Let's say you are shifting from 1st position on the G string with 3rd finger C to third position, 3rd finger E.
Are you shifting position:
- Before changing bow direction or
- After changing bow direction?
Ideally, you will be able to shift smoothly enough that you can do it imperceptibly no matter how you are bowing. But when you are starting out, it is easier to shift when the bow changes direction. The bow change leaves a break between notes which gives you an extra moment to shift.
But when practicing, shifting without stopping the bow lets you better hear when you aren't shifting smoothly, and will help you learn to shift smoothly. So learning to do it both ways will be best.
Shifting smoothly is easiest if you have a solid reference point. Most players will focus on the location of their first finger. So to shift to 3rd position on the G string when you are learning, think about where your first finger is in first position, and about where you will move it to when you shift. Once you know in your head where it will be, then shift your whole hand so the first finger will be in its new location. After the first finger is in place, you can start thinking about where the third finger will go to play the E. If you learn to place the first finger when you shift, the other fingers will fall into place without much trouble.
Before. (Your option 1.) Suppose you play the lower note as a down bow. Your upbow note will attack exactly when you arrive at the higher note. It sounds annoying to hear any sliding sound in the new note (the upbow). However, a tiny amount of slide happening at the tail end of the downbow is much more tolerable. It is imperceptible for the most part.
I find that the key to a successful shift is to let the arm be heavy on the lower note, then sort of bounce from that to the new note, and upon arriving, let the arm be heavy again. During the shift, your arm should be very relaxed. A good way to ensure this is to practice your shifts quite slowly. Ironically, the path to a crisp-sounding shift is to practice your shifts anything but crisply! Because if you're trying too hard to be crisp, you may end up jerking, and jerking introduces tension, and tension removes your control of what's going on.
I have heard good shifting described as a guided missile. You have a target, you set your missile on course, but you allow the missile pilot to be aware of what's going on so he can make small adjustments en route.
What is "changing position"? Obviously you change the finger tip of the 3rd finger on the bowing change but that's only the culmination point of the position change, like the tip of a whip is the culmination point of a whipcrack which in itself is a comparatively smooth move and turn. Since arm and wrist and hand are more bulky than the finger tip but influence its position/reach, they'll likely start earlier and end later than the finger tip and then settle into position so that you again have a good work point for vibrato and further changes.
So obviously, your hand and wrist and elbow need to be supple enough that the various involved parts can move under their own mechanic constraints without forming one bulky entity that changes position as a block.
Sounds like you’re learning shifting positions! This is a really beneficial skill that takes a lot of practice to develop. It’s a little bit like learning first position all over again.
When you go from the third finger on the G string to first finger in third position (still note G), you are in your mind trying to find the place for your finger to make good intonation.
Shift first, then change bow. Maybe putting third position finger tapes can help you. It will take time to develop good intonation and memorize where to land your fingers.