I was reading through the answers posted here, and I liked the idea of playing with the "finger per fret" method, but it's not always applicable. For instance I was practicing the Fmaj scale last night which requires that you fret 1-3-5 on the sixth and fifth string. What I'm wondering is, when you're practicing is it acceptable to slide your hand up a fret so that your hand covers frets 2-5, instead of covering frets 1-4 and reaching with your pinky for the fifth fret? Or should I be practicing that pinky stretch?
I would practice the stretch if i were you, all the modes can be played using 3 notes per string patterns, and you need to make similar stretches for all of them.
Spend an hour a day for a week playing three note per string scales and you wont have a problem stretching.
Most types of lead pattern based scale playing, is made easier using three notes per string, and your overall hand strength and technique will benefit, you'll find many other things easier once you can do 3 notes per string well.
If you are having trouble with the major scale, try playing the pattern higher up the neck where the stretch is less then move down to the lower frets as you feel comfortable.
As part of my practice regime, i used to play repeatedly through all the modes of the scale using 3 notes per string, applying different patterns on each run through.
Here are the modes 3 Notes per string:
Running through these daily will limber your hands up in no time, and teach you the modes if you don't know them already.
Edit: forgot to mention, if your having trouble with the stretch from your ring finger to the little finger, try using the middle finger on the 3 fret and your pinky on the 5. This is the technique I use.
How long is a piece of string?
Guitar scales can be interesting because there are lots of ways of playing the same note. That means there are lots of different scale patterns for a single scale. Going higher on the neck will give you even more scale patterns. So it really depends on what pattern you're using. Some will absolutely require you move your hand position while playing.
For your particular example, I would suggest stretching the pinky, it's a good skill to build. However, Fmaj actually gives you the largest possible 4 fret stretch. I'd suggest trying the pinky stretch with the same scale pattern for a different key, maybe Cmaj. For Fmaj, play the 5th fret (A) as the open A string instead of reaching. You can do the same thing on the A string 5th fret.
so instead of: