I moved prime focus without cutting the OTA (Optical Tube Assembly) on my Orion Astroview 6 telescope. Huh? How? No way? The first thing I did when the Canon EOS XTi DSLR camera arrived…put it on my 6 inch reflector telescope. I quickly discovered that focusing on stars, and DSO (Deep Sky Objects) was impossible.
Orion Astroview 6 – About The Scope
This telescope has a 150 mm aperture and a 750 mm focal length. This gives it a fast f/5 focal ratio. It’s great for viewing planetary and bright DSO. You can image with a smartphone most of the objects in the night sky using eyepiece projection, and with a webcam or DSLR camera, planetary objects. It comes with two counter weights (7.5 lbs and 4 lbs). All together it weighs 37 lbs. The OTA is 27 inches long. I’ve added a motor to the mount in order to track the objects I’m viewing. In addition, the Orion website clearly omits DSO in the “Best For Imaging” category. You know me, I love a challenge.
Orion Astroview 6 – Prime Focus & Moving It
The Orion Astroview 6 is a Newtonian or Reflector telescope. In a telescope like this, prime focus is the point where the light converges in the viewer. The image here shows where prime focus rests depending on the location of the primary mirror. If you follow the arrows which represent light, you see the light reflects off the primary mirror on the right. It is then reflected off the secondary mirror into the viewing tube. Viewing with your eye through an eyepiece works great on my telescope. That’s what it is designed to do. The focuser is simply moving prime focus up and down so your eye can focus on the object.
With a DSLR camera, it is more difficult because prime focus is too low in the view tube. The focuser cannot bring prime focus close enough to the camera. In the image above, it shows two locations for prime focus. These lower one is the designed location for observation. The upper is the modified location that is good for DSLR astrophotography. There are several ways to get a DSLR camera to work with the Orion Astroview 6 telescope. Everything you read on the internet or see on YouTube state that the modification is permanent. Meaning you have to drill holes in the OTA or cut off the back end of the OTA. These are good options for those with money to throw away. Here’s how I moved prime focus.
Orion Astroview 6 – The Primary Mirror
As we say in engineering, you can’t fix what you cant see. So I took the telescope apart. Shown here is the mirror assembly in its compnent parts. Shown next to the mirror are 3 rubber clamps which hold the mirror onto the frame on the right. I focused on these three for my modification. You know I like to 3D print parts for this hobby. My measurements, and some trial and error, revealed the prime focus needed to move about 20 mm. My design moves it about 30 mm, to give the focuser room to adjust for temperature changes.
Orion Astroview 6 – Mirror Extension
Let me introduce the Orion Astroview Mirror Extension. If you have access to a 3D printer, you can click the link and print 3 for yourself. What I like about this is that I reused the screws already in the telescope. It holds the mirror far enough in the OTA to achieve prive focus with my DSLR camera. I can also return the telescope to original condition for resale or a night of viewing. The base of it matches the original rubber clamps and the screws hold them tight to the mirror frame. The best part is that this is non-destructive to your telescope!
Orion Astroview 6 – DSLR Photo Results
Telescope: Orion Astroview 6
Camera: Canon EOS XTi
Frames: 49 @ 30″ (about 25 minutes total exposure)
Post Processing:
– Deep Sky Stacker
– StarTools
– Gimp
Orion Nebula 2019
Telescope: Meade ETX-125
Camera: Canon EOS XTi
With the Meade ETX-125, the field of view is small and only the Orion Nebula fits in the picture and barely. The increased field of view with the Orion Astroview 6 allows me to include the Running Man Nebula. the Mead is has a focal ratio of f/12 vs the Orion Astroview 6 focal ration of f/5. This means faster light gathering capability and more vibrant colors in the resulting photo. I’ve not seen an extension like this anywhere, so I hope you like and use on your own telescope.
Owning the Orion Astroview 6 telescope does not mean only viewing anymore. You can take great pictures of deep sky objects and view the Moon and planets when ever you like. You will get good at collimating your telescope and I recommend cloth mirror protection whenever you change back and forth. Enjoy this and clear skies.
