[Leica] 50mm lenses should be compulsory.

[jbcollier at shaw.ca (John Collier)]

Technically Neil is correct. You can crop the centre of a photo taken 
using a 15 mm lens and get the same results as if you used a longer 
lens from the same spot. The negatives being that grain will increase 
and resolution will decrease. However, that is not how it works in real 
life. We use the whole frame to compose the resulting photo.

The focal length chosen also sets the working distance and the 
relationship between the foreground and the background. These are not 
trifling matters and a 50 mm lens has a complete different "look" than 
a 35 mm lens. That does not mean one is superior to the other though 
different people may prefer one to the other.

I often carry a 35 and a 50 as my only lenses. Many times on separate 
bodies to facilitate quickly switching between the two. This is what I 
do. This is what I like. You may well prefer a different set up.

Neil's point about living with a single focal length for a good long 
while is a great idea for any amateur. Working pros do not have time 
for such indulgences except perhaps when they are holiday.

John Collier

PS: I am always amazed when people write that a person with a 50 mm 
lens should not make their next lens a 35 (or visa versa) as it is "too 
close to the 50". What the h*** are they talking about?!? Too close in 
weight? Too close in price?