By Tony Saunders-Davies
It can be tedious sometimes centering stops, whether they are dark-ground, phase contrast or whatever. Here is an idea I picked up many years ago from a note in the Journal by Gilbert Hartley.
Gilbert suggested fixing ‘magnetic rubber’ to the underside of the condenser, then one could mount a steel filter holder and slide it about easily to centre the stop. I have inverted the idea, and fit a steel plate of some sort to the bottom of the condenser, and use a stop holder with small (ferrite type) magnets glued on. I was lucky in obtaining some thin MAGNETIC stainless steel, which is the best, but supplies ran out and now have sometimes been reduced to cutting out the bottom of a tin. The holder here is somewhat scruffy, inasmuch as the sprayed on matt black (Halfords) has begun to scuff off.
Here is how one of my condensers has been modified.
Modified condenser with stop holder
A thin steel plate has been fitted to the bottom of the condenser. If you have the skill (and nerve!) small screws can be used – make sure you don’t interfere with the working of the iris. Otherwise use an adhesive – Araldite or something like Bostik, which can be removed later if required.
And this shows the underside of the stop holder:
Underside of stop holder
Any kind of stop – dark-ground, phase, Rheinberg etc., can be used. The ease with which these stops can be centred and manipulated makes this kind of device a real pleasure to use.