Electronic lens adapters

Started Feb 16, 2013 | Discussions thread
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Tom Caldwell Forum Pro • Posts: 30,512
Electronic lens adapters

Adapting various lenses on to a NEX body.

A huge subject but I will confine observations to those adaptions via an electronic connection.  I am sure other adapters have been well covered before.

My purpose is to bring together the various "special pleadings" on the use of these electronic adapters in a more extreme way into a more general topic on the subject.

I have two electronic adapters.  A conventional straight-through adapter made by RJ in Shanghai.  A Metabones "Speed Booster".  Both adapters support focus peaking.

The RJ works in much the same way as any dumb adapter but does allow electronic communication between lens and camera if the lens is a Canon EF variety.  It seems to "do" autofocus on all Canon EF lenses fairly accurately and the focus can be tweaked manually if soft press on the shutter is retained.   I have tested limited lenses but it does work on the 135mm f2.0, 50mm f1.8, 85mm f1.2 and 24mm f1.4.  I have no reason to believe that it will not work on all EF lenses.  I have seen no sign of vignetting on any of the lenses I have tried including several FD lenses: 200mm f2.8, 100mm f2.0, 35mm f2.0, and 20mm f2.8.  Bear in mind that this is a no-glass adapter and works with the standard aperture settings and a sensor crop factor of x1.5.  The adapter FD-EF I used is Zykkor brand and this has a glass correcting element.

The Metabones Speed Booster has glass elements that work by the focal reducer system to reduce a FF lens image to aps-c size.  Along the way the device improves the image quality and gains a stop of aperture in the process.  It also substantially corrects the crop factor in the process. The net combined crop effect on a NEX is x1.07 which is close to the rated focal length of the lens in use.  Much effort has already been spent on the ins and outs of the focal reducer on lens performance.  Although it is not 100% perfect the general consensus is that it is good.  Metabones published a white paper on the subject (which no one authoritive seems to have taken exception to).

It will take some time to investigate the limitations of the Speed Booster on a lens by lens basis - my comments are only in a most general sense.

The adapter does work and produces good images.  It is primarily designed to make Canon EF lenses talk to the body of a Sony NEX camera.  It also genuinely increases the lens speed and seems on a casual look to be also improving the image quality.  It will take a scientific analysis by others more thorough than myself to find formal conclusions.  Sufficient for me is that it seems to do its job well.  It allows control of the aperture from the camera body, the readings are "correct", IS seems to work and the EXIF is recorded.

Where further investigation of the limits will go on for months if not years is on the exact limitations on a per-lens basis.  This not only includes EF lenses but all the myriad of lenses that can possibly be attached through second adapters.

The Speed Booster has two possible sets of operating firmware that can be loaded at lens-mount - The Green Power-Save Mode (includes AF) and Advanced Manual-Focus Mode - each has its own strengths and weaknesses which I will not discuss further here.


The Speed Booster only does AF with certain lenses made from about 2006.  Other EF lenses are only supported as MF.  But in AMF mode the image can be magnified during the focus process automatically.  Those lenses that do support AF seem to focus reliably but with a slight pause in the routine which seems to be the change of pace of contrast detect when focus is nearly complete.  Manual touching up of focus can be done as long as the shutter is held at half press.

Some lenses vignette from about 100mm very slightly through to distinctly noticeable at edges at about 200mm.  However this area needs exploration almost on a lens by lens basis.  The FD 200mm f2.8 has borderline vignette at wide but this seems gone by f5.6.

Generally it is hard to give a considered opinion across the range of lenses that could be fitted and I have to note that the performance of these adapters seems to improve as the user discovers their nuances.

Certainly they do the basic job they were designed to do - how far they can be extended remains something that owners will no doubt test and report upon.

I share Brian Caldwell's surname but we are not related and we have no business connection.

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Tom Caldwell

Leica X1 Panasonic Lumix DMC-F5
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