Mar 21 2015 11:54 AM by Gil V
Review: Starlight Instruments Direct Drive System
Mar 21 2015 11:31 AM by Maz929
Innovations Foresight On-Axis Guide and Starlig...
Mar 17 2015 08:25 AM by GazingSkyward
The Celestron C80 ‘ Regal’ Spotting scope. And...
Mar 21 2015 07:54 AM by waxinggibbous
Categories See All →
- CN Reports
- User Reviews
- How to . . .
- Observing Skills
- Astronomical History
- Optical Theory
- Vision and Related Experiments
- How to Gain the Support of your Family for your Astronomical Pursuits
- Evaluation Tips
- Special Events
- The Elements
- New Articles in [!monthname!]
- Telescope Articles
- Submit a Review / Article
- Monthly Guides
- Behind the Scenes
- About Us
- Copyright ©
- Terms & Conditions
- Tiny Eyes on the Skies
- From the Editor's Desk
- What's Up . . .
- The Light Cup Journals
- Who is this Super Light Cup?
- Cloudy Nights T-Shirts
- Imaging Contest
- Small Wonders
- Previous Imaging Contest Winners
- This Month's Skies
- Mike's Corner
- The Cloudy Nights Friends and Family Discount
- Uncle Rod's Astro Blog
- Fishing for Photons
- Binocular Universe
- Article Submissions
Robert Royce 8 inch f/6 Newtonian Mirror
Voice your opinion about this subject in our forums
My first real telescope (other than the toy store junk) was a 4.1/2 inch 900 mm Japanese Newtonian with a solid equatorial mount on a wooden tripod. I had with it 3 eyepieces, a 20 mm, 10 and 5 mm plossls. The image at 180x with the 5 mm was decent but beginning to disintegrate. Never the less I used that scope for 6 years almost every night even if it was for a minute or two, from 12 years of age till I was 18 when I left for college. For a small country like the United Arab Emirates, that was significant enough that I was featured in the daily newspaper as the 13 year-old amateur astronomer. Now, I am 33 years old and the point I am trying to make is that I am not so experienced with telescopes, but I do have a decent observing experience. .
Living in the US for a decade, I got to learn more about the amateur astronomy movement and got to see the stars through a few other telescopes, mainly 8-10 inch SCT’s a 6 inch dob a 6 inch ED apo, and a 12 inch observatory class Newtonian in Waukesha Wisocnsin. Always wanting to buy a telescope for myself, I never had the time to do it. Then in Year 2000 I went back home to the UAE.
After working in US for a decade, I caught the American DIY fever and I decided I want to build my own scope. I couldn’t sleep well thinking of buying a commercial SCT with random optical quality. I was also on the list for an astro-physics 130EDF but I lost hope of ever getting it (now 4 years, and I am still waiting)
With the relocation came a budgetary strain not to mention horrific shipping costs, all of which motivated me even more to build my own scope. I decided that it will be an 8 inch dob (to start small and easy) and decided that it will be collapsible like the Teleports. I got suggestions from Tom Noe on how to mount the bogen struts, the spandex shroud and other things. His comments were very helpful. Then I contacted Mr. Carl Zambuto asking him to recommend me a good mirror maker (knowing well that he wasn’t into the ATM scene), and he recommended: Robert Royce, Larry Hardin and Mike Spooner. John Hall of Pegasus wasn’t making anything below 12 inches at the time (now they do), so I decided to go with Mr. Royce simply because the amount of information on his web site was excellent, and portrayed good customer orientation and technical know how.
The mirror was shipped on schedule, but took a while due to postal logistics between US and UAE. If I was in the US I would have received it within a couple of weeks. Mr Royce was very kind to help me consolidate a few items (buying online and shipping it to him) which saved a bundle in shipping costs. Royce stated that all his mirrors have a strehl ratio above 0.96. Sounds good but I didn’t think I had the experience to judge on this matter.
I spent a month designing the scope then about 2 months building it (in my one bedroom apartment, with a circular saw, router and drill, you can imagine the mess I made). Everything went according to plans, except that I was failing to build a light enough secondary cage like the ones on the teleports, so I decided to go easy and simplify the design (make a bigger more solid cage that doesn’t fully collapse into the scope) till I get better equipment Also I got the Kine Optics 2-inch helical crayford focuser which was not small but very light. The result is the R2D2 looking scope you see in the picture. The ground board is small to smooth the motion but the feet are extendable to provide stability.
Its compact enough to fit in the front passenger seat and solid enough to hold collimation within good tolerances (about half the diameter of the paper reinforcement ring marking the center of the mirror (thanks to Tom Noe for his advice. He uses machined duralin inserts for the struts, but I made mine from pc-7 filler cast in a plastic tube, then tapped). I mounted the mirror as per RF Royce’s recommendation (with no clips), but added a nylon thread attached to a small washer which in turn is silicon glued to the back center of the mirror to prevent accidental falling of the mirror. I also used Alan Adler’s cooling technique using a fan blowing air across the face of the mirror (I use 2 fans) and also used AC filter pads to prevent dust from settling inside the scope. Teflon on laminate was used for the azimuth bearings and Teflon on Velcro (tip from Rick Singmaster) for the altitude. The secondary was a straight 4-vain protostar. I also had the awesome skycommander and an Orion red dot finder. The total weight of the my R2D2 was 25 lbs (with 12mm ply), which is a bit heavier than what I hoped for, but not bad.
After precise collimation with a Techtron set. it was time for first light. My eyepiece set consists of: 2” 40 mm Koenig (not the MK/70), 25 mm televue plossl, 9 mm UO ortho, 7 mm Nagler type 6 a celstron Ultima 2x Barlow and klee barlow (2.8x). The Koenig was light and gave a nice 2 degree view at 30x. The plossl was incredibly sharp and gave a one degree view at 48x, while the nagler gives half a degree at 171x. The Ultima Barlow pushes it to 342X. With two and one degrees eyepieces and the orion red dot, I was able to find anything I wanted under dark skies and rarly used the sky commander except under light polluted skies.
The half moon was the first light the scope sees, beautiful and bright, but the seeing wasn’t very good so I couldn’t push the magnification higher. For a couple of months later I was testing and viewing different objects but mainly was doing so early evening and was disturbed by the seeing conditions. Mr. Royce reminded me that the best time was after midnight, a fact which I have forgotten. So I started observing around midnight to late morning hours and the experience was Zen like. There were some surprises to me over the course of the last year, mainly:
The Nagler shows no visual artifacts and is very sharp all the way. I know the hype about the naglers but didn’t think it was true to that degree.
The 40 mm Koenig was sharp to about 80% of the field. It was a good and light eyepiece, but got me confused at the edge. I didn’t know if I was seeing comatic distortions (at f/6 ?) or eyepiece distortions.
The Teflon on Velcro was working beyond my expectations (Many thanks to Rick Singmaster); I was hand tracking Saturn at 350x with the Nagler/Ultima with such grace and ease, it really impressed me. With the 7mm and klee (478x) tracking is not jerky, but does require that you are seated comfortably and track carefully. The only reason I would want a motorized platform is for astrphotos, or public viewing.
I spent years observing the moon with my older scope, but the 8 inch with a 7 mm Nagler left me stunned. With a half degree field, I was hovering over the moon not looking at it. I spent hours upon hours observing and pushing the magnification till the maximum my eye pieces were capable of 940X (NaglerkleeUltima)and with no breakdown whatsoever (except for the dust). Tracking by hand was messy and I was relying on the moon to drift across the field (I wouldn’t do it with a planet).
Saturn was at its best with its maximum inclination toward the earth. The Royce mirror was unbelievable.. The 350x view with the Nagler and Ultima was the best. During excellent seeing, it was a razor sharp image with superb contrast. The contrast was so good, I was counting numerous cloud bands, and razor itched rings. During this year (August 2004) I observed Saturn when it was low in the horizon (15 deg or so) around 4 am, and was startled to see it in different coloration (due to atmospheric refraction) There was a definite bluish tint to it and somehow I was able to see more colorful rings that when it was high in the sky. The atmosphere was so steady, I had the best view of Saturn in my life.
I have to improve my drawing skills or photograph it, cause I can see immense details, Forget about the red spot or cloud belts, I was seeing clearly turbulence in the cloud belts themselves and numerous white and black spots. The darker belts swirling into the brighter ones. I think this is due to a contrast phenomenon (like the Enke division on Saturn) I never though such features can be viewed with an 8 inch scope. Its also the first time I see the moons of Jupiter as sharp disks not as points. The Nagler/Ultima combo was best.
At its closes encounter, and with the 7 mm Nagler, I was looking at the red planet with detail I have never seen except in pictures. Polar caps, features and shades upon shades of colors. I saw as much detail as any hand drawing of mars or any armature taken ccd picture I have seen, though with lesser contrast than the image processed photos. Somehow I liked the view in the Nagler alone (171x) than with the Nagler/Ultima (342x)
I never get tired of this object. Now however I can see the trapezium stars with the 25 mm plossl and filaments upon filaments and detail like I have never seen. With the Nagler/Ultima, I had no trouble counting 6 stars in the trapezium. With the Konig in a 2 degree field and an O-III filter, the nebula was scary, reminded me of the Shadow ships on Babylon 5. The extreme contrast and subtle beauty of this nebulae stands in it own class, and no printed image can portray the demonic and imposing beauty of this jewel
First time I see the nebulosity around the Pleiades. Under tar-black skies of course.
