Can someone explain focal length and the f numbers?

[ppp]

Hi guys, another question as i am new to all this.

Can someone give me a explanation of focal length, i understand the smaller the number the wider the angle but do not get how this equates to usage in the real world and how much zoom/distance i would get from a certain focal length.

Also what does the f number relate to like f2.8 or f3.6? I have seen some lenses that are 28-300mm f3.5-6.3 and others that are similar but have lower f numbers, are these better?

Would a lens with 28-300mm f3.5-6.3 be ok for general photography and motorsport for someone on a budget (i.e me).

Thanks, sorry it's a lot to ask but with your help i am getting there slowly.

[markgray]

From the info i have picked up over the short period i have been doing this is.

The lower the F number the faster the lens is, it can also work better in low light conditions. The lower the F number is normally a lot more expensive than one with a higher number.

[ppp]

faster it is to focus i assume? is that not dependant on the camera or is it something inside the lens? would that be a problem if i was tracking something?

[RobertP]

There is a tutorials and guides section to the site. You will find lots of useful info there like this one (http://www.thephotographyforums.com/forums/showthread.php?t=1332) -scroll down to F :)

And focus speed is more down to the design of the lens or lens/camera combination...varies for different makes.

[ppp]

thanks

[SDK^]

faster it is to focus i assume? is that not dependant on the camera or is it something inside the lens? would that be a problem if i was tracking something?

When people refer to a lens as being 'fast' they are referring to the aperture, i.e. An aperture of F2.8 is faster than a lens with a max aperture F5.6.

It makes the lens fast because you can use a faster shutter speed at F2.8 than you can at F5.6


The lower the Aperture number the more light the lens lets through to the camera sensor
The lower the aperture number the less distance you get in focus.

Having a 'fast' F2.8 lens is better and generally speaking they cost a lot more than lenses from F3.5 to F5.6

There is a 'rule' in photography that says you need to at least match your shutter to your focal length to avoid blur from camera shake. So when using a 28-300mm at 300mm you should be using a shutter speed of at least 1/320, with an aperture of F6.3 you will need to use a high ISO setting to achieve a balanced exposure.

The downside of using high ISO (800+) is your photo will have more noise (grain) than a low ISO (200)

[ppp]

many thanks