FZ200 Diffraction Limit - Panasonic Tech Service

Started Aug 27, 2013 | Discussions thread
J C Brown
Senior MemberPosts: 1,401
Like?
Re: FZ200 Maximum Desirable F-Number to achieve adequate "Sharpness"
In reply to sherman_levine, Sep 4, 2013

sherman_levine wrote:

J C Brown wrote:

Sherm,

Your assessment that "Consequently, the "Which is the smallest line where I can find one good E?" test seems capable of testing the 1:1 situation" is entirely correct.

Unfortunately in order to achieve that in practice, even with a perfect lens and sensor, it would be necessary for the image of the vertical scale line to be exactly 400 pixels long and for the edges of the image of the first and last E in each group of eleven to be in exact register with the edges of the pixels on the sensor. IMHO even in the best of laboratory condition it would be extremely difficult if not impossible to achieve that.

The following image shows a comparison between a group of eleven 1.0 pixel black Es, a graphical simulation of the response of a grey-scale only sensor and crop from an FZ50 test image for which the scale and the alignment had been adjust very carefully to meet the requirements described above.

FZ50 test image compared with image of 1.0 pixel section of test chart and a graphical simulation of the response of a grey-scale only sensor to the 1.0 pixel Es.

As can be seen from the lower part of the above image even with very careful adjustment of the photographic scale and alignment my FZ50 has failed to record an accurate image of any of the eleven E in the test chart.

The following image shows an equivalent comparison between a group of eleven 1.5 pixel black Es, a graphical simulation of the response of a grey-scale only sensor and crop from the same FZ50 test image.

FZ50 test image compared with image 1.5 pixel section of test chart and graphical simulation of the response of a grey-scale only sensor to the 1.5 pixel Es.

As can be seen from the above image the FZ50 has succeeded in recording fairly accurate representations of the 1.5 pixel Es all of which are recognisable as an E and IMHO very similar in appearance to the graphical simulations of the expected images.

I hope that you will find the above images and comments helpful in explaining the reasoning behind the design of my test chart.

Jimmy

-- hide signature --

J C Brown

OK - Thanks - Sounds like I was wrong about the "look for the line with one visible E and compare that to 1.0" criterion and should use instead the "look for the line with all Es visible and compare that to 1.5 criterion for "perfect"

Is that correct?

Sherm

Sherm,

I would recommend that you simply look for the line in which all of the lines and spaces in at least one of the Es are recognisable.

Please bear in mind that the results may vary with the colour of the Es and that as shown in the above 1.5 pixel image, depending on the degree to which they overlap an adjacent row of pixels, the lines and spaces will have a thickness of either one or two pixels.

As you will see from the following image which was taken using a neighbour's Canon EOS 5D MkII some of the 1.3 pixel Es are clearly recognisable. For the 3744 pixel height of its 21 MP sensor that would correspond to a resolution of 2880 LPH.

Crop from a Canon EOS 5D MKII resolution test image. Colour cast removed using PSE.
I hope that helps clarify my recommendations for using my new test chart.

Jimmy

-- hide signature --

J C Brown

Reply   Reply with quote   Complain
Post (hide subjects)Posted by
Keyboard shortcuts:
FForum PPrevious NNext WNext unread UUpvote SSubscribe RReply QQuote BBookmark post MMy threads
Color scheme? Blue / Yellow