Mount Review: Orion Skyview Deluxe / EQ3 / CG4
Why an Equatorial Mount? Simplifying Polar Alignment How German Equatorials Work SkyView Deluxe EQ3 / CG4 Particulars Skyview Deluxe Model Changes The Bad News First And the Good News Improvement is Possible Wrapping it Up
Why an Equatorial Mount?
There's been a big movement away from expensive and tortuously unfriendly equatorial mounts over the last ten or twenty years. One reason is the advent of the "light bucket". EQ mounts for such scopes would have to be massive and expensive in the extreme!
But for those of us who have compact scopes (fast refractors, Maksutovs, SCTs such as those at left) the equatorial remains the cat's meow...
Why?
Because once an eq is aligned you can use the right ascension and declination to track precisely along the four cardinal directions when searching for very difficult studies. This because with an equatorial you know exactly where you are at all times. And this means you will also know what particular study you are looking at when you do find it!
So say you're searching for a 5 arc-second sized planetary nebula in Aquila. And you know that it is found precisely 1 degree forty five arc-minutes south of Delta Aquilae. To track it down, fine-align the right ascension and declination, center on Delta at low magnification and slew the required number of eyepiece fields south. If you're lucky and the sky is especially stable. Employ a high enough magnification and your scope has good optics, you just might turn up a slightly out of focus 10th magnitude star!
Then once you find the planetary, you can run the magnification up to 400X, lock in the RA drive (if you have one), and look for color, structure, orientation, and central star.
Are you convinced yet???
Simplifying Polar Alignment
One problem with equatorials is the need to precisely align to the Earth's pole. If alignment is poor, drift adjustments must be made using both slow motion controls. Meanwhile, that directional slewing technique could leave you completely "in the dark" while attempting to find a specific DSO.
To address this problem many equatorials come with a small "alignment scope" mounted in the declination axis. This scope can be used to get accurate polar alignment - as long as Polaris is not obstructed from view. (Ever considered what it's like from the southern hemisphere?)
One chill night while waiting for Argo to stabilize, followed various doubles. Soon began experimenting with the "drift method". This approach is pretty straightforward but requires a lot of patience. While following a particular star's movement across the field, adjust the declination axis "left-right" position each pass to get the star centered in the field. (Of course the "up-down" - declination position must already be set properly to local latitude.) After a series of adjustments, the star will eventually stay in the center while tracking.
But what if you have to pick up the scope and move it elsewhere? What then?
Once the mount is oriented perfectly, check the crosshairs in the finderscope. Then rotate the finder tube in a way to precisely align the crosshairs with the declination and RA axis of motion. Later, as you relocate the scope, all you need do is make sure the mount is positioned in a way that manual slewing causes any star to graze along the length of the crosshairs. Simple as that!
Once the finder is set up, you can quickly align by referencing any star anywhere - and not just Polaris. Meanwhile, the virtues of using such a "counter-intuitive" mount will alleviate your learning-curve frustrations.
How German Equatorials Work
OK, so everything above sounds pretty complicated, but at the same time useful. A well-aligned equatorial mount allows you to keep a particular study centered in the field by tweaking only one control. (An altazimuth - or the altazimuth's boxier dobsonian cousin - requires that you shift the scope on two axis. Something pretty hopeless at high magnifcations...)
Just how does an equatorial accomplish this?
As a globe, our earth spins around a central axis. Because of this stars appear to follow an arc in the sky. An equatorial takes the fuss out of tracking star arcs by placing one axis "parallel" to the earth's.
But one axis is not enough. You also need to point the scope anywhere you like. So two more axes are needed. One is attached to the polar-parallel axis and allows the scope to spin almost 360 degrees in a circle. This enables it to do nothing more than keep the pole at the same constant angle as the Earth turns. Not very useful, eh?
Well that's where that third axis comes in. This one is like a "wrist". It enables the scope to pivot around a longitudinal center. The scope can then orient anywhere in the sky. And from that "point" on, the right ascension axis may rotate to keep the pole correctly oriented. This "wrist" is also called the "declination" since it is used to setup the "up and down" angle of any study. When properly adjusted, it physically causes the scope to shift along the "north-south" or "declination" angle of motion. Meanwhile, only that other knob, (or right ascenscion servo motor in a driven system) needs to be turned to keep a particular study centered in the field.
Ingenious really...
