last updated 24 June 2006

Things to Watch For

The first section here will always be safety issues with your telescope. If you know of any that aren't listed, please e-mail them to me at <> and I'll put them here.

If You're Planning to Take Astrophotos

Since the C5+ has been discontinued, if you have a C5+, you may want to obtain the optional declination motors. Many of the C5+ accessories can still be found, since they work with other telescopes, but the declination motors are specific to the C5+. They can be controlled using the optional hand controller, if you have one; alternatively, you can build a hand controller according to the specifications below.

Another accessory that has been discontinued is the counterweight set. C5+ owner Stephen Tonkin became sufficiently irritated by its lack of availability to develop his own:

Anyone who is irritated by the fact that Celestron continue to advertise the C5 counterpoise set on their web site but mysteriously deny all knowledge of its existence, may wish to try this option. The only power tool I used was a hand-held electric drill.
It is based on the fact that I had some old dumbbells lying around (failed attempt to stave off the ravages of middle age). Using a hacksaw, I cut a 165mm (6.5") length of 25mm (1") diameter steel rod (which was once a dumbbell bar) — its weight is 570g (1lb 4oz). I drilled and tapped one end to a 1/4" Whit (1/4-20tpi) thread.
As it is, it counterpoises my Canon FTb/50mm lens, when the latter is mounted on the accessory bar with a ball-and-socket joint. Using my heaviest lens, I add two of the 170g (6 oz) collars which held the dumbbell weights in place. The bolts in the collars take the same hex wrench as do the altitude adjustment bolts on the C5+ wedge. With 4 collars, the total weight is 1.25kg (2lb 12 oz); this gives a tad of leeway for heavier accessories. In extremis, a standard dumbell weight could be added.
In general, this lash-up is a great deal more flexible than the stuff Celestron advertises but does not sell.

Other Tips

Questions answered in this section:

What accessories should I get first?

Obviously, the answer to this question depends on what you intend to do most with your C5+, but the following are a few things that I and others believe are most important:

My finder scope is out of focus, what should I do?

To find objects properly, the finder should be set so that infinity and the crosshairs are in focus at the same time. If not, do the following. (I've only tried this with the 6x30 finder. I don't know if the same steps are valid for the older 5x24 finder.)

The finder is focused at the objective, rather than the eyepiece. Take the finder out of its bracket. The light shield at the objective end screws off, leaving the body and an objective cell that are threaded together. You can screw the objective cell in or out to change the focus. Look through the finder and adjust the objective cell until both the crosshairs and a distant object—at least one mile distant—are in focus at the same time.

Then hold the objective cell in place and screw the light shield back on. This serves to hold the objective cell in place, and you should now be able to use your finder.

I'm having trouble doing polar alignment—when I try to look through the finderscope, my head keeps on bumping into the telescope!

This took me a while to figure out, too, and when I did, I scolded myself for being so dense. To do the polar alignment, your telescope should be set for +90 degrees declination (or –90 degrees if you're in the southern hemisphere). If your declination setting circle has been calibrated correctly, then turning the telescope in RA shouldn't affect what you're pointing at, only the orientation.

Therefore, simply turn the telescope in RA until the finder is more easily accessible. A good place is usually toward the back of the wedge.

Polar alignment is a big pain. How am I supposed to adjust the azimuth (the left-right alignment) without picking the telescope up and setting it down again?

Here's a message from a helpful reader:
I also made a tripod for my scope. Basically, build an azimuth base as you would for a dobsonian mount telescope. Mine is about 12 inches by 18. Drill three holes in the top-plate of this swivel base, and insert T-nuts in them (into these you can bolt down the scope's wedge). Put three legs on the bottom plate of the swivel base. Now after you have bolted down your scope onto the tripod, you can swivel the scope to easily polar align. Mine has a lock-down bolt so I can lock the azimuth adjustment after I polar align. (I cut an arched slot in the bottom plate, and a single round hole for a bolt in the top plate. The bolt is inserted from the top, through the arched slot in the bottom plate, and allows about 30 degrees of adjustment. Tighten bolt with a wing-nut to lock.) I spent $60 in hardware, and used spare lumber. The $300 Celestron tripod does not have an adjustable azimuth feature, so you have to pick up the entire assembly when trying to polar align. That can't be very accurate or easy.

How come sometimes the declination slow-motion knob doesn't work?

While the manual states that you can use the declination slow-motion knob when the declination clamp is either engaged or not, in practice you can often only use it when it's engaged. You could do it in principle when it's disengaged, but it has to be perfectly balanced (this is done by sliding the telescope back and forth on its dovetail plate until it no longer slips). This turns out to be a bit tricky to do to the point where you don't have this problem. On my particular scope, it also means that I can no longer store the scope with the rear cell pointing straight up.

