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PL mount modification


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#1 Chris_Burket

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Posted 04 August 2006 - 05:05 PM

I have seen a lot of PL mounts for the Konvas 2m for sale on Ebay. Many of the ads say that you simply take out 4 screws, replace the mount, and screw it on. I know converting other cameras to PL mount can be a very expensive and time consuming process... So would buying a mount such as this and converting your camera by yourself be a bad idea? I know that the mount position can play a huge factor in image quality, focus, backfocus, etc.... so is this just kind of a quick and dirty fix for those who are not extremely discriminating with their image quality... or are the Konvas cameras just built in such a way that a simple mount conversion at home is not a problem?
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#2 Chris Keth

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Posted 04 August 2006 - 07:08 PM

I have seen a lot of PL mounts for the Konvas 2m for sale on Ebay. Many of the ads say that you simply take out 4 screws, replace the mount, and screw it on. I know converting other cameras to PL mount can be a very expensive and time consuming process... So would buying a mount such as this and converting your camera by yourself be a bad idea? I know that the mount position can play a huge factor in image quality, focus, backfocus, etc.... so is this just kind of a quick and dirty fix for those who are not extremely discriminating with their image quality... or are the Konvas cameras just built in such a way that a simple mount conversion at home is not a problem?



If the mount is a well-designed and well-machined replacement, it could be nearly that easy. I'm not familiar enough with that camera to know how the mount is designed specifically.

The catch is that lens mounts have to be accurately placed in relation to the film plane. They must be EXACTLY parallel and must be EXACTLY the right distance out from it. If either of these of off by a couple 10,000ths-of-inch, the image will be out of focus, either partially or completely.

If you wanted to give it a try, you should still have it installed by a camera tech, simply because they will have the necessary tools like a depth gauge to check the backfocus to be sure it is correct.

Edited by Christopher D. Keth, 04 August 2006 - 07:12 PM.

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#3 david west

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Posted 04 August 2006 - 09:15 PM

http://www.rondexter..._dimensions.htm
http://www.cameragroup.com/435_es.html
http://www.arri.com/...0/tech_spec.htm


DISTANCE
51.98 - 0.01 mm

there are some flange distances... many places say 52, but arri is saying 51.98


you can get a cheapie 6inch digital caliper from harbor freight for 12 dollars on sale and measure that distance with the required accuracy.


the tougher part will be setting up a simulated film plane that is parallel to the flange on the mount that you install. if the adapter is machined correctly it should be easy, but would be much easier if you had a machine shop to make a jig to hold everything (basically a collumator -or however it is spelled)
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#4 Olex Kalynychenko

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Posted 05 August 2006 - 07:47 AM

If the mount is a well-designed and well-machined replacement, it could be nearly that easy. I'm not familiar enough with that camera to know how the mount is designed specifically.

The catch is that lens mounts have to be accurately placed in relation to the film plane. They must be EXACTLY parallel and must be EXACTLY the right distance out from it. If either of these of off by a couple 10,000ths-of-inch, the image will be out of focus, either partially or completely.

If you wanted to give it a try, you should still have it installed by a camera tech, simply because they will have the necessary tools like a depth gauge to check the backfocus to be sure it is correct.


Yes, the sellers of PL lens mount can tell you about very easy procedure replace of lens mount.
They need to sell lens mount.
From other side, the procedure replace of lens mount show easy, you need unscrew a few screws, replace lens mount and screw a few screws.
But, any camera technician, who service of professional cine camera tell you, the any operation with lens mount, body of camera, ground glass, must included full procedure of checking of flange focal distance.
The flange focal distance of lens mount of camera - base technical parameter of final quality of footages.
But, you will need checking of flange focal distance, if the body of camera have a adsusted OST-19 and Arri PL mount on set.

If your camera have OST-19 lens mount and you wish set Arri PL, you need :
- centering of new Arri PL mount on body with special measuring microscope.
You will need specail film gate with cross on centre.

- You need adjust of flange focal distance. This is distance must be adjust with high precision +/- 0.01 mm.
You can use high precision a clock sensing head and test plates.
Yes, The Arri cameras have flange focal distance of lens mount 51.98 mm, but, need draw attention, what Arri 435 cameras have film gate with air-gap.
The Konvas camera have film gate with clamping plate.
I think, need set standard flange focal distance of Arri PL mount 52.00 +/- 0.01 mm.
Any case, if you set 51.98 mm, this will not bad too.

The flange focal distance depend from volule of tightening torque screws.

The next procedure, you need check a flange focal distance on centre and all corners of film gate.
If the lens mount set not parallel with surface of film ( surface of film gate ) you will have different distances on corners. The distances on corners must be +/- 0.01 mm.

The final test of flange focal distance must be with auto collimator and real lens.
If you visit of my page
http://www.geocities.../rep-konvas.htm
You can see information about service and repair of Konvas camera. You can see special devices for adjust of flange focal distance. This is devices can be use for set Arri PL mount too.
If you need, i can send a picture of microscope for centering of lens mount.

I wish underline.
The procedure set new lens mount on camera not easy and need special tools and experience of camera technician.
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