First of all, why use a manual focus lens?
In my case I have a collection of them most of which I acquired in film camera days, but, having found them to be superior in many instances to the kit lenses supplied by Sony, I have since bought additional manual focus lenses. The emergence of the Chinese company Rokinon/Samyang now means that you can buy a quality MF lens new that will fit directly onto your Sony camera.
Then there is the consideration of cost. Cheap secondhand manual focus lenses, even those made many years ago, often provide superior image quality to the Sony zooms.
I should add that I have tried using manual focus lenses on my Canon DSLRs, but not obtained satisfactory results, as their viewfinder screens are not designed for the purpose. Live view is better, but not convenient for many purposes. Enter the Sony NEX 6 with an excellent electronic viewfinder (EVF) and we have a game changer. It brings back fond memories of focusing with an old Pentax film camera which had a large, bright, optical viewfinder, complete with focusing aids.
What are the snags?
If your manual focus lens was made to fit a Pentax, Canon or Nikon etc camera, you will need an adapter to fit it to your Sony camera. There is an incredible range of adapters available to suit most marques, but do check that one exists before you buy. I have found that adapters costing as little as £20 are perfectly acceptable for use.
As the name suggests, manual focus means just that, no autofocus. There are times when autofocus is a real benefit, for example when trying to photograph your young children or grandchildren, but most of the time you don't need it. Buildings don't move, while cars, trains boats and planes normally follow fixed trajectories and you can pre-focus to get a sharp shot. OK planes are a bit tricky! Using a lens wide enough to get interesting shots in the street, the depth of field is usually enough to see you through in most circumstances.
I have lost some shots due to not being able to focus rapidly enough, but I have also lost shots due to auto focusing systems missing the target completely!
Then there is the aperture. Automatic cameras focus with the aperture fully wide and then stop down to the required setting immediately before shooting. You do the same with manual glass, but you have to remember to stop down before you press the trigger.
You might miss lens stabilisation, although the new Sony full frame cameras have that built into the body. I'm hoping that, should it ever appear, the replacement for the NEX 7 will have that feature.
Finally not all old lenses are entirely happy with digital sensors, and this can result in the appearance of colour fringing due to chromatic aberration (CA), or ( I am told, never seen it) occasionally edge effects. CA can very largely be dealt with by a single key press in a raw converter like Lightroom. Again cheap, and not so cheap, modern lenses also produce CA but often software is used to reduce or eliminate the effect. I have a very nice copy of a Canon 24-105 L lens that revels in CA.
Lenses to avoid
You need to restrict your choice to those lenses that have a manual aperture ring - most modern lenses don't as the aperture is controlled from the camera.
Cheap plastic bodied consumer grade zooms from the film era are often pretty poor, even from the major players.
You can't go too far wrong with fixed focal length lenses badged by the original camera company e.g. Minolta et al, or lenses fitted as standard by some of those companies. e.g. Zeiss. Third party lenses are more problematic, there are no doubt some very good ones about, with Tamron and Sigma probably better than average, but we are getting into murky waters here.
Old lenses might have developed faults in use, sticky apertures, tight focusing, or be infected with internal fungus growth. You need to be vigilant and reject anything that isn't as it should be. Don't be put off by external condition, if the glass is clear and everything works properly, it could be a real bargain. Your'e not buying a collectible, rather something to use and earn its keep.
Camera Settings and Use
Firstly you have to tell your camera that a manual focus lens is fitted, as otherwise the lack of electronic contacts will have it assume that there is no lens at all and it will refuse to work. On the NEX 6 you need to tell the camera to "Release w/o lens", an option in the Setup menu. This does not affect the operation of your auto focus lenses in any way, so you might as well just leave it at that setting.
There are three viable settings on the control dial for use with MF lenses: -
A - Aperture priority, you set the aperture and the camera selects the shutter speed
S - Shutter speed priority, I'll come back to that.
M - Manual, you set both the aperture and the shutter speed.
Then there is the ISO setting on the rear control wheel
I try to shoot at the lowest ISO that will give me a fast enough shutter speed to avoid camera shake.
There is an Auto ISO setting, which will choose a value to enable a shutter speed of 1/60 th second or faster. Unfortunately 1/60 th is not fast enough for many situations, while it's over generous for others. A better system would enable users to select the minimum shutter speed associated with auto ISO, but read below for more on that.
(Edit - Apparently the Sony a6300 has the ability to select the minimum shutter speed to use with Auto ISO, a very welcome improvement, how about a software upgrade Mr Sony? - Pigs might fly)
Depending upon the circumstance I therefore either use Auto ISO or I set the ISO myself.
Most of the time I use Aperture priority, and keep a weather eye on the shutter speed that the camera has selected, adjusting the ISO if necessary. I probably use this setting for 90% of my shots.
Interestingly Auto ISO enables a greater number of possible choices than the dial provides.
When I want to freeze the action, or, conversely force auto ISO to allow a slower speed, I will occasionally select Shutter speed priority. Auto ISO then performs in a more reasonable fashion, selecting an ISO to enable that shutter speed. The problem with this selection is that it can lead to overexposure, as occasionally you need a faster shutter speed than the one that you have selected, even at the base ISO of 100. I therefore don't leave this as my default setting.
I normally only employ the Manual setting either when using an external flash, or when I take Panoramas and need a guaranteed uniformity of exposure.
