Originally posted by: lowtech
If I was to buy a Pentax brand 50mm only lens, how much poorer would I be then?
Used is around $50.00 or about $100.00 new.
Here is the rule of of thumb: Try to keep your shutter speed at least 2X the focal lenght for hand held (ie. 50mm @ 1/90~125s, 300mm @ 1/500~750s)
ISO 100 - f:16 @ 1/125s - Sunny in open blue sky, speed drop 2 to 3 stop in slightly shade area.
ISO 100 - f:8 @ 1/125 - Slightly cloudy little shadow.
ISO 100 - f:4 @ 1/125 - Heavily cloud or in shaded area on sunny day.
As you can see the ideal shooting shuter speed & f-stop drop drastically, therefore a zoom lens isn't ideal for shooting unless you load it with fast/grainny film with poor contrast.
Unless you have an expensive heavy pro lens, your 28~80mm is very likely a varible aperature lens that have a minimum aperature of f:3.5~5.6 (ideal sharpness for your lens is very likely somewhere around f:11~22) that will limit you to shootting fast film & mostly outdoor, unless you uses crappy flash or heavy & combersome tripod.
The standard 50mm have the best sharpness range of f:5.6~22, and even at f:2.8 or f:1.8 it is very likely that it match or sharper than the 28~80mm zoom at f:8. Not only it is sharper & faster, it let you experiment with the critical depth of fields that is a requierment in your photo class. The 50mm will be the lens that have the least compromise that you have to make therefore you will have a greater choice of film range & shooting condition.
You can live with the 28-80mm but your shooting will be limited, therefore a $50.00 investment isn't a bad deal when it will ease your understanding in photography in your class.