Appendix B: Macro Magnification Ratios
will be first to admit that much of the science of photography alludes me. I’m fully aware of the numerous conversations that take place in photo chat rooms worldwide in which science and mechanics are discussed in great detail, conversations that I rarely participate in and even rarer still understand. I’m a visionary first, and once I approach the viewfinder, I’m focused on one thing: making a compelling image. And, for the most part, making that compelling image relies on the following basic fundamentals: a knowledge of exposure, a vision that matches up with my lenses, and a willingness to entertain various points of view and consider the various compositional choices. Do I really care what the actual size of my subject is in real life? Heck, I’ve known what size honeybees, dragonflies, butterflies, houseflies, spiders, ants, and even worms were long before I picked up a camera! The same is true for most flowers, fruits, vegetables, wheat stalks, and feathers. When I see a bee in a photograph taken by one of my students, my first reaction is not, “Gee, just how big was that honeybee?” I can tell how big it is just by looking at other elements in the picture. My first reaction, almost without fail, is, “Wow! Just how close were you?” or “It’s too bad you didn’t (or couldn’t) get closer.”
The only photographers who really need to be at all concerned with magnification ratios are those who work in the science-related fields. Sure, I can see why it’s important to know the magnification ratio when shooting a newly discovered frog in the Amazon rain forest or photographing blood splatter at a crime scene, but this book is not about science. Rather, it’s about the art of the close-up. This isn’t to say there can be no “art” when shooting frogs or blood splatters, but what I’m saying is that, for the most part, a close-up photographer’s primary concern is in making a compelling image. If, by chance, he or she does so at magnifications greater than 1X, then technically that’s a macro image. But at the end of the day, is that really all that important? As I’ve been telling my students for years, if it looks good, if it’s compelling, if it generates a gasp from the viewer, then as far as I’m concerned, it’s a worthy close-up photograph! Of course, it’s important to know how I or another photographer made the shot. Did I use a telephoto with extension tubes or a 200mm macro or a wide-angle lens and the Canon 500D close-up lens? But in more than thirty years of shooting, no one has yet to ask me what the magnification ratio of that ant or bee or butterfly was. Sure, with the images I only recently started to make with my Canon 65mm macro lens, I may be asked this question a few times in the coming years, but the first reaction, if I did my job right, should be, “Wow! How did you do that?” Maybe (and I still insist this is only a remote chance), just maybe, someone will say, “What is the magnification ratio of that?”
Now that my position about magnification ratios is clear, I will add this: Invest the time needed to understand how your lenses “see.” This includes your macro, if you own one. What are their minimum focusing distances? Four feet, two feet, three inches? What are the minimum focusing distances when combined with a single 25mm extension tube, with two 25mm extension tubes, with a close-up filter added, when the lens is attached to a bellows, when the lens is combined with a 2X teleconverter and 50mm of extension tubes, and so on? I can’t answer these questions for you since I don’t know what kind of camera you own or what kind of lenses and other equipment you have. But you should know this ahead of time, before you head out to the pond and find yourself standing at its edge staring down a large bullfrog. Quick, what lens and combination of extension tubes makes the most sense for shooting that bullfrog?
Again, I can’t be as specific to your situation as I want, but the following setups are meant to be a rough guide into the world of close-up photography. This information is based on my camera gear, and unless you have the same exact system, you will need to invest a bit of time in making your own chart. The good news is you won’t really need the data for long, assuming you go out and practice with your gear. Developing a vision for close-up photography is no different than learning how to drive a car. You get in the “driver’s seat,” look out that “windshield” of your camera (better known as a viewfinder), and “see” where the varied combinations of your lenses and related accessories can take you.
Keep in mind that this setup is on the Nikon D300, which has the digital crop factor of 1.5. Therefore, you could argue that my Nikkor lens is, in fact, a 105–300mm.
Why is the magnification of that flower bigger at 70mm than at 200mm? The reason has to do with the length of the extension tube. Consider the focal length law: Focal length over mm of extension = magnification. Therefore, at focal length of 70mm with 36mm of extension, the magnification (70mm/36mm) is roughly 1/2 life size. Put another way, if I put 70mm worth of extension on a 70mm lens, I will be able to record life-size images (70mm/70mm = 1).
But do you really care? Think of this in a more usable way: The more extension tubes you put on a lens, the greater degree of magnification of your subject, but you will also be working much, much closer to the subject, and in some cases, that could spell trouble—particularly when you’re using a shorter-focal-length lens. For example, when using 70mm worth of extension tubes at a 70mm focal length, you could end up throwing your own shadow over the subject because you are physically too close (or you are now so close to the spitting cobra that death is imminent or you are now so close that you get stung by the honeybee). Perhaps this is another good argument for one of those tripod-collared 180mm or 200mm macro lenses that allow you a 1:1 magnification from a much safer distance of 11 inches!
With this setup (for which the specific camera model does not matter), my minimum focusing distance is a “constant” 3 inches at any focal length, from 70mm to 200mm, and the longer my focal length, the greater the degree of magnification. For example, when shooting a flower at 200mm, my magnification of the subject is greater than when that same flower is at 70mm. Constant focus simply means that the physical distance between me and the flower remains the same 3 inches, and the flower will remain in focus at this distance, no matter which focal length I use when I finally take the shot. Some shooters feel this is a distinct advantage over shooting with extension tubes, where with each change in focal length one has to move either the camera and lens or oneself to maintain focus. Personally, neither the tubes nor the Canon 500D close-up filter are the perfect solution, but given a choice between the two, I would still opt for a set of extension tubes, because greater magnification ratios are achieved.
With this lens’s 158mm crop factor, and without any additional extension tubes, my minimum focusing distance is roughly 4 inches, and magnification is roughly 1.5 times life size.
With this lens’s 300mm crop factor, and without any additional extension tubes, my minimum focusing distance is 11 inches, and magnification is roughly 1.5 times life size.