The Telescope and Me

an obsession with the TELESC0PE...

The AR6 lens (Better-Than-Decent, lower on the page) in cell showed me that it was worth the trouble to it mount into a tube and point it up, but I wanted to try to improve the views I had through it.

The fact is that the use of a diagonal requires a certain length tube, while straight through use needs nearly six inches more length, in order to accomodate eyepieces of varying designs and focal lengths without vignetting. In three inch and smaller scopes, a 2 inch EP capable draw tube can accomodate this requirement without vignetting, but apertures about 4 inches and up need either a larger (heavier and and more expensive) diameter focuser and adapters to 2 inches and smaller, or some other means.


The classic 80mm f/15 solves the focuser range problem with a sliding tube inside the focuser tube which sets the range of the focuser. I decided to try a similar idea, but could not find a suitable tube to slide inside the 7.5 inch Sonotube.

A Telementor I saw and bid on gave me the idea to recess the whole cell into the tube. I had a length of 8.5 inch sonotube handy. The cell fits snugly into the larger tube which made a better (double) dew shield. Then the original OTA is cut in two, with the front portion stilll attached to the cell and supported to keep the tubes coaxial while the rear 18 inches is used to provide the extension needed to set a ficus range.

The inner tube (last 18 inches of the original OTA now painted black) slides on plastic and composite, it leaves 12 inches of tube inside at full extension. I had to shim the focuser to cure astigmatism I saw initially, a half hour with the laser was necessary to straighten things up.

Better balance as the sun goes down, more like a yard missle now, I guess I better paint it so it is not so obvious from the air against the macadam background. (Lots of helicopters overnhead)

I thought I wanted a 6 inch f/15 or at least f/12 refractor. I had never had or even looked through one larger than the 102mm f/7.7 Meade/Jinghua I have. It is fine for what it is, and I actually saw the E component of Trapezium through it one Sunday night early this year.

But I have been spoiled by larger apertures. Between 8" and 10" Newts/Dobs and 8" SCT, I have found myself unsatisfied with the views through this scope in my opaque skies. I needed a larger refractor to satisfy my curiosity about how such a scope compared to 6-inch-and-up obstructed designs, and also to see whether the expected color would put me off.

Economic considerations guided me to buy a 127mm f/9 objective, more about that and photos below. Just after I ordered it, I found an AR6 (6" f/8) lens with damage on AM, in cell. I could not pass it up.

Halfway between the left edge and the center of this photo is the visible damage to this lens. (Do you see the bullseye?) The actual damaged area is quite small and is confined to the coatings, this view magnifies the area involved since the area is on internal surfaces. Having used camera lenses with extensive coating damage and knowing how forgiving human vision is, I doubt whether anything will be noticed looking at stars. The test might be Jupiter, but this f/8 will have color anyway.

If this lens works out OK, I will send the 5 inch to Asia, it should really be spectacular in those black skies.

I really just wanted to see if the damage caused bad views through the objective, so I jammed the cell into a length of Sonotube a bit too small for it. The 9 inches I cut off the tube to reach focus with a 2" Synta focuser temporarily affixed to the rear of the tube made a perfect (so to speak) dew shield.

Obviously, unblackened hardware is not something I will not leave in there when this lens and cell find a more permanent home.

Preliminary views through the lens look great so far, I saw the E component of the Trapezium in poor seeing, this weekend or the next will give me a better chance to wring it out.

I wanted to use this on the LXD, which is a quiet and precise GEM (if not overburdened) when computer location is unused, so I had to find a way to connect the OTA to something with a Vixen-style dovetail. I was going to build a plywood box center support for the tube, but darkness got me at the halfway point, so the resulting v-shaped half-box resulted. Since the knob to tighten the dovetail does not allow a flush surface above the bar, the 2x4 spacer became expedient.

The strategically spaced bungee cords hold the assembly securely while allowing balance to be adjusted.

More info after thorough checkout.

After having some sense talked into my head by members of a couple of yahoo groups, I went shopping for a lens in cell in order to at least taste what all the hulabaloo was about. After seeing very high prices on any doublet of six inches, I emailed my favorite telescope parts dealer, who had advertised 127mm lens sets last year. He had a new pullout 127 f/9 lens in cell, most likely an SC version of the lens used in the Meade AR5,

I shamelessly mounted it in the Home Depot stovepipe section I built my first reflector into last year, extending it with a coffee can (a perfect fit for the cell) in the same way. It is mounted on a simple multipurpose wedge on an Orion dovetail which fits the LXD mount.

127mm Single Coated f/9

The f/9 focal ratio allows a fair amount of color, but it is not distracting (OK, on Jupiter, a little) enough to be a problem for me.

The 1140mm focal length allows a 32mm eyepiece to display most of the Double Cluster, for instance, and the Perseus asterism (Mirfak and friends, the first area I ever became familiar with) fits nicely in a 22mm.

The views are crisp and clear, I think better than those with my very good GSO 6" f/8 Newt. It is certainly easier to use on the GEM, no awkward eyepiece positions to contend with. I am surprised at the huge difference between the things I see with this versus the 102mm of 800mm focal length from the same factory which is the largest refractor I have previously used.

OK, it did not originally look like this,but the previous owner did paint the tube red.

The C8 came to me via a swap on AM. I thought I wanted to take astrophotographs, so I bought a nice 70ED. But my enthusiasm soon faced reality, and I offered it as a swap for a C6 or equivalent, and ended up with this OTA. The mount came from the big auction site and acts my age, has trouble getting started sometimes, but performs adequately once it gets going. The AutoStar is familiar to me, it is accurate enough if the eyepiece is wide enough. The mount is not overburdened, it came with three counterweights and once held a 10" Mak-Newt.

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