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Obsession 18" classic for sale
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- John Dohmen
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Obsession telescope
Original Obsession Classic 18" F/4.5 with Servocat track and goto system and Argo Navis navigation computer. Completely automated goto and tracking system. Total new price for this system is $ 10,036.
When disassembled the telescope can easily fit in a SUV or pick-up truck for transport to a dark site; the cage with the secondary mirror is placed in a custom made box for storage and transport. Setting up the telescope, collimation and initial alignment can be done in about 15 minutes.
A Dobsonian telescope is primarily a telescope for visual use. Taking pictures is possible and done; it is depending on the weather conditions; in Curaçao there is always a rather strong wind which makes it almost impossible to work with longer exposture times. Imaging the planets and the moon can easily be done by making a movie and stacking the best frames. Deep Sky Objects is not possible in Curaçao because of the wind, but I have seen images taken with this kind of telescop from other countries that are quite good. Very long exposures cannot be used because of the alt-azimuth drive system.
If you are interested or in case you have questions contact me via
Observation session with the Obsession telescope
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- John Dohmen
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After a few sessions with the Meade ETX-125 it was time to also try the larger telescope, the Obsession F/4 18" telescope. The first tests in house during daytime showed that everything still worked. Only the mirror is quite dirty. It should be cleaned but that can wait. For observations is a dirty mirror most often not really a problem unless it is really really dirty. So for the first test I don't do anything about the condition of the mirror.
One of the problems I found was that the control computer, the Argo Navis, had lost the battery power. After buying a new battery, opening the controller and replacing the empty battery I had to set the date and time again. All other settings are in non-volatile memory so these were kept even with an empty battery. The motor drives worked good and also the motor controller, the Servocat.
Also the Telrad, the device that is used to visually point the telescope to the object in the sky, seemed not to work. After changing the batteries it still didn't work, but after checking again when it was darker, I saw the red rings. So apparently the device works but the rings are too faint to see them during the day.
Another problem, that I had found some time ago, is that the laser collimator was defective. I tried to repair it but without result, so I ordered a new one.
Observation session with the Meade ETX-125
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- John Dohmen
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After several years of not attending this hobby I decided to give it another chance. No longer a member of the Curaçao Astronomy club because I found their observation sessions turning more and more into social entertainment sessions than serious stargazing, my goal is to restart my astronomy hobby primarily at home.
But first I had to find out if my telescopes are still in working condition after many years of not being used. So I checked both of them during daytime. The Meade ETX-125 gave me a lot of problems. It didn't start consistently; especially the hand controller seemed unreliable. So I ordered a replacement hand controller. That didnt solve it completely because still sometimes the scope didn't start up. Apparently during the past years the connectors in the power panel on the scope are eroded till they are no longer reliably functioning. I cleaned them up as good as possible and that seems to solve the problem most of the time. But to be on the safe side I ordered also a replacement for this power panel. That didnt arrive yet.
The Pleiades
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- John Dohmen
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It is not easily possible to make pictures in my backyard through a telescope because of the ever-present strong wind. So as an alternative I tried to make pictures just with the camera and lens. Some time ago I have built a small wedge with motordrive that, after it is polar aligned, compensates the rotation of the earth. On Friday January 29, 2011, I have pointed that guiding platform roughly North with a compass. The wedge was still at an angle of 12 degrees from a previous experiment. The alignment is not very critical because of the relatively short exposures.
With the Nikon D90 and the standard 18-105mm zoomlens I have made several pictures of the Pleiades.
Sunspot has grown
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- John Dohmen
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The sunspot that I have sketched two days ago has grown in the meantime. The main spot has not changed much but the surroundings have changed considerably.
To the left the sunspot as I have sketched it this afternoon around 4 PM. The telescope was again the Meade ETX-125. Eyepiece Meade Super Plösll 26mm with 2x Barlow. To the right the same section from the SOHO satellite image.
This time I also have mentioned the scale and the orientation of the image. I have determined the orientation by switching off the guide motor (not practical if you want to go on observing). The part of the sun that moves out of the field of view is the West. Because in a Meade ETX the light is reflected three times North is 90 degrees clockwise from West. The image from the Soho satellite is rotated and mirrored to get the same orientation as the drawing.
This result shows that sketching can result is a quite actual represenation of the image. Especially after some more practice. The distances between the indivual sunspots are quite good but I made the main spot too large.
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