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Wow.. this is missing the entire point on why lens blur occurs. Lens blur in normal photographs is the price you pay because you want to focus sharply on a subj

by sytelus 13y ago

Wow.. this is missing the entire point on why lens blur occurs. Lens blur in normal photographs is the price you pay because you want to focus sharply on a subject. The reason photos with blur looks "cool" is not because the blur itself but its because the subject is so sharply focused that its details are order of magnitude better. If you take a random photo, calculate depth map somehow, blur our everything but the subject then you are taking away information from the photo without adding information to the subject. The photos would look "odd" to the trained eyes at best. For casual photograph, it may look slightly cool on small screens like phone because of relatively increased perceived focus on subject but it's fooling eyes of casual person. If they want to really do it (i.e. add more details to subject) then they should use multiple frames to increase resolution of the photograph. There is a lot of research being done on that. Subtracting details from background without adding details to subject is like doing an Instagram. It may be cool to teens but professional photographers know it's a bad taste.

blt 13y ago
That is not true. Stopping down the lens aperture increases the depth of field without reducing detail in the focal plane, until the diffraction limit (around f/16 for a 50mm lens on a full frame DSLR).
alkonaut 13y ago
> Subtracting details from background without adding details to subject ... Not sure what you mean by this. Blur is only due to focus distances and aperture sizes. Making the depth of field narrower (making the OOF regions more blurry) does not add detail to the areas that are in focus. Usually, it's even the other way around. Example: Say we shoot a portrait of a person at 5m with a forest 30m away in the background, at 3 different apertures: f/1.4, f./11 and f/20 At the largest aperture (f/1.4) the background will be completely out of focus and the face of the subject will have sharpness at "80%" of what my lens/sensor combo can do in terms of resolution. The less-than-excellent subject sharpness is because lenses aren't perfect and using the largest aperture will reveal this. Even if you use an expensive professional lens, it will have it's maximum sharpness at some aperture that is smaller than the largest. What does happen in the shallow DOF shot is that we have a form of perceived sharpness (usually referred to as "pop") which is an effect that is simply due to the fact that the subject is so distinct from the background. At f/11 the subject sharpness is better than at f/4. It is now probably near 100% of the maximum resolution the sensor/lens combination can deliver. The background is significantly more discernible/focused now. If it was a green blur in the f/1.4 shot is now a forest of very slightly blurred trees. At f/20 the subject's sharpness is again less (e.g. 90%), this time due to the physical limitation known as diffraction that occurs for very small apertures compared to the wavelength. This shot has completely focused trees in the background. To put it another way: when you take the f/11 portrait and go to f/1.4 you take away almost ALL of the background information, and SOME of the foreground information, while adding NO new information. The entire shot will be less focused when you do.
- swimfar 13y ago
  But there are still advantages. With a larger aperture the sensor/film is receiving more light which means the shutter speed can be increased. If the subject isn't perfectly still this can result in decreased blurriness. It's been a while since my HS photography class but I think that's correct.
  - alkonaut 13y ago
    Yes, my wall of text above applies to static subjects and cameras only. Whether the freezing of subjects results in more information (detail) or less (without movement info) is subjective.

by sytelus 13y ago

blt 13y ago

That is not true. Stopping down the lens aperture increases the depth of field without reducing detail in the focal plane, until the diffraction limit (around f/16 for a 50mm lens on a full frame DSLR).

alkonaut 13y ago

> Subtracting details from background without adding details to subject ... Not sure what you mean by this. Blur is only due to focus distances and aperture sizes. Making the depth of field narrower (making the OOF regions more blurry) does not add detail to the areas that are in focus. Usually, it's even the other way around. Example: Say we shoot a portrait of a person at 5m with a forest 30m away in the background, at 3 different apertures: f/1.4, f./11 and f/20 At the largest aperture (f/1.4) the background will be completely out of focus and the face of the subject will have sharpness at "80%" of what my lens/sensor combo can do in terms of resolution. The less-than-excellent subject sharpness is because lenses aren't perfect and using the largest aperture will reveal this. Even if you use an expensive professional lens, it will have it's maximum sharpness at some aperture that is smaller than the largest. What does happen in the shallow DOF shot is that we have a form of perceived sharpness (usually referred to as "pop") which is an effect that is simply due to the fact that the subject is so distinct from the background. At f/11 the subject sharpness is better than at f/4. It is now probably near 100% of the maximum resolution the sensor/lens combination can deliver. The background is significantly more discernible/focused now. If it was a green blur in the f/1.4 shot is now a forest of very slightly blurred trees. At f/20 the subject's sharpness is again less (e.g. 90%), this time due to the physical limitation known as diffraction that occurs for very small apertures compared to the wavelength. This shot has completely focused trees in the background. To put it another way: when you take the f/11 portrait and go to f/1.4 you take away almost ALL of the background information, and SOME of the foreground information, while adding NO new information. The entire shot will be less focused when you do.

swimfar 13y ago
But there are still advantages. With a larger aperture the sensor/film is receiving more light which means the shutter speed can be increased. If the subject isn't perfectly still this can result in decreased blurriness. It's been a while since my HS photography class but I think that's correct.
- alkonaut 13y ago
  Yes, my wall of text above applies to static subjects and cameras only. Whether the freezing of subjects results in more information (detail) or less (without movement info) is subjective.