Re: telecentric question

Dom Jaeger

On Wed, Feb 27, 2019 at 07:09 AM, Matthew Clark wrote:
2. The position of the aperture ring has seemingly changed position over time from older style lenses to newer style lenses. The first example that comes to mind is the Zeiss Standard Speed T2.0 lens set that had the aperture on the end of the lens while the newer version in the Ultra Primes has it inboard. How does the position of the aperture effect telecentricity? In newer designs with a bigger mount, will we see the aperture go towards an outboard position to give us better performance? Why did lens designers change up that aperture position from outboard to inboard?
The position of the external aperture ring has no bearing on the position of the actual iris inside. Many older lenses (like Zeiss Standards and Supers) followed an earlier vogue for having the aperture ring in front of the focus ring, nowadays it's more or less a standard to have it back near the mount. In all cases, the actual iris is activated by an intermediate mechanism - a barrel or a rod or both - that is seperate to the outer ring and often allows for the iris to mechanically shift forward or back with the optical block as the lens is focussed.

On Wed, Feb 27, 2019 at 07:17 AM, Merritt Mullen wrote:
I’m still curious if all digital cinema cameras use micro lenses on their CMOS sensors.
As far as I'm aware, they all do. Even cameras like the Sony A7RIII which has a Back Illuminated (BSI) sensor advertises a gapless on-chip microlens array in its promotional material. It seems there is always a gap between the photodiodes, and microlens arrays are needed to capture some of that lost light. Some arrays on larger sensors offset the microlenses at the edges to accomodate steeper angles of light, or change their shape to be more parabolic. It's hard to find this info about the high end cinema camera sensors though.

It should be mentioned that few lenses advertised as telecentric are truly so, they are usually near-telecentric. An image-space telecentric lens has its exit pupil (the image of the aperture seen through the back) at infinity. I've never seen a lens like that. Most of the modern lenses I've seen that are designed for digital cinema cameras have an exit pupil about 2 to 4 inches behind the rear element, which seems to be enough. There's also the fact that people have been using terribly non-telecentric lense like Cooke Speed Panchros on digital cameras and creating amazing imagery, so it's not always essential.

Dom Jaeger
Lens Technician
Panavision Melbourne

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