Purpose of camera lens with a fixed focal length?

[nwstudios]

Prime lenses = great bokeh, extremely fast, sharp, and shallow depth of field.
Zoom lenses = convenient.

There are some really crappy primes and outstanding zooms out there. A little research goes a long ways.

 

[Samuel H]

@heartfelt: you may want to play with my DoF/FoV calculator: http://www.similaar.com/foto/dof/dof2.php?f_x=1.9&f_r=1.778&f_f=3.5&f_ph=1

 

[NickG]

Thanks guys.

Will the 20 or 50 do waist up at 8-10feet?

20mm will, 50mm won't

 

[joe1946]

I use fast 25mm F0.95, 50mm F1.4 and 85mm F1.4 lenses and a 25-85 F0.95-F1.4 zoom would cost much more than the three lenses combined. A 14 mm - 35 mm (28-70mm 35mm eqiv) - F/2.0 Olympus zoom cost over $2,000.