Monday, October 22, 2012

Macro lenses for photographing "the tiny world"

Recently I've been asked by several camera-club members and several of my students independently for advice on selecting macro lenses for use with Canon SLRs. So to avoid having to repeat myself again (intentionally tautological) I figured I'd lay out some of the answers here. This is another of the technically-oriented posts which I will continue to post from time to time.

Definition of macro photography

Technically "macro" photography starts at 1:1 magnification. That's where a 1 cm object is projected by the lens to be 1 cm on the sensor/film. Note that this doesn't say anything about how large the object will appear in the final image (life-size as 1 cm on a print, or 50 cm on a poster?) but it does provide a reference point for comparing the magnification of different lenses.
However life isn't always so clear-cut. Many zoom lenses are marketed with "macro" in their model name, even though they can't get to 1:1. Sometimes it's only 3:1. It might be safer to refer to those lenses as "close-up" rather than "macro". I'm only going to refer to "real" macro lenses here. Of course, you don't have to only use the lenses at 1:1 all the time.

Teensy tiny fungii

Extension tubes

Many "regular" lenses can be turned to macro photography simply by the addition of extension tubes, which simply move the lens further away from the camera. My first macro rig was a 50mm prime lens combined with extension tubes. The further away the lens, the closer the focus. You won't be able to focus to infinity any more, but you can get very close. However because the light spreads out as extension is increased, the image will get darker. While this can have confusing effects on the metering sensor in SLRs, by using Live View and/or checking the histogram of images captured by the actual imaging sensor this isn't a major problem.

Note that the effect of tubes is more pronounced the shorter the focal length, and also that zoom lenses can behave "non-intuitively" with tubes due to the way their optics are designed.

They can provide a useful close-focus option for many lenses but a dedicated macro lens is much more convenient to work with and will generally produce higher-quality results.
Jumping Spider

Focal length

You'll see various focal lengths available. For example 50mm, 90mm, 100mm, 105mm, 150mm, 180mm. Don't make the mistake of thinking that the shorter lenses will give you more depth-of-field. At 1:1 magnification all these lenses will give you the same depth of field. There are two major differences in the behaviour:
  1. The longer the focal length the further away from your subject you will be at 1:1 (this explains why there's essentially no change in depth of field). By being further away you will be less imposing on your subject (unless you want your subject to react to a relatively-huge lens up close to them: "What is this thing about to eat me?"). You also have more freedom to move your light sources around without the lens casting a shadow across the subject.
  2. The longer the focal length the narrow the view of the background. The out-of-focus background of a macro image can have a big effect on the final result: with a bright yellow flower in the background you only have to move the lens slightly to one side to have it disappear with a long lens. With a shorter lens it can be harder to find a plain background.

Auto Focus

Some people get hung up on one lens having "faster AF" than others, but for a macro lens this isn't important. We usually manually set the lens to minimum focus distance (1:1 magnification) and then move the lens forwards/backwards until the subject comes into focus. Note that this is made easier with a dedicated macro focussing rail, or just an Arca-Swiss-style lens plate or body rail which allows the camera/lens to move forward/backward by tiny amounts when you loosen the clamp on your ballhead.

Where AF speed does come in handy is where you're using the lens for non-macro subjects. Most macro lenses can go all the way from 1:1 to infinity distances, and can double as "regular" lenses. Here AF is much more useful. One important trick is to use the lens's focus-limiter switch, stopping the lens from AFing to close distances and more than halving the time the lens needs to traverse between infinity and "minimum" focus for those times that the camera's AF doesn't lock on. These lenses probably won't manage to lock onto a runner or animal speeding towards you, but for most subjects I've found their AF speed to be more than adequate.

