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First light from old Danish 20" telescope

Started by RolandC, 06/05/2017 06:14PM
Posted 06/05/2017 06:14PM Opening Post
The 20" Danish telescope at La Silla in the Chilean Andes was recently decommissioned and was to be mothballed or removed. Some of the Chilean amateurs got permission to attach an imaging system to this scope and thus the instrument was spared from the wrecker's ball.

It is a very old instrument which had a simple Dall-Kirkham design that had tons of coma off-axis, which made it unsuitable for imaging. It was used only with a slit spectroscope, so it didn't need a field of view.

I recently made a special coma corrector and the guys down there attached it to the scope. It is not perfectly aligned yet and needs some tweaking, but this first light image shows potential for capturing very faint galaxies in pristine seeing.

Scope - 20" F15 Danish D-K Cassegrain
Camera - STL11K
Exposure - single 50 second RGB

Rolando

Attached Image:

RolandC's attachment for post 60918
Posted 06/05/2017 10:00PM #1
Hi Rolando, Very nice! And your mention of the corrector provided a nice gestalt. Years ago, one of our optics teachers had us design equivalent 2-mirror scopes: Classic Cass, Dahl, Gregorian, Ritchey, and then compare their theoretical performance. Only the Ritchey had good stigmatic field. Dahl was pathetic off-axis. But we never did refractive field groups. Now I understand why the field-widened Dahls (with correctors) are so popular. And still enjoys the simplicity of the spherical SM for fab and alignment. The teacher was Daniel Malacara, circa 1979... Tom

29-inch Dob in a dome
36-inch upgrade soon
LUNT 80/80 solar scope
FLI 6803 cam
APM 100mm APO Binos
JMI RB-16 Night Vision Binos
Zeiss 20x60 IS binos
Posted 06/07/2017 04:50PM #2
WOW! Thank you for helping save a scope from the wrecking ball!

Eric