Depth of Field and Macro Photography
In the discussion of Depth-of-field it’s important to emphasize that the distance from your subject affects your depth-of-field. The closer you are to your subject (lens-to-subject) the less depth-of-field you will have. The further away from your subject you can stay the more depth-of-field you can maintain. This coupled with our discussion of using f/stops to control depth-of-field becomes extremely valuable knowledge when we approach the subject of Macro Photography.
The most basic definition of Macro Photography is to create an image on the sensor (or film) the same size as the subject. So literally if your subject is 1” long in real life you will be creating a 1” long image on the sensor. This gives us the ability to record and display incredible details about our subject, but only if we maintain enough depth-of-field to preserve those details in our image. The trick gets to be the lens(es) and methods we might use for creating that Macro (1:1) image in the first place. There are many options for doing this including:
- Close-up filters: these filters screw onto the front of the lens adding another element that allows the lens to focus closer to the subject than it would normally be capable of focusing.
- The close-up filters will usually cost about $50 for a set of three and will work quite well, but like any other filter you put on your lens you might lose some sharpness unless you invest in a high-quality set.
- Macro Extension Tubes: these tubes move the lens further away from the camera making it possible to focus closer to the subject than normal.
- The macro extension tubes will generally cost at $85 and up for a set of three. You can get some for less money but they will not include contacts to maintain the auto-focus function.
- Bellows: this device has mounts for the camera and the lens with a flexible bellows between the two, allowing you to adjust how far the lens is from the camera and thereby modifying the focusing distance of the lens.
- The bellows will generally cost anywhere from $150 to $600 depending on your camera and the quality and accessories you desire and mostly usually will not maintain auto-focus.
- Adapter / Macro Coupling Ring: these rings allow you to mount two lenses front-element to front-element, giving you closer focusing distances.
- The coupling ring will cost about $5-$10 and is available in many various sizes and size combinations, so you’ll need one for each set of lenses you care to pair together.
- Macro Lenses: specifically designed to provide focusing at a specific distance to allow for 1:1 image captures. Not all macro lenses are a 1:1 ratio and it’s important for you to note what magnification factor a lens offers before purchasing the lens for a specific purpose. Some lenses might be 1:2 (meaning the subject will be ½ size) or 1:4 (meaning the subject will be ¼ size), and may be perfectly suitable for the shooting you desire.
- Macro lenses will generally be the most expensive option, but will also usually offer the highest quality images. Although you might find many lenses that are listed as “macro” you might find that the majority of them are not 1:1 image reproduction lenses.
Each of the methods listed above has some advantages for various applications so it takes a little more research to understand what method may be the best for your situation and budget. Keep in mind that depth-of-field is reduced every time you get closer to your subject, so the option that allows you to maintain the most distance from your subject may be the best. If you want to photograph small animals and insects you will need to stay far enough away to not scare off your subject. On the other hand if you are shooting flowers or hardware it may not matter how close you get to your subject. That being said, you must remember to use a small aperture (higher f/stop numbers) to maintain enough depth-of-field to preserve the details desired. In the example images included here you’ll see that I used a bolt and a Christmas light as my subjects.
In the photo of the bolt you can all the details of the years of rust on the bolt, but can barely see the bolts laying in the background. That’s because the depth-of-field is rather shallow since I was very close to this bolt when I shot the photo. This photo was actually taken at about 18” from the bolt with a 200mm lens using a Macro Extension Tube, since the normal focusing distance for that lens is over 48”.
The Christmas light in the foreground is quite clear while the series of lights behind it are quite blurred. If you look carefully you can see how shallow the depth-of-field is by the amount of focus shown on the wood beam the lights are mounted on.
In each of these shots it was critical to use a smaller aperture to preserve the details in my main subjects. One more note about getting closer to your subject: you may be getting close enough to block the light that would otherwise be available to illuminate that subject. That could cause you to need a reflector or ring flash to add the necessary lighting on your subject.
© 2010 Jeff Cowell, jrcowell.com