I have a little experience using some old lenses (cold war era Russian an East German) mounted on a Fuji X-E2 using an M42(screw mount) >> Fuji X adapter. I tend to use them wide or nearly wide open and close to the subject. With a little practice and "focus peaking" accurate focus is not difficult. As you may guess from the above, I'm deliberately using them in a way that results in some softness.

However, when these are stopped down and the composition needs sharpness only in the center you would be hard pressed to see any difference from modern lenses. AF even in the latest lenses often doesn't work too well close up. I find focus peaking when the subject is very close but not necessarily at macro distance gets more reliable results.

I also have an an older Nikon AF-D 105mm micro. I always found focusing hand held at very close distances was very difficult on a D7100. Adapted to the Fuji and using focus peaking its actually a bit easier.

Older lenses, in a simple sence, "splattered" the light on the film. This can be done because film was basically flat.

Modern lenses try to get the light going on the sensor in as straight a line as possible.

This is because of the small amount of depth a sensor needs to have. Looking at it in a simple way, think of a honey comb. Even though they have brought the sensor towards the front, there still is a touch of "wall" that blocks each sensor.

When the light travels "less straight" a very small part of it bleeds into the next sensor "honey comb". (Purple fringing and the likes.)

I think I said that right?

Older lenses, in a simple sence, "splattered" the light on the film. This can be done because film was basically flat.

Modern lenses try to get the light going on the sensor in as straight a line as possible.

This is because of the small amount of depth a sensor needs to have. Looking at it in a simple way, think of a honey comb. Even though they have brought the sensor towards the front, there still is a touch of "wall" that blocks each sensor.

When the light travels "less straight" a very small part of it bleeds into the next sensor "honey comb". (Purple fringing and the likes.)

I think I said that right?

I have two Zeiss c/y lenses which on my Contax body were only fair in their renditions. This even though they were manual lenses. However, since getting an a7ii I think I've achieved some impressive results with these so called "fair lenses". So I tend to think that these new cameras have the ability to bring out the best in any lens. I also rely heavily on all my old m42 lenses...they too are fantastic on this camera. Personally, since I don't shoot sports I find manual focus to be great on these (a7ii and a77) cameras. Focus peaking is a godsend.