The dealer taking people out for lessons....
Sounds like a very good idea to me ! I've never heard of a dealer doing this, but it kinda indicates to me that he's a good business man, and probably a "good guy" as well.
Let me explain something about lenses to you; before digital photography came along, 35mm was the most common film "format"; all 35mm cameras used the same size film; the "35mm" referred to the width of the film; as you probably know, 35mm film has a row of sprocket holes down each side; the film lays flat against an "opening" ( which is 36 mm wide, and 24 mm high; ) this is known as the "format"; ...........all 35mm cameras use the same format. So all lenses designed for 35mm cameras are designed to produce a cone of light that fits that 24mm by 36mm format. So..........
Let's forget about zoom lenses for a minute; let's talk about fixed focal length, ( or so-called "prime" ) lenses;
On a 35mm camera, a lens with a focal length of about 50 to 55mm is said to be a "normal" lens; which simply means, that lens, with that format, sees things just about the same as your eyes see things; things appear "normal", no bigger, no smaller. OK
.........so......as the focal length of lenses gets smaller, such as 35 mm, or 28 mm, the "field of view" becomes wider, and things appear farther and farther away, as the focal length gets shorter; anything shorter than, say, 28 mm is said to be a "wide angle" lens;
Going the other direction, as focal length becomes longer, the field of view becomes narrower, and things appear to be closer; just like a telescope. Zoom lenses are simply "variable focal length" lenses.
You need to understand all of this, because.............................along came digital photography; a "D-SLR", ( or Digital Single Lens Reflex ) camera looks just about like a 35mm camera; they are "similar" in some ways, but very different in other ways. To start with, as you know, they don't use film; they collect the light from the lens with a "sensor"; ( which is a very complex device, that goes by all manner of confusing names, and comes in "a bunch" of different sizes !
( all of which was apparently meant to "confuse" the hell out of anyone attempting to switch from shooting film to shooting "digital". ( I'm trying to "un-confuse" the differences between 35mm film, and D-SLR cameras )
In the beginning, sensors were very costly to make; so in the beginning they were very small; then they started getting a little bigger; it hasn't been but just a few years, that all but extremely expensive D-SLR cameras used sensors that were about the size of your little finger nail; so..........a lens from a 35mm camera used with that small little sensor.........much of the "cone of light" from that lens misses the sensor ! So they had to design all the lenses all over again. ( The lens used with a particular format (or sensor) needs to be designed so that all of light from the lens just fits on that size format. ) Looking on eBay, or any catalog, you'll notice lenses which are for DX and one that are for FX
Here's the good part; you can use a FX
lens with a DX body, but you can't use a DX lens with a FX
body. ( That has recently become a very costly problem for guys who have been shooting D-90's and have a bunch of lenses, and now want to "graduate" to a full frame D-700, or a D 3s. ( Playing with cameras is like having a giant vacuum cleaner attached to your pocket ! )
Finally, now, 2011, things have become a little better; now, most D-SLR cameras (up to about $2,600 range) use a "DX" size sensor ( which is about 2/3 the size of a "FX" or "full frame" ) sensor; so here's what that means. You can mount a 50mm lens from a 35mm film camera on the D-70, and it will "work", but because the D-70 uses a "DX" (read: smaller) sensor, the "sffective" focal length will become about 75mm; The DX sensor is said to have a "crop factor" of 1.5 ( or 1.4 ), so you must multiply the focal length by 1.5 X .
In the Nikon line, the first camera "UP" to have a "FX" ( or "full frame" ) sensor is the D-700. The FX
sensor is 24 X 36 mm, so it has the same format as a 35mm film camera, and in some cases is able to use the same lenses. ( but that's a whole "nother can of worms we won't worry about just now".
So with the 18-70 zoom lens on the D-70, you will have an effective focal length of about 27 to 105mm
I'm not familiar with either one of the lenses you mentioned, but as I mentioned before, I'd forget about the pawn broker and his 55-300mm lens.
With the D-70 body and one lens, the 18-70 zoom, you have all the lens you need until you learn to use the camera, and learn about photography. Then you can start thinking about what you want to take pictures of, and what you need to do it with. If you have a problem, or need to know something, send me an IM
and I'll try to help.
Stupidity: Doing the same thing over and over again and expecting a different result; Albert Einstein