N.B. This is in direct contrast to the RA knob, which you should only turn when the RA clamp is disengaged. If you try to turn it and you encounter significant resistance, then the RA clamp is tightened and you must disengage it before continuing. Otherwise, you may damage the RA pinion.

How do I set the RA setting circle?

I'll assume that you know how to polar align the telescope, since that's explained in the C5+'s instruction manual. Make sure that the declination circle reads 90 when the scope is pointed at the pole.

Now, point your telescope at a star that's not too close to the pole. These days, I sometimes use Capella. Now the coordinates of Capella are RA 5h 17m, Dec 46d. Point the telescope at Capella. Now the declination circle should automatically read 46, or something very close to it. What you need to do now is make the RA circle read 5h 17m.

Recall that the declination circle is held in place with a Phillips screw. The RA circle is not held that way. Instead, you can turn it by hand, although it's designed not to turn by accident. The circle has four little knobs set into it. Using these knobs, turn the RA circle until the position 5h 17m falls directly under the center line of the RA indicator (the indicator is the series of 7 lines just beneath the RA slow motion control). You're done!

Be sure to use the inner set of numbers if you're in the northern hemisphere, and the outer set of numbers if you're in the southern hemisphere.

The C5+'s RA circle only has hash marks every five minutes, so you have two choices if you want to set it to the minute. You can either eyeball it, or you can use the auxiliary marks in the RA indicator (the other six lines). Here's how to use those:

If you look closely, you'll notice that those 7 lines in the indicator are set just a little closer together than the five-minute hash marks. That's the key. To calibrate it to 5h 17m, turn the RA circle until the indicator line two lines to the right of the center line is directly over the five-minute hash mark two lines to the right of 5h 15m (that is, the 5h 25m line). Perhaps a crude ASCII diagram will help make this clearer:

                  |   |   |   |   |   |   |
                  |   |   |   |   |   |   |
        |    |    |    |    |    |    |    |    |    |
        |    |    |    |    |    |    |    |    |    |

        4    5    5    5    5    5    5    5    5    5
        h    h    h    h    h    h    h    h    h    h
        5    0    0    1    1    2    2    3    3    4
        5    0    5    0    5    0    5    0    5    0
        m    m    m    m    m    m    m    m    m    m

You go two to the right on both scales because 17m is 2 minutes greater than 15m. You would go one to the left for 5h 14m, for example. Of course, when you're actually using the setting circles, you turn the slow motion control and move the telescope, not the RA circle itself.

How do I adjust the RA clamp?

The clamp is tightened by means of a threaded bolt, and the bolt has a 90-degree handle. The handle runs into the base of the mount, and so only has roughly 180 degrees of travel. You may find that that travel is insufficient to totally release or tighten the RA clamp.

There are two small holes where the handle meets the threaded bolt, one on either side. Careful inspection reveals that these holes are hexagonal. It turns out that these are small screws that one can pull out using a small hex wrench. Loosening these just a little is sufficient to allow you to remove the handle.

This exposes the bolt, which has a slot for a flathead screwdriver. You can tighten or loosen this as necessary. Do not overtighten, as this will simply warp the washer that is evidently inside the clamp. Replacing the handle is then a simple matter of putting it back and tightening the little hex screws.

What is the polarity of the C5+ DC power adapter?

Lance, of Celestron technical support, reports that the DC power is 12 volts "tip-positive"; that is, the inside slot is positive and the outside ring is negative.

What is the schematic for the C5+ hand controller?

If you're like me, you hate the idea of shelling out $75 U.S. for a paddle that pretty much shorts four different wires to ground. And as far as I can tell, that's what the hand controller does, and it certainly does cost that much (at least from some places). It's especially galling if you're in the southern hemisphere and all you want to do is to get the RA drive to work in the correct direction. If that's you and you don't care about having a hand controller, see the end of this question for a quick and dirty way to do it that only costs about $5 U.S.

Here's the pinout for the hand controller. Looking at the drive base on the telescope (not at the hand controller jack itself), the pins are, from left to right:

  1. LED + terminal
  2. GND
  3. RA - (fast/west)
  4. Declination +/-
  5. Declination -/+
  6. RA + (slow/east)

An effect is in operation while the appropriate wire is shorted to ground (GND). The two declination buttons are opposites of each other. Depending on whether you're in the northern or the southern hemisphere, they are either + and -, or - and +. You can switch between the northern and southern hemisphere modes by pushing both declination buttons down at the same time.

This is just garnered from the net, so don't do it if you don't want to risk your warranty. Nevertheless, I went out to Radio Shack and purchased the necessary parts. The total cost was $25 U.S., most of which went to the project enclosure, which has a nice keypad already prepared for you. It's ideal for this project.

