The lamp comes off with the top half of the housing, and then you just lay the filter on top of the condenser housing. There isn't enough heat to worry about unless you were to leave the enlarger lamp on for several hours. I would suggest a 75 watt lamp rather than a 150 watt, as the printing times are more reasonable (longer, and there is less heat). I've been using Ilford Ilfospeed Multigrade II filters this way for many years, and have no problems with the filters being damaged.
Valoy II question
in Leica and Rangefinders
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