Is it possible for a fingertip to be too thin for vibrato?
I have a somewhat thin index fingertip and I've noticed that compared to my other fingers, it has a very weak vibrato. I'm wondering if I have a flawed technique or is it possible for it to just be impossible to get a wide vibrato with a thin fingertip.
I dont think the displacement of the finger in vibrato can equal or be greater than the width or girth of the finger...unless its too wide of a vibrato. Also depends on the angle of finger relative to strong no? There are vibratos closer to fingertip and others less lateral to string?
No. I would guess your position is wrong. Post a pic of your hand- that's the only way we can tell.
Pics are good. Also, you have to make sure the joint closest to your fingertip is flexible--controlling how much you let this joint flex is how you can control how much "big" your vibrato is. Simon Fischer explains all of this in his books, and Warming Up has exercises on it in particular.
You may have to get more motion. But whatever you have to do, you do. They're the fingers you have. We all have some weakness or other, including short 4th fingers.
I have known people who struggle with violin because their fingers are too pointy. Not sure what you can do. Sometimes, I wonder if such an individual might benefit from collagen implants or such. Those kinds of things are never without significant risk, however.
Or sticking plaster?
Having kind of narrow fingertips myself, I find playing double stops in high positions to be particularly problematic (especially G-D ones). But what are you doing to do other than find a way to make it work?