One other AF feature I find important for my own use is full-time manual focus ("FTM") override. When a lens allows this you can leave the camera and lens with AF enabled, and when using One-Shot AF you can manually tweak the focus before taking the shot without switching to manual focus. Actually I don't use my cameras that way: my cameras are usually set in AI Servo and with focus control detached from the shutter button. The camera will attempt to AF when I press the AF-ON button with my thumb, and stop focussing when I lift my thumb. If the lens has FTM I can focus manually at any time: with the camera on a tripod all I have to do to not AF is to not press the AF-ON button, and I can take repeated shots without the camera attempting to AF (and without having to remember to switch AF on/off on the side of the lens). All of my current lenses have FTM override, which makes life simpler by giving me one less detail to think about.

Elephant Seal fur

Recommendations

Asked for specific recommendations I can only point photographers at a range of lenses I could be happy with. I have my favourite, but many factors come into play when choosing a lens. For example:
  • Size/weight. A small lens can sit in your camera bag not taking up much space until you decide you want to use it.
  • Focal length (see above).
  • Image Stabilisation. Lenses with IS can provide more flexibility when shooting handheld, although this impact is reduced when using flash.
  • Tripod mount. If the lens has a "tripod foot" it allows you to rotate between horizontal/vertical without having to reset your tripod configuration and re-position the camera. Very useful!
  • Cost.

Actual lenses I would consider

For each lens I've provided links to B&H Photo so you can see comparative current pricing. Of course the prices may be different in your local stores, but these prices are a good starting point. Just to be clear, these are affiliate links: if you do purchase from B&H after following these links I'll get a tiny commission. It does help to offset the blog/web costs, so thanks!

Canon's 100mm/2.8 IS
The optical quality is great, and the "hybrid" IS is designed to deal with correcting shifts as well as tilts that become important for stabilisation at short distances. Offers FTM override. I would invest in Canon's tripod Ring D (unfortunately not included by default). B&H link

Canon's older (non-IS) 100mm/2.8 macro lenses
Especially at second-hand prices these are still decent lenses. The USM model has FTM override. B&H link


Tamron 90mm/2.8
The shortest macro lens I would consider using, I see its main advantage as being small, light, and cheap but without compromising on image quality. Switching to manual focus requires clicking the focus ring forwards/backwards (no FTM) but for an occasional macro lens I think that's an appropriate compromise for the price. B&H link


Sigma 150mm/2.8 OS
This is my favourite of these lenses. Not too big for me, great optical quality, decent price, and with FTM override.
Many people are understandably cautious about the sample-to-sample variability of Sigma lenses due to quality control issues, but I have found their macro lenses to be excellent and not subject to this problem. B&H link


Sigma 180mm/2.8
I've used an earlier version of this lens (before the 150mm was available). Good quality, but for me today it's out-shone by the Sigma 150mm. Has FTM override. B&H link


These are the ones I would recommend. Purchase any of these and you'll have a great macro lens. From there you just need technique, practice, and more practice!

I have not mentioned non-EOS-compatible lenses (I do use mainly Canon gear myself) however the non-Canon lenses above are also available with many other mounts. I have not touched on lenses which would only fit crop-factor cameras (e.g. Canon's "EF-S" lenses, or Sigma's "DC" lenses) as most of my students are either using full-frame cameras or aiming to add one to their kit eventually. There are other macro lenses also, but the prices can get extreme or there's some technical reason they haven't made it onto my list. Obviously I'm not going to list all the exceptions here!

Damselfly

Smaller (bigger) than 1:1

If you want to get into extreme macro (greater than 1:1 magnification) then the Canon MP-E 65mm 1x-5x lens is an obvious choice although it can't focus at anything smaller than 1:1 (i.e. it can't be used as a "regular" lens).
If you want to experiment without buying that macro-only lens you can combine any of the above macro lenses with extension tubes (which move the lens away from the camera and reduce the minimum and maximum focus distances). Even though the above lenses are not officially compatible with teleconverters, by putting a 12mm tube between the lens and teleconverter they do fit. If you have a 1.4x converter on hand then it's a cheap experiment and can produce great results.


By the way, there will probably be few opportunities for macro photography on my 2013 Botswana photo adventure (places still available: hint, hint) but the Tamron 90mm wouldn't take up much space in your kit...

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