The Leica Summicron 35mm f/2 rightfully enjoys the reputation of a fantastic option in documentary photography. The 4th revision of the lens, produced from 1978 and into late 1990s until the current aspherical successor, has a special place in the pantheon. Many people swear by how it renders out-of-focus areas (bokeh), and its general performance. How much that holds true is a subject for separate review. Here, however, we will focus on the issues of its construction and reliability.

I came across this lens in my friendly camera store. While browsing the shelves, Antonio, the owner, brought out of blue a grey box with a fully disassembled lens. There was some visible damage to at least one part, but all seemed to be in place. A modest amount of cash changed hands, and my new project went home with me.

There are several factors in play when you are in situation like that:

This is the damaged part: lens assembly casting. You can see chipped material on the bottom (which is really the top of the lens). The casting is made from the infamous das Silumin, the Nazi-era die-casting material, cheap and easy to produce, but fragile and cracking under mechanical stress. In some cases it can be used in cameras without ill effect, and indeed it is used in Hasselblad inner chassis, but here Leitz engineers made a critical mistake exposing the part to external stress. When you twist the lens by aperture ring or smash something with a hood, this part will crack inside. On this photo you can also see a brass helical ring over it with aperture selector insert made of plastic. In the ideal world without beancounters, the whole assembly would be brass.

After cleaning the lenses form debris and grime (Zeiss lens cleaning fluid is highly recommended), my first task was to determine the order in which lenses should go. All elements were measured with calipers, and sorted in that order. Next, the lens diagram was printed out and the lenses were enumerated. Easy enough.

Many thanks to Erwin Puts for his wonderful illustrations. The next big thing was the aperture.

First, I had to find a replacement for a missing rod in the aperture disc. It is indended to move the aperture when the selector ring is rotated. A properly trimmed screw did the trick. The sticking out part was darkened with permanent marker. Then, insert the lens module into external shell, and install the aperture ring.

Now, to the trickiest part: reassembling aperture blades. You will probably have to do quite a few attempts, it is not a job you can rush.

The thinner ends of the blades go to the bottom holes, while the thicker parts are engaging with the aperture selector disc above. Their strange shape is what makes aperture ring work linearly, as compared to logarithmic scale of lenses made before 1960s. Assembly goes easy enough until you fill out all visible holes. After that, you have to gently slide the blades underneath already installed ones, wiggling carefully until they click into holes.Your patience will be tested many times. After that, you can reinstall the aperture disc.

The easiest is to install it in F4 position. When you open it to f/2, blades are still visible in the ring; it's normal.

In the box there were a few bits that chopped off from the casting. I put them back with a 15-hour epoxy, carefully bit by bit. Use a toothpick to drop a fine drop of epoxy and smudge it, then insert the chops with pincers. Again, patience is a virtue here. Do not use quick curing epoxy, you will not be able to do it in time and likely to ruin the lens. Obviously, let it cure for how long it takes before proceeding.

Here is the earlier view of the assembly upside down: do not turn it over as the aperture blades will fall out. The focus ring is installed onto the brass helical in orientation as shown. There are several entry points on the helical, you will have to experiment unless someone was kind enough to mark a point during disassembly. A clue here is that infinity mark should align with aperture selector mark. There is about 1-2mm room between aperture ring and focus ring in infinity position.

In case you need to replace a broken focusing tab on the lens (it's plastic), you need to remove the screw circled in blue above.

Now it's time to install the DOF scale part. The focus ring tabs should go into its slots. The scales, of course, are supposed to align. Insert the front group of lenses, tighten carefully with the beauty ring. I use cellphone vibro while tightening the ring gradually - helps keeping the elements centered.

There is a hole, circled in red, for a rear lens module fastener screw. Insert the bottom elements, and screw in the rearmost. When you see the mark on the rear element through this hole, fasten it with the screw. Set in the chrome bayonet mount and tighten it well. Here we go, your King of Bokeh got a new lease of life!