• Panasonic Cameras

  camera heat and lens focus scale

  Posted by Bruce Greene on November 24, 2005 at 4:47 pm

  I wrote a few days ago but got no response, I think because my post appeared near another thread with similar theme. So I’ll try again.

  I’m the proud new owner of a varicam (model H) and a cine style wide angle zoom.

  Here’s the problem: When the camera is cool (1st 1/2 hour) and the back focus is set, the footage marks are right on. As the camera warms up focus drifts and I re-set the back focus.

  This much I kind of expected. After 2 hours of the camera powered on though, the footage scale shifts by about 5 witness mark thickness. In other words, to focus at 5′ one now has to focus at 4’8″. The focus looks quite good and tracks well from telephoto to full wide, but as the camera gets warm, the footage scale needs a new witness mark for focus by distance.

  Shouldn’t the focus stay accurate when the back focus is adjusted correctly?

  When the room is warm (ie. 85 degrees F) the problem is even a little worse.

  So is the footage scale shift typical of HD zooms, or do I have a lemon lens?

  Thanks all,

  -bruce greene

  PS. Since I made the original post, I’ve been told by someone from the manufacturer that:

  1. There are flourite elements in the lens and they may cause the witness mark for distance focusing to move with the change in temperature.
  2. When the back focus changes on a zoom lens, and the back foucs knob is used to correct this, the telephoto footage markings change as well. I was advised not to use the witness mark on the lens, but to put on a piece of tape and change the witness mark with the change in temperature of the camera/lens.

  So I’d like to hear of all your experiences with this phenomenon. I’m finding that pulling out the focus chart and tape measure is making the director a bit nervous…

  Varicam/Steadicam Owner
  Los Angeles, CA
  http://www.brucealangreene.com

  Bruce Greene replied 20 years, 5 months ago 2 Members · 2 Replies
• 2 Replies

• 

  Rodrigo Lizana

  November 25, 2005 at 6:46 pm

  Congratulation on your Varicam. Is a great camera and I still remember when i got mine. I was so excited. As for your lens issue I can tell you that I have experience the same thing with my zoom and as far as I understand it
• 

  Bruce Greene

  November 26, 2005 at 6:24 am

  Rodrigo, I’m using the Fujinon 4.5-59mm cine style zoom. I have actually been pretty impressed by the quality of images from the lens and that 4.5mm is really wide!

  -bruce

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