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

Thinking of Buying a Celestron C6-RGT As Your First Scope?

Before you purchase:

The scope is an excellent performer for the price and I am very happy with the purchase. But before you buy, there are several things you should be aware of:

1. Viewing positions in a large refractor are often very uncomfortable. Many interesting objects are directly overhead – given the low eyepiece position, viewing them requires laying on the ground – particularly unpleasant in the winter.
2. The scope is large and heavy though none of the pieces is unmanageable by itself. The mount and tripod (without weights) weighs about 35# and is easily moved with the legs at their shortest position. The OTA, although long, only weighs about 20# (25# after modifications) and is easily carried by the dovetail. Assembly requires 4-5 trips outdoors – tripod and mount, then balance weights, then OTA, then power unit and accessories and finally a viewing chair.
3. Slewing to position is noisy – equivalent to a power drill on medium speed. The noise is enough that I fear it is bothering the neighbors when I am out late at night. Fortunately, the motors are whisper quite during tracking.
4. Save at least 50% of your budget for accessories. The scope is only the beginning of the purchase – by the time you pick up the items you need to make viewing a pleasant and interesting experience, you will spend at least another 50% of the original purchase price in add-ons.

You will probably read books and articles suggesting a DOB for a first scope. Although I ignored the advice, in retrospect the suggestions were valid. I believe an 8” DOB is the best scope for someone just starting out. The scopes are very good performers at a reasonable price. Setup is simple, they are easy to transport to a dark-sky site, viewing positions are much more comfortable and the user can quickly move the scope to look at any object in the sky. The Skyquest XT8 Intelliquest from Orion is an excellent buy at $497.

You may find the DOB meets your needs for many years. If not, they are easy to sell or can be passed down to a younger family member. You can always pick up the large refractor at a later date if your interest in the hobby holds. And if you purchase your accessories wisely, they can move with you when and if you upgrade scopes.

When To Buy:
Depending on your location, winter can be a difficult time of year to get your first scope. Winter skies do have a number of wondrous sights, and seeing conditions can be quite good on clear, cold nights but freezing cold weather, dew, rain, fog and cloudy skies can quickly frustrate a novice astronomer. Learning to use your equipment correctly, and learning the layout of the skies, requires time and patience. Warm spring and summer nights make the experience much more relaxed and comfortable while you are learning.

Purchase and Shipping:
There are a number of excellent on-line vendors. I purchased my scope from Anacortes Bird and Telescope. The purchase experience was perfect. They stayed in touch by email during the transaction and advised me when the unit shipped - including links with the tracking numbers for all boxes. The scope was shipped in 3 boxes – 2 of which arrived on one truck (the tripod and mount) and a third 5 hours later on a second truck (the OTA).

The pieces were well packed and suffered no damage in shipment. The packing attention paid off because 2 of the 3 boxes suffered significant compression damage at the hands of the shipper but the scope was unscathed.

Assembly:
Assembly is fairly straight-forward. Read the manual carefully before starting. The instructions are adequate although the assembly drawings don’t supply as much small detail as I would have liked. A couple of things to note.

1. Tripod Alignment Bolt
The tripod ships with the alignment bolt between the legs. Some people feel this can lead to instability when the weights are installed and prefer that the weights be over a tripod leg. There are several threads on the internet discussing the pros and cons of each position. If you wish to move the bolt, it simply unscrews and can be easily screwed into the alternate position over a leg. I elected to move the bolt and find the mount to be very stable in that configuration.

2. Mounting Bracket
The instructions tell you to locate the small scope mount bracket which will be used to install the scope to the mount. You can ignore these instructions. The scope comes with a dovetail attached to the rings and the dovetail is inserted directly in the mount. The spare mounting bracket can be used if the mount is used with another scope.

3. Mounting Platform Safety Screw
Several people have suggested that the DEC index marks are 180 degrees off since the mounting platform safety screw points down rather than up. In my case, I elected to use the factory marks – the safety screw will still function as intended and keep the dovetail pressed into the mount should the main tension knob fail. If a failure occurred and the dovetail were to slowly slide in the mount, I believe the safety screw and dovetail retaining bolt would ensure that the dovetail could not slip completely free of the retaining bracket.

Accessories:
If you decide to order the scope, following are suggestions for several accessories that I found will improve the scope’s overall performance. The majority of accessories are under $100 and many are under $50. Don’t feel you have to add them all at once. Astronomy is a very enjoyable hobby that will likely keep you interested for the rest of your life. Add a few accessories each year as your budget allows.

1. Red Light (~$25)
If you don’t already have a red flashlight, protect your night vision and get one. The Rigel Systems Skylight is an excellent unit with 2 red and 2 white LEDs. The unit is well-made, reliable, very skimpy on battery use and brightness is continuously variable with a large control-wheel.

