dclark wrote:
Many of the comments about focal length are not correct. You need to learn about focal length, FOV, and focus breathing. A well designed lens will have a constant FOV as it focuses between infinity and its MFD (i.e. no focus breathing). That means it will not have a constant focal length. For example, the 600/4 focused at 6.0 meters does not have a focal length of 600mm, which is good.
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Choderboy wrote: dclark wrote:
Many of the comments about focal length are not correct. You need to learn about focal length, FOV, and focus breathing. A well designed lens will have a constant FOV as it focuses between infinity and its MFD (i.e. no focus breathing). That means it will not have a constant focal length. For example, the 600/4 focused at 6.0 meters does not have a focal length of 600mm, which is good.
Assuming TDP results have been accurately measured, at 10m shooting distance,
the 600 f4 has a longer focal length than the 200-600 zoom, at 600mm.
I assume you agree with that statement?
TDP measurements: (9920mm and 9491mm being shooting distance required to fill the frame with the same target)
Sony 600 4
600mm x 400mm Target:
600mm = 9920mm
Sony 200-600
600mm x 400mm Target:
600mm = 9491mm
I do not agree with that statement.
I agree that the FOV of the 600/4 is narrower than the FOV of the 200-600 at that distance.
I do not know where the principle plans and nodal points of the lenses are so it is unclear how the focal lengths compare.
Operationally I care about the FOV not the focal length. I want the FOV to remain constant regardless of focus distance.
This is off topic for this thread, and has been discussed in prior threads, Thread 1, Thread2.
Feb 04, 2025 at 12:08 PM
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