Maybe you have been attracted by the thought of the far lighter bodies of micro 4/3 cameras or the amazing array of functions (superb video and precision focusing aids for example) they boast but been deterred by the 2x crop factor from changing formats – or even adding a body via an adapter and using manual focus on your lenses. Metabones have produced a intriguing optical device – the Speedbooster XL 0.64 that lowers the crop factor substantially (to 1.28) and also produces an increase in the speed of the lens you are using by 1 and 1/3 stops… interesting, then read on.
Before I began using a Sony NEX 7 about three years ago, I had realised that there were certain advantages to using mirrorless cameras for my experiments with wide-angle macro imaging, macro and microscopy: I am still finding new ones. Everything stemmed from the fact that, thanks to the absence of a mirror (a feature of all DSLR cameras), the distance between the lens flange on the front of the camera body and the sensor can be made much less, making lens corrections easier to deal with because of a diminished air space. Thus, when you use so-called legacy lenses you have to use adapters that not only convert to the lens mount but also build in some distance (effectively an extension tube with different mounts at either end) because lenses meant for full frame (and other) DSLR cameras have their rear element further away from the sensor to accommodate the presence of the mirror. This allows some interesting experimentation and great flexibility in the use of legacy lenses.
NB. You can find a lot of detail on this and of making your own adapters in a previous post: Closer & Wider – the nitty and the gritty , including a table of distances between lens rear mount and the camera flange for a wide range of Camera mounts.
Metabones have a sterling reputation for quality engineering and their mechanical adapters, although not cheap, they are beautifully machined in brass and then chrome plated. They fit perfectly, with none of the sloppiness that can be a feature of cheaper items not subject to strict quality control. I had seen the Metabones speed adapter advertised and, mistakenly, just registered it as a more expensive way of coupling camera to a legacy lens because of the presence of a group of lenses within the tube…how wrong I was. This device is now used between all my Nikon fit legacy lenses and the Panasonic GH4 body. It was only when researching video capabilities for the GH4 that I really came to appreciate what it could do.
What it does and how it works
A Metabones Speedbooster slightly shortens the focal length of the lens to which it is attached and creates a brighter image. It works like a tele-converter in reverse: the rays leaving it converge rather than diverge as in the TC. Whereas a tele-converter essentially increases the focal length of a lens by making the rays leaving the lens diverge the speed booster collects all the light coming through the front of a lens designed for a larger format and condenses it into a smaller image circle. Thus light energy (and putting it in basic fashion..information collected in the wavefronts of the light) is concentrated into a smaller area and the effect of this is a brighter image with increased detail if the sensor will resolve it.
The Metabones Speedbooster XL 0.64, has an integral threaded mounting foot for tripod mounting (it can be detached if needed) and also a rotating diaphragm ring to close down the aperture on ‘G’ lenses that have no mechanical aperture ring. Here again, the quality is obvious and action is smooth with none of the sloppiness you sometimes find in cheaper adapters on-line.
There are three things the device does when connecting a legacy lens to a micro 4/3 camera for which it is designed:
It is worth considering each of the properties claimed in turn:
Focal length reduction
When I have used the 15 mm f/4 Laowa macro lens on a Sony NEX 7 via a ‘normal’ adapter it behaves in effect as a 22.5 mm f/4 wide-angle because of the x1.5 crop factor).
However, when the same lens is used with the Speedbooster on a micro 4/3 camera there is first the reduction of focal length and then the 2x crop factor e.g. with Metabones Speed Booster XL 0.64x the focal length is reduced by a factor 0.64 and then one has to take into account the crop factor of x2.
The effective focal length (compared with full frame) is thus 2 x 0.64 = 1.28 greater. Which is much better than a lens with a normal adapter used on my Sony NEX 7 (crop factor x 1.5) or the Panasonic GH4 (crop factor x 2) in preserving wide angle impact, to say nothing of a brightness increase.
Thus with the 15mm f/4 Laowa wide angle macro mentioned the Speedbooster converts it as follows…
a. Effective focal length becomes 15 x 1.28 = 19.2mm
The lens, even on micro 4/3 has wider angle of view than it did with a standard adapter on a camera with a smaller crop factor (x1.5 on APS-c gives focal length of 22.5mm). Close focus is unaffected….
b. Aperture Increase
An aperture of f/4 increased by 11/3 stopes becomes f/2.5
c. Effective Sharpening
I always have my doubts about inserting more glass between the rear of one lens and a sensor. In theory, the Metabones Speedbooster could not only concentrate the light coming from the larger image circle of the legacy lens but also the detail in the wavefronts it transmits.
I have not done detailed tests but can safely say it does not reduce image quality in the slightest when scrutinised in Lightroom 6. In fact, when used with a Sigma 10-20mm wide angle zoom the chromatic aberration (CA) at the 10mm end used in the closest focus was visibly reduced. This is remarkable and the device really does work – the optical quality is exceptional.
To sum up….
The Metabones Speed Booster XL 0.64 used with a legacy lens and a micro 4/3 body provides the equivalent of a full frame lens of focal length 1.28 x greater but 1 1/3 stops brighter. The closest focusing distance is unimpaired…and so is sharpness.
Further examples from the lenses in my camera bag:
NB. Metabones make an incredible range of adapters of high quality: Canon users fare much better than others (especially Nikon) because some of the adapters permit full electronic connection between micro 4/3 or Sony E mount bodies and Canon lenses. This includes the Speedboosters – presumably Nikon will not permit the licensing of their lens mounts to any third parties even if they do not (or have no intention of) producing any adapters between their lenses and any other device – a long running problem for Nikon users unable to use innovative products with electronic coupling such as those from Novoflex and Metabones.
It is not cheap…but you pays yer money and takes yer choice, as they say. The Nikon G-mount to micro 4/3 version of the Speedbooster 0.64 XL is $479.00 rrp whilst that for Canon EF is $649.00 – more, because it also supports electronic coupling.
NB. UK prices will be more than a straight $ to £ conversion because of the way photographers in the UK are ripped off by many importers.
© Paul Harcourt Davies – neither images(s) nor text may be used in whole (or in part) without the express permission of the author.