can't achieve focus on Letus Extreme with PL mount ?

doondoon

doondoon

Well-known member
I haven't been able to achieve consistent focus with the EX1/Letus and PL mount. Infinity focus was never achieved.

Wider lenses were especially difficult. 18, 25, 35 - It was strange, you could get focus at about six to eight feet, but beyond that nothing.

Longer focal lengths seemed to work ok..

I know many people have had success with this set up. Any suggestions?

The ground glass was sharp, and we had all the latest EX1 pieces from Letus and Zacuto.

My gut is that the back focus is off... but I haven't been able to get tech support at Letus to call me back and there is no real documentation on how to achieve accurate and repeatable back focus (at least that I'm aware of).

Anyone? Phil Bloom maybe?

thanks.:huh:
 
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Michael if you want me to set your backfocus here in LA I can do so for you.

=P You'll just have to respond and set up a time.

However, Backfocus off or not, the focus shouldn't change each time you go to use the unit. If it's off it's simply off.
 
The PL mount distance from flange to the surface of the GG should be 52mm and tolerance for error is much less than for SLR lenses. The first place it shows up is with your wide lenses that may not be able to achieve any sharp focus, and then at ininfity with your longer lenses. Check the clip "Collimation - 35mm SLR and Cinema Lens Setup " over at the Cinevate University at http://www.cinevate.com/website/index.php/videouniversity. Our mounts are a bit different in that we have a micro-collimation system built-in, but I suspect your PL mount must have some fore aft adjustment. Either way, same principle.

Cheers,
Dennis Wood
 
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