How to convert Vivitar S1 70-210mm 2.8-4 Konica Mount to Pentax K mount

This article was approved by Pentaxforum's Admin (Adam).


Following the requests of Hin and OregonJim, I create a new topic on the lens conversion to PK mount. Hope it will be useful for the others who interest in the lenses conversion. If it is not convenient in this section, mod or admin, please, move it to the convenient place.

1) Introduction

Following Marks Robert, the Vivitar 70-210 S1, version 3 is the best among three versions. The mine is KONICA mount, I decided to convert it to Pentax K mount.

The flange focal distance of Konica system is about 40,5mm, whereas the Pentax one is 45.5mm. Therefore, we must shave the lens about 5mm in order to focus to the infinity.

Here is the image of the lens before the conversion (sorry, because it from the seller)

Required things:
- A M42-PK adapter ~ 6$ (I bought from a seller on ebay)
- Some small screwdrivers
- A ruler
- A saw (A lathe will be better)
- A file
- A drilling machine with 2 drills: 2mm and 2.5mm

This conversion simply consists of two steps. Firstly, cut off 5mm and secondly replace the Konica mount by the M42-PK adapter.

2) Disassembling the lens and cutting away 5mm

Unscrew 4 cross-screws from the bottom of the lens to take out the Konica mount.

The M42-PK adapter is thinner than the Konica mount about 1mm. Therefore we must shave the other parts of the lens about 4mm.

This ring is associated with the aperture system of the lens by the trigger. I decided to shave the aluminum ring. Firstly, I sawed this ring, cut away 4mm. This ring screws on other part of the lens which has the thread as the image shown.

Secondly, I also sawed this part about 4mm as the below image. After that, I filed them, it would be better if I had a lathe instead of sawing.

The trigger were also cut away about 4mm in order to function correctly.

3) Drilling the mount and reassembling.

The Konica mount is totally inside the aperture ring. Therefore, we must shave the aperture ring in order to place the M42-PK adapter above. If not, 1mm economized from the difference between two mounts is useless.

Throw away the ring with red dot (the thickness of this ring is about 5mm)

Drill 4 holes respectively on the M42-PK mount. Re-screw 4 cross-screws with 4 new holes.

Voilà, the conversion is done.

Here are the results of the quick test.

IMHO, its colors are beautiful.

I have not yet converted to Pentax KA. I think it is more difficult and it needs more precise tool to convert.

PS: You can find the originated post from here