AcaPixus - Samyang 7.5 mm modification for EF-M

Adaptation of Samyang 7.5 mm f/3.5 UMC fisheye to EF-M mount

Recently I changed my mirror less system from a micro 4/3 system to a Canon EOS M system, partially because it coexists better with my other Canon EOS gear.

One lens I would have missed from the m43 system was the minute Samyang 7.5 mm f/3.5 fisheye lens, so I decided to keep this lens and try to modify it to fit the EF-M mount, as no corresponding lens is available for the EOS M system (as of late 2013).

While the rear flange distance is 19.25 mm for the m43 system it is 18 mm for the EOS-M system, so the extra 1.25 mm should make it possible to make the m43 Samyang fit the EOS-M system. Actually, some day an adapter may even come into production.

My initial plan was to procure a rear EF-M mount from either Canon or Samyang. While Canon refused to sell the mount Samyang never replied to my request.

So, plan B was to recess a EF-M camera cap to go over the m43 mount of lens. However, at the end I came up with a much better solution ...

Unscrewing the m43 mount from the Samyang lens revealed that it is actually a 7.2 mm tall flange, which could be replaced with a 8.45 mm (7.2+1.25 mm) tall EF-M flange - if one could be made.

On Amazon I found a ca US$ 15 metal EF-M to OM adapter - it could have been any other front mount. Since none of my tool-gifted friends had a proper lathe (?) I had to manually modify the adapter using a metal saw, a metal file, 1.5 mm, 2mm and 3 mm drills and some sand paper

The outer diameter of the adapter is 59 mm as opposed to an outer diameter of of 55.1 mm of the Samyang m43 flange - hence a small 2 mm deep recessment would have to be made for the modified EF-M flange to fit under the aperture ring of the Samyang lens.

The steps for making the EF-M flange were as follows:

1) Saw of the rear EF-M end of the adapter at a flange height of ca 9 to 10 mm.

2) File down the height if the flange to approximately 8.6 mm using the file

3) Mark the 12 o'clock position of the flange when mounted on the camera and fit the Samyang m43 flange on the front of the modified flange making sure to align the 12 o'clock positions of both flanges.

4) Mark the positions where holes should be drilled and recess the inner surface before drilling - will make sense when you see that the drilling initially will go at the very edge of the metal making exact positioning impossible. Reattach the Samyang m43 flange and hold tightly together.

5) Drill 1.5 mm holes through the modified flange from the FORWARD side using the pre-existing holes in the Samyang m43 flange as guides.

6) Remove the Samyang flange and drill the holes to a diameter of 2 mm. Recess the holes on the other side (camera side) ca 2 mm deep using a 3 mm drill - to fit the heads of the mounting screws

7) Using the file recess the outer diameter down to < 55 mm to fit the flange under the aperture ring.

8) Carefully sand down (level) the height of the modified flange to 8.5 mm and attach it to the lens. Now try it on the camera and carefully test for infinity focus. Gradually reduce the height of the modified flange until infinity focus exactly is attained.

9) Optionally shave the sides (and very little of the top and bottom) of the sun shades to utilize the full 180° horizontal angle of view of the lens.

Finally, you will be able to enjoy a 180° horizontal fisheye lens - the Samyang 7.5 mm f/3.5 home-made EF-M - on your EOS M system. Be careful where you put your fingers during photography :-)

Higher resolution drawings can be found in this pdf - link.

Sample images can be seen on this page.

Kjeld Olesen - AcaPixus
Copenhagen - January 3rd 2014

Software for remapping fisheye
images into a rectangular projection

Recently I changed my mirror less system from a micro 4/3 system to a Canon EOS M system, partially because it coexists better with my other Canon EOS gear. One lens I would have missed from the m43 system was the minute Samyang 7.5 mm f/3.5 fisheye lens, so I decided to keep this lens and try to modify it to fit the EF-M mount, as no corresponding lens is available for the EOS M system (as of late 2013). While the rear flange distance is 19.25 mm for the m43 system it is 18 mm for the EOS-M system, so the extra 1.25 mm should make it possible to make the m43 Samyang fit the EOS-M system. Actually, some day an adapter may even come into production.
My initial plan was to procure a rear EF-M mount from either Canon or Samyang. While Canon refused to sell the mount Samyang never replied to my request. So, plan B was to recess a EF-M camera cap to go over the m43 mount of lens. However, at the end I came up with a much better solution ... Unscrewing the m43 mount from the Samyang lens revealed that it is actually a 7.2 mm tall flange, which could be replaced with a 8.45 mm (7.2+1.25 mm) tall EF-M flange - if one could be made.
On Amazon I found a ca US$ 15 metal EF-M to OM adapter - it could have been any other front mount. Since none of my tool-gifted friends had a proper lathe (?) I had to manually modify the adapter using a metal saw, a metal file, 1.5 mm, 2mm and 3 mm drills and some sand paper The outer diameter of the adapter is 59 mm as opposed to an outer diameter of of 55.1 mm of the Samyang m43 flange - hence a small 2 mm deep recessment would have to be made for the modified EF-M flange to fit under the aperture ring of the Samyang lens.
The steps for making the EF-M flange were as follows: 1) Saw of the rear EF-M end of the adapter at a flange height of ca 9 to 10 mm. 2) File down the height if the flange to approximately 8.6 mm using the file 3) Mark the 12 o'clock position of the flange when mounted on the camera and fit the Samyang m43 flange on the front of the modified flange making sure to align the 12 o'clock positions of both flanges. 4) Mark the positions where holes should be drilled and recess the inner surface before drilling - will make sense when you see that the drilling initially will go at the very edge of the metal making exact positioning impossible. Reattach the Samyang m43 flange and hold tightly together. 5) Drill 1.5 mm holes through the modified flange from the FORWARD side using the pre-existing holes in the Samyang m43 flange as guides. 6) Remove the Samyang flange and drill the holes to a diameter of 2 mm. Recess the holes on the other side (camera side) ca 2 mm deep using a 3 mm drill - to fit the heads of the mounting screws 7) Using the file recess the outer diameter down to < 55 mm to fit the flange under the aperture ring. 8) Carefully sand down (level) the height of the modified flange to 8.5 mm and attach it to the lens. Now try it on the camera and carefully test for infinity focus. Gradually reduce the height of the modified flange until infinity focus exactly is attained. 9) Optionally shave the sides (and very little of the top and bottom) of the sun shades to utilize the full 180° horizontal angle of view of the lens.
Finally, you will be able to enjoy a 180° horizontal fisheye lens - the Samyang 7.5 mm f/3.5 home-made EF-M - on your EOS M system. Be careful where you put your fingers during photography :-) Higher resolution drawings can be found in this pdf - link. Sample images can be seen on this page.
Kjeld Olesen - AcaPixus Copenhagen - January 3rd 2014