How to use lenses in K mount on an A850?

Zav · 01-07-2012, 10:26 AM

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Hello!
I have found a A850 for a good price. Is it possible to use my lenses in K mount on it, using an adaptater or hacking a little my lenses?
Thanks

RioRico · 01-07-2012, 01:36 PM

Search eBay CAMERAS for (sony,minolta,alpha) pentax adapt* -m42 and you'll find many adapters just crying out, BUY ME! BUY ME!

Zav · 01-07-2012, 02:00 PM

Well, I was thinking more of an adapter without this cheap piece of glass affecting the image quality...

Laurentiu Cristofor · 01-07-2012, 05:24 PM

Originally posted by Zav

Well, I was thinking more of an adapter without this cheap piece of glass affecting the image quality...

Do you want infinity focus or not?

Zav · 01-07-2012, 05:34 PM

Yes, I want infinity focus, I understand that there no easy way to mount my lenses on the A850 with an adapter. Has any of you heard of "hacking" of the lens in order to change the mount for example?

Laurentiu Cristofor · 01-07-2012, 06:11 PM

Originally posted by Zav

Yes, I want infinity focus, I understand that there no easy way to mount my lenses on the A850 with an adapter. Has any of you heard of "hacking" of the lens in order to change the mount for example?

Are you familiar with the concept of flange focal distance? Because this is the problem that you are facing. And you can't change that - you might just as well build a lens from scratch.

Jasvox · 01-07-2012, 09:58 PM

Originally posted by Zav

Well, I was thinking more of an adapter without this cheap piece of glass affecting the image quality...

Adapters usually (always?) have no glass, simply threads on each side to join your lens to another type of mount.

Jason

Zav · 01-08-2012, 01:51 AM

Originally posted by Laurentiu Cristofor

Are you familiar with the concept of flange focal distance? Because this is the problem that you are facing. And you can't change that - you might just as well build a lens from scratch.

Yes and I was thinking of something "a la Leitax"...

Raffwal · 01-08-2012, 02:00 AM

Originally posted by Laurentiu Cristofor

Are you familiar with the concept of flange focal distance? Because this is the problem that you are facing. And you can't change that - you might just as well build a lens from scratch.

But the K mount flange distance is about 1 mm longer than Minolta/Sony A mount, so in principle that should not need a correcting lens AFAIK. But is it a question of how thin an adapter is possible due to mechanics in this case? Actually K mount and M42 distance is the same and people are using M42 glass on Sony FF bodies.

KevinR · 01-08-2012, 02:17 AM

The glass in some adapter is all about correcting the focal rays for flange focal distance, and necessary. Optically, if the FFD of the camera is longer than the lens, then it is a relatively easy matter of pushing the lens outwards; however, if the FFD of the camera is shorter than the lens, then you need a glass element to correct the focal rays. Only other option is to "hack" away material from the lens to get it closer to the sensor. Simple laws of optics.

Extract from Pentax K mount - Wikipedia, the free encyclopedia "Only K-mount cameras have the right flange focal distance (45.46mm) to accept old M42 lenses without any optical correction or loss of infinity focus/changed close focus distance. Other SLRs with smaller flange focal distance can also accept M42 lenses with dedicated adapters: Canon EOS (44mm), Olympus 4/3rd (38.67mm), Sony (same mount as Konica-Minolta/Minolta, 44.5mm), Sigma (44mm), and other companies, but significantly not Nikon (46.5mm)."

But then there are also practical problems of the mount interface design which might also force the lens out beyond it FFD, or just render the whole idea as bad.

Laurentiu Cristofor · 01-08-2012, 02:30 AM

Originally posted by Raffwal

But the K mount flange distance is about 1 mm longer than Minolta/Sony A mount, so in principle that should not need a correcting lens AFAIK. But is it a question of how thin an adapter is possible due to mechanics in this case?

Right. The alpha mount is wide enough that it cannot fit inside the K-mount, which prevents you from mounting it within 1mm from the K mount.

Originally posted by Raffwal

Actually K mount and M42 distance is the same and people are using M42 glass on Sony FF bodies.

That's because the M42 fits inside the K mount and it fits inside the alpha mount as well. But you need the reverse to be true (the Sony mount to fit inside the K mount) for an adapter without optics to be possible.

