FZ200 Diffraction Limit - Panasonic Tech Service

Started Aug 27, 2013 | Discussions thread
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Detail Man
Detail Man Forum Pro • Posts: 16,403
Re: Diffraction Limit - A bit of revision.

Ron Tolmie wrote:


I have always discussed angular resolution, not linear resolution, and have noted that basis in my comments. If you try to use linear resolution units then you have to append the focal length to just about every comment you make.

It seems to me that the Effective Focal Length [ EFL = FL * ( 1 + M / P ) ] remains rather close to the Focal Length (when focused at "infinity") in all but rather close-up shooting situations.

For example, you can buy Tessar lenses in many focal lengths from 2 to 800mm and they all have about the same angular resolution but their linear resolutions are radically different. Back in the days when we were using 35mm film cameras and most of us were mainly employing lenses that had a normal field of view the linear resolution values (lines per mm) were useful. Now that we are using many different sensor sizes and a wide range of view angles that method of measurement is obsolete. We need to move on and use a more sensible approach. Most of the confusion surrounding discussions on resolution is attributable to the reluctance to abandon that archaic practice.

How so ? How are linear resolution metrics (pairs/cycles per distance, or per image-size) "archaic" ?

The realization that a 3mm aperture size is needed for sharp images is very useful. For any given sensor size you can calculate the minimum f/ stop that will produce sharp images with a lens that has a normal field of view. For example, the FZ200 has an (actual) focal length of 9mm for normal FOV images. At the WA setting the FL is 4.5mm and at the telephoto extreme it is 108mm. For the normal FOV the actual aperture diameter is 3.2mm, slightly greater than the 3mm objective. At the WA setting the actual diameter is 1.6mm, again slightly larger than the 1.5mm objective. At the long FL setting the actual value is 38.6mm, again slightly wider than the 36mm objective (The FL is 12x the 9mm standard FOV so the angular resolution needs to be increased in proportion).

The FZ200 therefore has a rational choice of settings that will yield sharp images providing the lens aberrations do not reduce the resolution. Many cameras (including my own ZS20) do not meet those objectives so the users have to accept lower resolution as an unavoidable consequence of some other design priority, such as building a camera that you can put in your pocket.

The 3mm "standard" produces images that most people would accept as being sharp enough but for those who want the sharpest possible images the aperture needs to be larger. Going beyond the f/2.8 aperture of the FZ200 would be a considerable challenge but if Fujifilm were to put a constant f/2.8 lens on their S2 it could (theoretically) compete with just about anything on the market in terms of sharpness (although it would also need more pixels). The somewhat larger sensor should also deliver lower noise, higher ISO values and a wider choice of apertures so we begin to get a glimpse of where camera development is going.

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