Timeline for Does field of view change for different lens model for the same focal length?
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| Feb 28, 2019 at 22:31 | comment | added | relatively_random | @rackandboneman And in both systems, breathing can be compensated for. In order to do it with a unit lens, though, the focusing mechanism would need to move both the sensor and the lens at the same time. I don't know if such systems are used in practice. | |
| Feb 28, 2019 at 22:26 | comment | added | relatively_random | @rackandboneman Yes, both methods of focusing an imaging system can produce field of view changes or breathing. But that doesn't necessarily mean that the focal length is changing. In fact, a unit lens can't change its focal length by definition. Breathing there can only possibly be caused by changes in relative distances between the object, the lens and the sensor. | |
| Feb 28, 2019 at 22:23 | comment | added | rackandboneman | @relatively_random does field of view change when moving a unit-focusing lens into focus or does it not? | |
| Feb 28, 2019 at 22:15 | comment | added | relatively_random | @rackandboneman An internal focusing lens, on the other hand, doesn't rely on this movement to focus the imaging system. It provides a mechanism for changing the optical characteristics of the lens itself so that the image moves towards the sensor. Since the lens itself gets modified and not just moved around, focal length (in other words: light-bending power) can change. | |
| Feb 28, 2019 at 22:04 | comment | added | relatively_random | @rackandboneman Focal length or focal distance is a property of the lens, not the imaging system. It is a measure of how strongly the beams of light get bent by the lens. A unit lens doesn't have a mechanism for changing this focal length so an object at a fixed distance from the lens creates a sharp image at a fixed distance on the image side. If you want to focus that kind of an imaging system, you need to put the sensor at that exact distance from the lens where the sharp image is. This is usually achieved by a built-in mechanism that moves the entire lens relative to the sensor. | |
| Feb 28, 2019 at 8:36 | comment | added | rackandboneman | An internal focusing lens on a shelf would also only be focused on anything at all if there was a sensor, film, or screen? Or are you using "focused" to mean "a focusing distance has been dialed in that would result in focus if there was anything at the focal plane"? | |
| Feb 27, 2019 at 22:57 | comment | added | relatively_random | @rackandboneman "the focal plane moves further away from the focal point, and this has a bearing on field of view" Yes, but this has nothing to do with focal distance, which is a property of the lens itself and doesn't change if you move the lens forwards, backwards, sideways or put it on a shelf. | |
| Feb 27, 2019 at 21:09 | comment | added | rackandboneman | It literally does - the focal plane moves further away from the focal point, and this has a bearing on field of view too.... | |
| Feb 27, 2019 at 18:17 | comment | added | relatively_random | @rackandboneman By definition, unit focusing lenses don't change when focusing. All optical elements move as one fixed unit. So focal length can't change. What does change, if you keep the camera body fixed, is the distance between the object and the lens. So the focal length is not changing, you're just effectively moving closer towards the object when you focus closer. | |
| Feb 26, 2019 at 22:22 | comment | added | rackandboneman | Also, the opposite is true for unit focusing lenses - their focal length increases when you focus closer. Calibrated focal length regardless of focus is what makes cine grade lenses so godperished expensive (probably a balancing combination of internal and unit focusing in these)..... | |
| Feb 26, 2019 at 21:08 | history | answered | xenoid | CC BY-SA 4.0 |