Most of my lenses are in the old rangefinder M39 screw mount. Being able to use these smaller lenses is one of the big advantages of mirrorless cameras - the bellows length on these are much shorter than SLR mounts like the sister M42 screw mount common on vintage SLR lenses.
M39 will usually equate to a rangefinder lens, but be careful when buying - in the 50s and 60s, the Soviets started using an M39 mount with a longer bellows length to accommodate SLRs. When I picked up a 1965 Mir-1 M39 mount lens on eBay, I expected to be able to use it with a standard M39 adapter, but it needed a longer SLR bellows length. Luckily there are little M39 to M42 adapter rings available for a few dollars, and the usual M42 adapters will hold those lenses at the right distance.
For reasons I wrote about before, I sold my heavy, ginormous Zeiss Distagon 35mm f/1.4 native ZA E-Mount lens. I wanted to replace it with a compact manual 35mm for under $500. After a lot of research (I was also tempted by an M39 mount Canon 35mm f/1.5), I bought a 1951 Leica Leitz Summaron 35mm f/3.5 for $300. I hadn't expected to settle for something as slow as f/3.5, but I liked samples of shots made with that lens. And it is terrifically compact:
I also like that it has a focus lever. Focus levers, in addition to having great vintage steam-punk-y aesthetics, are functionally a lot of fun. You can snap them to infinity almost instantly, and in time you get a feel for where your focus is by where the lever is, and you can get lightning fast at focusing at any distance without looking - something particularly useful for street photography.
I had a problem when the lens arrived. I alway use the great little $9 Fotasy M39 to E-Mount adapters. The lenses fit very flush against the base of the adapters, which is fine for most lenses. But with a lens like this that has a locking focus lever, there's not adequate clearance for the spring-loaded locking/unlocking mechanism to engage. With the lens fully screwed in, It wasn't able to get it in and out of its infinity focus.
This was an easy fix though, thanks to the adapter design which allows you to remove the inner screw mount ring. A 1/16" flathead screwdriver can loosen the three little screws in the body.
In theory you can mount the ring to stick a bit out from the adapter if you need to microadjust the distance of your lens to get proper focus. This is possible, and I've done it, but it's very tough. The sides of the ring are tapered, which will often cause the ring to return to flush as you tighten the screws...
It's also tough to keep the ring exactly on-plane with the adapter (and ultimately camera sensor) when re-installing it at a longer length.The good news is that if your lens isn't wonky then adapter should work perfectly fine with the ring in its snug, flush position.
So here's how I adapted the adapter to work with my new (1951) focus lever lens. I removed the screw mount ring from the inside. I then selected a spot on the body where I wanted the focus lever to be while at infinity. The adapter bodies always fit the same way onto an E Mount - with the adapter lettering ending up on top while mounted. Ergonomically this focus lever (and most focus levers, if I'm not mistaken) should sit close to the bottom of the camera while at infinity. At about 7 or 8 o'clock while looking at the lens will put the lever's entire range in easy reach of your left hand.
Once I had a spot picked, I started filing the heck out of that spot on the front of the adapter body. This is why I'd removed the inner thread ring -- I didn't want to mess the threading up, and there was no reason to file the ring anyway. It took a lot of filing to get a nice deep groove, but once I did I simply first screwed the inner thread ring all the way onto the lens, and then dropped the lens and ring into the right position on the adapter body. so everything was in its right place. I then tightened to the three screws bit by bit until voila...
By the way, that trick of readjusting the position of the inner thread ring is useful for properly fitting on any lens so the aperture and focus indicators are properly positioned in sight. You don't ever have to use your lenses upside down! The threading on these lenses is quite precise, so they'll always fit onto the same adapter the same way. Once I have a lens properly adapted, I always keep it on that adapter though. I buy a separate adapter for every lens. At less than $9 an adapter, it's worth the convenience.
Anyway, now that I've got it adapted I've been happy with the Summaron so far. It looks and feels like new. The handling is wonderful - I particularly like aperture adjustment, which subtly clicks and every spot, but is also tight enough to hold in-between apertures. The lens is sharp enough for my purposes, and it has nice lens contrast. Like most any uncoated vintage lens, it can drunkenly spill light all over the place in high-light settings, but learning how to tame and use that is half the fun. Samples shots: