Telescope Reviews: Thinking of Buying a C6-RGT As Your First Scope?

Ask almost anybody thinking about buying their first scope how they intend to use it and they almost always say the same thing - "Well, I want to look at the moon and planets, and see DSOs - and oh yeah, I also want to use it to take photos and by the way, it should cost under $1000". I know because I said the same things myself several months ago. The reality, of course, is that it is difficult to find one scope that does everything well, particularly when dealing with a restrictive budget. After weeks of research, I ended up with the C6-R and hoped that it would handle each of the 3 areas I was interested in an acceptable manner. Well, after owning the scope for 4 months, I decided to take a few moments and record my latest thoughts:

C6R OTA
Overall, the scope has performed quite well and fully meets my expectations for a 6" achromatic refractor. I have spent dozens of enjoyable hours out under the stars (between the never-ending rain clouds) and have memorable views of the moon though it's various phases, Saturn's rings, Jupiter's bands, M42, M45 and a number of globular clusters. I have also split many close doubles and have spent hours examining craters, searching for faint stars in the trapezium and locating tiny moons around Saturn. CA is present but well controlled by a filter - the only times I really notice it are on Jupiter, the full moon and splitting doubles on bright stars like Rigel. Crater detail on a waxing or waning moon is breathtaking and stars generally resolve into tiny pinpoint white dots.

AS-GT Mount
The AS-GT mount has also fully met my expectations. The 2" steel legs on the tripod are very steady and the scope settles down in a couple seconds after a bump. I experienced some initial difficulties with gotos but, as I suspected, they were my fault, not the mount's. Be sure to carefully level the mount, align on Polaris and enter a precise time - stars will rotate out of the selected location if you are off by a minute or so due to the natural rotation of the earth. I also found that an illuminated reticle EP is a worthwhile investment - since acquiring a 10mm, my gotos have been flawless and every object appears close to center in a 13mm Nagler.

I also confirmed that the mount does learn. The first night after a reset, the scope will miss the alignment stars by a wide margin. By the second night, the mount will learn how much adjustment was required on the previous night and will be much closer to the alignment stars. By the third night, the alignment stars are nearly centered. If you make an error and have a bad alignment, I found it helpful to use the menu "reset" command to clear the computer's memory. Please be aware though that you will have to re-enter the site and date/time information.

Finally, the tracking is excellent. Although I don't recommend it, I have left the mount tracking and gone out to dinner - returning to the back yard a hour or so later, the object was still in the EP. WARNING - if you leave the scope on, ALWAYS be aware of the scope's projected path so that it doesn't accidently contact a leg. I only do this on objects well below zenith.

One final note - do yourself a favor and get a new power cord. Scopestuff sells a heavy coiled cord just long enough to reach from a Powertank to the mount - $12.00 including shipping - fused auto-adapter on one end and Celestron plug on the other - even has a red led on the auto-adapter to confirm the cord is getting power. Well worth the money!

Astrophotography
Besides enjoying time at the eyepiece, one of the main reasons I purchased the scope was to dabble in astrophotography. I am pleased to report that it is possible to take very nice photos using the scope BUT it does have its limitations:

1. Weight
In general, a scope used for astrophotography should weigh less than 50% of mount capacity to minimize jitter - the C6R exceeds that recommended limit by a wide margin. As a result, there is some jitter on exposures over 2 minutes long.

2. Chromatic Aberration
Yes, CA is a problem on bright objects. While you may not notice the CA when using the scope visually, the blue fringe will be quite evident in a long exposure. For example, on a 2 minute exposure, bright stars will have a broad blue band around them whose width is equal to approximately 50% of the star's diameter. Fortunately, much of it can be adjusted away in post-processing using Photoshop CS or Elements.

3. Aperture
At F8, the scope is fairly slow for photographic use. As a result, longer exposures will be required and the FOV will be smaller than a faster scope.

Limitations aside, taking photos through the scope is quite enjoyable. I do not have a webcam so I have not attempted to photograph Saturn or Jupiter but have taken numerous pictures of the moon, globular clusters, M42 and star groupings using a Nikon D70 DSLR. A few examples can be found at this link:
http://www.cloudynights.com/photopost/showgallery.php?ppuser=6252&cat=500

If you decide to go forward with photography, take a few minutes to read this article on the Televue site - it explains in easy to understand language the various ways to connect a camera to your scope.
http://www.televue.com/engine/page.asp?ID=236

Prime Focus
The telescope acts as approximately a 40x lens (1200mm flocal length / ~30mm chip diagonal) - the exact magnification will depend on the diagonal measurement of your CMOS or CCD (figure 43mm for 35mm film). To attach a SLR or DSLR, you will need a T-adapter and T-ring. NOTE: Not all T-adapters will fit the Mercury Systems visual back - I found that the WO T-adapter is machined to exactly the same size as the WO 2" diagonal and fits perfectly. Add a Celestron T-ring for your specific camera and you are good to go. To achieve higher magifications, replace the T-adapter with a TV 2x or 4x Powermate with a T-adapter ring attached.

