How often do you tweak the back focus?

B

Brad Neal

Well-known member
Those of you shooting with the 500's, how often do you check the back focus?

It is recommended to check it each time you change the lens, after extreme temperature changes, after transporting, etc.

I have been trying to stick with the recommendations but have really never noticed either of my cameras shifting out of alignment.

-Brad
 
At lens changes and when there are wide swings in weather conditions from hot to cold.

e
 
I've heard that for years, since I started using video cameras regularly in the early 80's.

What no one has ever successfully explained to me, though, is why, given the same varying weather conditions, I never have to readjust the back focus on my film camera lenses... The zoom lenses I use for super16 and 35mm cameras are adjusted by an optical technician who actually inserts shims in the back of the lens and - obviously - that is not something I'm going to do when I get off the plane in DC...

I have, for my own amusement, set the back focus of the Fujinon on my HPX500 and have never touched it again, without any noticeable image degradation.. And I've shot over 100 hours of material in LA, NY, SF, Boston, and Atlanta.

Now, admittedly, if I was traveling to the tropics I would probably check it out of paranoia...
 
Its worth a check every time you set-up. If there needs to be an adjustment, its WAY better to do it before you shoot than to see a days footage ruined. Just make a habit of checking it, it only takes 30 seconds.
 
Hunter; believe me, I'm not arguing with you, but in my experience (I worked for network news - shortly - in another life) many people actually screw it up when they re-adjust ANYTHING... If you know what you're doing and have the time and place, do it for peace of mind - but if there's any doubt, shoot a test first.

Where the problem becomes most noticeable is at infinety with the lens fully wide... Shoot something - zoom in, focus, zoom out - and look at it on a good monitor (one of the essentials and not, unfortunately, always available in the field). If it looks soft at infinety but sharp when zoomed in - in other words the focus is shifting during the zoom - read the manual again and do what it says.

I shoot documentaries - not "run and gun", I dislike that phrase because I usually spend more time waiting with the camera in my lap than running and gunning - but neverless situations where dicking with the camera may not be possible. I do check my footage regularly and have my AC , who has better eyes, check everything regularly as well.

Old Volkswagon adage - "if it works, don't fix it".
 
I have shot 2/3rd inch chip cameras for 25 years. Once I set the back-focus on a lens for my camera, I never have to set it again. I've shot in extreme weather. Are you going to let the camera warm-up or freeze-up, and then take off the lens in those conditions?,,,,,no.


JohnnyD



I
 
In digital cinema, you're changing glass a lot more often than you would in a documentary or news situation. I always have a pie / backfocus chart in my AC kit and definitely when I'm operating.

On the last feature I AC'd, we had the good fortune of having a SharpMax in the kit from Panavision. We would check those lenses a few times a day for drift because the F900 lens mounts are notorious expansion/contraction wanderers. Anyway, maybe the old cold B4 cameras don't drift, but the digital cinema stuff does for real. Regular collimation is good, simple practice and excellent insurance toward keeping your job in the camera department.

SharpMax... talk about sexy. If you have the means, I highly recommend picking one up.

e
 
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