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#31
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film vs CMOS
In article , +++ATH0
wrote: One other factor to bear in mind: the depth of field varies with lens focal length, not field of view of the subject. actually, it's aperture. actually, it's the ratio of focal length to aperture. nope. depth of field is a function of physical aperture. what you describe is f/stop, which is used for exposure purposes, and in some cases (usually movies), t/stops are used, which is actual light transmission through the lens, not a simple ratio. Are you claiming that focal length has no bearing on depth of field? for the same subject size and same image quality (coc), no. That's an interesting viewpoint. not really. it's just math. |
#32
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film vs CMOS
+++ATH0 wrote in
: On 2018-08-14 09:08, nospam wrote: In article , NY wrote: One other factor to bear in mind: the depth of field varies with lens focal length, not field of view of the subject. actually, it's aperture. actually, it's the ratio of focal length to aperture. That is correct. For any given focal length, the smaller the aperature, the greater the depth of field. That is why pinhole cameras focus from closeup to infinity without a lens. |
#33
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film vs CMOS
nospam wrote in
: In article , +++ATH0 wrote: One other factor to bear in mind: the depth of field varies with lens focal length, not field of view of the subject. actually, it's aperture. actually, it's the ratio of focal length to aperture. nope. depth of field is a function of physical aperture. what you describe is f/stop, which is used for exposure purposes, and in some cases (usually movies), t/stops are used, which is actual light transmission through the lens, not a simple ratio. Are you claiming that focal length has no bearing on depth of field? for the same subject size and same image quality (coc), no. That's an interesting viewpoint. not really. it's just math. No matter what the focal length of the lense is, the further away the focal plane is, the greater the depth of field will be for any aperature. As an example, if one is taking a head and shoulders portrait with a large aperature, it is quite likely that part of the subject will be out of focus slighty. Moving back a few feet with the same lense and aperature will result in a deeper depth of field, so that all of the subject should be in focus. The drawback is that the image size will be smaller, and thus require more enlargement to obtain the same size image, with the resulting loss of resolution with the enlarged image. |
#34
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film vs CMOS
On 08/25/2018 06:06 PM, nospam wrote:
In article , +++ATH0 wrote: One other factor to bear in mind: the depth of field varies with lens focal length, not field of view of the subject. actually, it's aperture. actually, it's the ratio of focal length to aperture. nope. depth of field is a function of physical aperture. what you describe is f/stop, which is used for exposure purposes, and in some cases (usually movies), t/stops are used, which is actual light transmission through the lens, not a simple ratio. For an ideal optical system, the depth of _focus_ (on the image side) is a function only of wavelength and numerical aperture, i.e. the sine of the half-angle of the cone defined by the rim rays (i.e. the illuminated cone). That's where wave properties come in. On the object side, the depth of _field_ equals the depth of focus scaled by the square of the magnification. Magnification is of course the ratio of the object distance to the image distance. Aberrated optical systems degrade a bit more slowly because they're not as good to begin with. Cheers Phil Hobbs -- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC / Hobbs ElectroOptics Optics, Electro-optics, Photonics, Analog Electronics Briarcliff Manor NY 10510 http://electrooptical.net http://hobbs-eo.com |
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