For the classic short telephoto range between 85 mm and 135 mm, there is a variety of lenses that can be adapted to a system camera.
The ideal lens should have a good to very good optical quality with a wide aperture. And on top of that they should be as light and small. If it would have not to be too expensive, then the selection is reduced to a few lenses. A good decision is the Leitz Elmar-C 90mm with a maximum aperture of f/4.0.
It is only used to acquire and the price is significantly lower then 300, - Euro. For a Leica lens is a real bargain. The Elmar-C was made in the period between 1973 and 1978 for the Leica CL system. It weighs only 246 grams and has a length of 61 mm with a maximum diameter of 51 mm. The minimum focus distance is one meter. A collapsible rubber lens hood is usually included with the system. That does not look very nice, but it is very effective.
It is already at full aperture used very well. Stopping down to 5.6 or 8.0, the image quality and sharpness is just about perfect.
Aperture ring and focus ring can be operated very well. Focusing is easy and hassle free.
Note: you should not use a commercially available 39mm filters. The lens has a rare filter thread pitch of 0.75 instead of the normal 0.5 pitch. If you put on too tight, the thread is destroyed irrevocably.