Preliminary to photography for one quark? (3,6)
I believe the answer is:
say cheese
'preliminary to photography' is the definition.
I can't tell whether this defines the answer.
'for one quark?' is the wordplay.
'for one' becomes 'say' (both can mean 'for example').
'quark?' becomes 'cheese' (I can't justify this - if you can you should believe this answer much more).
'say'+'cheese'='SAY CHEESE'
Can you help me to learn more?
(Other definitions for say cheese that I've seen before include "Photographer's phrase" , "Term used by photographer" , "Water feature" , "Show your teeth" , "Words required when one is about to be shot!" .)