2. Planisphere (~$10)
The alignment process is highly dependent on accurately centering the scope on 3 selected stars. The large version of “The Night Sky” by Chandler is easy to read and plastic coated for protection against dew. Be sure to select the version designed for your latitude range.

3. Celestron Powertank (~$60)
The scope comes with a long power cord with an auto lighter adapter. You need a 12v power source to plug the adapter into in order to run the scope’s motors and electronics. I purchased the Celestron 7ah Powertank - fully charged, it will handle the scope’s power needs for 4 hours or more. Celestron also makes a larger 17ah unit that is useful if you intend to also run a dew heater. One note – the power cord shipped with the scope has a quick-blow fuse in tip of the auto adapter. If your scope won’t function, replace the fuse (Radio Shack carries them – part #270-1054 3A-250v-5mm x 20mm-Fast Acting) or try the shorter power cord that comes with the Powertank (some people feel the scope also operates more reliably with the shorter cord).

4. Right-Angle Mirror Diagonal (~$130)
With the exception of viewing objects near the horizon, don’t try to view without using a 90 degree diagonal. The diagonal that ships with the scope is adequate for the first few weeks but a good diagonal will enhance the quality of the scope’s performance. I elected to purchase the William Optics New Generation 90 degree diagonal. The product is very well made, includes a 2” to 1.5” adapter and adds needed weight to the rear of the scope to aid in balancing. Additionally, the unit uses a brass retaining ring to securely hold lenses in place.

Note: The diagonal is fairly heavy – I don’t recommend replacing the stock diagonal until after the visual back is replaced.

5. Right-Angle Finder (~$80)
Just as a right-angle finder is a necessity for the scope, it is also mandatory for the finder. The Celestron 9x50 finder works quite well but is inaccessible at many viewing angles. Save your back and get the Orion 90 degree RACI (right-angle correct image) finder. It is well made, offers the same power as the Celestron unit, is a perfect color-match and the included bracket fits the same dovetail as the stock finder.

6. Focus Knobs (~$30)
The focus knobs that come with the scope are completely inadequate and give the scope a cheap feel. I ordered the 2” brass focus knobs from focusknobs.com. The knobs are very, very well machined. They fit perfectly, look beautiful and give the focuser a much more professional look. In addition, the larger, heavier knobs give a much better feel to the sticky focuser mechanism and help shift the balance point lower.

7. Visual Back (~$35)
The 2” visual back that ships with the scope has an inexpensive feel and uses a single retaining screw to hold the diagonal. Mercury Systems supplies a well-machined replacement that uses a brass retaining ring to hold the diagonal securely. The unit installs easily by simply unscrewing the old back and screwing on the new one. Check mercurysupportsystems.com and look for part #SFA2. Highly recommended.

8. Fringe-Killer (~$70)
The scope is not an APO and will have some degree of chromatic aberration (CA) on bright objects. Fortunately, several manufacturers make inexpensive filters which can minimize the affects. I elected to purchase the Baader Fringe Killer. The filter removes 60-70% of the CA while maintaining a natural color rendition. You will only use the filter on a few bright objects such as Mercury, Saturn and the moon. On deep-sky objects, the scope’s performance is excellent without a filter installed. For those of you that can adjust to an overall color-shift in the image, the Celestron (Baader) Contrast Booster will completely eliminate CA at the expense of a noticeable shift to a yellow-brown image. Personally, I found the Fringe Killer a more acceptable compromise between CA and natural coloration. The Baader Moon and Sky filter, used in combination with the Fringe Killer, seems to enhance the image further.

9. Polarizing Filter (~$25)
Orion makes a very nice 2 part rotating polarizing filter. The filter is particularly useful on the moon. The moon is very bright when viewed through an EP and will quickly erase your night vision. The polarizing filter will allow you to dial the brightness to a comfortable level while leaving the color neutral. In addition, the filter will dramatically reduce the CA.

10. Eyepieces (~$180)
The 20mm Plossl that comes with the C6R is an adequate performer but additional EPs will be needed to take full advantage of the scope. EP selection is highly personal but, in general, it is best to buy quality EPs as you will likely keep them for many years. Start with a high-power EP for planetary work and a low-power objective for wide angle views.

For wide-sky viewing, I selected the 30mm Celestron Ultima. Be sure to get the latest model that has the machined retaining groove. The EP is of very high quality and offers beautiful views of objects such as the Pleiades.

For planetary work, I ordered a 9mm HD Ortho from University Optics. Again, a well-made high-power EP that offers sharp contrasty views of the moon and planets. I have since added a 7mm HD Ortho, a 12mm HD Ortho and an 18mm Ultima. The 18mm is now my favorite EP.

