Focus Pulling on a Panasonic Varicam with One Zoom Lens

[stelo]

Hi everybody
I am an Italian focus puller and I am approaching my first job with the Panasonic Varicam. It's a very low budget film and I will have just one zoom and no lenses. The only thing that worries me is about the back focus of the zoom: is it so easy that it goes out of focus? (this is my second day of camera test and I touched it twice!!) Does the back focus uncorrect influence the depth of field too: is it possible that if the focus is good in tighter and wider position I have a reduced depth of field?
I tried to put my target at 3 mt, the zoom seems in focus always (tight and wide) but it seems that even on 7,5 mm lens position there is not so much focus near the lens.
Does anybody can suggest where I can find the HD lenses and zoom depth of field tables?
Thank you very much for any suggestion

 

[Ale Reynoso]

Hi: I couldn´t understand all of your explanation.
What "not so much focus near the lens" mean?
First, you should adjust your back focus with a proper chart (i.e. Siemens star) WIDE OPEN, so the adjustment is more precise: focus the chart in the tele end, open to wide angle, DON´T TOUCH the focus ring, then unlock and adjust the focus in the chart with the back focus ring. After it, lock it (which lens are you using?)
Then it should remain fixed and adjusted, unless the camera shoots in places with radical changes in temperature (check out this issue in cinematography.net) or the lens is changed.
When the back focus is not adjusted, you can have focus in your target, meters away from the camera in tele position, but when you change the focal length to wide angle, the focus is missed. In fact it is shifted towards the camera, as if you were engaging the macro (you could notice macro and back focus share the same ring).
If you cannot perform back focusing, or you are missing it during the day, perhaps the lens is damaged.

I cannot remember where, but I think I read in some place that for HD, the depth of field is the 35mm D.O.F. (with the same angle of view that 2/3 video) closed 2 1/2 stops.
i.e D.O.F of a 22mm at f5.6 (2/3 HD video) is the same D.O.F. that a 50mm at f2 1/2 (35mm film).
So you can convert available 35mm DOF tables. For SD the DOF is greater.

Check this out



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