Helix 250 - specifications |
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optical system |
250 F/3 Houghton in Newton configuration with field corrector |
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| free aperture | 250 mm | |
| focal length | 750 mm | |
| focal ratio | F/3 nominal, F/3.4 effective | |
| primary mirror | 265 mm (Astro Sital) | |
| field of view
|
43 mm (CCD). 52 mm (film cassette) | |
| 43 mm: 3,3°. 52 mm: 4° | ||
| definition | < 10 micron for all colors over the entire FOV Diffraction limited after color channel focusing (click here for spot diagram) (click here for polychromatic diffraction modulation transfer function) |
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| color correction | see
definition |
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| vignetting
|
very
small (click here for relative illumination diagram) |
|
| circ. 43 mm ~ 5 % | ||
| distortion | 0,0002% (click here for distortion diagram) |
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| max. diameter | 300 mm | |
| max. length | 800 mm | |
| max. weight | ~ 25 kg | |
| materials
|
special resin tube and aluminum castings | |
| temperature compensation with the help of 3 invar rods. | ||
| focusing | moving the primary mirror by a micrometer (0,01 mm) or motor focus | |
| finish | 2 component paint | |
| CCD-adapter | Special spacing adapter and quick-release bayonet available for most CCD-camera’s | |
| spider effects | no | |
| ghost images | no | |
| easy of use | No need for collimation or adjustment | |
| easy to operate and to focus | ||
| dew Shield | Light weight dew shield with quick release bayonet | |
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