A number of “first lights” and test reports will be coming up in the next several weeks as I continue to reshuffle equipment around and acquire some new gear!
Let’s start with the telescope. I have always been a fan of the classic Newtonian telescope since the days of my old Cave Astrola! Hard to beat the crisp star images with their beautiful diffraction spikes. I think these add tremendous depth to an image. Of course I have a couple of small refractors too but on a bigger scale the Newtonian wins out. They are also much less expensive to produce. The “Newtonian” reflector was designed by Sir Isaac Newton and he completed his first telescope in 1668! It has to be the simplest optical design with just one primary parabolic mirror and one secondary flat mirror. Many amateurs make their own newtonians and these are really great scopes!
The basic design has not really changed much except for modern telescopes designed for astrophotography the secondary mirror is larger to improve illumination at the edges of the field and focal length or the point where light comes to focus is much shorter than it used to be. The advantage to that is that you can capture the same amount of light in a much shorter amount of time while producing a much wider field of view. Astrophotographers often refer to this type of optics as “fast”. So for example my old Cave Newtonian had a focal ratio of 7 which means that for a 10 inch mirror the focal length was 1750mm or 250mm x 7. This is considered an intermediate length. The new 14” or 350mm scope has a “fast” focal ratio of 3.8. That means the focal length is 1330mm despite the fact the mirror diameter is 4” greater!
Historically the faster Newtonians had issues with star deformities along the edges of field called “coma” where the stars look like small comets (see above image). The basic parabolic mirror surface is able to reflect all rays of light to a single point but as the F number decreases this property seems to breakdown some. The advent of modern “corrector lenses” with multiple optical elements has reduced this problem to almost nil. The lens is placed just in front of the camera.
The Orion Optics 14” Newtonian astrograph is manufactured in the UK. They are all hand built with “extreme precision” so they say. Like everyone looking to purchase something like this I did my research and of course looked at the images obtained. Needless to say the image quality I have seen for these is outstanding. The market for Newtonian scopes larger than 12” is fairly limited right now. OOUK (Orion Optics UK) has a pretty solid track record. A couple of features besides the mirror quality that I liked was one: their usage of carbon fiber optical tubes. These are very resistant to temperature changes and are extremely rigid and light weight.
The second feature I liked was this: there can be some small yet irritating effects created on long exposures of objects on these scopes which may have a bright star in the field. This effect, if not corrected, can detract from a perfect image of stars and give a little roughness to the star’s edge. It is caused by microscopic ground pits around the extreme edge of the chamfer of the primary mirror which can disturb ever so slightly the light and create this problem. I saw it on my old Newtonian. To counter act this small problem, the mirrors at OOUK are produced with a circular field stop placed around the chamfer of the mirror, so that is another plus.
It took about 15 months for the telescope to arrive! The company was shutdown for half a year because of COVID. At any rate assembly for this once it arrived was pretty straightforward. They shipped the primary mirror separate from the optical tube. The primary is housed inside a “mirror cell”.
The best optics in the world can be literally ruined unless they are supported correctly in a telescope’s body. Finely hand figured surfaces, no matter how good they are, will not give their best unless the mirrors have a firm but resilient method of holding the mirror.
Shown above is the mirror cell which has machined, anodized aluminum surfaces. Anodizing adds a protective layer to the aluminium which gives the aluminium protection against corrosion and also produces a harder surface which reduces the risk of scratches or wear in the threaded holes. The cell also has 3 fans for cooling, indispensable for this type of optic.
Assembly basically consisted of placing 6 screws through the optical tube into the cell. The cell actually “snaps” into a support ring in the tube so all you have to do then is rotate the tube until the screw holes line up. One person can do this although just to be safe I had my wife help me out 😊
Of course the telescope comes with tube rings for mounting but I did have to order the mounting plate as an extra. The optical tube assembly weighs about 40 pounds which isn’t bad considering the size.
Next step was putting the telescope on the mount, which I will discuss in the next post, and then collimating the optics. Collimation is the process of aligning the mirror elements in your optics so the light truly does arrive at a single focus point. Both the primary and secondary have collimation screws. In this case the secondary alignment was fine and it was only the primary that needed adjusting. I have a fair amount of experience collimating Newtonian optics over the years and have been accustomed to a “two step” approach. First is alignment using a device known as a “sight tube” with cross hairs which can be done during the day and the second step is fine tuning at the telescope with a software program.
I decided on the Optec Leo focuser (above images) for this setup. The folks at OOUK did customize the mounting base for this focuser. It is very low profile and one nice feature is an adjustable “split clamp tube” that you can change the position of the Wynne corrector lens which you can see is very large. This eliminates the potential need to figure out additional adaptors to reach focus.
Finally putting it all together, a “first light” image! This is a raw 10 minute guided red filtered image of the Veil nebula. The gibbous moon was very bright so the filtering I felt was necessary. I do not see any coma or any major deformities throughout the full field. There might be a slight adjustment needed on the focuser centering as at full resolution a couple stars show a hint of double diffraction spikes but overall it does look like the 16 megapixel APS-C size sensor is a good match for this scope! Slight guiding issue likely due to my 4 arc minute polar alignment error. More on this in the next post.
Overall I think the AG14 has definite potential. It’s still a little early to put a definite rating on it but so far I like what I see!
Next up, the 10 Micron GPS 2000 mount test report!
Thanks for reading!
DrDave
daveandtelescope 