Learning birds

Whilst my eyesight is pretty good, due to an old injury I struggle to adjust from near to far very quickly. Normally this isn't really a problem - but it does make recognising (or sometimes even spotting ) some birds quite difficult.
I'm good with birds that soar or wade or perch - but woodland or garden birds that flit around are hard. Today I saw two of these having a mighty battle in the garden - eventually this chap emerged victorious and sat on his perch long enough for me to focus and grab this shot.
I've narrowed him down to a Willow Warbler or Chiff Chaff and am leaning towards the former - but id help, correction or confirmation is welcome.