Orion Astroview 6: Equipment Spotlight [Moving Prime Focus]

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

Orion Astroview 6 telescope
Orion Astroview 6 Telescope

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

Newtonian Prime Focus Diagram
Newtonian Telescope view of Prime Focus

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

Orion Astroview 6 Mirror Assembly
Mirror Assembly

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

Orion Astroview Mirror Extension
Orion Astroview 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

Object: Orion Nebula & Running Man Nebula
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

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.

Canon EOS XTi: Equipment Spotlight [DSLR Camera]

Canon EOS Digital Rebel XTi

The Canon EOs XTi joins my astrophotography family. I started using my Google Pixel Really Blue to photograph night sky objects. I’ve captured the Orion Nebula, Sun, stars, planets, star clusters and the Andromeda Galaxy with my smartphone. The smartphone can capture, with the same quality, most night sky objects. Deep Sky Objects present a challenge for the smartphone. I acquired a used Canon EOS XTi DSLR Camera. It was donated by Chuck Marshall of Chuck’s Camera Plus in Hampton, VA. It is gently used and has a damaged card reader.

Canon EOS XTi Specs

Crop Sensor vs Full Frame

I don’t yet know enough about this comparison to speak to it. At minimum I know the crop sensor removes the edges from your field of view increasing focal length. Full Frame gives you everything which has its place in your astrophotography tool bag. More on this in future posts.

Light Sensitivity

The details of this camera can be found on the Canon website. So let’s discuss the inportant ones related to astrophotography. Light sensitivity allows you to adjust for the brightness of the planned target. Having this flexability is needed with the different objects night sky. The Horsehead Nebula for example is very dim in comparison to the Orion Nebula which you can see with the naked eye. The Canon EOS XTi has an ISO range of 100-1600. Bright objects like the Moon or Sun need low ISO to capture clearly. This model requires a filter to reduce the light intensity and/or very fast shutter speed to compensate. The Google Pixel is capable of ISO less than 50 with a max of 10000. Certainly the Canon EOS XTi, released in 2006, will be used for specific photos since it can’t compete with the smartphone.

Shutter speed

Shutter speed with the Canon EOS XTi is maxed at 1/4000 sec. Compared to my Google Pixel at 1/8000 sec, the smartphone wins. On the opposite end where DSO objects live, the camera slows shutter speed to a minimum of 30 sec. The Google Pixel, 0.6 sec. And the winner goes to the Canon.

Canon EOS XTi Capability

Orion Nebula 2019
Orion Nebula 2019
Telescope: Meade ETX-125
Camera: Canon EOS XTi
Orion Nebula November 2017
Orion Nebula November 2017 Telescope: Orion Astroview 6 Camera: Google Pixel

Yes there are many differences to point out between pictures. You can see the difference between the crop sensor (Canon) vs full frame (Google Pixel). The difference between a 30 sec shutter time and a 0.6 sec shutter time. The Google Pixel has elongated stars because polar alighment is difficult in my yard. I have to drift align for polar alignment and that works best with a long shutter opening time. Of course the pictures show how much post processing improvement I’ve gained since 2017.

Canon EOS XTi Conclusion

Super Blood Wolf Moon 2019
Telescope: Orion Astroview 6
Camera: Google Pixel

The Canon EOS XTi currently works with my Meade ETX-125 Telescope. The scope has a smaller field of view so getting all of an object in the frame is a challenge. I’ll explain why it cannot work with the Orion Astroview 6 telescope in another post. The Canon camera will perform great with DSO and I’ll keep the Google Pixel dedicated to solar system objects. I’ve learned enough in the short period to help my neighbor sucesssfully capture photos of the Super Blood Wolf Moon. He too uses a Canon product and the results match the picture here. My own experience aside, I’ve not seen anyone else sucessfully capture a detailed DSO photo with a smartphone that rivals a DSLR camera. Get one and clear skies!