A 100mm macro lens is a classic choice for closeup work. It’s the first macro lens many photographers use. It’s great handheld or on a tripod, and there are versions from different manufacturers with excellent sharpness and bokeh. But for a number of subjects, such as medium-sized flowers and insects, it’s hard to get a good background with a 100mm lens.
Compare the following examples. The image on the left was taken with a 100mm macro lens, and the image on the right with a 300mm lens, both at f/5.6:
The background is a tree a few feet away, and the subject is teasel. With the 100mm lens, the outline of the tree is soft, but obvious and distracting. The 300mm lens renders the tree as a soft brown blur with a bit of the cleft visible. The subject was at different distances from the camera, less than a foot from the camera with the 100mm lens and three feet or so with the 300mm lens.
The different appearance of the background is due to the field of view (or angle of view) of the lenses. The field of view of a lens determines how much of the scene is visible behind the subject. At 100mm on a camera with a full-frame sensor, the lens sees 24 degrees of background behind the subject. A 50mm lens sees almost twice as much background, 46 degrees behind the subject. A 300mm lens has an 8 degree field of view on a full frame camera, a fraction of the field of view of the 100mm lens. The longer the focal length of a lens, the narrower the field of view, providing a greater freedom from background distractions.
With a longer lens, you can pick a pleasing pattern or a solid color from the scene as a background for your image. Slight changes in camera position can bring a different background into view. Telephoto lenses make the subject and the background appear to be closer together. In landscape photography, the effect is called compression. In closeup photography, the effect is more a matter of background selection.
The following images all use longer lenses to simplify challenging backgrounds. This image of a Costa Rican Red-eyed Tree Frog was taken with a 300mm lens and a 1.4x teleconverter (420mm) at f/5.6:
The focal length was critical in reducing the effect of foliage in the background, which was in uneven light. The same lens combination is at play in this image of an eyelash viper, also from Costa Rica:
This following image of a North American orchid, a Grass Pink, was taken with a 180mm macro lens at f/5.6 in a crowded bog habitat. The key to reducing the background distractions was getting low and shooting in soft, diffuse light:
If you don’t have a 180mm or 200mm macro lens, you can attach a teleconverter to a 100mm lens to get a narrower field of view. With some camera and lens combinations, you may need to put a 12mm extension tube between the teleconverter and the camera.
Even with a narrow field of view, the scene and the light are limiting factors in getting a good background. Background elements that are close to the subject can be distracting regardless of the field of view of your lens. Bright spots and deep shadows in the background can also create distractions. With a narrow field of view, you can work around the distractions. You can also use a diffuser more effectively because it has to cover smaller area of the background.
A longer focal length isn’t always the best choice, despite these advantages. If you are shooting down on the subject, the greater working distance may put the camera in an impractically high position. When you want to show the full context of a scene, only a shorter focal length will capture the subject in a wider setting. But when you want to simplify a complex background, a longer lens is the best choice.
Enjoyed this article. I like close-up photography and have used my 300mm lens often and got great backgrounds that I could not get with my 100mm. Your article explained it clearly.
Thanks
Len
Great article! Thank you Tom!