Murph,

If you do a little research on the size of an Ilex 5 or a Compound 5, relative to a Copal 3 it might be more evident.

As big as a Copal 3 is, it is just so much smaller than the Ilex 5 or Compound 5.

A big lens requires a big (and often expensive and / or obsolete) shutter.

And if it is too big, you might not be able to fit it into a shutter at all...

Regards,

Len