Afocal Imaging
One of the problems attaching a camera for prime focus photography is the fixed magnification. Since I have a growing selection of high-quality EP's, I have been looking for a way to take photos through the EP at various magnifications. I have had good results holding a small digital camera to an 18mm Ultima but have had much less success taking pictures through various Naglers. Although I have not tried it yet, Scopetronix makes a product called Maxview II which allows any EP to be attached to the camera. Quality of results unknown.

Software
I'm not going to go into any detail on software packages used in astro-photography. Suffice it to say, 50% of any astro-photo is done at the camera - the rest is done at the computer. Expensive to purchase, Photoshop CS is the most popular software for photo-editing. The package has a steep learning curve but allows near total control over all aspects of the final image. I elected to purchase the less costly Photoshop Elements. Although less full-featured, the software was only $80 and reads the Nikon NEF raw format. Lots of good tutorials are available on the web for both packages.

Starbound Chair
This chair is fantastic - very comfortable and adjusts easily to any height - a must with a large refractor since the viewing positions cover such a wide range of heights. The only flaw is that the rubber feet on the chair need to be replaced every 2-3 months - the steel tube pushes through the rubber long before the rubber wears out. Fortunately, Ace Hardware in my area sells exactly the same feet - buy those made for 7/8" tubing - about $0.65/each. The feet will last much longer if you put a steel washer in the rubber feet before installing them. Buy a 1" OD steel washer and press it into the bottom of the rubber feet with a screwdriver - the washer will prevent the tube-end from cutting the rubber.

Mount Extension
The default low viewing position of the C6R-GT is one of the weak points of the package. Adding a WO diagonal, 2" brass focus knobs and Telrad mounting plate helped a great deal but I have continued exploring ways to raise the raise the viewing position. I ordered the Orion 16" extension for the Skyview Pro mount but returned it a few days later - although it did mate reasonably well to the AS-GT mount and was very well made, it was too heavy, too long, had an overly-large azimuth bolt alignment hole and had a fairly flat bottom that barely engaged the tripod bolt.

I recently located a company named Astrosky that agreed to machine a similar extension in a shorter length (see picture in gallery link above).

The Positives:
The entire unit is 7" long and weighs about 3#. The end caps are well machined and mate well with the mount and tripod. The bottom end cap extends 3/8" into the tripod and engages approximately 8 threads of the tripod bolt. The top cap includes an Allen-head bolt with 2 washers and engages the bottom of the mount by 7-8 threads. Overall the quality of the machine work seems good - the caps fit tightly in the pipe and mate snugly with the tripod and mount. The caps are attached to the 4" pipe with 3 Allen-head screws on each end.

The unit feels very solid when installed and height is sufficient (with the other balance changes I made earlier) to prevent the scope from hitting the tripod legs when viewing at zenith. With the extension, I find that I am able to pull-in the lower leg extensions by approximately half of their length and still view objects directly overhead while seated in a Starbound chair. The mount doesn't feel tippy and seems quite stable with a 6" refractor installed.

Minor Quibbles:
(1) the bottom cap was manufactured much like the Orion bottom cap and the azimuth receiver hole is much wider than the peg - this allows the entire extension to twist slightly and could throw off a polar alignment if it shifted in use.

(2) the aluminum tube is painted a flat black - it actually looks kind of cool with the aluminum edges on the caps showing but doesn't match the pebbled finish on the tripod and mount.

Overall, the extension serves its purpose and is a bargain at a cost of around $60. James at Astrosky was good to work with and communicated well during the transaction.

Conclusion
The C6R-GT fully meets my expectations. The scope introduced me to a whole new world of astronomical observing and astro-photography - it has been a joy to use and great fun to modify. Although I intend to hold onto the scope for the next few years for visual use, I am planning to supplement it this year with an 80mm APO to expand my interest in astro-photography and allow me to take a scope on the road. Long-term who knows - at present I am thinking that the perfect combination may be an 80mm APO for travel and photography and a 12" DOB with Zambuto glass to reach those elusive DSOs.

Regards,