Sigma Zoom-Master 1:2.8-4 f=35-70mm. Repair and Adaptation for Nikon F

Once in the sale of Sigma Zoom-Master 1:2.8-4 f=35-70mm for Canon FD mount, it has broken diaphragm control mechanism, and the seller gave it for a knockdown price. I decided to buy it purely out of curiosity, with the possibility of alterations in the lens mount Nikon F. Flange distance of Canon FD lenses was 41.9 mm, while the Nikon F - 46,5 mm. The Nikon F lens unit's mount of such lenses needs to bring closest to the sensor at 4.6 mm. The distance is not small, and if there is no margin distance (rear element is close to what to look out of it), to adapt such lenses is unrealistic. Scan lens Sigma Zoom-Master 1:2.8-4 f = 35-70mm belonging to other systems, I found that this object was produced under different systems, including Nikon (as is usually the case with lenses of the third firm). Therefore, the stock is exactly the distance, and modifications will be reduced to a mechanical reduction. Only after such an analysis, I decided to buy this lens. So, we face two problems: fixing the aperture control mechanism and adapting the lens system on the Nikon F. Let's go...  

Remove the Canon FD mount.

Canon FD lens mount is a complex mechanical unit, and it takes a lot of space. If it is removed and replaced with a bayonet mount Nikon F, we will arrive at the correct flange distance of the lens. This is the key throughout the adaptation.

Bayonet Canon FD

This is bayonet Canon FD. Conversely put, we will not have it. But beyond that, we need to understand why the aperture ring is not working.

Remove the aperture control ring.

I do not know how the mechanism worked initially; to me, it was already inoperative. But precisely, the control was automatic and came with a camera through the lens mount. 

After the modification is automatically run, it will not be. Now I need to figure out how to get the ring operated in manual mode.

The ring is fastened with metal parts. I suppose that it adheres to the mechanism located deeper. She lacks the authority to control, and I need to replace it.  

I did this here piece, improvised. And fasten it in place of the current part.

Now the clutch ring to the control aperture ring works there. But now, the aperture value is not correlated with the marks on the barrel. We have already fix later.

Customized Desired Flange Distance

For the Nikon F lens bayonet, I chose the Chinese adapter M42-Nikon. Wearing it on the camera and attach the lens closely focused, not infinite, in the viewfinder, however, infinity field was not. This means that you need to approach the read element. After the aperture ring, we still have a plastic washer, which has a groove depth of about 2 mm. This is our stock of the distance that we can use.

The result was such a washer. Be careful; plastics compared to metal are soft, and I broke it in a small place.  But that did not stop install it back. Now drill the necessary holes in the washer and M42-Nikon adapter.

Carefully set all these parts in place, aperture ring, washer, and bayonet.

Turn the screws

The old screws from the lens mount Canon FD are now kept long, and I took the other shorter. Same way with this mount when it was dismantled.  Everything is now our lens is ready to shoot. Here are review and sample photos of Sigma Zoom-Master 1:2.8-4 f=35-70mm