I have a yashica minster d and the rangefinder was difficult to use - the patch just wasn't bright enough.I suspect the half silvering has become tarnished/degraded a bit. I found a tip which I tried and works well - black out the centre of the front viewfinder window to the same size as the rangefinder patch - I have done mine with just marker pen. Now the rangefinder patch is the only thing visible in the centre and it is simple to align edges as in any split image focussing, rather than trying to superimpose a dim rangefinder image on the main viewfinder image.