If this is your first visit, be sure to check out the FAQ by clicking the link above. You may have to register before you can post: click the register link above to proceed. To start viewing messages, select the forum that you want to visit from the selection below. |
|
|
|
Thread Tools | Rate Thread | Display Modes |
#16
|
|||
|
|||
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 |
Ads |
#17
|
|||
|
|||
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 |
|
Thread Tools | |
Display Modes | Rate This Thread |
|
|