Focal Plane Mark??

[MichaelA]

Doing some repetitive talking heads interviews and having to get an accurate measure from talent to camera. Other cams I have have a focal plane mark, pin, or other reference. Does the DVX?? I thought it did, but now I can't seem to find one! Been measuring back to the leading edge of the vertical carbon fiber trim on the left side for consistency, but heck... shouldn't there be a mark?! I guess it's a bit academic, but even my old 70D has it.

 

[JPNola]

I found several sources online saying that you measure from the front of the lens when using zoom lenses like that of the DVX200-


"With ENG lenses, you measure from the front of the lens."

http://www.theblackandblue.com/2011/04/25/focus-measurements/

"Professional video uses the front of the lens as the measurement point, not a marking on the body. Unless it's a special type of lens like a DigiPrime.

Even the EX1, which has a focal mark on the body, doesn't use it -- you still measure from the front of the lens."

http://www.dvxuser.com/V6/showthread.php?123851-HVX200-Focal-Plane




https://books.google.com/books?id=VbA5VEbgMKAC&pg=SA4-PA90&lpg=SA4-PA90&dq=camera+assistants+distance+measure+plane+front+of+lens&source=bl&ots=R7vvyylN5F&sig=JkcJzpHYVCwznESLu11G5EXdZl8&hl=en&sa=X&ved=2ahUKEwj7uMPF86fdAhWIx4MKHRPyDggQ6AEwDXoECAIQAQ#v=onepage&q=camera%20assistants%20distance%20measure%20plane%20front%20of%20lens&f=false



This is the first I've heard of this. But both David E. Elkins [ quoted in the screen-grab ] and Evan Luzi [ of "The Black and Blue" blog ] are highly knowledgeable and highly experienced.

 

[MichaelA]

Thanks so much for the informative reply and links! I am always grateful when those with so much more experience than I share it in a response, and always learn something new from it. Thanks again!

 

[JPNola]

I am curious as to why those sources recommend to measure from the front of the lens and not from the sensor, when the lens is an "ENG zoom". Why for an "ENG" zoom and not also for a "cinema" zoom? None of the sources go into detail as to why they recommend measuring from the front of the lens. This is the first I have heard of this. If anyone with knowledge of lens design / concepts of measuring for focus as it relates to lens design cares to chime in here, please do.

I found yet another source online recommending to measure from the front of ENG or "video" zooms, from the "nodal point". But again, no explanation as to exactly why:

http://www.cinematography.com/index.php?showtopic=27419

My best guess after reading what the sources have to say is that the reason is that witness marks for distance on ENG lenses are measured from the front element of the lens, not from the focal plane, and as a result-if pulling focus using the witness marks on the lens- you measure distance from the front element. That's the only explanation that makes sense, at least.

 

[MichaelA]

I think many of the early ENG cameras didn't have a mark due to their intended use. Rapid deployment, shoot while you can, etc. with little or no time to rig up a shot and take a measure from subject to camera. They sort of went down a separate evolutionary path for a while from "cinema" cameras and are now merging back together. I guess I'm old school in wanting to measure from a mark, but I try to be consistent. The references of measuring from the front of the lens probably came out of necessity; one needing to measure requires a fixed datum and that is an easy and fixed one to reference. But still, one would think the manufacturers would acknowledge that modern camcorders, be they aimed at ENG, cinema, or whatever will find their products appealing to many cross market users and the occasional need to measure will arise. Not a deal breaker, but a curious discovery of its omission on the DVX which has been a great camera for me.