I'm not much a backpacker, but would something like a Stelllervue finder, aka SparrowHawk, at 50mm... Would that be rugged enough and gather enough light for your purposes? One of those little scopes might arguably be smaller than full-size binocs, assuming the selected tripod isn't too bulky in a pack?
I don't think it is waterproof, nitrogen purged, any of that good stuff.
I am going with 11 others on a 10 day hike covering about 85 miles in the darkest skies of my life (New Mexico). I can offload some gear to others to accommodate the weight of the scope. I like the aperture of the ST80, the price isn’t too bad and I can use it as a guide scope after the trip! I’m going to get to a store to check out the weight and size! thanks, dom
For true backpacking the overall system weight is the most important factor. I like Tom's suggestion of the monocular, but I would prefer a lightweight binocular. The advantage of either is that they would be easy to use for daytime birding, etc. If the binocular has a tripod adapter socket, all the better.
Otherwise, I'd go with the recommendation of the SV50 (or one of the 66EDs if you can handle the extra weight) on a light photo tripod. Maybe one of the other hikers is a photographer who would share his tripod at night for the scope. Dedicated photo tripod heads are not the best for astro use unless they're 3-way types that can flipped onto the side to get better balance. Otherwise get the lightest alt-az mount you can find that will fit whatever tripod you're going to use. The original UA Microstar comes to mind for this.
I have backpacked for over 30 years now and when it comes to carrying any thing optical in the field I lean toward weather proof gear. I also do a small amount of birding and have taken my Pentax 65ED out and used it for Astronomy when backpacking. It is lightweight and mounts easily on a lightweight tripod. It come with its own padded tight fitting case and if you upgrade to the XL Pentax zoom or fixed fl eyepieces you have a great combination. Nice thisg about the Pentax spotters is that they take 1.25 astro eyepiece, so you can take out a cheap eyepiece when you think the weather will be iffy. I use a strap on Rigel finder for a finder.
Its a birder during the daytime, and can be used for digiscoping and then it is a telescope at night.
It gets used more than all my other scopes because of this. Next would be my TV76 as a travel scope and grap and go scope. The my C102F for planets and my 8" SCT for lunar and planetary imaging or binoviewing of the planets. For deep sky I go to my clubs darksky site and use the club 16" dob.
I have a Celestron 50mm scope and--if you can steady the mount--the optics aren't actually too bad. The mount is simply super jiggly. The scope and mount are very lightweight and you can get .965-inch eyepieces from various places. It's too bad that the telescope companies don't get with the program on these types of scope. If I ran the zoo, I'd put an erect image 45-degree diagonal, replace the useless spotter with a rifle sight and provide a red dot. Then, I'd upgrade the tripod just a bit. I think they could provide a very versatile spotting/astronomical scope for $50. Then, I'd provide a catalog in the box and get people on the eyepieces and accessories. 8)