The Sony SAM 30mm lens uses counter-intuitive thinking, where the front elements do the traveling while those at the rear sit and watch.
Compose through a viewfinder, at eye level, and you'll prefer a so-called macro tele zoom to a conventional macro lens for close-ups. You can work from a comfortable distance, no crawling around, no need to get right in to the subject.
But watch consumer camera owners - or camera phone users - and they compose close-ups on the rear screen, holding the camera close to the subject, at arm's length. Many such cameras focus down to one or two centimetres. They capture unfamiliar close perspectives, the Honey I've Shrunk the Kids effect, which have their own appeal.
In March 2009 Sony patented an unusual retrofocus macro lens design where the focusing is done by a front group that includes the aperture assembly and part of what would once have been the rear group. What's left of the rear group stays fixed. This design is of no use for a wide-angle retrofocus lens, as the angle of view is limited.
But it allows a 30mm macro lens that can mount on a camera that needs 35mm of clear back focus for the mirror to operate, yet still focus on infinity. Focusing shortens the focal length of the lens, so that by 1:1 focus it's about 25mm with an image plane to subject distance of 125mm, and a 25mm internodal space.
The front nodal point is placed 30mm behind the front element, which is only 20mm from the subject. The aperture, in the meantime, has not been reduced to an effective f/5.6 as you would expect for an f/2.8 lens extended for 1:1 repro. The shortening in focal length, without compensating the aperture diameter, results in a brighter f/4.5 focusing image (the camera display, as with regular macro lenses, still reports this as f/2.8).
Why would any maker want a 30mm macro that only covers APS-C and requires a working distance where the lens barrel will touch many subjects, or cast a shadow in sunshine and with flash? Well, the lens has hardly been off one of my camera bodies since it arrived. It is a classic standard lens focal length - 30mm on APS-C matches 45mm on full frame.
The optical quality is much higher than a £130 plastic-barrelled Chinese-made lens promises; the primitive focusing motor is noisy, but it works well enough. Wide open there is a minimal hint of aberration towards the edges at infinity, but stopping down to f/4 removes it. Close up, the quality is maintained all the way to 1:1. There is no visible distortion and the field is flat.
Sony's Alpha predecessor Minolta made a budget priced macro, a 50mm f/3.5 AF that only went to half life size on film. This lens is 1:1 on the 16×24mm format, framing a shot that would have needed 1.5:1 magnification back then. It crops in to one-third of the linear dimensions and one-ninth of the visual area. If fitted to a full frame Sony, auto crop to APS-C is activated.
In short, it does what the consumer composing ultra-close on a pocket camera expects. And, with the articulated screen of the Alpha 550 folded out like a waist-level finder, I found the lens and camera at 1:1 could be placed so low they could look up into the flowers of snowdrops without even resting the camera on the ground. I did try composing with the pentaprism viewfinder, but it's uncomfortable to get so close. Using the live view screen transforms the experience.
The bonus is that it's one of the best standard lenses I have used for years. It has high contrast, can be used into the light without a hood, it weighs almost nothing and is only 45mm long, taking 49mm filters. The focal length reduction also means I can use a portable copy stand with the APS-C camera for A4 to A3 originals - my 50mm macro needed a longer column. And I've converted a lens hood into a slide copier.
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