just Tony wrote:Closing down the entrance pupil also closes down the exit pupil.Here is the wording I should have used:If the entrance pupil is acting as a beam limit then that would also place a limit on the exit pupil, if I can trust what I know about ray tracing.I have to disclose that I assumed that the macro lens in question is unit focusing, not a variable focal length design, about which I don't know much regarding ray tracing. I'm open to learning a subtle technical point if I've missed something.

JimKasson wrote:bclaff wrote:Hard to believe. As the exit pupil is pulled away from the image plane making the physical aperture larger would almost certain just get a hard vignette from the rear lens elements.Ive thought more about this, Bill, and I don't understand your point.Say you have a non-compensating macro lens. You set the focus ring for 1:2. You want f/22, so you set the aperture ring to f/16.Say you have a compensating macro lens. You set the focus ring for 1:2. You want f/22, so you set the aperture ring to f/22.In either case, the diameter of the aperture is one 16th of the lens focal length. I don't see how vignetting plays into the situation.If the compensating lens makes the physical aperture larger then at low f-numbers (like wide open) the aperture might no longer be a stop, the front lens element would be the stop, an no additional light would enter. This would depend on whether or not the entrance pupil position moves sufficiently as you focus closer.This is why I'm hoping to find a patent to enter into the Optical Bench. Then I (we) would have a concrete example to check.Regards

bclaff wrote:JimKasson wrote:bclaff wrote:Hard to believe. As the exit pupil is pulled away from the image plane making the physical aperture larger would almost certain just get a hard vignette from the rear lens elements.Ive thought more about this, Bill, and I don't understand your point.Say you have a non-compensating macro lens. You set the focus ring for 1:2. You want f/22, so you set the aperture ring to f/16.Say you have a compensating macro lens. You set the focus ring for 1:2. You want f/22, so you set the aperture ring to f/22.In either case, the diameter of the aperture is one 16th of the lens focal length. I don't see how vignetting plays into the situation.If the compensating lens makes the physical aperture larger then at low f-numbers (like wide open) the aperture might no longer be a stop, the front lens element would be the stop, an no additional light would enter.Gotcha. I think the mechanism was just a cam biasing the diaphragm setting, so at 1:2, there would be inadequate compensation with set f-stops wider than f/5.This would depend on whether or not the entrance pupil position moves sufficiently as you focus closer.

JimKasson wrote:bclaff wrote:JimKasson wrote:bclaff wrote:Hard to believe. As the exit pupil is pulled away from the image plane making the physical aperture larger would almost certain just get a hard vignette from the rear lens elements.Ive thought more about this, Bill, and I don't understand your point.Say you have a non-compensating macro lens. You set the focus ring for 1:2. You want f/22, so you set the aperture ring to f/16.Say you have a compensating macro lens. You set the focus ring for 1:2. You want f/22, so you set the aperture ring to f/22.In either case, the diameter of the aperture is one 16th of the lens focal length. I don't see how vignetting plays into the situation.If the compensating lens makes the physical aperture larger then at low f-numbers (like wide open) the aperture might no longer be a stop, the front lens element would be the stop, an no additional light would enter.Gotcha. I think the mechanism was just a cam biasing the diaphragm setting, so at 1:2, there would be inadequate compensation with set f-stops wider than f/5.This would depend on whether or not the entrance pupil position moves sufficiently as you focus closer.As I hypothesized:Notice that the slot on the aperture fork is slanted instead of straight. This is necessary so that as you focus your lens closer, the iris opens up. This is a clever trick to compensate for the lost light as the lens gets longer and hence the unofficial nickname of “compensating” that is given to lenses of this type, now you know.https://richardhaw.com/2017/01/18/repair-micro-nikkor-p-55mm-f3-5-auto/Jim, in one of the links you provided earlier someone stated that it's possible to undo the compensation mechanism by swapping those two blades, resulting in the same straight path that is present in my f/2.8 model.