FZ200 Diffraction Limit - Panasonic Tech Service

Started Aug 27, 2013 | Discussions thread
Detail Man
Forum ProPosts: 15,270
Re: Diffraction Pattern Dimensions are a function of Lens-System F-Ratio
In reply to Detail Man, Aug 30, 2013

My sincere apologies. "What one sees" is clearly not "what one gets" with the DPreview editor. In the quoted version below, I have re-inserted the characters lost in the DPReview display system.

Detail Man wrote:

Ron Tolmie wrote:

What the equation states is that if you want to achieve a given angular resolution then there is a corresponding aperture dimension that will produce that resolution so long as some other factor (like optical aberrations) does not override the consideration.

Looking at it the other way around, if the aperture diameter is 3mm and the lens is intended to be used for imaging a "normal" field of view (equivalent to what you get with a 50mm lens on a full frame camera) then the image will be sharp, and it doesn't matter what the focal length of the lens is. You might have a different opinion on what constitutes a "sharp" image, but in that case the dimension might be a little bigger or a little smaller than 3mm, but the point is that there is a particular diameter that will satisfy your objective.

You have not responded to the following inquires addressed to you (posted on this thread):



Depth of Field is inversely proportional to the diameter of the entrance-pupil (virtual aperture as measured from looking into the outer lens-system element) - which is the "aperture diameter" which is used in the derivation of F-Ratio ("F-Number").

Note that that the "virtual aperture" is not the same physical size as the actual mechanical aperture opening wothin the lens-system, and it's measuarble physical diameter changes in the case of a variable Focal Length lens-system.

A pin-hole camera can achieve a very high numerical value of Depth of Field - but always at the price of (also) very significant loss in the spatial frequency (MTF) response magnitude due to diffraction effects. Deep DOF and low lens diffraction effects (upon MTF response) are mutually exclusive.

The intensity of the Fraunhofer diffraction pattern of a circular aperture (the Airy pattern) is given by the squared modulus of the Fourier transform of the circular aperture:


is the maximum intensity of the pattern at the Airy disc center,

is the Bessel function of the first kind of order one,

is the wavenumber,

is the radius of the aperture, and

is the angle of observation, i.e. the angle between the axis of the circular aperture and the line between aperture center and observation point.

, where q is the radial distance from the optics axis in the observation (or focal) plane and

(d=2a is the aperture diameter, R is the observation distance) is the f-number of the system.


DM ...

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