viewers will naturally assume it is an average size leaf.

Example

To illustrate just how much the size of the subject compared to the perceived size of the subject matters, I photographed text on a page—something everyone is familiar with and has a sense of what's "normal" size—at different font sizes. All the images in this series are RAW images from the D7000 that have simply been cropped slightly, all taken through the same lens at the same focal distance under the same light.

f8 1/60s ISO 100 SB-800 and SB-600 flashes

First I'll start with an example of what not to do. I accidentally printed a huge map onto a small piece of paper a while ago while planning a camping trip, and kept it because it looks interesting even though it's illegible. However, even though this map looks interesting on an 8.5" by 11" sheet of paper, it makes a really low-impact macro image because no viewer will expect that the map was tiny, they will assume it was badly printed and this photo isn't very close to the paper at all.

f8 1/60s ISO 100 SB-800 and SB-600 flashes

Then, this is an example of a macro image of something "normal" sized, Didot font at 12 pt. Because the subject of this image is the size the viewer expects, it looks like something you could see through a magnifying glass, not something unusual and special.

The 12pt font looks far more interesting than the map, but still lacks any impact, it looks more like bad printing on rough paper than a high magnification photo.

f8 1/60s ISO 100 SB-800 and SB-600 flashes

At 24pt we begin to feel like we're zooming in and the photo gets a little more interesting, but still looks easy to take and lacks the ability to capture and hold a viewer's eye.

f8 1/60s ISO 100 SB-800 and SB-600 flashes

Stepping up to 48pt allows a single character to fill the entire frame. This gives the viewer the sense that they are looking at a good print on nice paper that would look smooth and perfect to the naked eye, but at such a high level of magnification that they can see otherwise invisible imperfections. Remember that there's no zooming in these photos, all four were taken with the same fixed focal length lens the exact same distance from the camera.

Application

In the real world, where people use cameras to capture pictures instead of pretending they're scanners, this technique still applies. Macro photos of oranges will seem more magnified than macro photos of clementines, pictures of large leaves with complex vein structures will look more interesting than smaller leaves that reveal less detail, and so on. Obviously there are many factors that effect the viewer's perception of scale, but it is possible to skew that size assumption in your favor so you can create sharper, deeper images of smaller looking things.