Microcollimation issues with Brevis

robmneilson

robmneilson

Veteran
To Dennis, and other Brevis users.....

I've just completed production on a feature film I've been working on for quite awhile. We did a two week cross country drive, and the rest of the time have been shooting off and on during weekends in NY.

It seems to me that nearly every week I'm resetting the microcollimation despite using the same lenses and mount.

What could be the issue regarding this? Two shoots ago I set it with an 85mm @ 10 feet and the focus was perfect....and then the last shoot I set up a shot and everything is out of whack with the same lens.

We were shooting in the cold however...could that be a reason to make the microcollimation breathe?

Could it be the vibration while its in the camera case in the car?

Much of the time I've been holding the camera on my lap while we drive to a different location (since ours is a road film) could that be the cause?

That's pretty much the only two excuses I could come up with for this constant change in backfocus.

However this is small change since its basically the ONLY problem I've had with the Brevis during the past year of shooting...but Id still like to know.

thanks!
 
Also my director just asked me why don't we tape down the microcollimation ring. If I did that is there any way that could damage the unit?
 
Rob, it is indeed the first issue of this type I've seen reported. Normally the micro-collimation ring is used to seat the lens mount perfectly square and at the right distance, only while securing the lens mount in place...after that it should not be movable unless you loosen it. If it is moving, there must be something else going on. We could do a quick SKYPE session with video and go over it with you. Just give us a call during business hours to set it up....the software is free, and it would only take 5-10 minutes to go over everything.
 
Thanks very much Dennis....We're renting out our HVX for a friend until Jan 20th. Id assume that I should wait until we have that back to do a skype session, however if this would work with just the Brevis unit that would be great as well...
 
Where would you put the tape?
You could mark the position of the microcollimaton ring with a pen. Next
time your collimation is off, take off your mount and check if the ring has moved.
If not, the problem is somewhere else.

If things are in focus that are farther away than the distance you set your lens, the lensmount is too far out.
It's unlikely, but vibrations and a heavy lens could theoretical cause that. If you travel, take off the lens.
 
I'll actually mark with a pen next time, sometimes the simplest solutions are the first things overlooked.

Several times I had a Nikkor 35-135 on the brevis inside the kit, but this last time I had not. I'll def. mark with a sharpie on our next shoot, that way I can show some slippage to Dennis and prove that its not a figment of my imagination. It was just way off this past weekend. I had a subject six feet away from an 85mm lens and he was sharp at 15 feet on the lens.
 
Have you ever opened your brevis? If the carbon-tube is somehow loose
on the back of the brevis, your collimation will change.
 
Dennis Wood said:
Rob, it is indeed the first issue of this type I've seen reported. Normally the micro-collimation ring is used to seat the lens mount perfectly square and at the right distance, only while securing the lens mount in place...after that it should not be movable unless you loosen it. If it is moving, there must be something else going on. We could do a quick SKYPE session with video and go over it with you. Just give us a call during business hours to set it up....the software is free, and it would only take 5-10 minutes to go over everything.
Click to expand...

Thread hijack! :Drogar-BigGrin(DBG)

http://www.dvxuser.com/V6/showthread.php?t=155146

Dennis, at your earliest convenience, please have a look at that and then contact me. :dankk2:
 
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