Televue Naglers and Panoptics offer superb wide-field performance and are well worth consideration if your budget allows. Televue Plossls are also high quality EPs offered at a very reasonable price.

11. Barlow (~$105)
A good Barlow lens will double number of magnifications you will have access to. Don’t skimp – the Barlow will be used to increase magnification near the limits of seeing and optics. You don’t want to introduce any distortions at high magnifications when you are looking for contrast and detail. Celestron makes a highly rated Ultima 2x Barlow that works quite well (in contrast to the low quality Barlow that ships with the scope). I elected to spend a little more to get a Televue 2x Barlow – superb optics and it uses a brass retaining ring to hold the lens in place – rather than a retaining screw which will scratch the lens barrel.

12. Chair (~$160)
Although the purchase of a chair threw me well over my intended budget, it quickly became a mandatory purchase. Using a large refractor, you will find yourself in a variety of uncomfortable viewing positions. A good quality, adjustable chair makes all the difference between taking a quick look and spending 30-60 minutes watching shadows along the terminator on the moon. Starbound makes an excellent chair that is lightweight, strong and easily adjustable.

13. Telrad (~$40)
The Telrad is a strange looking box that makes finding objects a breeze. The Telrad will get you in the general area, then the finder can be used to center on the object. Get one – after a few days, you’ll find it an invaluable addition.

14. Dew Shield (~$45)
Many users have elected to remove the stock dew shield and replace it with a lighter foam shield made by AstroZap. Again, this is one of many incremental changes owners make to reduce weight on the forward-end of the scope to aid in balancing. For time being, I decided to stick with the stock shield. Although a bit heavier than the AstroZap product, the steel tube provides protection to the large lens element.

15. Polar Scope (~$50)
A polar scope is not necessary to obtain an alignment adequate for visual use but is a nice addition to the mount. If you do decide to buy a polar scope, skip the Celestron scope and buy the Orion model designed for the Skyview Pro. Simply remove the entire polar scope mounting ring from the AS-GT and the Orion scope screws directly into the same hole. The Orion scope is etched with Casseopia and the Little Dipper for precise alignment on the North Celestial Pole.

Note – the Orion scope comes with a plain aluminum ring around the polar scope. If you like the current numbered Celestron ring (I did – it looks more scientific), the rings can be easily switched by removing 2 very tiny screws and unscrewing the front retaining ring from both the polar scope and Celestron polar mount.

16. Sky Atlas (~$65)
The sky is a target rich environment a good sky atlas is critical if you are going to locate DSOs. The Sky Atlas 2000 by Wil Tirion is one of the best (this is a different book than the Cambridge Star Atlas by the same author). The book comes in 6 versions – white stars on black, black stars on white, black stars on white with color and then laminated versions of each. Personally, I like the Sky Atlas 2000 2nd Edition Desk Laminated version which shows black stars on a white background. Although the color version is nice, the cost is over $120 laminated and some of the objects can be difficult to see at night under a red light. The laminated versions cost a bit more but will protect your investment when the book is outside on dew filled evenings. Additionally, you can make notes on the laminate and wipe them off when you move on to a different section of the sky.

Viewing Height:
My only serious frustration with the stock scope has been the low eyepiece location when viewing objects high in the sky. Although the brass knobs and WO diagonal helped add weight to the rear of the scope, the ultimate solution was to add a 3rd mounting ring close to the eyepiece and bridge the 2nd and 3rd rings with a heavy steel plate. The plate makes a perfect home for the Telrad.

AllMetalsInc (http://www.allmetalsinc.com/crflat0375.html) sells small steel plates (~$3-4 ea) in a variety of sizes that can be painted to match the scope. The addition of a 3/8” x 2-1/2” x 8” CR plate with ring, bolts and Telrad added another 2-1/2 lbs to the rear of the scope and allowed me raise the scope several critical inches.

Note: If you do make modifications to the OTA, keep an eye on the total weight. With all the changes to date, the OTA/finder/diagonal/Telrad/eyepiece combination now weighs 25.8 pounds. This is well below the 30 pound mount capacity and allows for the use of a heavier eyepiece such as a Nagel or a mid-range camera for astrophotography.

Alignment:
Warning: The scope’s computer is not very smart and it will select slews that force the OTA into the tripod legs. Should the scope impact the tripod, you could cause significant damage to the drives. You can press any of the directional arrows to immediately stop the slew. Be cautioned when pressing “undo” to skip a star during alignment - if you are near a leg, the scope may abruptly change direction and impact a leg before you can react. I’ve found it preferable to use the arrows to slew well away from the legs before selecting the next alignment star.

