Originally posted by Imp I had an idea: adapt either Pentax M43 or full-frame Pentax K-mount lenses to Canon EF mount, and then putting that combo on a a Viltrox or Fotodiox speedbooster, to adapter to a micro four thirds camera. This is for video, mind you.
Been there, done that, here's the issues.
First, there is no 'Speedbooster' for K-mount - "Speedbooster" is a Brand Name, for product by the company Metabones, and that company refuses to make products for K-mount lenses - I have an email from them from about 4 years back stating "We will never make products for Pentax lenses".
So, they do C/Y mount, with identical FFD, but won't do K,... as we say DownUnder, "Slack ****ers".
(I'm an Aussie, my language is Culturally Appropriate, look up the song "I may a ****, but I'm not a ****ing **** " by T.I.S.M. if you'd like to understand more.)
The brand name is also why StarTroop's search results varied.
Okie, so a "Focal Reducer", as invented waaaay back in the 1930's or '40's, for use in Astronomy,.. there are Kipon and other brands that do K to m4/3, and there's EF to m4/3 that you can use a K-to-EF ring adapter on. Or you can grab a cheap mechanical K-to-m4/3 adapter, remove the mount, and attach it to a generic EF-to-m4/3 focal reducer.
I've used these sorts of combo's to film on GH4, G7, G9 and AF-100 - all work great with Mechanical adapter and Focal Reducer adapter.
I also use them on a custom machines mount on my AJA Cion Cinema Camera.
Pentax K, KM, KA and M42 lenses can all be regarded as "able to resolve 4K".
P67 and P645 can be regarded as 8K capable.
Adding a Focal Reducer improves the sharpness on ALL of these Film Era lenses.
Here's where you'll likely run in to the same issues I have - Manufacturing Tolerances and Quality Control.
A lot of them aren't great, certainly not up to the standards needed for cinema use, and really require re-machining if you want precise FFD. My current focal reducer and EF ring combination is about 0.4mm longer then it should be, leading to lack of Infinity focus on wide angle lenses.
Which becomes a real P.I.T.A. if you want to shoot with camera on the shoulder and lens set to infinity while actors work at beyond Hyperfocal distance,... as they're out of focus when they should be sharp.
Don't forget, all Focal Reducers require you to adjust the Back Focus - the optical element can be screwed closer or further from the sensor, and then locked down with a grub screw.