The figure below plots the apparent magnitudes of DSOs versus their maximum apparent sizes. Different markers represent various types of objects.

The histogram at the bottom shows the number of DSOs within each 1.0 magnitude interval. 

Informative discussion can be found in this post, such as, why do open clusters dominate at the big, bright end? Why are there fewer galaxies at larger magnitudes and sizes?

Source of data: https://github.com/mattiaverga/OpenNGC