Originally posted by ntrao I just acquired K1 and using M20 with a vented lens hood is giving problem.
FWIW, while vented hoods may look cool, they are intended for use on rangefinder cameras where a hood may intrude into the viewfinder. The "vents" serve as windows for the photographer to look through while framing. They don't affect which focal lengths a hood is good for.
As noted above, any hood at 20mm with a FF camera will have minimal depth and even a thick filter ring may cause vignette, hence the use of step-up rings as hoods. The nice thing is that step-up rings are cheap and a useful thing to have in the filter box. Good luck on finding something that works and please post back when you find a solution.
Even better would be to post here and write a review of the M 20/4 for this site that includes your hood solution. I just noticed your M 20/4 review, so perhaps editing it to include your adventures in finding a hood would be good.
Steve