Helix 250 - color correction |
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| The use of modern RGB filters is used by many photographers to obtain a well balanced color image. These filters normally work in the spectral range from 400 to 700 nm. (click
here to see the filters characteristics of
SBIG).
A lot of efforts has been put in the optical design to minimize the size of the spot for the RGB-filter curves. And we are very proud of the result! As can be seen in the spot diagram below, the spots of the Helix 250 are all smaller than 10 micron for wavelengths between 397 nm and 673 nm. Although this is already an outstanding result, it can even be better! Even smaller spot-diagrams can be obtained by refocusing. Refocusing means that for each color-channel (RGB, H-alpha) the focus is slightly adjusted. This results in almost diffraction limited image quality. In the diagram below we show the spot diagrams for 656 nm (H-alpha). As you can see the spots are smaller than 3 micron! In the table below more diagrams can be found for those who are
interested. There are two series of diagrams. One for a field of 42 mm
(CCD) and one for a field of 50 mm (roll film). To view a diagram,
simply click on the hyperlink and a new window opens with the diagram. |
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| 42 mm | 397 nm, 435 nm, 486 nm, 546 nm, 656 nm, 673 nm | |||
| 42 mm | all colors |
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| 50 mm | 397 nm, 435 nm, 486 nm, 546 nm, 656 nm, 673 nm | |||
| 50 mm | all colors | |||