Not a definitive list, but one which covers a few of the “tech” issues. More will be added as I think of them.

Are all lenses built the same?

Most manufacturing companies provided a good, clean environment for constructing lenses. That’s not to say that there won’t be lousy copies of a particular lens, as well as outstanding copies, due to manufacturing tolerances. This is exacerbated in some lenses from the USSR, mostly because the same lens could be manufactured in a number of different factories, all with differing levels of quality (which during the period could be true of any company running multiple manufacturing locations).

Are vintage lenses radioactive?

There are some lenses that produce low-level radiation because they contain one or more optical elements made using Thorium. It was useful in lens design because it gave optical glass of the period a high refractive index, so fewer lens elements would be needed in a lens.

What sort of aberrations do vintage lenses produce?

No lens is perfect (not even modern ones). Lenses can suffer from soft edges, chromatic aberrations, and vignetting. But that’s not to say these things are negatives. Some vintage lenses can create the same sort of distortions that app filters do – using the lens aberrations.

Do vintage lens have coatings?

Lens coatings first appeared in the 1930s, yet many early vintage lenses only had a single layer coating and as such many lenses are susceptible to internal reflections and lens flare. Lens coatings were made from a variety of materials, including rare-earth elements. Lens coatings were primarily created to eliminate or reduce light reflections. Through the practical application of lens coatings, a significant reduction in the reflective index of the lens allowed for more complex optical designs to be constructed. The lack of coatings can add to a lenses’ character.

Are vintage lenses sharp?

Vintage lenses may not be as sharp as modern ones, but then again vintage lenses aren’t really about sharpness. Older lenses are often sharp in the centre, but decreasingly so as you move to the corners. Stopped down to f/8 many produce good results. The reduced sharpness is due to the use of fewer low-dispersion optics, fewer anti-reflective coatings, and the widespread use of spherical elements in lens construction. The use of low-dispersion glass and aspherical elements has lead to finer detail in modern lenses.

Does bokeh matter?

Does it? Look honestly, buying a lens just for its ability to produce “creamy” bokeh is fine, but you still have to have the right circumstances so the lens will produce bokeh. Bokeh certainly adds interest to a picture, but it’s not the be-all and end-all some people make it out to be.

Is faster better?

An f/1.2 lens is often (incorrectly) considered to be better than an f/1.4 lens, which is turn is better than a f/1.8 lens, while an f/3.5 lens is not even considered. This misconception is derived, in part, from the fact that large aperture lenses are more costly to design and manufacture. However a high cost is not necessarily associated with better quality when all aspects of lens performance are considered. Large aperture lenses do benefit from superior light-gathering power, good in low light situations – but how often is this needed? Large aperture settings also suffer from a very shallow depth-of-field.

Why do later lenses have so few aperture blades?

Lenses of the 1950s often had a lot of aperture blades, from a low of 8 to a high of 18-20. This means that the apertures produced in scenarios such as Bokeh are almost perfectly round. However with the introduction of fully automatic aperture in 1961, there was a need to reduce the operating resistence of the blades, hence many manufacturers chose to reduce the number of aperture blades to 6.

Can vintage lenses be stabilized?

Vintage lenses don’t come with built-in stabilization. This is not a problem with cameras that have in-body stabilization like Olympus, but can be an issue with those that rely on lens-based stabilization.

Do vintage lenses produce EXIF data?

Vintage lenses do not have an electronic connection, so that means the camera will only record metadata (EXIF) for images relative to camera settings like shutter speed, ISO, FPS, picture profiles, etc. However, no lens data will be included, such as f-stop, or focal length. The camera also won’t think there is a lens attached, so it is necessary to change the setting “Release without lens” to activate the shutter release. This can really hamper some people as it requires taking notes while out shooting, and it isn’t always practical – like when you are taking a few shots in sequence. With no lens specific information, the camera has little ability to correct for things like vignetting.