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DoF has little to do with how big the lens is (unless that’s your way to say large aperture, but you can have 1.8 with small lenses too). But it has some to do

by rimliu 8y ago

DoF has little to do with how big the lens is (unless that’s your way to say large aperture, but you can have 1.8 with small lenses too). But it has some to do with how large the sensor is.

dboreham 8y ago
Perhaps you should think about how f-number is defined? https://en.wikipedia.org/wiki/F-number https://en.wikipedia.org/wiki/F-number Then read up on depth of field : https://en.wikipedia.org/wiki/Depth_of_field https://en.wikipedia.org/wiki/Depth_of_field It should be clear that DOF has everything to do with the physical size of the lens because aperture for a given focal length defines the front element diameter. Your example very small f1.8 lens has to have a very small focal length and therefore deep DOF. Edit : found the math I was looking for : https://en.wikipedia.org/wiki/Depth_of_field#Use_of_absolute_aperture_diameter https://en.wikipedia.org/wiki/Depth_of_field#Use_of_absolute...
- rimliu 8y ago
  Did you miss the part where I introduced F-number into discussion instead of the lens size? What do you think will happen to DoF when I take my huge 70-200 and close it down to 22?
  - vortico 8y ago
    In that case the aperture diameter will decrease. f-number does not directly affect depth of field, except through the aperture diameter.
    - rimliu 8y ago
      F-number describes the aperture diameter, it has no way to affect anything. The same as meters do not affect the distance. However, when you close the aperture on the large lens, the lens still stays large. That was exactly my point: it is about aperture, not the lens size. I get what you say about physically larger lenses having larger apertures in absolute dimensions, not the ratio, however that does not help smartphones, because of the distance of the focal plane and the sensor size. And this where the limiting factor is.
      - vortico 8y ago
        This discussion is about shallow DoF. You cannot have shallow DoF with a lens with a small aperture diameter. Both the aperture diameter and sensor must be large.
vortico 8y ago
With everything else constant (f-number, sensor size, magnification, etc), increasing the aperture diameter will increase the circle of confusion and therefore decrease the depth of field.

by rimliu 8y ago

DoF has little to do with how big the lens is (unless that’s your way to say large aperture, but you can have 1.8 with small lenses too). But it has some to do with how large the sensor is.

dboreham 8y ago

Perhaps you should think about how f-number is defined? https://en.wikipedia.org/wiki/F-number https://en.wikipedia.org/wiki/F-number Then read up on depth of field : https://en.wikipedia.org/wiki/Depth_of_field https://en.wikipedia.org/wiki/Depth_of_field It should be clear that DOF has everything to do with the physical size of the lens because aperture for a given focal length defines the front element diameter. Your example very small f1.8 lens has to have a very small focal length and therefore deep DOF. Edit : found the math I was looking for : https://en.wikipedia.org/wiki/Depth_of_field#Use_of_absolute_aperture_diameter https://en.wikipedia.org/wiki/Depth_of_field#Use_of_absolute...

rimliu 8y ago
Did you miss the part where I introduced F-number into discussion instead of the lens size? What do you think will happen to DoF when I take my huge 70-200 and close it down to 22?
- vortico 8y ago
  In that case the aperture diameter will decrease. f-number does not directly affect depth of field, except through the aperture diameter.
  - rimliu 8y ago
    F-number describes the aperture diameter, it has no way to affect anything. The same as meters do not affect the distance. However, when you close the aperture on the large lens, the lens still stays large. That was exactly my point: it is about aperture, not the lens size. I get what you say about physically larger lenses having larger apertures in absolute dimensions, not the ratio, however that does not help smartphones, because of the distance of the focal plane and the sensor size. And this where the limiting factor is.
    - vortico 8y ago
      This discussion is about shallow DoF. You cannot have shallow DoF with a lens with a small aperture diameter. Both the aperture diameter and sensor must be large.

vortico 8y ago

With everything else constant (f-number, sensor size, magnification, etc), increasing the aperture diameter will increase the circle of confusion and therefore decrease the depth of field.