SkyView Deluxe EQ3 / CG4 Particulars
The SkyView equatorial mount features a sturdy, heavy-duty equatorial head with fully enclosed 360° worm gears. Azimuth fine-adjustment, dual slow-motion control, lever-style lock knobs, high-visibility setting circles, and latitude scale. Distinctive gold-anodized aluminum tripod with accessory tray. A terrific mount for small and mid-size telescopes. Optional AccuTrack single and dual-axis electronic drives available. Weighs 23.4 lbs.
from Orion B&T's own website dated 05/27/2002
The Skyview Deluxe is a classical tripod supported german equatorial mount. The OTA rides on a saddle machined to spin a full 360 degrees. Saddle rotation may be initiated by pressing on the side of the OTA or by twisting a knob. Rotary cable motion is transferred to a worm-roundgear combination. The use of hand deflection or knob rotation is determined by a lever-actuated clutch. Engage the clutch, and OTA rotation is supported by the slow motion declination knob. Disengage it, and hand pressure against the OTA deflects it along the axis. (Typically when the clutch is engaged, the "knob" is used for fine-position control, while gross-position control is done by simply pressing on the side of the scope tube clutch disengaged.)
NOTE: More expensive EQ mounts automatically "de-clutch" when you manually slew the OTA around the RA or dec axis. In such a mount there is no need to release a clutch lever when re-orienting the tube by hand. Of course such mounts often come with dual-axis drives. Dual drives allow for 2-speed pushbutton slewing along with synchronized right-ascension tracking as the earth rotates about its own axis. Dual speed slow motion slewing is especially useful when orienting an outsized OTA towards a particular study in the heavens. Geo-synchronous tracking is essential for astro-photography, CCD-imaging. It is also extremely useful when observing the Moon, planets, close double stars, or small planetary nebulae at magnifications exceeding 120x...
Like the declination axis, right ascension may be actuated by direct pressure or knob actuated cable. Again, internal motion is achieved as a threaded wormgear turns against straight cut teeth on a round gear. Meanwhile once again, a manual clutch supports the two modes of actuation.
The declination axis on the SkyView Deluxe is adjustable. This simplifies alignment to the Earth's pole. A graduated compass is fixed on the side of the declination pivot. Usually indexing the up-down position of the axis to local latitude is enough to setup the mount. However, care should be taken to plumb things for best tracking results. No levels are included on the mount to assist in leveling. Adding target or bubble levels is a suggested user-upgrade (see below).
Both the right ascension and declination axis include setting circles. Some limited success is possible with their use. Especially when "teeing off" a nearby star or study of known coordinates. Personally I only use circles when short on time or after repeatedly failing to turn up a study after star-hopping or cardinal axis slewing. They are a good inclusion on any equatorial, but digital setting circles are much more useful since they automatically track the sidereal motion of the heavens. Otherwise you have to reset manual circles just before leaping from one study to the next.
The heaviest scope Orion Binocular and Telescope sells on the EQ-3 mount is the 200mm Fast-Newtonian (F4). This pretty much sets the laden limit for the mount to about 20 pounds in weight. Keep in mind that this is a "short tube" instrument. An F10, 4 inch achromatic refractor weighing half that is probably the upper limit due to "torsional-stress" and "leverage gain" associated with long tube lengths.
Skyview Deluxe Model Changes
I now have two EQ3 mounts. So before compiling lists mount strengths and weaknesses, let's get a sense of how the newer unit differs from the older one...
That first Skyview Deluxe came along with a 150mm Maksutov Cassegrain later rejected and replaced by Argo in September 2000. The second mount was picked up as a relatively inexpensive ride for either the 80mm Pup or 102mm Vicki. That mount was purchased new (not as a second) in May 2002.
- The newer mount has a longer counterweight shaft. Thus the 2002 model easily adapts between the ST80 Pup and Argo by shifting a single ten pound counterweight. (Previously, added or removed a three pounder when switching between the two.) There appears to be only one drawback to the new shaft: It doesn't easily fit into the travel bag purchased early on. I suspect the need for the longer shaft was driven by one main concern: The new mount supports Orion's 8 inch shorttube (F4) 200mm newtonian. And that scope needs a pair of ten pounders. (Two come with the mount.) It is likely that this scheme just barely works when both weights are placed near the extreme of the shaft.
- The new mount junks the crappy stick on RA and DEC setting circle pointers. Arrowheads are now carefully painted on instead.
- There appears to be less lubricant on wormgears used to drive the two equatorial axis. (I swipped mine with litium grease.)
- The two hand clutches used to engage the manual slewing cables appear to be more robust.
- The two manual slewing cables themselves are shorter than those received earlier. This is a welcome improvement since Argo is a folded optical system and doesn't need the long ones to begin with. (They are helpful however when using the old mount with Vicki.)
The Bad News First
Now lets talk about the down side of these mounts.
- The accessory tray (a good thing) must be installed (a bad thing) to stabilize the tripod and head. This makes for a far more complex setup/break down procedure than would be necessary had the legs included extendable struts.
- Manual slewing wormgears are improperly adjusted / and or lubricated coming out of China. Just like their OTA's, the Chinese make no effort to adjust stuff properly. And why should they anyway? These things are inexpensive! (Not necessarily "cheap".)