First, buy the 25 foot 6-wire line cord (RJ25), Radio Shack Catalog No 279-422. You only need one end of this; I cut off about six feet of cable. The plug end naturally goes into the socket on the drive base. You will need to strip five of the six wires on the other end. The blue wire is pin 1, which is the positive (+) terminal for the LED. You can leave this unstripped, since its only function is to indicate that the polarity of the RA drive motor has been reversed. Pins 2 through 6 are, respectively, yellow (GND), green (RA -), brown (Dec +/-), black (Dec -/+), and white (RA +); these all need to be stripped.

The keypad/project enclosure is Radio Shack Catalog No 270-215. Its main functional parts are an array of 15 (3x5) keys and a 8-wire ribbon cable leading from the keypad. Each button shorts together two wires—the columns are hooked up to wires 3, 4, and 6, left to right, and the rows are hooked up to 5, 7, 8, 2, and 1, top to bottom. The wiring diagram that comes with the enclosure repeats this information.

I used the center cross—buttons E, G, I, and K on the diagram—but it would be easy to use any set of four buttons. Using my configuration, connect the yellow wire to ribbon cable slots 4 and 8 (use a jumper to connect 4 and 8), the green wire to slot 6, the brown wire to slot 7, the black wire to slot 2, and the white wire to slot 3. Make sure that you don't wire them backwards! Then close up the project enclosure with the included Phillips head screws, and you're all done. Make sure that you've left room for the phone cable to come out. I used the battery enclosure and a filed away spot on the bottom of the enclosure for the cable outlet.

I can report that this hand controller apparently works well with both the stock RA motor and the optional declination motor. In RA, the left and right buttons work as you would expect them to, although the correct direction may depend on whether you're observing with or without the diagonal in place. To get faster guiding, as mentioned in the manual, push left and hold, then push right as well to slew positively in RA at 3x sidereal speed. Doing the reverse guides negatively in RA at 3x.

Up and down move the RA motor north and south, respectively. In addition, the motor has an undocumented fast mode which is exactly analogous to the fast mode for the RA motor: push up, hold it, then push down to guide at 3x toward north; vice versa to guide at 3x toward south. The only problem I've had is that the declination motor seems to sporadically reverse direction when going north at 3x. This seems to have something to do with insufficient torque, but it's hard to tell, and since I don't have a need to guide north at 3x for long periods of time, this shouldn't be a big deal. Again, I wouldn't want to slew with these motors; they're strictly guiding only.

Switching northern and southern hemisphere operation is similarly simple. With the drive off, push and hold down both up and down buttons. Now turn on the drive. Wait for two or three seconds, during which the drive will not move. When you let go, the drive will begin operating, but in the opposite direction, appropriate for southern hemisphere driving. The C5+ manual indicates that the LED (on the controller, presumably) will blink when the switch has been activated, but I didn't hook up an LED. The direction of the motor changed, though.

Those of you who want to be able to switch this way without having to build the hand controller can simply buy the cable, strip yellow, brown, and black, and push them together to get the same effect.

Is there anyway to turn the C5+ into a GOTO scope like the Ultima 2000 (Celestron) or LX200 (Meade)?

Yes. Sell it and replace it with the Nexstar 5. Seriously, though…

Sadly, no, not without a lot of additional hardware. The RA motor in the C5+ and the optional declination motor are both intended for adjustments during long-exposure astrophotography, not for slewing. You can attach digital setting circles, though; these make it possible to find objects with a great degree of accuracy and precision without perfectly aligning the telescope. (Objects will still drift slowly out of the field of view unless the scope is aligned perfectly, however.)

For those of you who, like me, are too cheap or don't care enough to get DSCs, I've written a C program that you can use to do something like DSCs. Basically, you roughly align the telescope (setting it down toward north will do just fine), and then you point the telescope to two stars that you indicate to the program. The program will ask you to enter in the coordinates for each star as seen on the analog setting circles.

Thereafter, when you want to find an object, you enter its true coordinates into the program. It will return the circle settings that will point the telescope to the correct position (within about a degree). Of course, it's limited to the precision of the setting circles on the scope already (about 1 minute of RA, and perhaps half a degree of declination).

You can get the program source, called goto.c, here. I'll admit that goto.c is something of a misnomer, since it doesn't actually control your scope—as I said, that's impossible with this mount. Instead, it works like a set of digital setting circles, using only your eyes as encoders. I've only tested it under Linux, where it worked fine. Please let me know if you have any problems compiling it or using it. The user input is very rudimentary right now, and the code is completely undocumented, so please bear with me while I make it a little nicer.

