I have a Durst M605 with both the colour and standard heads. My problem is I changed from one to the other today and when I put everything back together I found I could not focus an image on the paper. I have a nikkor 50mm F4 lens and the dished lens mount and it was working fine the last time I used it. I am using the colour head as it is great for using the dial in filters. Does anyone know what I might have done wrong when re assembling? Everything looks fine to me. Many thanks for any support.