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Joined: 09 Mar 2013
Posts: 1170
Location: Vallentuna, Stockholm, Sweden

PostPosted: Sun Nov 26, 2017 8:16 am    Post subject: Outresolved Reply with quote

Here I am trying to show the effect of tube lens length for a specific sensor pixel size. Comments are welcome.

The distance of the stripes "clearly" visible in the first picture is 4 to 5 pixels wide. A pixel on the sensor (canon 6D) is 6.54µm. The objective was a Mitutoyo 10x and the tube lens was an apo Ronar 360mm. So the actual enlargement on sensor was 10x*(360mm/200mm) = 18x and the distance on the subject is between (4*6,54µm)/18 = 1,45 µm and (5*6,54µm)/18 = 1,82 µm.

The second picture shows the distance between the stripes.

The third picture is se same set-up as the first picture, but the tube lens is changed to a 150 mm apo Gerogon. This means that the enlargement on the sensor is 10x*(150mm/200mm) = 7,5X and that the stripes on sensor will be between 1,45µm * 7,5x = 10,9 µm and 1,82µm * 7,5x = 13,65µm or just covering 1,7 to 2,1 pixels. The sensor probably needs close to 3 pixels per stripe not to be outresolved, meaning that some parts of the stripes are visible, and some are not.

The fourth picture is an up-sampling of the third picture showing that up-sampling might be useful sometimes.

Best regards Jörgen Hellberg

360mm tube lens shown at 200x

Stripe distance 4-5 pixels

150 mm tube lens shown at 480 x

150mm tube lens, upsampled 100% shown at 240x

Jörgen Hellberg, my webbsite www.hphoto.se
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