Lens advice please

[Beanymonster]

Hi,
I am looking at getting a longer lens for my new D5000 (with standard lens) and as I am new at this, I would appreciate any advice on the difference between the two lenses below (if indeed there is any). Primary aim is lots of outdoor shots of active kids etc.
Lens 1:

Lens 2:

Many thanks in advance

[drprasannabhat]

Originally Posted by Beanymonster

Hi,
I am looking at getting a longer lens for my new D5000 (with standard lens) and as I am new at this, I would appreciate any advice on the difference between the two lenses below (if indeed there is any). Primary aim is lots of outdoor shots of active kids etc.
Lens 1:

Lens 2:

Many thanks in advance

I am not an expert. But what I've understood by my self studies and research is that the smaller and constant 'f' number is better like f 1.4 or f 2.8, so that you can give very shallow DOF and you can take good pictures in low light situations also. However, they will be more expensive lenses. All the best.

[kirbinster]

You are showing two ads for the exact same lens. Its a good lens for the money. You cannot compare it to a fast lens like the 70-200 f/2.8, but for the money it is very good.

[Beanymonster]

Originally Posted by kirbinster

You are showing two ads for the exact same lens. Its a good lens for the money. You cannot compare it to a fast lens like the 70-200 f/2.8, but for the money it is very good.

Thanks - the links are to different lenses - just noticed one is 4 - 5.6, the other is 4.5 - 5.6 so I guess the first would be slightly better in lower light levels?

for my learning, what is it about the 70-200 f/2.8 that makes it a "fast" lens? does the f2.8 mean the aperture is wider and therefore you can use a faster shutter speed? (sorry if that is stating the obvious - I am v new at this )

[kirbinster]

Both are the same lens, one is a misprint.

A fast lens means that it has a small f-stop number and opens quite wide. By letting more light in you are able to shoot at a faster speed than a lens that does not open as wide. Also, the wider f/stop allows you to obtain shallower depth of field, which can be useful at times.