FZ200 Diffraction Limit - Panasonic Tech Service

Started Aug 27, 2013 | Discussions thread
Detail Man
Detail Man Forum Pro • Posts: 16,789
Re: FZ200 Maximum Desirable F-Number to achieve adequate "Sharpness"

sherman_levine wrote:

J C Brown wrote:

I too have adopted a relatively simple approach to assessing and measuring the resolution of a digital camera as described in my FZ50 report which is available for download as a 6 MB PDF file from here.

As discussed in Section 2 of that report, due to the effect of the edges of the lines of a black and white grid partially overlapping adjacent pixels, the resolution of a line pair, i.e. one black line and one white line, requires three pixels, i.e. 1.5 pixels per line width. Consequently the maximum resolution of a digital camera can be estimated with reasonable accuracy by dividing the number of pixels in the height of the sensor by 1.5.

Thus for the FZ200 which has a 4000 x 3000 pixel sensor the maximum resolution would be estimated to be 2000 lines per picture height, LPH. That value is within 5% and 10% respectively of the vertical resolution values for the JPEG and RAW images in the DPR FZ200 review.


With your most recent stepped-baseline chart, where you select the smallest line in which one E has all 5 bars (B-W-B-W-B) visible, it seems to me that "perfect" zero-diffraction optics would yield one-pixel-per-line resolution (i.e. 1500 B-W pairs in the 3000-pixel high FZ200 sensor). The 1.5 pixels per line calculation (1000 B-W pairs...) would apply if your criterion were "the smallest line in which all the Es have all 5 bars visible).

Is that not correct?

Some relevant thoughts that occur to me are:

Line-pair patterns are composed of a series (of odd integer multiples, amplitude-scaled in inverse proportion to the harmonic-number) spatial frequency "lines" of periodic variations - representing a periodic "square wave" in the spatial domain.

Rather than being a single sinusoidal "line" of periodic variation in space represented in the spatial frequency domain at the Shannon-Nyquist spatial rep-rate that you are proposing (equal to the spatial sampling frequency divided by 2), we are talking about the additional presence of 3rd, 5th, 7th, etc., harmonics that will result in spatial frequency domain aliasing-distortion products.

If the variations are (spatial-frequency) "band-limited" by a composite spatial frequency (MTF) response that decreases with increasing spatial frequency (as is always the case to certain unavoidable extents, in particular because there is no such thing s "perfect zero-diffraction optics"), then we would not expect an ideal, flat magnitude response up to the Shannon-Nyquist spatial frequency limit that you are proposing (or zero or linear phase-shifts, either).

Additionally, one is not ever able to physically line up the rows/column of photosites on an image-sensor with the line-pairs as projected onto the image-sensor surface. Results will be essentiall random (as to the relative phase relationships between the projected image and photosites).

It seems a wonder that an alternating dark/light line-pair can be resolved by only 3 photosites ...

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