Top tip for anyone caught out by sudden rainfall.
If you have either waterproof overtrousers or a spare lightweight raincoat, just shove the lens end down the leg/sleeve and view through the waist opening. The legs/sleeves often have either a Velcro or elasticated cuff to make it snug on the lens. Not ideal but keeps the camera/lens dry but you might get a bit wet.
Some Sony stuff and now some Nikon stuff (shock horror). Sony cannot supply what I want so rightly or wrongly I'm branching out to someone who does.