Hi ukasz. This is probably the best picture in your portfolio. That's because you took it just in a perfect moment in time. I can really see the passion on the boy's face. That's great!
On a technical side, I agree with Thilo (he made a point about the tonal range here and indeed it would be better with a little bit higher contrast and more greys. The composition is also something that could be improved, I mean that on the left and right there should be more space (his arm and the violin's bow are cropped and in my opinion it shouldn't be that way), there could be a bit more space at the top as well.
The quality could also be improved, but it's a matter of bad scanner I suppose:)
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