light meter with smallest aperture

Hi! Which pentax m measures the timing with full open aperture ? So the viewfinder doesnt get darker when focusing? Thanks!

Assuming we are talking about K bayonet cameras and lenses, and looking for lenses that will work with modern DSLRs, then you need A series manual focus lenses and any AF lenses.

Where there is an aperture ring on a lens, set it to "A" and all will be well. If there is an aperture ring but no "A" setting the lens can still be used using the stop down metering technique. The technique is described in this review: https://www.ephotozine.com/article/vivitar-auto-macro-55mm-f-2-8-vintage-lens-re...

A fully manual lens at full open aperture is allowing as much light in as possible, so it won't get darker when focussing. If you can say which camera and lens you're using it will help others to be able to help you get it sorted out. Otherwise it's all a bit of guesswork and you might be given an inappropriate answer!

thanks guys