Originally posted by Debussy20:
I'm in the learning stage of the Mendelssohn concerto in G minor. In the opening piano solo the pianist plays a D-Major scales in parallel octaves. My hand just won't stretch to the 1-4 on the black keys without creating some sort of tension and eventually hurts my hands. I have to use 1-5 on the scales but I keep my finger higher up on the key istead of near the edge. [/b]
I used to play octaves exclusively with 1-5. Now that I've gained a bit more flexibility in the hand, 1-4 is comfortable for legato passages, and for staccato if it's not too loud. But for the sort of "brilliant" concerto-style octave playing that you have in the Mendelssohn there, I would still do 1-5 all the way--it lets me use more power without worrying about hurting myself while I'm at full stretch. The price you pay is that moving between black and white keys is a little less comfortable so you need to spend more time practising carefully for accuracy--your comment about keeping the fingers higher up the (white) keys is spot on.
If your hands are big enough that 1-4 feels comfortable, then you should use it as much as possible. But those of us with smaller hands have to find ways to work around it.
Have fun with the Mendelssohn--it's a very lively piece!