Review: Canon EF100mm f/2.8 Macro USM
Are you looking for something versatile and close to optical perfection at a relatively affordable price? This macro lens might please you. It's been in the Canon catalogue for a while, and it's a funny shape. But the shape helps you a little with getting light onto your subject, especially with a macro flash.
Macro lenses are primarily for extreme close-up photography. The Canon EF100mm F/2.8 Macro USM is currently available for £500 or less new. Used examples are available at a little over half that. That's not a lot in professional camera lens terms, although this one is not marketed as an 'L'-series. In terms of optical performance, this is one of the best out there even by the standards of Canon's newer releases, if mine is a representative sample. It probably is; most other people say similar things. It's been joined by the 100mm f/2.8L IS which adds sophisticated stabilisation and costs about twice as much. The 'L'-series are Canon's nominally professional-grade lenses and do often seem to offer a noticeable improvement in colour and contrast over equivalents without the 'L' status. I haven't tried it; most people say it is similar optically, although a new design. Both these designs focus out to infinity for general use. Note this is not the case with some extreme macro lenses or with most regular lenses adapted to macro with a spacer ring.
How do you evaluate a camera lens? Well, technically, there are several parameters, mainly regarding the optics but also other factors; primarily autofocusing performance. Some lenses go for a 'character'; they add a certain look to the subject. This is frequently the case for top-end portraiture-oriented lenses. Although colour rendition and contrast are usually superb, they often lack a flat focal plane and may have significant field curvature. Even peripheral chromatic aberration, or colour-fringing, adds artistic effect for some users. This lens is more your 'technically correct' model. I don't think it's any the worse for it, and it will actually do decent portraiture.
Incidentally, a camera 'lens' contains many internal lens elements, each of which looks like a separate 'lens'. They are all in a row, with air spacings between most of them, and with the centres aligned, as you'd expect. This one has 12 internal 'lenses' with various curvature profiles. Eight of them are in contact pairs, 4 are separate. Different types of glass are used to minimise aberrations.
Sharpness and Resolution
Sharpness of course concerns how well resolved the image produced by a lens is, assuming best focus has been achieved. High resolution means high levels of recorded detail. Resolution is often tested by observing how close a pair of lines on a test target can be discerned in the recorded image, whilst maintaining a specified level of contrast, say 50%. Another closely-related result is the level of contrast at a specified line spacing. This test can be repeated at various lens aperture settings. The same tests can be performed over various regions of the lens image circle. It is very common for lenses to perform differently at different apertures. A really good design will perform well wide-open, that is, at maximum aperture. This 100mm f2.8 is one which does. There's no need to reduce aperture to improve sharpness and contrast, allowing optimally short exposures.
The growing capabilities of smartphones are arguably driving development of even better interchangeable lens camera equipment at relatively affordable prices. Specialised items like fast long telephoto lenses for wildlife are still extremely expensive. Those big objective lenses require very high quality glass blanks, often made from exotic materials such as fluorite, for the first few elements. And a lot of precision polishing, often by hand. Canon seem unwilling to compromise on these lenses and don't offer cheaper versions. Likewise the professional cinematic lens market. New car -priced lenses are commonplace there too.
Back to lens tests, and physics. Lenses unavoidably render a point light source into a tiny, approximately-circular spread of light (see the sensor size article). Away from the centre of the image, this is likely to be appreciably non-circular, as effects such as coma kick in. The degradation components therefore have to be measured in two directions: along the radius, and tangential to the radius. Computerised analysis of the generated image allows precise analysis of these radial and sagittal variations in resolution and contrast.
Lens design is complex, but a moderate focal length prime such as this is one of the easier categories to get right.
Sharpness is also often evaluated subjectively. It can, surprisingly, often be perceived pretty accurately in an downsampled, lower pixel count, image. I haven't done any scientific testing of this lens myself; most people who have are impressed. A good lens will 'snap' into focus when adjusted manually. This one certainly does that, aided by a fairly smooth and backlash-free focusing ring, although perhaps not quite up to the best 'L' lens standards. A good lens will simply be sharp and contrasty over the entire frame when focused correctly.
Subjectively, I find this lens is spectacularly sharp. That's all I really need to say. It stays sharp from wide open, at f2.8, until diffraction limiting kicks in. This is an unavoidable effect resulting from a small absolute aperture. This lens visibly looses resolution progressively beyond about f5.6, and that is actually a measure of how good it is! Unavoidable physics is governing the results, not the lens design.