01-07-2012, 10:26 AM	#1
Zav Pentaxian Join Date: Feb 2009 Photos: Gallery Posts: 1,371	How to use lenses in K mount on an A850? Staff note: This post may contain affiliate links, which means Pentax Forums may earn a small commission if a visitor clicks through and makes a purchase. If you would like to support the forum directly, you may also make a donation here. Hello! I have found a A850 for a good price. Is it possible to use my lenses in K mount on it, using an adaptater or hacking a little my lenses? Thanks

01-08-2012, 02:17 AM	#10
KevinR Veteran Member Join Date: Jan 2010 Location: Cape Town, South Africa Photos: Gallery \| Albums Posts: 653	The glass in some adapter is all about correcting the focal rays for flange focal distance, and necessary. Optically, if the FFD of the camera is longer than the lens, then it is a relatively easy matter of pushing the lens outwards; however, if the FFD of the camera is shorter than the lens, then you need a glass element to correct the focal rays. Only other option is to "hack" away material from the lens to get it closer to the sensor. Simple laws of optics. Extract from Pentax K mount - Wikipedia, the free encyclopedia "Only K-mount cameras have the right flange focal distance (45.46mm) to accept old M42 lenses without any optical correction or loss of infinity focus/changed close focus distance. Other SLRs with smaller flange focal distance can also accept M42 lenses with dedicated adapters: Canon EOS (44mm), Olympus 4/3rd (38.67mm), Sony (same mount as Konica-Minolta/Minolta, 44.5mm), Sigma (44mm), and other companies, but significantly not Nikon (46.5mm)." But then there are also practical problems of the mount interface design which might also force the lens out beyond it FFD, or just render the whole idea as bad.

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01-07-2012, 01:36 PM	#2
RioRico Veteran Member Join Date: Jun 2008 Location: Limbo, California Posts: 11,263	Search eBay CAMERAS for *(sony,minolta,alpha) pentax adapt -m42** and you'll find many adapters just crying out, BUY ME! BUY ME!

01-07-2012, 02:00 PM	#3
Zav Pentaxian Join Date: Feb 2009 Photos: Gallery Posts: 1,371 Original Poster	Well, I was thinking more of an adapter without this cheap piece of glass affecting the image quality...

01-07-2012, 05:24 PM	#4
Laurentiu Cristofor Banned Join Date: Nov 2009 Location: WA Photos: Albums Posts: 3,055	Originally posted by Zav Well, I was thinking more of an adapter without this cheap piece of glass affecting the image quality... Do you want infinity focus or not?

01-07-2012, 05:34 PM	#5
Zav Pentaxian Join Date: Feb 2009 Photos: Gallery Posts: 1,371 Original Poster	Yes, I want infinity focus, I understand that there no easy way to mount my lenses on the A850 with an adapter. Has any of you heard of "hacking" of the lens in order to change the mount for example?

01-07-2012, 06:11 PM	#6
Laurentiu Cristofor Banned Join Date: Nov 2009 Location: WA Photos: Albums Posts: 3,055	Originally posted by Zav Yes, I want infinity focus, I understand that there no easy way to mount my lenses on the A850 with an adapter. Has any of you heard of "hacking" of the lens in order to change the mount for example? Are you familiar with the concept of flange focal distance? Because this is the problem that you are facing. And you can't change that - you might just as well build a lens from scratch.

01-07-2012, 09:58 PM	#7
Jasvox Veteran Member Join Date: Oct 2007 Location: Melbourne, Australia Posts: 3,107	Originally posted by Zav Well, I was thinking more of an adapter without this cheap piece of glass affecting the image quality... Adapters usually (always?) have no glass, simply threads on each side to join your lens to another type of mount. Jason

01-08-2012, 01:51 AM	#8
Zav Pentaxian Join Date: Feb 2009 Photos: Gallery Posts: 1,371 Original Poster	Originally posted by Laurentiu Cristofor Are you familiar with the concept of flange focal distance? Because this is the problem that you are facing. And you can't change that - you might just as well build a lens from scratch. Yes and I was thinking of something "a la Leitax"...

01-08-2012, 02:00 AM	#9
Raffwal Veteran Member Join Date: Oct 2010 Location: The North Posts: 879	Originally posted by Laurentiu Cristofor Are you familiar with the concept of flange focal distance? Because this is the problem that you are facing. And you can't change that - you might just as well build a lens from scratch. But the K mount flange distance is about 1 mm longer than Minolta/Sony A mount, so in principle that should not need a correcting lens AFAIK. But is it a question of how thin an adapter is possible due to mechanics in this case? Actually K mount and M42 distance is the same and people are using M42 glass on Sony FF bodies.

01-08-2012, 02:30 AM	#11
Laurentiu Cristofor Banned Join Date: Nov 2009 Location: WA Photos: Albums Posts: 3,055	Originally posted by Raffwal But the K mount flange distance is about 1 mm longer than Minolta/Sony A mount, so in principle that should not need a correcting lens AFAIK. But is it a question of how thin an adapter is possible due to mechanics in this case? Right. The alpha mount is wide enough that it cannot fit inside the K-mount, which prevents you from mounting it within 1mm from the K mount. Originally posted by Raffwal Actually K mount and M42 distance is the same and people are using M42 glass on Sony FF bodies. That's because the M42 fits inside the K mount and it fits inside the alpha mount as well. But you need the reverse to be true (the Sony mount to fit inside the K mount) for an adapter without optics to be possible.