Welcome to our community

Be a part of something great, join today!

Log in
  • Hey all, just changed over the backend after 15 years I figured time to give it a bit of an update, its probably gonna be a bit weird for most of you and i am sure there is a few bugs to work out but it should kinda work the same as before... hopefully :)

Back Focus Level Marking?

Brook Willard said:
It's plastic... focus hook set.

It is pretty astonishing that there's no witness mark on a camera like this... but you win some and lose some. Use tape for the time being and a dremel later. :)

Putting a screw in the front tapped hole on top of the camera will give you approximate focus readings - to within about 1/4". Don't tape out charts to that measurement, but it's close enough for most on-set work.
Click to expand...

It is not plastic... it is machined aluminum.

Jim
 
The REDONE is a loss leader...

The REDONE is a loss leader...

Jannard said:
It is not plastic... it is machined aluminum.

Jim
Click to expand...

The REDONE is a loss leader... he's losing money on every one - but gonna make it up on the focus hooks. :)
 
Brook Willard said:
It is pretty astonishing that there's no witness mark on a camera like this... but you win some and lose some. Use tape for the time being and a dremel later. :)
Click to expand...

Before anyone takes a dremel to their camera...

Is it possible that a sensor upgrade might cause a shift in the focal plane due to a change in sensor design? If this be the case, switching out a focus hook would probably be a little easier than "switching out" a witness mark ;-)
 
We are going to add a witness mark in future cameras. There is no downside to a dremel mark except a permanent blemish. How about a piece of this yellow tape until your focus hook shows up?

Jim
 
Jannard said:
We are going to add a witness mark in future cameras. There is no downside to a dremel mark except a permanent blemish. How about a piece of this yellow tape until your focus hook shows up?

Jim
Click to expand...

Thanks for clearing that up, Jim. So, would you define #793 as a "future camera?":usd:
 
Yes it is... It's been there since camera #700 or so.
 
REDTeam,
Thanks for getting the witness mark on.
 
RED ONE back focus measurement.

RED ONE back focus measurement.

:sarcasm:
chuck colburn said:
Might be better to remove the PL mount and with a micrometer measure the distance from the lens seat to the back of the mount where it mates to the camera body and subtract that from 52mm. That will put you in the ballpark but it will not count the distance that the optical filter affects the flange focale depth (appx. 1/3 the thickness of the filter). But it will be close.
Click to expand...

Chuck, I have been very busy and just saw your reply to my post. If you are satisfied with the back focus at the lens flange and trust that the factory adjustment is correct, the method of measurement will be correct (yours or mine). Yes, a micrometer can be used but many operators do not have one, so a metric tape or ruller will do. A skilled camera or lens technician will have no problem removing the PL lock ring but others may struggle a little. There is a set setscrew under one of the lockring ears (in open position at 2 o'clock).Take the two retainer allen screws (2 mm allen wrench)out and remove the lock ear. You will notice a set screw, loosen this setsrew (1.5 mm allen wrench) but do not completely remove it. You should be able to turn the PL lockring about 1-1/3 turns counterclock wise and the ring comes off at about 10 o'clock. Now put a staight endge accross the PL mounting flange and measure the straight edge side back to 52 mm, this is your 52 mm image plane distance (in air distance is more than 52 mm but that is what Chuck meant - refractive index of glass-OPLF filter,sensor cover glass and lensletts.....). When the factory sets the back focus all the glass is taken into account. You can put a white tape on the approximate area so that you can indicate the image plane mark. Then proceed to reasemble the PL mount lock ring in reverse. Make sure that you do not bottom out the 1.5 mm set screw, it only needs to go deep enough to act as a stop in the stop slott. Again, you need to trust the flange setting at the factory (our camera was near perfect - index mark and wittness mark matched within the marks) and you can verify the footage mark with a known good lens with your just scribed mark. Permanent marks can be made after that. Of course all this is best performed by an experienced camera or lens technician. As for the hook position, our camera is almost perfect where marked according to the picture on this post......

I have taken pictures of this measuremnt seequence and will post them if anyone is interested.

Sorry about this loooong delayed comment to your post Chuck.

CAMERA DOCTOR
 
You must log in or register to reply here.
Back
Top