This Caspian Gull was actually seen very well but some hove great shots were missed including photos of the opened wing. Hopefully I can relocate this gull and obtain a more decent documentation. The ID was nevertheless straight forward as it suddenly stood in the front row of a large gull roost. Through the telescope the snow white head was confirmed without any traces of head streaks, the eye was relative small and very dark, the bill was strong male-like in appearance though with flat gonys angle; in the photo the bill appears rather short due to a slight turned head.
The primary pattern was perfect for a Caspian gull with the outermost p10 having a large white tip and a grey tongue running up the inner web, isolated white mirror on p9 and broad black band on p5. Note hove long the black extends along the outer edge on p5 which is just visible below the lower edge of the white tertial crescent.