Update: I've recently made some new modifications to this code, and I'm fairly satisfied with the inner workings of it—the only thing I'd improve now, really, is the user interface. It has a new simpler algorithm based on dot products (the old one was based on Euclidean distance, which was very unwieldy), and it also includes a time correction based on the misaligned scope. It still will fail if the scope is poorly aligned and you take too long between measuring the two calibration stars, but otherwise it should work reasonably well. In a recent field test, which unfortunately was cut short by weather, I was able to place target stars within about 20 minutes of arc of the center on average, with no star appearing further out than 30 minutes of arc. Number of stars was only five, however…

Incidentally, this code corrects for a misaligned scope, but it does not correct for non-perpendicular axes. That would require a third alignment star, and would have complicated the algorithm considerably. Besides I'm not sure how I would do it. :)

I thought the C5+ had a wedged fork mount! What is this C5 GEM?

What you are probably thinking of is Celestron's CG-5 mount, which many people have mistakenly called the C5. Celestron does have a number of very similar-sounding numbering series for its mounts and scopes, and it's not always easy to tell which is which. It used to be much worse. Now, the C and G series are scopes, and the CG series are GEMs. Got it? <grin>

The CG-5 is a Vixen Great Polaris clone. Reports are that it is approximately as sturdy as the GP, but may in many cases require a lot more TLC to get it to perform as well and as consistently as a GP.

You may also be thinking about the G5, which is a C5 OTA that comes on a GEM—the CG-3, by the way, as if that doesn't confuse matters any more.

What eyepieces should I add to my collection?

This wasn't a question that I originally felt dealt very specifically with the C5+ and Celestron's other 5-inch SCTs, but I've gotten the question so often in the past that I've decided to include it here.

Ultimately, this is something that each user will have to decide on their own, but here are my eyepieces and my reasons for selecting them. The C5+ came with a 25 mm SMA (Kellner) eyepiece, and that is the point of departure. It's not a great eyepiece, but it's probably the best of the SMAs, and it's perfectly serviceable. It's very poorly baffled, though—stray light is very evident on the moon.

For planetary observing, you want a good range of powers from about 80x all the way through to perhaps 300x. I chose a 15 mm Tele Vue Plossl and a 9 mm ortho from Pocono Mountain Optics. Along with my 2x Barlow, this gives me 83x, 140x, 167x, and 280x—a good range to select from depending on how the seeing is on any given night.

For deep-sky observing, you want all of the above, plus you want a nice wide-field eyepiece. I chose a 32 mm Tele Vue Plossl, and it's a great tool to use with the C5+. With my f/6.3 reducer/corrector, I get about 25x with nearly a 2 degree true field of view. Some people don't like to use such a wide field (and exit pupil) with light polluted skies, but I disagree. Often the easiest way to find a deep sky object is to use a wide-field eyepiece; then, once it's found, you can use higher magnifications to make the object stand out from the dark sky.

That brings me to the last point—auxiliaries. I have two, the aforementioned Barlow and reducer/corrector. Among Barlows, the Celestron Ultima often gets good ratings as the best modestly-priced Barlow on the market. It sells for about $80 U.S. But many less expensive Barlows are good, too. The things to look for are fully multi-coated lenses and good baffling. With a Barlow, the light cone is very thin and skinny, and stray light will tend to affect the image more adversely than normal. I have a Orion Barlow that I bought for about $45 U.S., and it's quite good.

As far as the reducer/corrector goes, I have to count that as perhaps the best $120 U.S. I've spent on the telescope so far. It not only gives you a wider field of view, giving truly impressive views of those open clusters, but it also flattens the field by quite a good margin. There's still a bit of curvature—I'd say there's about 20 percent of the amount there is without the R/C, but it's much less objectionable. Not that it's so bad without it, but there's no question it's a noticeable improvement. Celestron and Meade R/C products both work equally well on the C5+; the Celestron is less expensive, so I'd recommend that one. If you do buy Meade, take care to buy the f/6.3 R/C; Meade also sells an f/3 R/C which is only for CCD use.

My last recommendation isn't an optical aid at all, at least not in the ordinary sense. It's an eyepatch, and it's advertised in the Orion (U.S.) catalogues. What it does is allow you to observe without squinting your off eye (the one not at the eyepiece). This $2 piece of fabric has made it much more comfortable for me to observe, and it is absolutely true that greater comfort means better detail. You're simply not distracted by your sore eye muscles. Orion sells them at a nominal cost, but unless you're buying a large order with them, you can get them much more inexpensively and quickly from your neighborhood drug store.

How do I collimate the C5+?

This is an important question and has been moved to its own page.

Copyright (c) 1998, 1999 Brian Tung