Thanks! Why was it a 50s shot?
ifotu's partly right.
The shot was taken indoors using natural light from a north-facing window. So, there wasn't a huge amount of light to start with. My base exposure was 4 seconds at f22.6
Factor in the lens extension, which was 275mm (lens extension squared / focal length squared), gave a 1.71x increase in exposure. Add 2x for the yellow-green filter, brings the total exposure factor up to 3.71x or almost 15s at f32. Using the little graph that comes with Ilford HP5 plus, I then applied the correction for reciprocity failure, taking the exposure up to 50s.
Suffice to say, it wasn't hand-held
Hope that explains it.
Cheers
Mark