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Test Shots with Ajai's 20" Folded
Newtonian
Ajai Sehgal sent us a couple of test shots taken
with his recently completed 20" ObservatoryScope. These images were taken
during the first weekend in October, 2003, during first quarter lunation.
Remarkably, these are raw images without bias frame, flat frame, or dark frame
subtractions. The excellent contrast is a direct result of ObservatoryScope's
proprietary baffling techniques.
M27 tricolor, taken while the 1st quarter Moon was present
in the sky. |
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M27 in LRGB Color . .
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This photo of M27 exhibits excellent
contrast even with a first quarter Moon in the sky. Take particular note of the
excellent correction provided by the TeleVue Paracorr even though we had not
performed the final tweak of the Paracorr's spacing relative to the CCD chip.
Off axis coma from the F/5 primary mirror is almost completely absent across
the very broad 28 arc minute field of view. The complete lack of any traces of
lateral color (so common with zoom lenses and SCTs, for example) is
particularly noteworthy. TeleVue's Paracorr is significantly superior to older
conventional Ross correctors in correcting coma, since Al Nagler's design
allowed him six additional degrees of freedom for aberration corrections.
The slight vignetting in our Folded
Newtonian design is deliberate, as this is readily removed with proper flat
fields. ObservatoryScope optimizes the Folded Newtonian's baffling for optimal
contrast rather than optimizing for even field illumination as is desirable for
photographic film. The vignetting, which occurs only near the edge of the
field, amounts to about 15% at the corners. The field measures approximately 29
by 29 arc minutes. |
A 15 minute unguided exposure of a random star field.
The really "bright" star is actually only 9th magnitude. |
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15 Minutes Unguided . .
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This 900 second (15 minute) unguided
exposure of a field surrounding a 7th magnitude star completely verifies the
raw tracking accuracy of an ObservatoryScope. Note that this was merely a test
shot to verify tracking accuracy, and thus was slightly out of focus. To
perform this tracking test, we randomly picked a star fairly close to the
zenith since tracking errors due to refraction would be almost nonexistent
during exposure.
Note that this tracking test was performed
without any modeling or tracking corrections being applied. Thus this test
confirms the accuracy of our proprietary polar alignment technique and confirms
the raw tracking performance of our proprietary Hybrid Band-Worm Drive System.
No periodic error correction (PEC) was used. |
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