Design goals for my 12.5" binewt

About half to two thirds of my viewing will be done at home, in my backyard, front yard, or driveway. The remainder will be done at the HAL observing sites, about 20-30 minutes drive from my home.

The majority of my viewing will be of deep-sky objects (clusters, nebulae, galaxies, etc.), but this may be problematic because of the light pollution in my area, so I will likely also want to focus on lunar and planetary viewing, which will require relatively high power (150-300x). However, I would like to maximize the field of view, since this is one area where binoculars often out perform telescopes, and I would like to be able to frame objects like large nebulae, clusters, and the like (like the Pleiades), which you typically cannot do except in really short focal length scopes (typically called "rich field" scopes).

At home, the scope is likely to be stored in a utility shed in my backyard. The shed is 51" deep x 65" wide, and the doors are 34" wide x 68" tall, so the scope has to fit in that space. For ease of viewing, it would be nice if the scope fit in that space when fully assembled, and could simply be wheeled out of the shed into the backyard for viewing within 5 minutes of opening the shed. The shed can be ventilated to the outdoors, which should help the primaries stay in equilibrium with the ambient temperature. A concern with this setup, however, would be the humidity in our area (I live in Maryland, 10 miles from the Chesapeake Bay), and how this might affect the coatings on the mirrors. For example, I would need some mechanism for keeping dew off of all six mirrors while the scope sits in the shed.

For transport, the scope needs to disassemble to a size that will fit in the back of my 2005 Toyota Prius, *without* putting the rear seats down (so that I can bring my family with me to observing sites). The cargo space of my Prius is 38" wide x 23-27" deep x 16-23" high, and the hatch back opening is 38" x 23". The floor of the cargo area is relatively flat to the bumper, and is about 24" off the ground.

I suspect the vast majority of viewing through this scope will be done by me, with some by my wife and some by my 5 1/2 year old daughter. However, when taken to club star parties, I suspect other club members will want to look through it, and the club runs a number of public outreach events, at which there are usually quite a few kids. I am not sure, however, whether I would really want to bring this scope to such an event; the logistics of operating the scope for so many different IPDs seems more troublesome than it is worth.

Given all of these constraints, I have the following design goals:

1. The scope, when disassembled, should be no larger than 38" wide x 16" tall x 23" deep.
2. The scope, when disassembled, should be relatively easy for me to wheel into and out of my car (I am 6' tall, 240 lbs, and I can easily deadlift up to 100 lbs without fear of injury, though for convenience, I would like to keep the equivalent deadlift weight less than 40 lbs.)
3. The scope, when fully assembled, should have its eyepieces no more than 60" off the ground when pointed at the zenith (so that I won't need a step stool).
4. The scope, when fully assembled, should be able to be wheeled into and out of my storage shed.
5. It is a binocular telescope - it should have a binocular finder scope. For convenience, the binoculars should be mounted to the secondary cage in a position such that the observer merely has to change their head position slightly. This will require, I think, the use of a mirror mount. The weight of the mirror mount and binoculars and their effect on balance will be a concern.
6. The observer should never have to leave the basic viewing position in order to perform any action with the scope. That includes collimation, convergence of images, focusing, point the scope with the finder scope/binoc, etc.
7. The observer must be able to adjust convergence of the images while viewing through the eyepieces.
8. Changing IPD should not change focus.
9. I want to be able to use both 1.25" and 2" eyepieces.
10. The scope should have a nice balance of contrast versus size of fully illuminated field; choosing the right size secondary will be important here.
11. The scope must be able to be built with modest hand tools, and without great woodworking or metal working skills.
12. I should not have to machine any of my own parts, as I am not able to do that.
13. I should be able to build the scope in less than one year, while devoting one hour per night, and an additional four hours per weekend.
14. I should be able to completely build the scope for less than $2,000 (not counting eyepieces, for which I could justify another $1,000).

Given the design goals above, it seems obvious that a truss tube design a la Dave Kriege and David Moorhouse is in order. I do not have the skills to build something like Bruce Sayre's gorgeous instruments, but I think I have sufficient woodworking capabilities to build an Obsession-stlye dob. Given that I obtained the primary mirrors for only $560, I still have about $1,500 to work with, and given my limited fabrication/machining capabilities, I suspect I will purchase commercial parts for many of the tricky parts of the scope (e.g., the truss tube mounts, spiders and secondary mounts, etc.).