i am building a small 8 inch truss type telescope. In order to make it easier to collminate my mirrors "easier" i was wondering if they make a flexible cable for attaching to the bottom nuts of the telescope that can be attached to the sides for ease of use. also does someone have a good design for a primary mirror cell that i can make for this 8 inch mirror. also a good source for star wheel screws larger the better cheaper even better as i live on disability here in freezing rushville, indiana. i am thinking about trying to get a crawford focuser any pluses or minuses i should be aware of. I plan to make this a suitcase telescope and would also like some ideas on the truss tube design and a supplier if possible. thanks in advance

doc

I've seen articles in the past couple of years about motorized collimators (motors attached to the collimation screws) to make it easier for a person to collimate solo.

However, if you're using a truss-tube design, there is an even more convenient solution: use a barlowed laser with a target on its face. Howie Glatter sells something called a "blug" that is a commercial version. The idea is that the barlow spreads the light so that the reflection on the face of the laser target in the focuser is a large circle of light.

This "circle" is actually an out-of-focus image of the center marker of the primary mirror.

You adjust the collimation screws to center that circle on the target and/or the bright point where the laser light exits the collimator. You can see the target from the rear of the scope since there is no "tube" to conceal it.

Here's a link to a PDF file of a Sky&Telescope article showing the process for a truss design.

If you have a closed tube, you can still use this method if your collimator has an angled viewport like a Cheshire eyepiece (you simply rotate the collimator so this port is visible from the rear of the scope. Here's a link to an illustrated description of the process.

 thank you for your response and the links i will read about them i have a lot of figuring to do and a few more parts to get before i build so i hope i get some more answers to my questions also.

doc

Hi,

You can take a look at my website to see how I connected truss tubes. You can find truss tube suppliers by using Google. I just used wood dowels, which were readily availible and inexpensive. At one time I remember seeing a website that used plumbing compression fittings to attach the truss tubes, but this web site no longer exists. If I remember correctly, the idea is to drill and attach a small length of metal tube into the end of the truss tubes, then the plumbing compression fitting is hooked onto the tube. This screws into a similar fitting (opposite gender) on the primary and secondary boxes. With regard to a mirror cell, there was a very nice 3 installment article in Astronomy back in the summer of 1980 that gave a very simple design for a primary cell ("How to Build a Dobsonian Telescope" by Bob Kestner and Richard Berry); I think one of the three issues may still be availible through Astronomy.

Good luck with your project

Bill

You probably can't build a mirror cell for less than this one.

http://www.universityoptics.com/telescope-making-supplies.html#Aluminum_Mirror_Cells

Truss poles can be made from aluminum tent poles. For an 8" they won't have to have to large of a diameter.