Lots of questions ....

Hello,

I have never posted in this forum before. I am a college student at the university of nebraska and have recently become interested in building my own telescope. I own a Meade 8" Lx200gps and it is decked out for astrophotography, but I have recently began finding objects with out GOTO. I have used a couple of the big truss tube dobs and i think i would like one for my visual endeavors.

I was thinking of maybe a 12 inch f5 scope would be good. I may even be able to go to a 10. I am a big fan of the truss tube design. But Im not exactly sure how to construct it so that it is easy to take down and set up or where to get decent mirrors at for a good price. Also, what math do i need to do to determine howfar away the secondary needs to be and all that stuff? Also, typically how much money should i be expecting to spend on a 10 or 12 inch scope? If anyone can help with any of these things, i would appreciate it. If you have a pic of your homemade truss design, please post it if you would like to share your idea. I appreciate your help.

Taylor

Taylor,

You should try to get hold of Kriege and Berry's "The Dobsonian Telescope: A practical manual for building large aperture telescopes". A great many very nice telescopes have been built following the designs laid out in this book. Fairly simple construction, though access to a shop and tools will be a necessity.

I'd also explore some of the newer truss designs that have been developed by amateur astronomers. There are lots of pictures and plans on the internet and you can look for help in a number of ATM forums also (lots of experienced ATMers to guide/confuse you as needed! ). In any case, consider your needs, limitations (e.g. transportation, etc.) and budget for awhile before deciding upon a design. E.g. do you want an airline transportable scope? Is a more traditional Obsession-style scope more to your liking? How about an aluminum or wire/string ultralight scope? Lots of options!

As for the math, the basic constants that you'll be working with are the primary mirror's focal length and it's weight. The focal length is fixed and unless you are considering a slightly folded design (i.e. secondary mirror angle of reflection is less than 90 degrees relative to the primary mirror's optical axis), it pretty much determines the eyepiece height. Also, as balance is a critical factor in the performance of a truss dob, the weight of the primary mirror is a very significant design factor, especially for ultralight designs.

The spacing between mirrors, secondary mirror sizing, etc. can be figured out using the NEWT software (freely available online).

Anyway, check out lots of different designs first in any case.

Cheers!
Tim Cross

A 12" F/5 would be great, they are a nice size and will perform well. Here is a picture of my 12.5" f/4.8 for starters. It is a simple design and not too heavy. IT weighs in at about 65#.
Floyd

Attached Image:

Discovery sells reasonable quality large aperture mirrors relatively inexpensively (10" is $499, 12.5" is $699). I believe Orion and several other dealers sell 10-12" primary mirrors also. These aren't top quality (same mirrors as are found in cheap imported dobs), but are good value if you are working with a tight budget (Orion 10" is $299, no 12" listed on website). Higher accuracy mirrors will cost a fair amount more ($1000 to $1500 for 12.5" mirrors).

Best of luck!
Tim C.