The best way to know what your lens is capable of is to shoot slides. No observer's paradox, no postprocessing relativism due to scanner, PS, etc etc.
So I was glad to see that my Isolette II with Apotar lens was capable of very nice results on slide film. It's not a Tessar or a Planar lens (the Apotar is a triplet), but it's about the quality of colours you would get with a Yashica D.
The lens does not appear to have a perfectly flat field, but in most situations that does not create much trouble.