Yeah it dont fit I have them both...its great on the Sony nex 16mm though. It seems to improves sharpness and af performance. Its like a nice cheap compact fast (ish) wide angle when combined.
Not sure it'll even fit on the 14mm f2.5...It uses a twist lock mechanism. Not sure if the ebay sellers legit.
@Vitaliy_Kiselev thank you , i don't have any more 20mm 1.7 (sold) as i bought DG 25mm 1.4 and have 14mm 2.5. will test on these even different wide angle adapters ... There is: Digital King DSW Pro 0.7x Wide Angle Lens 52mm, good reviews ... Will report back.