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According to AC Magazine April 2020 edition " The Pupil Marks the Focus Spot The next thing to understand about the entrance pupil is that it is at that point — not at the film plane (or sensor plane) — from which focus should be measured. It’s a long-standing practice in cinematography to take focus measurements from the film or sensor plane of the camera. " (read the attachment) Well, the topic seems to be fine and interesting but, the basic question is never raised nor answered - WHY FOCUS SHOULD BE MEASURED FROM ENTRANCE PUPIL? Can some one explain these : 1) Do all of the points of light from the scene converge to a single point at the entrance pupil and then expand back out to the image plane ? 2) What role does exit pupil play in measuring focus ? 3) Can Iris be located not at aperture stop ? 4) How is DoF related to entrance & exit pupil ? And please provide a reference website or material to understand these technical concepts clearly. Thanks, Ram Nanda.

According to AC Magazine April 2020 edition " The Pupil Marks the Focus Spot The next thing to understand about the entrance pupil is that it is at that point — not at the film plane (or sensor plane) — from which focus should be measured. It’s a long-standing practice in cinematography to take focus measurements from the film or sensor plane of the camera. " (read the attachment) Well, the topic seems to be fine and interesting but, the basic question is never raised nor answered - WHY FOCUS SHOULD BE MEASURED FROM ENTRANCE PUPIL? Can some one explain these : 1) Do all of the points of light from the scene converge to a single point at the entrance pupil and then expand back out to the image plane ? 2) What role does exit pupil play in measuring focus ? 3) Can Iris be located not at aperture stop ? 4) How is DoF related to entrance & exit pupil ? And please provide a reference website or material to understand these technical concepts clearly. Thanks, Ram Nanda.

Hey y'all. Currently I am working on a Cine Lens Database to be able to provide free lens "data points" to the public. There's a lot of great information out there and the best DBs I found where these. https://www.fdtimes.com/2011/05/06/motion-picture-lens-database/ http://www.cinelensdb.com/ http://forum.mflenses.com/the-macrolenses-database-t78420.html Right now most of my work is filling in the gaps of Richard Bradbury's DB. It looks like not much has been updated in it since 2011. I reached out to him and cinelensdb.com, but no one got back if they were interested in continuing to update their projects. Currently I think it is a really good idea to attach these lenses with their respected "tech sheets" or "product brochures" in the excel I'm working on. Right now I need help finding the number of iris blades in the Ultra 16 set, as well as the entrance pupil sizes. I have linked the ARRI Ultra 16 Technical Details for all whom would like them. I have reached out to Zeiss, whom told me to contact ARRI for the missing data. I then reached out to ARRI, who told me to reach out to Zeiss. I'm thinking about reaching out to some lens servicing companies for the remaining data, however I think that might be a waste of time for a skilled technician to answer my email. Let me know what you think. THANK YOU FOR YOUR TIME!!!!