NexStar 5 Technology

Some posters to sci.astro.amateur have been wondering what the NexStar sounds like. This can be a big issue because a number of people complained that the ETX 90 EC sounded like a meat grinder. Well, the NexStar 5 is pretty quiet - when it is slewing slowly you don't hear it. When it is tracking, it makes a faint chuffing noise. The only time it really cranks up is when slewing at full speed. Here are some samples:

Folks have also been wondering about how the thing is put together. Some of my observations follow. You can also see pictures of the guts of the NexStar5 at the ScopeTronix web site.

The controller can be removed from telescope via an RJ11 6 conductor jack.

ns_jack.jpg (17440 bytes) Here is the jack.

ns_plug.jpg (13481 bytes)
Here is the plug.

It is difficult (in my opinion) to hang and keep the controller on the fork arm. You have to hang it on the hook pictured below with the two points at the bottom poking into holes on the bottom of the controller. When you are using the thing, it really needs a Velcro attachment to the base, so it is handy but doesn't bang against the tripod.

ns_hook.jpg (21940 bytes)

There has been much discussion about how to package the thing. Some folks are quite enamored with putting it in its shipping foam and placing that in a Rubbermaid plastic tote. I don't think the shipping foam will stand up all that well. Here is what it looks like:

ns_foam.jpg (15523 bytes)

32mm Televue Plossel	39x
25mm Celestron Plossel	50x
32mm+barlow	78x
25mm+barlow	100x
9mm Vixen Lanthanum	138x
6mm Vixen Lanthanum	208x
9mm+barlow	276x
6mm+barlow	417x (only on good nights!)

The Vixen Lanthanum's feature 20mm eye relief which makes them usable - Plossel's at 6mm or 9mm would have about 3mm eye relief. I also have a Meade 15mm but I'm not sure I really need it - I bought if for my ETX90RA but it doesn't look as nice as the Celestron and Vixens.

Tripod/Wedge [back to top]

I wanted a tripod with a wedge so I can polar align and do deep space astro photography. The Celestron tripod is an obvious place to start but doesn't include a wedge in its $200 price tag. I looked at the JMI Megapod - they have one for the N5 for $220 with integrated wedge, eyepiece holder, controller rest, blinking LEDs on the legs.

One aspect of the JMI design that concerns me is that when the scope is canted over, its center of mass is located off tripod center between two of the legs. I am concerned that someone bumping the 3rd leg would push the center of mass beyond the two legs and tip the thing over. However, several owners of the Megapod have indicated that they do not think this is a problem. You can see several pictures of the Megapod at the Starsafaris website.

Another popular concern with the Megapod is that there is no fine adjustment for the angle of the wedge. Basically, you loosen bolts that secure two corners of the wedge surface opposite the hinge and just tip it up and down. With an 18lbs scope on it, this might make fine adjustment difficult.

I briefly owned a Meade ETX tripod with wedge. That wedge had a screw adjustment for altitude and another for azimuth - turn the screw and it pushed or pulled the scope in the relevant dimension. These allowed fine, controlled adjustment of both axis. This seems like the right way to do it.

In this picture you can see the heads of two allen bolts, the forward one is the pivot and the rear one is on a scale which tells you the angle in degrees. You adjust this wedge by loosening the bolts on the scale while keeping the pivot bolts tight enough so that the thing is stiff. Then you can try to make fine adjustments (this advice is from the wedges owner). This wedge will not work with the N5 because the N5 base won't fit between the uprights. Notice how this wedge tips the scope over the center of the tripod (located at the base of the "V" in the front). Here is a top view of the wedge:

In this view, if the wedge was on a tripod you would be looking right down the center of the tripod.

Celestron hasn't announced their wedge for the N5 yet and I don't think anyone knows what it looks like but if it is a slightly bigger one than this (9" between the uprights instead of 8" on this one) then it will have the good feature of pitching the scope over the tripod center and the bad feature of no fine adjustment in altitude or azimuth.

The significance of fine adjustment becomes apparent if you think about the "drift method" of polar alignment. I won't try to explain it here because you can read about it at the STAR Astronomy Club here. The bottom line though is that you measure how much a star drifts in the field of view and then make fine adjustments in altitude or azimuth to compensate. This type wedge on the Celestron tripod, or the Megapod, doesn't allow for those fine adjustments. For example, if you are not quite pointed north with this thing bolted to the top of the tripod, the only way to turn it is to lift and turn the tripod - very difficult to do precisely and it would ruin your tripod leveling.

I am hoping that Celestron makes a wedge for the N5 which has fine adjustments but I am not optimistic since they didn't do this with the C5.