The Tom Osypowski equatorial platform
Part I: The platform
|Top left: The 16" f/5 dobsonian (made by Dieter Martini in Germany) with its Carl Zambuto quartz mirror on the Tom Osypowski platform.||Top right: All parts of the telescope. Everything fits nicely into an old Ford Fiesta car. The red rubber stuff between the two parts of the platform is for protection only.|
|Dobsonian telescopes usually have no built-in motors to track objects in the sky.
Everything is reduced to a minimum with the only expensive part being the primary mirror. If an observer wants to follow heavenly
objects, he / she has to push or pull the dobsonian telescope. If low magnifications (below 150x) are applied, pushing or pulling the
telescope is no problem. But for observing at high magnification (above 150x), moving the telescope manually can be very cumbersome.
As a planetary observer, I often use magnifications of 350x-450x (moon, planets) and up to 1200x (double stars).
Tom Osypowski from equatorialplatforms.com produces equatorial platforms which are placed beneath almost any dobsonian telescope and track objects in the sky for about 80-85 minutes. After a short reset, the platform tracks for another 80-85 minutes and so on.
In April 2010, I've contacted Tom Osypowski by mail. I was fascinated by the images on his website taken through dobsonian telescopes on equatorial platforms and by the observing reports. Tom replied to my mail on the same night but it wasn't until mid October 2010 that I've decided to order one of his platforms (after trying to observe Jupiter at 350x for a couple of hours on different nights :-) ).
Will the platform have an impact on the stability of the dobsonian telescope? Will it track accurately enough for high magnifications? Will it take a lot of time to get ready for observing? Will it add a lot of complexity to a beautifully simple system? I had many questions but somehow I trusted Tom's advertisement.
|In December 2010 -
much earlier than anticipated, a huge box with the equatorial platform arrived (the biggest and heaviest box I've ever received in my life).
"Wow, that platform looks awesome" was my first thought. This was my very first encounter with an equatorial platform. What a piece of exquisite
In January, I put the platform to a first test. On the very first night my 16" f/5 dobsonian followed the planets and stars. No vibrations at all, not even at 1000x-1200x when looking at the multiple star Almanach (Gamma Andromedae) and other double stars. The dobsonian was as stable as without the platform and tracked as perfectly as any equatorial mount at the highest powers. What a walk in the park! During the following nights, I've observed more and more objects and was impressed by how well the platform performed at very high powers.
Hmmm. How about a little bit of astrophotography? After a few weeks, I've organized an off-axis guiding system, an autoguider, and a coma corrector. In April, my Canon 20Da had a "first light" through the 16" f/5 dobsonian. The results of my first astrophotography attempts and my current work can be found here and here . All these images were taken with a 16" dobsonian on an equatorial platform.
|Top left: The globular cluster Messier 3 in the constellation Canes Venatici on April 8/9, 2011. This image was taken through a 16" f/5 dobsonian telescope on a Tom Osypowski equatorial platform. Three 8 minute exposures, two 4 minute exposures and two 2 minute exposures at ISO 1600 were added for this shot. A bigger version of this image and other images taken with the equatorial platform can be found here and here.||Top right: Another shot taken with the dobsonian telescope on the equatorial platform, showing Messier 66 (left) and Messier 65 (right) in the constellation Leo on April 8/9, 2011. Four 8 minute exposures and a 3 minute exposure at ISO 1600 were added for this shot. A bigger version of this image and other images taken with the equatorial platform can be found here and here.|
|Astrophotography might sound like a romantic activity. It consists of the romantic
fields of astronomy and photography. But astrophotography is one of the toughest disciplines in astronomy and photography with little
room for romance.
It's a painstaking 100-step procedure from the point where you have decided to drive up a mountain and take a picture of a galaxy. If any of those 100 steps fails, there will be most likely no astrophotography during that night. A missing or broken cable (there are many of them), a missing or broken or loose screw (there are even more of them), dew on an optical element, low batteries (of the autoguider, the platform, the camera, the telrad finder, the laser collimator, the guiding eyepiece, the polar finder or of a simple flashlight), a missing memory card, a cute little fox or a hundred other things I haven't listed here can ruin the night.
I've done astrophotography with a telescope on a German equatorial mount when we had to put film into a camera. I've mostly worked with a 10" f/6 reflector and an off-axis guider. It was difficult back then and I feared it would get even more difficult with the platform.
So how about astrophotography with the platform? In short, it's as easy or difficult as with a "normal" German equatorial mount. After arriving at the observing site, it takes me about one hour to set up the platform and the telescope, collimate the optics, connect all cables, properly align the platform with the star drift method, balance the telescope, reset the platform for a 85 minute guiding session, search for the first object, focus the camera and autoguider and find a guiding star and push the cable release. If anything goes wrong, it will take more time.
|There are things which are easier with the platform: E.g. it's much easier to balance
the dobsonian telescope on the platform. And it will stay balanced during the exposure. Balancing a big Newtonian telescope on a German
equatorial mount can be very difficult and during the guiding process, the torque changes. On the other hand, wind is the enemy of the
dobsonian on the equatorial platform. If there is wind, it can ruin the guiding quite easily. I work at 2.3 m focal length (the TeleVue
coma corrector slightly increases the focal length of the 16" f/5 primary mirror) so the guiding needs to be extremely precise.
Astrophotography is a demanding task but the results are rewarding and exciting. I've always felt it's worth the efforts. I probably could get more resolution out of a 16" f/5 mirror when put into a solid tube and onto a heavy-duty German equatorial mount. But such a mount would be very expensive (costing at least three or four times as much as the platform) and it wouldn't be a mobile solution anymore. I feel the equatorial platform is one of the most important innovations in amateur astronomy since the invention of the dobsonian telescope. It doesn't make the good old German equatorial mount obsolete but it turns a simple dobsonian telescope on an altazimuth mount into a full-valued observatory with exciting capabilities.
I've mainly ordered the platform for observing. I love to sketch at the telescope and without the tracking capabilities things get difficult. Now I can even take pictures with the telescope.
Part II: The guiding / imaging setup