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01-15-2020, 10:24 PM   #1
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K-mount speedbooster to m43

Is this laughable or plausible??

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.


The (hopeful) result: a reasonable focal length that is not too telephoto with the crop factor of m43, and a faster aperture to help shoot at lower ISOs. All with well-built Pentax glass that has buttery smooth focus rings (although no declicked aperture).

A Pentax 50mm 1.4 m42 lens would be effectively reduced by 0.71x to be a 35mm equivalent, and a stop brighter aperture would make it an f/1 equivalent.


Is this a ridiculous idea or could it actually work with reasonable results?

01-15-2020, 11:49 PM   #2
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I would say plausible.


There might be an issue with mechanical tolerances. With multiple adapters they add up. I use a K mount to NX mount adapter on mt Samsung bodies. With heavy lenses especially, I find that when focusing I have to take up the slack in the mount before anything happens. It is not a lot but it is noticeable. When I add an extension tube into the mix the effect is more pronounced.
01-16-2020, 08:47 AM   #3
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The high end speed boosters also take lens system properties into account. This gets way beyond me, but the angle of entry into the adapter may vary with additional adapters. What if any effect that will have is unclear.

As far as crop factor, your 50 would appear like a 70 in terms of field of view rather than 100 which would be seen with a 50 on m43 normally)
01-16-2020, 09:03 AM   #4
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QuoteOriginally posted by Imp Quote
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.
Good idea

Also, Viltrox has an AF speedbooster EF to M43.it works with many but not all EF lenses(not efs).

Crop ends up 1.42x.

01-16-2020, 02:29 PM   #5
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I believe direct k-mount to m43 focal reducers already exist. When I first searched for this idea, I couldn't find any information about k-mount to m43 "speed boosters", but "focal reducer" is just another word for the same thing, and I found several options using that search term instead.
01-29-2020, 08:01 AM   #6
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I recently bought a Panasonic GH4 to use as my video camera because my Pentax cameras were no longer up to snuff in that departmet. I have a K-mount to m43 adapter that's fine for the Pentax lenses I have now, but it effectively doubles the relative focal length so I'm left without much of a wide angle option other than buying a non-Pentax lens or using a focal reducer. Apparently Metabones doesn't make a speed booster for Pentax lenses so that made me start wondering if this might be a way for Pentax to address their video issues. Why not build a fairly high-quality focal reducer that has all the electronic connections to work well with Pentax lenses? It might be a way for Pentax to make a mark in the world of video with a minimal amount of development.
01-29-2020, 09:15 AM   #7
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QuoteOriginally posted by boriscleto Quote
Because Pentax only recently introduced KAF4. Other lens mounts with electromagnetic aperture have been around for a lot longer, and there are more than 2 or 3 lenses available...
How does this factor into video? With stills stopped down aperture darkens viewfinder but with video how does this pose a challenge? Or is there another aspect to kaf4 that I misunderstand?
01-29-2020, 10:05 AM - 1 Like   #8
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QuoteOriginally posted by UncleVanya Quote
How does this factor into video? With stills stopped down aperture darkens viewfinder but with video how does this pose a challenge? Or is there another aspect to kaf4 that I misunderstand?
I misread the post. TaoMas is asking Ricoh to make a focal reducer. I thought he was asking a third party to reverse engineer KAF which will never happen because the market for such a thing is miniscule. Also the same teason Ricoh will never do such a thing even though they wouldn't have to do the reverse engineering part...

01-30-2020, 03:44 AM - 2 Likes   #9
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QuoteOriginally posted by Imp Quote
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.
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