Hi Alex, yes, it will be hard to tell if it is ok unless you use the cable :0)

If it still has problems, you may need to check the focus: with the camera on a tripod, set the rangefinder to infinitiy and point it at an object that you can see clearly, then place a piece of ground glass across the film plane and look at that image with a magnifier and see if it's truely sharp. I have heard that you can substitute a strip of 'magic' tape across the back for the ground glass.