I purchased this scope because of its incredible value and tremendous
light gathering capabilities. The Meade Starfinder dobsonians are well known
for their quirks, and I was aware that I’d probably be doing a lot of
modifications to make the scope more comfortable to use. But, right out of
the box, the biggest problems with this scope were the weight and the fact
that there was no way that it would fit into my small car for trips to dark
skies. I was planning to eventually convert the scope to a truss tube dob,
but what about using it in the meantime?
Right away, I noticed that the base was pretty tall. There was a good 6 inches
between the bottom of the scope and the baseplate. I assume Meade made the
base like this in case someone wanted to change the balance point, but using
counterweights would be another alternative. Wanting to make sure that there
would be enough clearance, I cut 4 inches off of the bottom of the base, reducing
its height from 30” to 26” tall (I later added wheels which increased
the height to 27”). Doing this allowed me to fit the base into the hatchback
of my Toyota SR5 wagon (for smoother movements, I also installed some “Magic
Sliders” to the base). Now to do something about the portability of
the OTA….
Several companies make truss kits and split tube kits. The
problem was that I’d just spent a lot of money on the scope, so I didn’t
want to sink another $1000 into a truss kit right away. I also didn’t
want to buy a split tube kit that I’d only use until I converted the
scope to a truss dob. So I began trying to think of a way that I could make
my own split tube kit. I had installed a lightweight and inexpensive open
design mirror cell (from University Optics), and I noticed that the shafts
that Meade had used to secure the original mirror cell were made of thick
steel and had 3 bolt holes in them. I decided to use the mirror cell shafts
for my split tube conversion.
The first step was to remove the wing nuts and paint the threads
flat black. Then I began the nerve racking process of cutting OTA in half.
Complicating matters were the fact that my power tools collection consist
of a jigsaw and a cordless drill, and I’d be doing all of this in the
living room of my small apartment. I believe strongly in the old saying “Measure
twice, Cut once.” This is especially true with a telescope OTA, as you’ve
only got one shot to get it right. I carefully measured each section at several
points and drew a cutting line across the entire circumference of the tube.
I then cut the laminate along the cutting line using a box cutter. I figured
that doing this would make for a smoother cut. Then, using my jigsaw, I carefully
and meticulously cut the OTA in half.
To make the tube sections fit together better, I cut a 3”
section on the bottom of the OTA slightly crooked. There’s something
slightly disturbing about seeing your brand new telescope in pieces on the
living room floor…
Drilling the holes for the split tube brackets (in this case,
the Meade mirror cell shafts) is a critical step. The holes are spaced 3”
apart on the bracket. You should also figure on whether you’re going
to add some sort of decorative trim to the cut sections of the OTA, as this
will alter the hole placement and how the scope fits together. I chose not
to use any trim, and instead, I simply used Elmer’s Wood Glue on the
exposed sections that I’d cut. This works great, although it’s
not as attractive looking as trim (but then again, this is a dob!). I then
installed each bracket. I used oversized washers painted “flat black”,
behind the shafts on the bottom section of the OTA, to make installing the
top section easier. Doing this is important. Without the washers, the top
section will be difficult to fit over the exposed shafts. By using a washer
behind each shaft, the tube has enough room to fit, and is still securely
and rigidly attached. I also replaced the standard 1/4”-20 bolts on
the top section (the ones I remove to take the tube sections apart) with 1/4”-20
hand knobs. These are available at most hardware stores, and make assembly
and teardown in the dark much easier.
First Light:
That Saturday, I drove 60 miles to Coyote Lake State Park near
Gilroy, Ca. for some dark sky observing. (You get some strange looks pulling
up in a small car with a 16” non-truss scope inside!) The seeing was
poor, and the dew was as bad as I’ve ever encountered at this site.
But even so, the scope performed great. After spending about 5 minutes taking
it out of the car and putting it together, I was ready to go! I spent a few
hours observing some showpiece objects and finally left when the seeing got
worse. After many more uses, I’ve found that the collimation isn’t
a problem at all. Not only does the tube maintain its structural stability,
and doesn’t suffer from tube flex, but if I line up the marks that I
inscribed on the tube sections carefully, it rarely needs collimation at all.
When it does need collimation, it only requires a 1/4 to 1/2 turn of one collimation
bolt to get it perfect.
Summary:
When I originally decided to make this scope into a split tube,
I was planning on it being a temporary fix until I got a truss conversion
kit. But this modification has worked so incredibly well, that now I’m
questioning whether I’ll ever make the conversion. A closed tube design
has several advantages over a truss design, including less collimation issues,
easier assembly and teardown, less problems with ambient light entering the
light path, and protection from the elements. And because the mirror cell
needs replacing anyway, you might as well put some of the parts from the Meade
cell to good use!
Other worthwhile modifications I’ve done to this scope
include installing the curved spider (no more diffraction spikes!), building
bigger 10”1/2 hubs to replace the undersized Meade hubs (this gets rid
of the creaking every time you move the scope!), installing a sliding counterweight
shaft for better balance, flocking the OTA, and installing a new focuser and
moving it 1/2” further down the tube to line up with the secondary mirror.
I’ve got several other modifications that I’m planning on this
scope, but the split tube is the best thing I’ve done to it, and I can’t
recommend this modification highly enough (especially if you ever plan on
transporting a behemoth like the Meade 16”!). Clear skies to you!
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