What's a good step up from 7x50 binoculars? I own a Nikon OceanPro 7x50 pair of binoculars, but I find that when I look at the moon, I would like more magnification.

My requirements are:


costs less than $400
weighs less than 10kg
the length is less than 1-2 feet
much higher maginification than 7x (I already have a pair of 7x binoculars, as I said)
at least an 100mm objective I (I already have a device with a 50mm objective)


What kind of device should I go for? A spotting scope? Binoculars? A telescope of some kind?

Ideally, I'd go for binoculars, so that I can see with both eyes, but I'm told binoculars don't come with objectives larger than 100mm, for my budget.

I could buy a spotting scope, like this, but Wikipedia says that spotting scopes are not designed for astronomy.

I live in an apartment, so I can't use a big, heavy telescope, like a 4-feet 20kg thing. I don't have room in my apartment for such a big telescope, and I can't carry it over the threshold into the balcony.

So, what kind of device should I consider, and what are the tradeoffs? What kind of astronomical objects will I be able to see?
For higher magnifications, you are going to get into the territory where a tripod becomes a must. I mention this because you didn't say anything about a tripod, so the implication may not have crossed your mind. Unfortunately, the cost of a tripod will eat into your budget. 

I am inclined to think that your best option would be a telescope. (Unless you also want to view terrestrial objects, then a cheap spotting scope might be what you want.) Maybe your best bet, to get a good one, would be to ask around on forums like cloudynights or iceinspace that have some support from astronomers local to you, let them know you are looking to buy, and maybe you can get one second-hand off someone who is trading up. You might get a better telescope for your money than trying to buy new.

If you want a smaller length telescope, you may be put off something like a newtonian reflector or another simple 2-mirror reflector. Still, try one out (maybe you can attend a local star-party and see some up close, even if there isn't a telescope store handy). A 114mm newtonian on a tripod would meet almost all your requirements including budget, even purchased new. It will be a bit less than 2' long; slightly bigger newtonians like 130mm start getting longer than 2'.

Otherwise, what might fit the bill is a small cassegrain-style reflector - these usually also have a corrector lens, making them a catadioptric type telescope - such as a Maksutov-Cassegrain. The extra manufacturing cost of making the lenses pushes up the price of these well past the simple reflecting telescopes, however. 

Refracting telescopes with an objective of 100+mm are probably in your "too big" basket, and you're also not likely to find one with that budget. 

You use different eyepieces to provide different magnifications using the same telescope. If you buy a telescope as a kit, it will come with at least one eyepiece, and it's likely the magnification provided will be more than 10x (divide the focal length of the telescope by the focal length of the eyepiece to find out).