Extension tubes, E-M5, 60/2.8

Just took delivery of the FOTGA 10mm and 14 mm tubes off eBay, thought I'd post some findings.

The tubes are very light, a combination of aluminium mating surfaces and plastic barrels.  The lock pin is steel and its edge is bevelled, so if two tubes are joined it will not tear up the aluminium on the other tube unduly.  The three exterior flanges to mate to the camera body are part of the aluminium surface, and slide on reasonably well, the final fit being snug with negligible play.  Not zero play, just "negligible". You can feel that the aluminium sliding against the steel of the body or of the lens is not smooth like glass or polished metal, but slightly gritty, just like aluminium sliding against, erm, anything else...

The three interior flanges that mate with the lens are plastic.  They each have a steel spring set in to protect the plastic from wear and give reasonable feedback when turned onto the lens.  They give a snug fit when in position with zero play.

The tubes pass the mft lens signals through to the body just fine.  The takeaway words here are aluminium, plastic, reasonable.  I'm perfectly happy with these given their price, but they will not outlast rough treatment or frequent mounting and dismounting...

The Oly 60/2.8 macro has a useful 1:1 position on its dial, so you can set maximum magnification very easily.  I mounted the camera on a focus rail, and viewed a ruler to see what filled the frame.  Without the tubes, the ruler showed 17mm side to side, the sensor plane was around 185 mm away, and the front of the lens about 105 away.

With the 10 mm tube, the rule showed 13 mm side to side, sensor about 190 mm away, front of lens about 100 away.  With the 14 mm tube, these numbers were about 12 mm, 192 mm, and 97 mm.  With both tubes stacked together, 10 mm, 196 mm, and 93 mm.

No problem with leaving the system to auto focus rather than manual focus, as long as the target was within the focus "window", lock achieved no matter what tubes were set.