I found the alignment process initially frustrating because the accuracy of the GoTos varied from night to night. Assuming it was primarily my fault, I took the following steps and find that the process has become much more reliable.

1. Level the tripod - CAREFULLY
If the tripod isn’t level, the mount has no way of making an accurate determination of position as it skews. The bubble balance in the tripod may not be accurate. Check it at least once with an external level.

2. Locate Polaris in the polar scope
If you don’t have a polar scope, carefully center Polaris in the polar scope mounting hole.

3. Align the RA index stickers and lock the clutch.

4. Loosen the DEC clutch and center Polaris in a 20mm eyepiece. Lock the DEC clutch. Ignore the DEC alignment stickers.

5. Before starting the mount alignment procedure, be sure that the Telrad and finder scope are aligned with the OTA.

6. Enter the correct time, date, time zone, daylight savings setting, longitude and latitude for your viewing site. Be as exact as possible. You can find the time and lat/long settings for your address at various sites on the internet.

7. Select “Auto 3 Star Align” rather than “Auto Align”. The scope will allow you to select 3 stars from a list (2 will be on one side of the Meridian and 1 on the other side). When selecting stars from the list, try to pick stars which are between 30-60 degrees above the horizon, are NOT within 5 degrees of Polaris and are far enough apart to form a broad triangle. Do not attempt to center the star until the scope asks you to do so – this may be a few seconds after the scope appears to stop slewing.

You will probably find that the slew to the first star is off by several degrees. The second and third star should be visible in the finder. Be sure to verify that you are centered on the correct star – centering on the wrong star will lead to grossly inaccurate GoTos.

8. Center the scope carefully on each star using the Telrad to be sure you are in the correct vicinity, then narrowing in with the finder and EP. A 9-12mm Ortho EP works well for centering since the field of view is fairly narrow. If you are uncertain if the star is centered, take it out of focus and center the larger unfocused image. A 9-12mm illuminated reticle eyepiece will obviously help make this process much easier and exact if you have access to one.

When centering on a star, make all final adjustments using only the RIGHT and UP arrows. If you need to use the LEFT or DOWN arrow, overshoot the mark by a wide margin (1/2 the FOV in the eyepiece) then use the RIGHT and UP arrows to make the final adjustments. This will minimize the effect of backlash in the gears and enhance the accuracy of the alignment.

9. Once all stars have been centered, the scope will perform its calculations and advise if the alignment was successful. Several people have suggested that a shorter calculation period (5-10 seconds) indicates a more accurate alignment than a longer calculation period (15-20 seconds).

Note – Celestron periodically releases firmware updates for the mount (the software in the hand controller is only upgradeable at the factory) At the time of this writing, the current version is 5.06. If you are on an earlier version and experiencing runaway slews or other problems, you should consider upgrading (the version can be checked through the menus). A Celestron port expander and programming cable are required for installation of the patch.

Future Plans:

1. Mount Extension
Despite the changes I’ve made so far, the viewing position is still 6” too low for comfort. Since the AS-GT mount is apparently very similar to the Orion Skyview Pro mount, I will probably pick up the 16” extension Orion offers for the Skyview Pro and see if I can have it machined to a 6” length.

2. Focuser
If I decide to keep the scope long-term (My dream scope has always been a 115-120mm AP or Takahashi APO), at some point I will replace the focuser with a better machined unit. Although the stock unit is adequate, it is a bit jerky when trying to achieve fine focus at high magnification. I imagine that this is partially due to the Synta-glue clogging the stock unit but is also attributable to the poor mechanics of the focuser. I have also noticed that the focuser shifts axis slightly when changing rotation direction of the focus knobs. Both Moonlight and Feather Touch offer high-quality, well machined replacement units. I am currently leaning towards the Moonlight since it’s a directly bolt-up to the existing screw holes – the unit’s 3 lb 8 oz weight will allow the scope to balance slightly lower than the stock focuser.

3. Cases
I would like to start taking the scope to dark-sky sites once or twice a month as time and weather allow. Before I do, I plan to pick up a soft case for the tripod and mount and a well-padded case for the OTA. Orion sells soft, padded cases for $60-$80 which fit the scope nicely (#15164 for the OTA and #15175A for the tripod). An extra foam rubber camping pad inserted in the case will give the OTA additional protection.

Summary:

The CR-RGT is a great scope and I’m glad I bought it. I appreciate the light gathering capacity of the 6” optics and have really enjoyed making minor enhancements to improve the usability of the scope. The mount seems very stable for visual use and the price for the mount/OTA combination is unbeatable. If you decide to purchase the C6R, have fun personalizing it to meet your needs. But most of all, take time to enjoy the skies!