- #1
peter.ell
- 43
- 0
Hi there, I understand somewhat how diffraction works in terms of the aperture of a camera lens and the resulting loss in resolution in the image, but my question is:
Is the degree of diffraction only dependent upon absolute aperture size, or the size of the entrance pupil? For example, f/22 shows noticeable diffraction with a wide-angle lens where the size of the aperture is, say, 1mm. But if I keep the f/22 but change the focal length to get longer on a zoom lens with a constant f/stop (it does this by magnifying the size of the entrance pupil to compensate for the longer focal length, essentially just a magnified virtual image of the aperture), then would I get less or the same amount of diffraction? I would guess it must be the same, but since the light passes through the 1mm aperture as if it were larger, perhaps there would be less diffraction?
Also, how is it that simply having a magnified virtual image of a small aperture give the same exposure as an aperture that is bigger? Why doesn't light just respond to the actual size of it?
And one more: I heard that diffraction in camera lenses is always present, but just begins to occupy a greater percentage of the total light hitting a sensor when the aperture is small. If this is true, then why is the airy disk smaller at larger apertures? Isn't diffraction just due to passing by the aperture blades, thus a larger aperture should either have the same sized airy disk or more since light would diffract over a greater area on a wider aperture?
Thank you so much or the enlightenment (pun intended).
Is the degree of diffraction only dependent upon absolute aperture size, or the size of the entrance pupil? For example, f/22 shows noticeable diffraction with a wide-angle lens where the size of the aperture is, say, 1mm. But if I keep the f/22 but change the focal length to get longer on a zoom lens with a constant f/stop (it does this by magnifying the size of the entrance pupil to compensate for the longer focal length, essentially just a magnified virtual image of the aperture), then would I get less or the same amount of diffraction? I would guess it must be the same, but since the light passes through the 1mm aperture as if it were larger, perhaps there would be less diffraction?
Also, how is it that simply having a magnified virtual image of a small aperture give the same exposure as an aperture that is bigger? Why doesn't light just respond to the actual size of it?
And one more: I heard that diffraction in camera lenses is always present, but just begins to occupy a greater percentage of the total light hitting a sensor when the aperture is small. If this is true, then why is the airy disk smaller at larger apertures? Isn't diffraction just due to passing by the aperture blades, thus a larger aperture should either have the same sized airy disk or more since light would diffract over a greater area on a wider aperture?
Thank you so much or the enlightenment (pun intended).