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S*T*A*R astronomy home

This page is all about the telescope I've finished building (well, perhaps finished isn't the right word - there's always one more thing to do...) Actually, I'm onto bigger scopes. See my page on my Coulter Makeover on the STAR ATM page.

Here is me standing behind my telescope at a S*T*A*R Astronomy Club meeting, to give you some sense of scale. It is a 6" f/7 newtonian on a dobsonian mount. Aside from the focuser and diagonal mirror, I made it all myself (including grinding the primary).

Some interesting features are visible in this photo. The optical tube assembly, which began life as a concrete form tube at a local building supply center, weighs in at about 15 pounds, and the mount at about 20, so this is a fairly portable, easy to set up scope. There is a brass drawer handle on the side of the altitude bearing facing the camera, to help me carry the scope easier. The formica azimuth bearing surface began life as a counter top. The rest of the scope was constructed from ordinary plywood, except for the small wooden parts, which were cut from a length of maple molding I had around the house.

Here's the best picture I have of the spider. It is one of the more unusual features, based on a design I found here. It is made from a small block of wood and one and a half hacksaw blades. The ends of the blades are clamped between wood blocks and strips of aluminum held together by screws and wing nuts. Not very elegant looking, but actually quite easy to collimate. I collimate the secondary by loosening the wing nuts, grabbing the ends of the blades, and sliding them up/down, then tightening the wing nuts. No tools, and I can do it all while looking through the drawtube.

The finder is a daisy electronic gun sight, which is a good inexpensive alternative to a telrad (I have nothing against telrads, this is just cheaper and smaller). This photo shows a modification that a friend made for me. It is a piece of double sided PC board with a 5.6K resistor soldered between the two sides. It slips in between the battery and battery clip and dims the LED in the sight so it's just right for nighttime use.

The tube (which is a concrete form tube from a local building center) sits in a cradle which can be opened in order to rotate the tube (to make the eyepiece accessable to different people) or to slide the tube (to balance it when heavy and light eyepieces are interchanged).

The cradle has a piano hinge on the bottom, and a window latch on the top to keep the scope secure. The inside of the cradle is about one eight of an inch bigger than the outer diameter of the tube, and small pieces of self-adhesive foam weatherstrip were put in between to get the feel ``just right.''

The mirror cell is made of 2 pieces of 3/4" square aluminum tubing attached with epoxy and screws into a ``T'' shape and painted flat black. The mirror is attached to the top of this with three blobs of silicone adhesive (caulk). The bottom has holes drilled in it to accept tee nuts and washers (the washers let the tee nuts pivot some, which makes collimation smoothe and easy). Long screws pass through a plywood ring and screw into the tee nuts, to allow for adjustments with an allen wrench. Stiff springs keep the screws in tension. The plywood ring has brass threaded inserts in it, which allow it to be fastened to the tube with 4 brass machine screws and washers (which are visible in some of the other pictures, but not this one).

I plan on getting better pictures of the mirror cell, but I didn't want to take the scope apart when these pictures were taken. I was getting set to observe.

Here are two more shots of the scope.

The questions I get asked most often about it are:

	Was it hard to build?
	No, it wasn't. My woodworking skills are minimal, and I've never made a mirror before this. A scope like this can be buit by hand tools, but some power tools are very useful, like a router for cutting circles. The optics require no tools other than hands and patience. Someday I'll post more on the construction, but right now I just want to enjoy the scope.
	Was it expensive?
	No, it wasn't. If you do everything right the first time, and keep costs in mind, a similar scope can be built for about $150. Here's a cost breakdown: Willman-Bell's 6" kit is $70. If you can find a friend who'll split the cost, you can make 2 mirrors with one W-B kit, so the lower bound is $35/mirror. Get it coated by Clausing for $28. Buy a 1.25" secondary from University Optics for $24. Buy a Sonotube ($6) and a 1/2 sheet of plywood ($15). Scrounge some formica (I got mine from a friend redoing a kitchen, but you can buy a 2x4 sheet for something like $10). Add some screws or nails, and some glue and paint (which I'm not counting in the $150 price). You can even throw in a Daisy finder ($12) and a Rini Plossl eyepiece ($17.50).
	Why did you do it?
	Because I wanted to.
	How well does it work?
	Very well, thank you. The mount feels solid and operates pretty smoothly (I'd like to tweak the azimuth bearing slightly, as it moves more easily in altitude than in azimuth). It is easy to track by hand, up to 300x (my highest power eyepiece/barlow combination). The hacksaw spider design makes it a snap to collimate the scope (the only times I've had to recollimat is after I've taken the scope apart and reassembled it). I'm very pleased with the finder. If I can see an object, I can put the dot on it and see it through the eyepiece usually without any hunting, even at high power. The optics are very nice (pat pat pat). At f/7, the scope is just right for getting good planetary views as well as some deep sky stuff. With a 32mm TV Plossl, the real field of view is a whopping 1.6 degrees, which gives me great views of objects like M31, the Pleiades, and the double cluster. At 300x, planets come in nice and crisp (when the seeing is good enough, which is pretty rare around here). One of the first times I had the scope out was at the South Jersey Star Party, where I received lots of compliments on the scope, both mechanically and optically.