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Below is data compiled by using the same specs from
the f12 CC and RC but now it is a f12 Dall-Kirkham Cassegrain. |
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23.6 |
RMS spot size at edge of 2.0" diameter field
is 71.3 microns. |
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Notice how quickly the Dall-Kirkham design passes
out of the airy diameter, lower left corner on the above chart.
Optically even at f12 this design is very poor compared to the
CC and RC designs, unless it is used on-axis only. |
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Point Spread Function illustating the star at the
edge of the field. |
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f12 Classical |
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f12 Ritchey-Chretien |
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f12 Dall-Kirkham |
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22.8 microns |
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22.3 microns |
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71.3 microns |
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As noted earlier, defocus can help reduce the off-axis
size of the stars but there is almost no benefit of defocus to
the Dall-Kirkham design. |
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