- Axis slewing clutches must be manually dis-engaged and re-engaged to support "brute force" vs "fine tuned" target acquisition. Fine mounts use "slip clutches". These allow you to either manually or cable / electronically slew without special preparation.
- The manual thumbwheel clutches on tripod legs will eventually fail due to lack of robustness. After about 100 uses, you will need to clench the metal spars togther with a hose clamp in order to keep the tripod legs from slipping under the weight of the OTA. Keep three 2 inch hoseclamps on the mount at all times!
- Setting circles lack precision. Rarely will you acquire a study anywhere near or in the center of the field of view. To work, setting circles must be graduated to less than one degree on both axis. This requires the RA be setup with, at minimum, 15 graduations.
- Damp down time: The scope is sold to carry up to 20 pounds (based on the 200mm scope). Argo weighs about 15 and even with Argo it takes 2 to 3 seconds to damp out a focus change or after fine correction of the RA or DEC. Precise focus at lunar-planetary magnifications can be a bit of a challenge. And when going after Mars or Dawes-limit doubles at 500x watch out!
- Wind and Gust Susceptibility: In general the scope is a barely satisfactory ride for Argo on a calm night. Once winds exceed 5 knots or so, frustration levels begin to "mount"!
And the Good News
- The mount and tripod is inexpensive. (Bought used without drives about $150 including shipping. New, about $250 with tax and shipping.)
- Has decent fit and finish (although requires user adjustments to get the best "feel" when adjusting RA and DEC.)
- Can be fitted with electronics (slewing and clock drive - though mine failed within a few months of installation. It also was ergonomically incorrect and lacked consistent synchronization).
- Includes rubber-feet vibration dampers on the tripod.
- And an alignment scope - which I never use.
- Most importantly the EQ3 / CG4 does the basic job any EQ must do: When properly setup allows you to find stuff, focus, and keep things in the field of view even at high magnifications.
Improvement is Possible
- Adjust the aluminum tripod leg lengths to optimize between stability and eyepiece access. Keep the legs as short as tolerable to minimize wind sheer, tube torsion, and damp down time.
- Spread the three legs out as far as possible to lock in greater stability. This is especially useful during focusing at higher magnifications.
- Clean the RA and DEC worm gears with solvant and apply lithium grease to smooth out operation.
- Remove any thread "burrs" from worm gears to prevent periodic errors in gear engagement.
- Adjust the "mesh coefficient" between the wormgears and axis gears to optimize backlash versus ease of motion. (Both the DEC and RA wormgear heads have 10mm bolts that can be loosened to set the degree of engagement by trial and error. The RA head also includes set screws to adjust perpendicularity of wormgear engagement as well.
- Loosen wormgear capture collar nuts slightly to reduce the amount of "drag" experienced when turning slewing knobs. (This is especilly important if electronic servos are installed in order to prevent wear and damage!)
- Replace aluminum tripods with properly sized wooden ones once you determine how long they should be. Build into the legs some length variability so you can level the scope on variagated surfaces. Implement a set of extensible struts to simplify mount setup. Include a means to attach the accessory tray to the struts.
- Carefully add two perpendicular bubble levels (or a single target level) to the mount. These will assist in setting up tripod leg lengths to keep the mount plumb to local terrain.
Of all these changes the ones I've yet to implement are the addition of a target level and construction of wooden tripod legs. Should I do so, I'll add a note here to let you all know if it was really worthwhile.
Wrapping Things Up
Overall, the heads on these mounts are pretty solid. I suspect they will support the 200mm Newt, but honestly, wooden legs or a pier is probably required. Certainly the mount gives 150mm MCT Argo a passable ride (with above adjustments implemented). But a wooden tripod (or pier) along with electronic slewing is essential for a positive experience using an F10 4 inch refractor (such as Vicki).
In general we are talking a barely satisfactory mount for most scopes out of the box. By making the improvements cited above (exclusive of pier or wooden legs), most issues may be obviated for visual use. This for six inch (and smaller) catadioptics and 4 inch (and smaller) refractors. Clearly the mount is insufficiently robust for long exposure photography.
A SkyView Deluxe is in fact, a wonderful mount (after making all adjustments and even with aluminum legged tripod) for a ShortTube 80 or similar sized/weight catadioptic. When used with such a scope, the remaining issues are the ultimate deterioration of the leg-extension tighteners, and necessity for manual axis release clutches.
It is this last statement that is most compelling. I assume the mount was originally purchased to support a "scopists" instrument intended for lunar-planetary and double star observing. Later, as finances permit and commitment is demonstrated, a fine equatorial mount replaces it. Meanwhile, the EQ3 / CG4 ends up as a ride for a small, fast achromat. Like such a wide field instrument, a tuned SkyView Deluxe should remain part of even the most avid amateur's toolkit in perpetuity.