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02-22-2015, 03:53 PM   #1
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Can C-mount lenses (CCTV) be used with the K3 or the K-cameras?

Hello everyone.

I am new here and my wife is an avid amateur photographer and owns a K3 (my wedding present). I discovered some interesting c-mount lenses made by Fujian, which I would like her to try with the K3. Is this possible? I have tried in vain to find an adapter. I did find a c-mount to q-mount adapter though. So if there is any way to use Pentax Q-mount lenses on the K3, that would do it too.
Can someone help?

Greetings from Tokyo.

02-22-2015, 04:09 PM   #2
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The image circle is much to small, so no. You can, however, use a lost of legacy Pentax and non-Pentax lenses with your K-3:

Pentax Lenses - Pentax Lens Reviews & Lens Database
Pentax Lenses by Sigma, Tamron, Zeiss, and more - Reviews and Specification Database - Pentax Lens Review Database

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02-22-2015, 04:44 PM   #3
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Adam, thank you for your prompt reply. If I understand things correctly, then the K3 has the same size sensor as for instance the Sony E-mount cameras (I am using a QX1), namely the APS-C sensor. It seems to be possible to use the Fujian CCTV lenses with the Sony, as I found a wealth of c-mount to e-mount adapters. If the Sony APS-C adapter can handle CCTV C-mount lenses, why can't the Pentax K3?

I would also try my sony e-mount lenses with my wife's K3, but so far was notable to find an adapter for this. On the other hand there are many adapters to be found which let you use K-mount lenses with a Sony E-mount body, so I could easily use one of my wife's Pentax lenses with my Sony, e.g. her 100 macro, which is terrific.

You see, I am confused, because both the the Sonys and the Pentaxes have the same size sensors, but lenses are only compatible in one direction. What could be the reason be?

---------- Post added 02-23-15 at 08:48 AM ----------

I can see I made a few mistakes in my last post:

notable = not able

What could be the reason be = What could be the reason.

Is it possible in this forum to edit a post I have already sent?

---------- Post added 02-23-15 at 08:53 AM ----------

See for example this website:
35mm F/1.7 CCTV Cine Fujian Lens with Sony NEX Adapter, $45.02 | DHgate.com
02-22-2015, 05:00 PM   #4
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I think it can work because the c-mount flange focal length is very close to that of the e-mount.
The flange focal distance for the k-mount is much greater. K-mount can be used on an e-mount body by having
an adapter that moves the lens far enough away to be at the proper distance, (45.46mm for the k-mount). However,
the e-mount lens needs to be 18mm from the focal plane and would thus hit the mirror on your K-3 if mounted that close
to the K-3 sensor.

02-22-2015, 05:32 PM   #5
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The flange focal distance is 17.526 millimetres for a C mount. It's 45.46 for K mount. So you'd need to put the lens about 30mm inside the K3's mirror box to get the lens to be the proper distance from the sensor. And then you'd end up with a tiny circle image in the middle of the frame.
02-22-2015, 05:34 PM   #6
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The e mount lenses have fully electronic aperture control and focus by wire too, which means that even if a glassed adapter allowing them to mount on PK existed, you wouldn't be able to focus or control the aperture.
02-22-2015, 05:50 PM   #7
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The E mount was designed for mirrorless. The K mount was not. Sensor size is irrelevant - lenses are designed to focus at a specific distance from the lens, which is where the film or sensor would be when the lens is mounted. A K mount lens is designed for film or sensor that's 45.46mm away from the lens. An E mount lens is designed to focus on a sensor that's 18mm away. A C mount lens is designed to focus on film or a sensor that's 17.52mm away. A Q mount lens is designed to focus on a sensor that's 9.2mm away.

That's why you can put a K mount on a Q, or on a Sony with an E mount, using an adapter - it just has to be farther away. But the reverse is typically impractical. The C mount to E mount adapter mounts the C lens very slightly inside the camera body compared to an E mount lens.

Even on that, you'll likely end up with a shot like this:

02-22-2015, 06:49 PM   #8
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Thank you for your very informative and elaborate answers. Now I can finally stop looking for these elusive adapters. They just don't exist, because they can't exist.

This seems to be a very good forum. Within half an hour I received five answers to my question. This is pretty impressive. Thank you again.

02-22-2015, 06:59 PM   #9
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There are also no adapters available for Q to K mount or even a C to K mount.
02-22-2015, 07:45 PM   #10
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QuoteOriginally posted by Ryuno Quote
Hello everyone.

I am new here and my wife is an avid amateur photographer and owns a K3 (my wedding present). I discovered some interesting c-mount lenses made by Fujian, which I would like her to try with the K3. Is this possible? I have tried in vain to find an adapter. I did find a c-mount to q-mount adapter though. So if there is any way to use Pentax Q-mount lenses on the K3, that would do it too.
Can someone help?

Greetings from Tokyo.
Just get a Q. You can put all sorts of lenses on that.
https://www.pentaxforums.com/forums/136-pentax-q/209474-adapted-lenses-tested...ce-thread.html
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