It's what I do for nearly all my photography. Why might you want to?
- Low cost: old lenses can be cheap. Not all are, and the really good ones aren't usually very cheap, but much cheaper than buying really good new lenses.
- Character: most modern lenses are designed to be as close to perfect as they can be. Old lenses usually were too, but they didn't get as close, and the 'faults' in the designs can be pleasing to the eye.
- Reliability: yes, a good modern lens is a pretty reliable thing. Good old lenses were built to last, though, and there are no electronic parts to go wrong.
- Small size: doesn't apply to all old lenses, by any means, but with no space needed for electronics and motors, they can be smaller than modern lenses. They can be lighter too, but they tended to be all metal rather than plastic, so they can also be quite heavy.
- Good looks: yes, vain, I know. But it's surprising how often people comment on how good it is to see someone using a 'real' camera when I'm out taking photos. They presumably think it's a film camera, but the lens is part of what makes it look so good.
The Basics
The lens has to put an image of what's in front of it onto the sensor behind it. That bit is just some carefully shaped glass held in the right places. Focussing is usually just a matter of moving that glass a bit further away from the sensor to focus closer. That part is just a screw thread with stops in the right places. The aperture mechanism is made up of a number of 'blades', which can open and close a hole somewhere within the lens, to control how much light is getting through.
With a modern lens, a whole lot of electronics and motors get added in there. Zoom lenses are a little more complicated.
Lens Mounts
To connect a lens to a camera, there's a lens mount. Different cameras use different mounts. When a camera maker designs a lens mount, they'll generally use it for a whole range of different cameras and lenses, so they're all interchangeable. But there are still a lot of different lens mounts.
Each lens mount has a 'flange focal distance'. It's the measurement from the circular mount where the lens attaches to the camera to the image sensor (or film in film cameras). The Sony E-mount has a short FFD of 18mm. The very old 'M42' lens mount had an FFD of 45.46mm - much longer. That means that if you wanted to use an M42 lens on an E-mount camera, the lens would have to be held over 27mm away from the camera's mounting plate. That's rather fortunate.
There are third party companies who made adaptors. An M42 to E-mount adaptor is a short tube that attaches to the camera's E-mount place at one end, and an M42 lens at the other. There's no need for any lenses inside - it's just a tube with the right fittings.
There are quite a few companies making these, at quite a range of prices. I usually buy cheap ones, but some people think the more expensive ones are worth the extra. I have some adaptors that work ok with some lenses but not with others, so they might have a point. Cheap ones tend to be around £15, while expensive ones can be £50 upwards, so I'll take my chances.
There are adaptors available for almost any lens mount you'll find. If you have access to old lenses already, find the adaptors (eBay is pretty good for this) and give them a go.
My approach was to find lenses, and then pick up adaptors for whatever mount they happened to be. After a while, I settled on mainly Leica-M mount lenses. They're almost always good, and usually smaller than others. I also use Canon FL, M42 and Pentax K mount lenses, though - you don't have to stick to one type!
An Old Lens is No Lens
OK, so we now know we can mount the lens on the camera with an adaptor. There's a small problem, though. This is a modern camera. It expects a lens to be attached with a lot of electronics in it, and it expects that lens to talk to it. Attach an old manual lens, and there's nothing for it to talk to. By default, the camera won't even try to take a photo. There's a setting in the menu to shoot without a lens. You need to turn that on.
The next problem is focussing. You need to do it yourself, and that's not easy on a modern camera. Old cameras used to have special focussing aids, to make things easier. Fortunately, so does your Sony. It's called Focus Peaking. Find that option in the menu and turn it on. I usually have it set to 'medium' and 'yellow'.
It looks for high-contrast areas in the image, and highlights them in the colour you chose. If there's a sharp contrast, it's probably because it's in focus. So as you turn the focus dial on the lens, parts of the view sparkle in yellow to show you they're in focus.
You probably also want to set a custom button to magnify part of the image for easier focussing. Once you do, hit that button to zoom in on part of the view so you can check the focus.
I grew up with manual focus, which probably made it a bit easier, but it's easier to get the hang of than you might think. If you've ever tried to focus manually, it was probably very difficult. Autofocus lenses are hard to focus manually, and you probably didn't have peaking enabled.
If you're not sure, the total cost to give it a try is pretty low - pick up any old 50mm lens for about £5, and then £10 or £15 for an adaptor, and give it a go.
The Character
I mentioned above the character a vintage lens can have, and it's the main reason I use them. I've used decent modern lenses, and I just prefer the images I get from older lenses. You could think of it as a built-in Instagram filter, if you like. Old lenses will often give an image some style that would be difficult or impossible to add later.
That can include something as simple as some vignetteing, where the corners of the image are darker than the centre. It will often include a bit of softness around the edges, with the centre being reasonably sharp, but corners and edges being a bit soft. It can include a bit of a colour cast - I have lenses that give a distinctive yellow tint to images.
In some cases, the way the lens renders out of focus areas of the image - the bokeh - can be quite different to a modern lens.
Some Favourites
Voigtländer Nokton Classic 40mm f/1.4
This is my most used lens. It's not really a vintage lens, as it's still in production. They're made by Cosina in Japan, who have licensed the Voigtländer name. (It's a German name, so it's pronounced something like 'focked-lender'.) The 'Classic' in the model name is because it's designed to give a 'classic' look to images - it's an old lens design, not an old lens.
They're available with single- or multi-coated optics, with the single-coated one considered a little better for vintage-style black and white photography, while the multi-coated is a little better for colour, with a bit more contrast. I've seen side-by-side shots from the two versions, though, and there's very little difference. Mine doesn't say either SC or MC, which I think means it's from before they started making the single-coated model, so it's multi-coated.
I picked mine up used, for around £200, but a new one would be around £450 now. Still a great value lens for something so solid and so versatile.
40mm is a good focal length for general use, and the f/1.4 maximum aperture makes it good when the light levels aren't so high.
At f/1.4 is's reasonably sharp in the middle, with softer edges, and some vignetting, It has quite a nice warm look, too, with a bit of a colour cast. The distinctive look is reduced quite quickly when it's stopped down, though, making it a good lens to use all the time - a quick flick of the aperture dial, and you can take a nice straightforward shot with very little of that character.
The focus control is a bit unusual, especially for a modern lens, as it's got a large controller you put a finger in to adjust the focus, with a fairly small movement between extremes. On old rangefinder cameras, this wasn't so uncommon, and it makes it really quick and easy to focus.