Bought this lens cheap at an estate sale, but now I'm trying to figure out the adapter I need to get it to fit my Rebel XS body. I've looked at dozens of pictures on the internet, but cannot narrow down what this mount is exactly. pic of connecting end of lens

pic of front end of lens

per request here are a few additional shots to show the flanges. 1st additional pic with the aperture bar at the top (like the previous pix) and the second additional pic at a slight angle to show flange definition, and the third additional pic with the aperture bar at the bottom to show flanges that weren't quite viewable in 1st pic. enter image description here enter image description here enter image description here

Any help would be appreciated.

  • \$\begingroup\$ A straight-on picture of the back of the lens could be helpful... this is not showing the flanges very well. \$\endgroup\$ Feb 3, 2020 at 0:40
  • \$\begingroup\$ Thanks, I added 3 pics. Hope this show them clearly enough. \$\endgroup\$
    – joncow
    Feb 3, 2020 at 1:21
  • 1
    \$\begingroup\$ Mystery? Beston is etched right on the front. \$\endgroup\$
    – Alaska Man
    Feb 3, 2020 at 1:31
  • 1
    \$\begingroup\$ Every time I googled adapter Beston to Canon--nothing came up, I assumed it was a minor brand \$\endgroup\$
    – joncow
    Feb 3, 2020 at 1:38
  • 3
    \$\begingroup\$ Why do call it a breech mount? Does the lens stay in the same orientation with respect to the camera body when you mount it (like the Canon FD breech mount lenses), or do you just rotate the lens onto the camera body (like all modern bayonet mount SLR lenses do)? \$\endgroup\$
    – scottbb
    Feb 3, 2020 at 3:25

1 Answer 1


It appears to be an early Pentax "K" mount. The recessed Aperture Simulator slot opposite the Aperture control lever is the clue. This slot is clearly visible in your first photo.

enter image description here

There are lots of inexpensive adapters available to mount Pentax "K" mount lenses on your Canon EOS Rebel XS. This one costs about $15.

Vello Pentax K Lens to Canon EF-S-Mount Camera Lens Adapter

enter image description here

  • \$\begingroup\$ Worth to mention that the aperture lever should be unmounted before using K/EF(-S) adapter. Otherwise it will cause damage of the mirror in camera. \$\endgroup\$ Feb 3, 2020 at 7:37
  • \$\begingroup\$ Thank you, Mike, for the answer. \$\endgroup\$
    – joncow
    Feb 4, 2020 at 0:39
  • \$\begingroup\$ Thank you, Artur. How would I "unmount" the aperture lever? \$\endgroup\$
    – joncow
    Feb 4, 2020 at 0:41
  • \$\begingroup\$ Some lenses can interfere with the larger mirror of a full frame camera like a 5D or 6D. Since you are using an APS-C crop camera, the mirror is much smaller and won’t be a problem. \$\endgroup\$ Feb 4, 2020 at 4:26
  • \$\begingroup\$ @joncow you'll have to partially disassemble the lens. Unfortunately, the exact steps are rather manufacturer specific. Alternatively ... you can just saw the lever up, but that makes the lens permanently unusable as an actual Pentax lens - and be careful where the metal dust will go. \$\endgroup\$ Feb 6, 2020 at 10:30

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