FZ200 Diffraction Limit - Panasonic Tech Service

Started Aug 27, 2013 | Discussions thread
J C Brown Senior Member • Posts: 1,595
Re: Diffraction Limit - A bit of revision.

Hi Ron,

Thanks for your further comments and analysis.

Having used a variety of optical measuring techniques throughout my career in mechanical engineering R&D I am very familiar with both linear and angular measurements and well aware of the advantage of using angular measurements to compare the resolution of lenses.

However as the final recorded image takes the form of a flat two dimensional surface it is necessary to use the focal length of the lens in order to relate the angular resolution of the lens to the linear dimensions of the sensor and vice versa. As the flat two dimensional surface is the final form of a digital photograph I prefer to use the focal length to convert the angular values from the lens to their linear equivalents on the sensor.

While I agree that the wide range of sensor sizes, aspect ratios and pixels densities makes comparing resolution more complicated I don’t have any significant problems in making comparisons based on LPH (lines per picture height) and lp/mm line pairs/mm data.

The resolution of any digital camera in LPH can be estimated fairly accurately by dividing the number of pixels in the height of the sensor by 1.5. To convert that figure to a 35 mm equivalent lp/mm figure it is only necessary to divide by 48. IMHO both of these calculations can easily be done with sufficient accuracy using simple mental arithmetic.

After using a spreadsheet to calculate the angular resolution and the diameter of the Airy disc and create a table of results for a range of aperture diameters and focal lengths I examined the results. In view of the wide range of pixel dimensions associated with the range of sensor sizes and pixel densities I failed to notice any evidence to justify your choice of a 3 mm aperture as having any particular advantage in terms of the size of the Airy disc in relation to the range of pixel pitches in the various available camera models.

With regard to the resolution of your ZS20 it may interest you to know that when I examined at high magnification a hand held shot taken at maximum zoom I found that I could just detect the cables attached to the sides of a TV transmitter mast which was about 12 miles away.


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J C Brown

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