Awcine

to put it another way, a front anamorphic 100mm lens has a cone of light in image space that is vertically a 100mm image, and horizontally a 50mm image. Since a 100mm lens has 4x less depth of field as a 50mm, it will defocus at 4x the rate of the horizontal axis, while the image will be desqueezed at a constant 2x, meaning the further you throw something out of focus, the taller it will get. Conversely, a rear anamorphic 100mm lens has a cone of light in image space that is 100mm vertically and horizontally, and is then squeezed at a constant 2x, so you wouldn’t have the same asymmetric depth of field.

Actually, I am incorrect on this, on older anamorphics the astigmatism is the most prominent feature and you get fatter out of focus points in front of the focal plane and very tall focus points behind, but I believe the correct answer is that the vertical focal length of a 2x anamorphic lens is twice that of the horizontal focal length and that the aperture reflects this if the anamorphic element is in front of the entrance pupil. Say you have a 50mm anamorphic at t2.8, the vertical axis of the aperture is 17.8mm, the horizontal is 8.9. Subsequently the vertical axis will defocus to a greater extent than the horizontal axis. So this then is why you get the vertical stretch and squash when you rack in and out of focus on front anamorphics and not rear (since the entrance pupil is what matters when you are talking about aperture transmission). I will have to do more thinking on rear anamorphics, I was under the impression they still had this stretch, but perhaps that’s just the result of my previous answer, the natural astigmatism that comes with anamorphic photography. I stand corrected on my previous answer, old anamorphics you do get very strong astigmatism which is often more noticeable than the difference stated above, but if you look at modern anamorphics like the master anamorphics that have largely eliminated the effects of astigmatism, you do see them stretch vertically in the foreground as well, it’s just usually not as far out of focus as the background.

All of these answers are wrong... anamorphic lenses are designed to squeeze 2x at the plane of focus, but the anamorphic element squeezes less than 2x in front of the focal plane and greater than 2x past the focal plane. This is why you get stretching and squeezing when you rack focus, anamorphics are essentially controlled astigmatisms. If you rack focus through a point source on an anamorphic lens, it will be a circle when it’s in focus, start to stretch vertically when it’s behind the plane of focus, and stretch horizontally when it’s in front of the plane of focus. We’re just used to looking at out of focus backgrounds a lot more than out of focus foregrounds. all anamorphics have it, front or rear. I haven’t personally done extensive tests on the optical differences between the two, it’s possible rear anamorphics have less dramatic astigmatism (and I would venture to guess more extreme petzval field curvature?)