A 4.5 inch telescope is an inexpensive way to start out in astronomy
Generally when we refer to a 4.5" telescope we are referring to some kind of reflector telescope. This is a telescope with a mirror in it rather than lenses. 4.5 inches is about the smallest size reflector telescope you want to get. It is a reasonable telescope if you are just beginning in the hobby and with this size you can really keep the budget low.
There are lots of twenty and fifty dollar telescopes out there and for the most part they under perform and give a bad name to telescopes. If you really want to make a modest start in astronomy and get a decent look at the moon, planets and other celestial objects you have to start with a 4.5 inch telescope. It is the absolute bottom to start at while getting decent performance at a rock bottom price.
What do we mean when we say 4.5 inches? Typically when we talk about reflector telescopes we are referring to the diameter of the primary mirror. This is the biggest mirror at the bottom of the telescope. the illustration shows where the primary mirror is located on a newtonian telescope.
In this picture of a reflector telescope the primary mirror is located at number 4. The diameter of the mirror there would be 4.5 inches on a 4.5 inch telescope.
Let's take a look at some 4.5 inch reflectors and compare prices and features.
Orion StarBlast 4.5 Equatorial Reflector Telescope - Considering how many adults have told us they love our StarBlast "mini Dob," we weren't surprised that some of them suggested we offer the StarBlast optical tube on a full-size telescope mount. Sounded like a good idea to us. So here it is, the StarBlast 4.5 EQ. It's bound to become a favorite of both adults and adolescents alike. It combines the much-heralded StarBlast wide-field (f/4.0) parabolic optics with a sturdy, adjustable height EQ-1 equatorial tracking mount. So if you're an adult (or a parent) looking for an exceptional starter scope on a tracking mount, or an experienced amateur astronomer seeking a more portable alternative to your "light bucket," then get a StarBlast 4.5 EQ. The name says it all!
Meade DS-2114AT-TC 4.5 - This is a Meade telescope which means quality. And this telescope is a bit more expensive than the Orion dobsonian but you get a lot more. It includes a motorized alt-azimuth mount which means once you calibrate it to understand where it is it will automatically point to objects in the night sky. This telescope also comes with 2 plossl eyepieces which is a great addition. Plossl eyepieces are a good quality eyepiece. It makes a big difference. If your budget is a little bigger you might consider this telescope rather than the dobsonian.
Lets look at some other 4.5 inch telescopes
Celestron 21045 114mm Equatorial PowerSeeker Telescope - Celestron makes awesome telescopes and this one is a real bargain. You get good quality optics but at this price something is going to be minimized. In this case it's the mounting system. While it is a standard equatorial mount it is a bit small for this telescope. Even with this deficiency this is a great deal for a standard neewtonian telescope. the longer focal length of this telescope makes it better than the previous telescopes when it comes to viewing the moon and planets.
The best 4.5 inch telescope you can get
Celestron Nexstar 114GT 114mm Go-To Reflector Telescope This is probably the best 4.5 inch telescope you can buy. Simple as that. It is made by celestron which means great optics and it comes with a very sturdy mount and goto software which means it will find objects for you. If you want the best at this aperture then this is the one to get.