There are two types that are useful for service (they shouldn't be mixed with centering setup/machine). Both have their advantages and disadvantages. Simplified description:
1. Adjustable lens autocollimator where there is a graduated lens for focusing. Advantage is easy direct readability, quick use, fixtures aren't required for different lenses but can be used if wanted.
Personally, I use Rollei factory autocollimator of this type. Graduation on it shows tolerance for 75mm TLR lens and everything else would need to be calculated to know the exact displacement.
2. Autocollimator with fixed and calibrated focus. Fixture is required for each lens but micrometric readout for exact displacement of the fixture's mirror can be easily read out without any calculations.
Disadvantage is that a fixture is a must. I use Hilger-Watts collimator of this type. It's not lens specific but more for precise machine alignment with precise angular readout.
Most service manuals specify allowed displacement of the image plane.
Both types have some type of angular readout. Some are more precise and on some it's more of a secondary purpose if they were made for collimation. For example, Leica manual states that parallelism between film gate and lens mount needs to be checked after setting of the focal flange length.
Collimator or Autocollimator can also be assembled on the optical bench with ready made components. Nikon service manuals and some others are showing the basic setup.
Centering machine will center elements on the optical axis. It does contain some type of collimator but it doesn't serve 'collimation' purpose. It measures reflection of the element. Next element in assembly is added and reflection is measured again of that element. The goal is that all elements are centered in relation to each other.
If mirror is used with the collimator, reflection will show levelling of the mirror. Ideally mirror would be leveled and fixture with the mirror would be centered on collimator's optical axis before using it for collimation.
With lens mounted over the fixture with the mirror, angle reading doesn't work anymore as the lens collimates light from any angle within its coverage. In case of lenses with pronounced field curvature this can cause issues since measurement could be taken away from the center of the imaging area.
I've used the often suggested camera with long lens as a collimator and it worked reasonably well. It's not as precise as the collimator setup as there's no readout for any of these values.
Can't be used for angle checking. Had plans to make a proper autocollimator but in meantime I found the factory made ones. They both work very well even though there are features that would make them much better, faster and more precise for camera and lens calibrations.