This is a common defect, often found even in expensive lenses. Individual glass lens elements refract (bend) light rays of different wavelengths (corresponding to different colours) by different amounts. A lens which focuses blue light to a point may focus red light to a point in front of or behind the blue point. This will result in 'colour-fringing' in the image, usually most pronounced away from the image centre. Colour-fringing, or Chromatic Aberration, is most easily noticed on high-contrast edges. In some circumstances it might be considered to add character to an image, but macro is not one of them. It detracts from sharpness and resolution.
This lens displays very little chromatic aberation right across the frame at any aperture.
The macro capability of a lens is traditionally measured by how large an object looks when projected onto the camera sensor or film. A 0.21 macro capability, typical for a more general purpose lens, for example, means a 10mm object will occupy 2.1mm on the sensor. If that doesn't seem much, bear in mind that if the sensor is 35mm, the object is taking up about 1/15 of the frame width, and if you display it on a 17inch diagonal monitor, it will be about 22mm or nearly an inch long. It will appear substantially magnified.
The Canon 100mm f/2.8 macro has a full 1:1 macro capability. The 10mm (about 3/8 inch) long subject of the photograph would be over four inches long on the monitor.
For a given focal length, macro capability equates to how close the lens will focus. The closer the focus, the greater the macro capability. This lens will focus with an object within about 1 foot of the camera sensor, or within about 6 inches, or 15cm, of the front of the lens. Don't bash it into anything! A 60mm 1:1 macro will need to be nearer the subject. If it's alive, that can be a problem. 100mm is good for bugs and other little critters.
Canon products usually do colour well. They do vary somewhat, mostly because light transmission varies with wavelength. But this one conveys colour nicely.
Uses and Technique
100mm focal length is short telephoto, especially on an APS-C body.
The lens can also be used for portrait or general short telephoto, but for the latter the lack of zoom means you need to anticipate the requirements for the shot. You'll likely be pleased with the result.
Whether used as a short prime telephoto or for macro, the theoretical match of the lens with a 20 Megapixel-or-so APS-C camera is excellent; see the article on sensor size. All the macro shots on this site to date were done with this lens on an EOS7D.
Macro technique is worthy of another article. It can be harder than you think, as tiny subject movements result in large angular displacements. Similarly the depth of field is spectacularly small, and precision with subject distance is essential. Using the Canon AI Servo setting or similar tracking focus is likely to help with lively little critters and/or no tripod. It may help with flying insects although they will probably need to be hovering! Focus-stacking software for stationary/dead subjects can give some amazing results. It works by combining several pictures each with different points of focus. The software selects the well-focussed areas from each frame and combines them. Serif Affinity Photo is a low-cost general purpose editing suite which includes an effective focus-stacker, as does the ubiquitous Photoshop. Remote shutter release and perhaps mirror lockup can be useful to minimise vibration with macro, although I've not really found the latter to be necessary. Manual focussing is often the way to go, but with moving creatures it's very likely to be too slow. One method is to focus manually with a reasonably 'rapid fire' camera. For a moving subject, try to estimate where you think it might end up and focus there. The 7D is fairly decent for frame rate, with 8 (or 10 on the mk2) fps available and a good buffer depth. Spray away and look for best focus afterwards. If you or the subject move, hopefully some frames will be in good focus. You can deliberately rock back and forth very slightly while you hold the shutter. It's a crude method but can be quite effective. In practice a lot of wildlife photographers end up throwing away a lot of their frames for various reasons, and with digital it's not a problem. Autofocus systems still aren't fast and precise enough to deal with these macro situations reliably. If you have a static subject, it's much much easier. Use a tripod and manual focus for best results, combined with focus-stacking if necessary.
For those requiring the very best capability with insects and the like, macro-optimised flash or strobe units are available.
A great lens to expand your photographic opportunities into 1:1 macro. In addition it may well improve your results in some other situations.
Close-up of focusing window of another lens.
Taken at about f14 for depth of field. DoF and resolution is always a trade-off with macro work. Use focus-stacking if possible to get round this.
Rooftop scene, complete frame shown left. Most 1:1 or lower macro lenses will focus to infinity. Below is a 1:1 crop 1000 pixels wide, from upper right of centre of the approx. 5200-wide original.