M13 and M5:
M13 always appeared to me as a cotton blob in my old 4.5 inch. Now I was seeing hundreds of separated stars with direct and averted vision. Stephen James O’Meara mentions (in his “Messier Objects” book) that a 4 inch apo under dark skies was equivalent to an 8 inch reflector under suburban skies. With 8 inch first rate optics, ultra dark skies and averted vision, well… M5 broke down almost entirely into diamond dust
Omega Centari: Yes, from latitude 24 of Dubai I can view it, a bit low but still at a decent height. What a beast! Cannot count. However, for some reason I like M5 better, its just more pleasing l than this old monstrosity.
M81: Ok, so I had to go to dark skies to see the arms of this galaxy. I drove just 1/2 hour south of Dubai (not ultra dark, but the milky way is clearly visible. we are still lucky here)
M51: The spinning structure is visible from moderately dark skies, but under Oman skies much clearer and more distinct. Also the connecting arm is clearly noticeable.
NGC 253: The galaxy in sculptor. A marvel. Very sharp and distinct texture. But I was under some of the darkest skies on earth (mountains of Oman 6 hours drive south, 6.5 magnitude I estimate).
M31: Excellent. So much detail but I had to go out of the city again. Several dust bands can be seen under Oman skies.
M57: Very sharp hole, and a puff of smoke, as you can see the smokey textured remains of the star.
The double double:
I was splitting this dual pair with my 4 inch newt, so I just looked at it again. Of course a much cleaner split.
I did have to drive away to see this one, even with an OIII filter. Once under dark skies, I spent 4 hours gazing into this marvel with the filter on my 2” 40 mm Konig (2 degree field). The filter does work with the 2 degree view even in dark skies as it eliminates sky glow. Never seen anything like it. The detail on the filaments was visible and marvelous. I never regretted the money on the OIII filter
Over two years I observed from dark skies and suburban skies. Too numerous to list. I am surprised how many beautiful objects are not listed in non NGC catalogs. I think it’s time for a new catalog of deep space gems to be compiled.
I cannot overstate the importance of collimation even in an f/6 instrument. While auto collimation makes a slight difference, accurate Cheshire collimation makes a big difference on all objects, planets or seep space. I also found out that under dark skies (which by the grace of God is only a 1/2 hour drive away for me), a 2 degree field of view gave me far more satisfaction than a 1 degree field. The mystical and profound beauty of a wide field view of the night skies outweighed my desire for high magnification and detail . I understand now why people like Al Nagler and Stephen James O’Meara run around with small wide field Apo refractors. I think that O’Meara’s great deep sky work was just an excuse to get immersed in the profound beauty of the dark night skies. Why would anyone spend hours over several nights on M103 except to get ones soul lost in the majesty of the Cassiopeia star fields. Despite the beauty of the planets, and their ready availability, they are no match in my humble opinion for the magic of those ghostly deep space entities.
The Royce mirror is superb. I am glad I took Carl Zambuto’s advice before deciding on a mirror. I never though an 8 inch can do this. I saw more detail and contrast than the 12 inch Newtonian in a Wisconsin observatory. The Robert Royce mirror also showed planetary detail I never though possible. From dark skies this mirror will keep me busy for a life time I think. I also have to recognize that no matter how good a mirror is, the execution of the scope matters a lot. The Newtonian design, though simple is very tricky compared to refractors. Proper collimation is important even in an f/6 like mine. I would also rank thermal management as important as collimation. The views drop down to moderate when I turn the cooling fan off, especially with the temperature variations of the desert/sea climate in Dubai.
Another problem I faced was dew. It’s very humid in summer here and dew forms quickly specially with the cooling fans. Using heating elements alleviate the dew problem but introduce thermal currents that degrade the image noticeably. But with the fans on, the image is sharp with no dew forming. Basically, keep the mirror warm and keep blowing off the face boundary layer. This was a tip from Bryan Greer of Protostar. The combination created razor sharp images even in the heavy summer dew of the Persian Gulf.
Finally I wish to express my gratitude to the master opticians and telescope makers who spared no effort in providing me guidance and technical tips. Special thanks to RF Royce for his assistance, insights and first rate optics.