I find that the exposure provided with manual focus lenses tends to be rather less than the optimum, you normally get a usable shot, but it's often beneficial to dial in a half stop or more of over exposure. The (exposed) histogram is your friend, adjust the exposure and take another shot if necessary. Lenses vary in this regard, you have got to learn by experience, while, of course a white cat against a white wall will fool all metering systems, and you occasionally have to make quite radical adjustments.
Perfectionists might use an incident light exposure meter and set the camera accordingly, but life is too short, take a few shots, look at the histogram and adjust if necessary.
The NEX 6 has a very good electronic view finder, enabling a 5x and almost 10x magnified view. This, coupled with full aperture focusing, generally allows a very precise focus to be obtained. The viewfinder on the a6000 does not have as many pixels, and I've not had the chance to try it, so I can't comment on that.
An alternative is the contrast detection system that the camera provides, when sharp edges show up in colour. There are three levels of contrast detection available for selection on the NEX6 and my camera is permanently set at the lowest level. Despite this, it occasionally picks out a false positive, so I much prefer to rely upon the magnified viewfinder image.
As a pensioner, my eyes are not getting any younger, but I find that the range of dioptre correction on the viewfinder eyepiece is more than sufficient for my purposes, allowing me to focus without glasses.
Do be aware that many adapters do not provide a sufficiently accurate register to allow you to use the distance scale on the lens, most providing focus beyond infinity. I guess that this is in order to enable rather slacker manufacturing tolerances and so hold the cost down. I do have some cheap Pentax bayonet adapters that provide a sufficiently accurate alignment for the shorter focal lengths - and this is very convenient, shooting a distant object you just wind the lens up to infinity on the scale and fire away - but even they go slightly past infinity with the longer telephotos. You need to test your gear!
Using Unstabilised Lenses
Modern lenses generally have some kind of anti shake mechanism built in, while older manual focus lenses do not. I was taught to shoot at at least 1 over the effective focal length in order to have a decent chance of getting a sharp result, e.g. a 100 mm lens would require a minimum of 1/100 th second. Of course the angle of view is reduced by the crop frame Sony, effectively increasing the focal length by 1.5x, so you need to fire at 1/150 for a 100 mm lens etc. Always check to see what speed the camera is coming up with, and, if necessary, use Shutter speed priority along with Auto ISO to ensure that you have a realistic chance of avoiding camera shake.
Being brought up with unstabilised lenses this does not bother me, and I use the techniques learned with film cameras to get sharp results. For example if you are shooting with a telephoto try to find a wall, post, or doorway etc to lean against, while you might also employ the delayed time setting on the camera so that you don't vibrate it while the shutter is released. Don't snatch at the shutter button, squeeze it gently. I rarely use a tripod, but for long telephotos you need to, while, a monopod is better than nothing.
It is relatively difficult to get sharp images with a handheld unstabilised telephoto lens, I generally take a few shots in order to increase my chances of a success.
Of course if you are considerably more affluent than me, you might just shell out for a Sony a6500, which comes with in body stabilisation.
Practice Makes Perfect
You can't reasonably expect to fit a manual focus lens and immediately start taking super sharp, perfectly exposed, photos, there's so much to remember and to do. Take heart, and persevere, with practice you will become a very slick and skillful manual focus operator!
I'm not, I hope, a "fanboy" having used a range of photo gear over time, including Rollei, Bronica, Canon, Pentax, Sony and Olympus, so I don't have any axes to grind or want to get into Canikon warfare.
The NEX is a wonderfully compact and light camera, and I see no sense in hanging large and heavy lenses onto it. I therefore tend to use a collection of Pentax and Olympus lenses that were notable in their day for their compact dimensions. Old rangefinder camera lenses would also be a worth a look, although many are out of my price range.
I have experimented with some old Canon FT lenses, but don't see any significant difference in their performance over the Pentax or Olympus glass of the same period, while they are more bulky and require a more complex adapter. If I had an arsenal of FT glass I would probably use it, but I'm more than content with my other gear.
The bargains have to be those lenses that were fitted as standard to film cameras during that era, and the popular additional lenses that most people bought to enhance their range of shooting opportunities, i.e. those lenses that were mass produced by the leading marques.
The "Standard Lens" would normally have been a 50 mm at around f1.8 (Pentax f1.7) and you can buy these very cheaply. There are also f1,4 variants that command higher prices, but they are larger and heavier and not necessarily any better at say f8 where most of your shooting is going to happen.
A 50 mm lens on a NEX 6 or a6000 is equivalent to a 75 mm lens on a full frame camera, it makes a good portrait lens, but I also find it a generally useful focal length out and about.
The next choice of our film era photographer might have been a 28 mm, at f2.8 or f3.5. There's loads of these about and they are not expensive. 28 mm was harder to get right than a 50 in days gone by, so you will probably see some distortion and CA, but nothing that would break the deal.
A 28 becomes a 42 on a Sony NEX, which is a very useful general purpose focal length. It's my fitment of choice as I leave the house.
The next buy for many photographers in the past would have been a 135mm lens, but this is becoming 202 mm on the NEX, and not abundantly useful.
Both Pentax and Olympus made 75-150 f4 zooms however and they provide a more practical solution. They're both sharp, but the Olympus design lacks contrast and I prefer the Pentax. A 2x zoom at this focal length range was not too much of a challenge at that period, so the lens is more than OK. I bought a Pentax 75-150 new for around £75 many years ago, but, much more recently, picked up a pristine example for less than £20.
Very wide is much more of a problem. Wider tends to be harder to get right, and I would be tempted to steer you in the direction of a new Samyang/Rokinon lens rather than an antique. Voigtländer (Cosina) make some very nice lenses, but you need deep pockets to be able to afford them.