Difference between macro lens and extension tubes

Factual Questions
1

I have a basic DSLR, a Sony Alpha 300, and basic amateur skills. I have a penchant for close-ups, particularly in our garden, which got me looking into macro lenses. Initially shocked at the price (a lens costing as much as the body), I began wondering if extension tubes were a suitable replacement.

Extension tubes run under $200. Macro lenses can run between six and eight hundred dollars. I (think I) understand the basic principles underlying extension tubes and assume the $500 makes a difference, but would like to get a better grasp before making a purchase.

Other than some settings needing to be done manually (something I’ve been working on for a while), are the differences something that only a professional photographer will be able to take advantage of, or are they two separate worlds? Is it possible to tell the difference between similar images taken with each?

2

Macro lenses are more convenient as the can focus from infinity to just a few cm. Extension tubes are a pain in the field as you need to remove them if taking non close-up pictures. Macro lenses often also have a smaller minimum aperture than a regular lens which can help with the shallow depth-of-field, though it is probably only going to be one stop.

As for quality, lens design is always a compromise. Most lenses are designed to work best focused on more distant objects, macro lenses compromise (slightly) the sharpness for distant objects for (slightly) better sharpness when focused real close. If you saw the same shot taken on both lenses side by side, assuming good tripod etc, you probably could spot the difference. If you just saw the one image you may not be able to say which lens was used.

I have an old manual focus Nikkor macro lens which I love. If you want to go super-close it still needs a short extension tube. Manual focus is fine for macro work because a) you are probably going to take your time and b) autofocus may not always chose the right bit of the scene to focus on. Check out the second hand market.

3

A flat focus plane vs a (possibly) curved one. Helpful for documents and slide reproduction, but often not an issue with 3D subjects.

4

Have you considered a magnifying add-on? I got a +4 macro magnifier for about $20.

5

Two other ideas, depending on how much you want to magnify whatever you are shooting.

If you have two lenses, you can put one of them on the camera, and the other one – backwards – on the front of the first lens. You then have to hold the second lens’ aperture open. There are fittings to accomplish these things. Your magnification ratio is now the focal length of the first lens over the focal length of the second lens.

Or, if you have extension tubes, you can use one single lens, but again pointed backwards, on the end of the tubes.

The thing to keep in mind is that camera lenses are optimized to pass rays between something at a distance in front of them and something very close behind them. Usually these are whatever you are photographing, and the film, respectively. But if you want to trade the close and distant roles between object and film, it works fine. Just keep whichever thing is closer on what is normally the camera side of the lens.

6

The response by ticker covers most of the key issues.

I bought a 105/2.8 Micro Nikkor for my camera a while back (older model, used, on Craigslist), and i love it. I’m actually considering buying a few extension tubes, though, to allow me to get even closer.

You didn’t say whether or not you own a tripod, but if you want to do decent close-up work, whether with extension tubes or a macro lens, it’s an essential piece of equipment. Firstly, if you want any depth of field at all, you need to stop the lens down, leaving you with slower shutter speeds. Also, the depth of field is so shallow that any slight movement as you point and shoot the camera will cause your subject to move out of focus. Having the camera mounted on a tripod helps alleviate these issues.

I’ve taken some pretty decent macro shots without a tripod (the images in this gallery were taken handheld), but you need good light, something to brace yourself against, and a LOT of shots so that you have a better chance of getting a good one.

It’s also good to spring for a tripod that is better than one of the cheapo things you can buy at Target or whatever. Shooting macro involves getting in close, and a tripod that only allows you to stick your camera on top isn’t going to cut it. Ideally, you want one that allows the legs to spread out individually, at different angles, to allow you more freedom in locating the camera. It’s also nice to have a removable center-post, which you can then reverse to get the camera right down near the ground. For real versatility, there are brands like Benbo, which allow you to move the camera to almost any height and any angle.

The magnifying add-ons mentioned by AaronX (usually called close-up lenses) can be a useful, and much cheaper way of getting up close, although if you buy cheaper ones, they can have a noticeable effect on image quality, especially at wide-open apertures. You need to stop the lens down to minimize this problem. This isn’t an issue with extension tubes, as they don’t add any glass to the equation.

Napier’s solution of reversing the lens will also work, and i think you used to be able to buy fittings that would actually allow you to mount your lenses reversed. Seems like a lot of effort, though. Also, with digital cameras it’s often best to minimize the number of times you take lenses on and off the camera, because dust can get in and get on the sensor.

One thing that is important to some photographers who shoot macro is something called bokeh. That is basically the shape of the out-of-focus or blurred areas produced by the lens. Because depth-of-field in macro photography is so shallow, there are often pretty large areas of out-of-focus background in the shots, and the way that these out-of-focus areas look can have an effect on the aesthetics of the image. Some lens are known for having nice smooth bokeh, while others produce bokeh that is not as pleasing to the eye. It’s a rather subjective thing, though, and not everyone likes the same type of bokeh effects.