DIY Video Tap

[Phil Rhodes]

I have an FDM printer; if anyone needs anything done in the UK, more than happy to oblige.

[Gregg MacPherson]

On 12/12/2023 at 12:01 PM, Geffen Avraham said:

Hey, I'm curious to know more about this. For the types that fit between VF and camera, how do they get a beam splitter and sensor in so thin? And wouldn't you need a rather high ISO?.......

As an example, the AZ Spectrum ACL taps are inside a box about 19.5mm wide. This displacement of the VF doesn't really affect operating, and there is room for the beam splitter and camera inside. I assume the camera is like a lipstick camera oriented longitudinally. Little beam splitters, triangular prisms with a partially silvered surface that will deflect, say 20% into the tap camera, are cheap on eBay.

I once tried removing an AZ Spectrum tap from the optical path of an ACL (with big Kinoptik VF) and found that the eyepiece diopter adjustment was unusably out of whack. Memory is hazy, but I don't think simple shimming fixed it. I asked Paul Scaglione and Andrjez if they made optical mods to the ACL VF when installing the vid tap, like adding a neg diopter, but I never got a definitive answer. Weirdly, I think I tried the same thing with a camera having the Ang orientable finder, and did not have that problem.

If you use a 20mm VF displacement as a start point, you could test your VF eyepiece diopter adjustment with a crude 20mm shim. It will show if optical adjustment is needed. There is room at the camera end of the VF to add a neg diopter element, but I wondered if the pro techs just shift the existing  optical elements at that end.

I like the idea of a tap that replaces the optical VF for steadicam, jib arms etc, but I'm not excited about plural remote monitors or focusing off the monitor. A lot of focusing can be done with the optical eyepiece, and most carefully controlled shots used to be at  measured focus.

Gregg

Edited December 18, 2023 by Gregg MacPherson
more words

[Gregg MacPherson]

31 minutes ago, Gregg MacPherson said:

... a partially silvered surface that will deflect, say 20% into the tap camera.....

Sorry, hasty language...I meant reflect, not deflect...

[Geffen Avraham]

On 12/18/2023 at 12:13 PM, Gregg MacPherson said:

 like the idea of a tap that replaces the optical VF for steadicam, jib arms etc, but I'm not excited about plural remote monitors or focusing off the monitor. A lot of focusing can be done with the optical eyepiece, and most carefully controlled shots used to be at  measured focus.

Gregg

Thank you! I will try something like that!

I think the true solution to focusing film cameras is with some kind of depth/ToF camera. There is a company now selling a $24,000 "AI focus" solution, but I think it can be practically replicated for under $2,000 with an OAK depth camera and a Jetson Nano.

They also have IR illumination, so they will work in total darkness. If you can calibrate one, you can start with a truly accurate focusing assist screen, and the added Jetson will let you pick objects and lock onto them, if you can get it to control a Tilta motor.