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I've been shooting for 10 years and didn't know this at all!! I just saw a photo of a lens mounted in reverse and my mind is blown. Time to go down a rabbit hol

by ksml 5y ago

I've been shooting for 10 years and didn't know this at all!! I just saw a photo of a lens mounted in reverse and my mind is blown. Time to go down a rabbit hole trying to understand why this works...

paulmd 5y ago
lenses pass light in both directions, if you flip it around then it bends the light the opposite way ;) http://hyperphysics.phy-astr.gsu.edu/hbase/geoopt/image.html#c1 http://hyperphysics.phy-astr.gsu.edu/hbase/geoopt/image.html... the lens is designed to take rays traveling from optical infinity, and converge all those rays at a focal plane that's (eg) 30 millimeters away, right? well, if you flip the lens around backwards, then it will send out rays towards optical infinity from a focal plane that's 30mm away... which is what a macro lens is. in fact in the old days people used to use their camera as an enlarger to expose their negative onto prints. The theory was that using the same lens that took the image in reverse would help to correct the abberations of the lens... I am not sure that's actually supportable compared to using a real enlarger lens that's optimized for high-magnification work but it's a neat theory, and possibly better than just using a random crap enlarger lens ;) now if you really want to have fun... ever wonder why diffraction makes your image softer at smaller apertures? ;) https://www.cambridgeincolour.com/tutorials/diffraction-photography.htm https://www.cambridgeincolour.com/tutorials/diffraction-phot...
michrassena 5y ago
Are you also familiar with extension tubes? I think in both the reversed lens and extension tube the lens sits further from the film or sensor (focal plane). Somewhat counter-intuitively, at least for me, is when the lens is focused at infinity, it's at its closest point to the focal plane. Moving it further from the focal plane focuses closer.

by ksml 5y ago

paulmd 5y ago

lenses pass light in both directions, if you flip it around then it bends the light the opposite way ;) http://hyperphysics.phy-astr.gsu.edu/hbase/geoopt/image.html#c1 http://hyperphysics.phy-astr.gsu.edu/hbase/geoopt/image.html... the lens is designed to take rays traveling from optical infinity, and converge all those rays at a focal plane that's (eg) 30 millimeters away, right? well, if you flip the lens around backwards, then it will send out rays towards optical infinity from a focal plane that's 30mm away... which is what a macro lens is. in fact in the old days people used to use their camera as an enlarger to expose their negative onto prints. The theory was that using the same lens that took the image in reverse would help to correct the abberations of the lens... I am not sure that's actually supportable compared to using a real enlarger lens that's optimized for high-magnification work but it's a neat theory, and possibly better than just using a random crap enlarger lens ;) now if you really want to have fun... ever wonder why diffraction makes your image softer at smaller apertures? ;) https://www.cambridgeincolour.com/tutorials/diffraction-photography.htm https://www.cambridgeincolour.com/tutorials/diffraction-phot...

michrassena 5y ago

Are you also familiar with extension tubes? I think in both the reversed lens and extension tube the lens sits further from the film or sensor (focal plane). Somewhat counter-intuitively, at least for me, is when the lens is focused at infinity, it's at its closest point to the focal plane. Moving it further from the focal plane focuses closer.