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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 - 3 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.
09-18-2020, 01:06 PM   #10
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Fotodiox does not make a focal reducer and speed booster. Their product is only a "focal reducer".

I own various brands of focal reducer speed boosters for my MFT cameras (for my 4K videos). The overall performance of the Metabones is much better any of the other brands.

I currently use various Nikkor lenses on a Metabones Nikon F to MFT adapter. The best adapters out their are made by Leitax in Spain. They make a Nikon F to Pentax K adapter. Put that on a Pentax lens and then attach the Leitax lens mount to the Nikon F to MFT Metabones. You'll find that the Leitax mount is actually better/stronger than the original Pentax OEM mount.

Also, if you don't care to dedicate a Leitax mount to each of your Pentax lenses, the Leitax mount can fairly easily be swapped between your favorite Pentax lenses.
09-19-2020, 11:01 AM   #11
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I'm not sure how a focal reducer is expected to not amplify light. By it's very nature it does the reverse of teleconverters which lose light as they magnify only a portion of the total light. Reducers increase light by taking light that would otherwise be outside the image circle and adding it in.

Fotodiox Pro Fusion Redux Adapter, Smart AF Adapter - Canon EOS (EF) D ? Fotodiox, Inc. USA

Metabones are however the best of those types of devices by a long shot.
09-19-2020, 11:45 AM   #12
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QuoteOriginally posted by UncleVanya Quote
I'm not sure how a focal reducer is expected to not amplify light. By it's very nature it does the reverse of teleconverters which lose light as they magnify only a portion of the total light. Reducers increase light by taking light that would otherwise be outside the image circle and adding it in.

Metabones are however the best of those types of devices by a long shot.
Metabones has developed one, a K-mount to Q-mount one, or so they say. Several years after they released an F-mount to Q-mount one,
Metabones®
there was excitement here over a K-mount to Q-mount one
Now you can order a Metabones K to Q Speedbooster! - PentaxForums.com
I even ordered one from B&H back at the end of July - but now they seem to have second thoughts about actually producing it, so I will just have to wait, and wait.
https://www.pentaxforums.com/forums/106-ask-b-h-photo/411725-metabones-k-mount-q-mount-speedbooster.html

Last edited by reh321; 09-19-2020 at 12:23 PM.
09-19-2020, 02:54 PM   #13
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QuoteOriginally posted by reh321 Quote
Metabones has developed one, a K-mount to Q-mount one, or so they say. Several years after they released an F-mount to Q-mount one,
Metabones®
there was excitement here over a K-mount to Q-mount one
Now you can order a Metabones K to Q Speedbooster! - PentaxForums.com
I even ordered one from B&H back at the end of July - but now they seem to have second thoughts about actually producing it, so I will just have to wait, and wait.
https://www.pentaxforums.com/forums/106-ask-b-h-photo/411725-metabones-k-mount-q-mount-speedbooster.html
I'm sorry but I don't understand why this is quoting me. I think there's a disconnect. I didn't say anything about k mount or q. I was responding to the user who said fotodiox didn't make a focal reducer that was a speed booster. He said it only was a focal reducer. However, all focal reducers concentrate light and make the attached lens faster. What's true - and maybe his point - is that many cheaper ones have such poor performance wide open, the gain in light isn't very easily leveraged since resolution suffers. (just like bad teleconverters).
09-19-2020, 03:09 PM   #14
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QuoteOriginally posted by UncleVanya Quote
I'm sorry but I don't understand why this is quoting me. I think there's a disconnect. I didn't say anything about k mount or q. I was responding to the user who said fotodiox didn't make a focal reducer that was a speed booster. He said it only was a focal reducer. However, all focal reducers concentrate light and make the attached lens faster. What's true - and maybe his point - is that many cheaper ones have such poor performance wide open, the gain in light isn't very easily leveraged since resolution suffers. (just like bad teleconverters).
You ended by talking about Metabones, who does sell a Nikon-to-Q "speed booster", but seems to be dragging their feet now on the K-to-Q "speed booster" that they have been promising for several years now. but seem to reluctant to build any more now that B&H and Adorama had them listed.This K-to-Q "speed booster" seems to be their only K-mount effort. I believe that a "speed booster" that starts with a Canon EF-mount or a Nikon F-mount would find a better choice of "speed boosters" from Metabones.

Last edited by reh321; 09-19-2020 at 04:25 PM.
09-21-2020, 03:43 AM   #15
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QuoteOriginally posted by Fenwoodian Quote
Fotodiox does not make a focal reducer and speed booster. Their product is only a "focal reducer".
Didn't I already explain that?

MetaBones "Speed Booster" is a BRAND NAME, for a Focal Reducer. And their optics are no better then many of the competitors, but their Marketing is most definitely better.

It is a function of a Focal Reducer to 'amplify' the brightness, that's what they were invented to do for Astronomy. They do so by compressing the light in to a smaller image circle.

The links to the K-to-Q Metabones product all 404. From my contacts with then regarding video products, their dislike of Pentax K-mount is almost pathalogical, especially given they already do a product of near-identical FFD, in the Contax-Yashica mount.
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