Re: DSLR Camera questions.
 

Folks please correct me if Im wrong with any of the below.


The bigger the aperture (Smaller the f number) the much shorter the depth of field.

18mm focal length will mean that the lens is capable of wide angle shots, over the standard 35mm

The compact I have has 12x Zoom or theoretically a range of 450mm. That gives you an idea of what 200mm is if you work in compact numbers for focal length.

For sports photography, large lenses and fast shutter times are required to stop the action. The bigger the lens, the easier it is to take shots as you dont have to be as close to the action and if you're panning on a bike, then from a further distance, its easier to control.

Re: DSLR Camera questions.
 

Correct, but remember that a long lens has "sees" much less light because of it's field of vision so you need a fast one if you want action photography in low-light (without bumping up the iso). Fast long lenses are very expensive compared to fast short lenses - check out the price of Canon L lenses if you wanna feel ill!!!

Re: DSLR Camera questions.
 

Good post, but I'd reckon if you can afford a bigger lense than 200mm, get one. I have a 70-300mm lense and even then the photos I could take at Brands for example, were limited.

Although as you say, the f number is more important as you can have the longest lense in the world, if it's not good quality your pics will look carp anyway.

Re: DSLR Camera questions.
 

Out of interest, what do you mean by a 'fast' lense? One that'll focus quickly?

Re: DSLR Camera questions.
 

One that has a larger maximum aperture - f2.8 is "faster" than f4 so lets in more light for a given focal length

Re: DSLR Camera questions.
 

:scratch: But that's just apature size as you say, that doesn't really make it any faster or slower. Is refering to the speed of a lense a widely used term to describe apature size?

Re: DSLR Camera questions.
 

I think he means that because it lets more light through the shutter can be faster?

Re: DSLR Camera questions.
 

Correct.

As an example of how price increases with lens speed. Canon offer a f4.0 and an f2.8 70-200mm zoom. One is £600 and the other is £1150 rrp

Re: DSLR Camera questions.
 

Yes I knew that, it just seems like a rubbish term. It might allow faster shutter speeds, but it doesn't make anything about the lense its self faster.

It's like describing tarmac as 'faster' than gravel.

Re: DSLR Camera questions.
 

The depth of field (i.e. the amount in focus does depend on the aperture, the wider (smaller F number) the smaller the depth of field yes but this also changes depending on the focal length of the lens also. A wider angle lens (say 18mm end) at a certain aperture will have a larger DOF than a longer focal length (say 100mm) at the same given aperture.

Most DSLRs have a smaller sensor than a 35mm film frame and as such the angle of view from a lens is different than when used on a 35mm. Generally there is a multiplication factor of around 1.5x so an 18mm lens on a DSLR will give the same angle of view as 1.5 x 18 i.e. a 27mm on a 35mm camera. A 200mm lens on a DSLR will give the same angle of view as a 300mm on a 35mm camera.

For sports shots where you want to pan to give the impression of movement a slower shutter speed should be used or a fast moving vehicle will look like it's stood still.

Panning example below I took using A Nikon D70, sorry it's not a bike:
http://i157.photobucket.com/albums/t...pix/Marcos.jpg