Focus Issue - Urgent

[Andrew Swisher]

I rented 18mm, 25mm, and 50mm Cooke Panchros to use with the Red One MX for a short this weekend. When I try to set the back focus, it simply doesn’t work. The Cookes won’t focus no matter how far I turn the back focus at the set distance. Maybe I’m just doing it wrong. Can anyone offer advice or point me in the direction of detailed back focus instructions? Thank you

-Andrew

 

[jimhare]

Andrew, do you see the focus changing at all as you adjust the back focus? What method are you using? I take you you loosen the adjustment bolt and then turn the entire back focus ring?

I once found that I couldn't get the back focus anything like right on the Red ONE. Turned out the PL mount was installed backwards after being on a Nikon mount for a while! Actually worked, but back focus was impossible until I corrected it.

Give us some detail on EXACTLY what you're doing and we can try to help.

 

[Douglas Underdahl]

http://www.youtube.com/watch?v=IhmolBMtDzg

http://www.youtube.com/watch?v=pRicc1HU44c

 

[Andrew Swisher]

Andrew, do you see the focus changing at all as you adjust the back focus? What method are you using? I take you you loosen the adjustment bolt and then turn the entire back focus ring?

I once found that I couldn't get the back focus anything like right on the Red ONE. Turned out the PL mount was installed backwards after being on a Nikon mount for a while! Actually worked, but back focus was impossible until I corrected it.

Give us some detail on EXACTLY what you're doing and we can try to help.

Funny you say that because I had a Nikon mount on it for a while as well. That may be the problem. Is there a link to something that can show me the correct way to install the PL mount to make sure it’s correct?

 

[jimhare]

The big problem is there are two or three different pieces and that can fit together back to front! I happened to have access to another mount that was already in the correct order and orientation so I got lucky.

At a later time I remember doing a number of web searches and found one that showed the correct orientation, which helped with later mount swaps.

Been a few years now so unfortunately can't point you anywhere.

But if you're finding no joy just take off the mount, flip the bit that can be flipped, and see if you can back focus the camera. If it can then this was the problem.

 

[Andrew Swisher]

Got it figured out. Not sure what the hell was going on. Thanks for the help!

 

[moviemach]

my advice:
grabs the 18mm, put the focus on infinity mark, regulates the backfocus of the camera focusing on an object far away.
Then, put the focus on the brand 18mm minimum, and put an object in front of the camera, move the object to the camera until it is at the point of focus, measure the distance between the object and the body backfocus mark of the camera, the distance must be the same than the mark distance on the lens.
Then, do these checks with the 25mm and the 50mm, it should work.
If not, then, are des-collimated optics, but we can not know which one, unless you find two that work well with the collimation, for its focus marcs.
think, that 18 mm will give the maximum precision for backfocus adjustment.

Manuel García.