Possibly a daft question...

[Gaina]

I'm pondering lense sizes and I've realising that I don't actually know what these measurements mean (I've scoured my photography books but couldn't find the answer believe it or not).

Does it mean that (taking my 18-55mm as an example):

A) The lense performs best when I'm between 18 and 55 mm from my subject

or

B) My subject looks 18-55mm closer to me than it really is, depending on how I set the lense?

Thanks for your patience on what will seem like a totally obvious answer to some. I'll get back in me box now .

[eeyore]

The length of the lens refers to how far the lens element is from the film or sensor, thus an 18mm lens is 18mm from the sensor giving a wide angle , 55mm is further away giving a narrower angle of view and thus more magnification , 500mm is much further away giving greater mag still etc

(by the way if photo buff people reading this , I know this is oversimplified , and am aware of the complex science but am trying to put it in laymans terms)

[speckled wood]

Another bit of confudion with many Digital SLRs is that the effective telephoto is not the same as on a 35mm camera for instance my canon eos300D 18 to 55 is about equivilent to how a 28 to 75 would be on a 35mm camera. This is down to sensor size I think.

[digi]

Originally Posted by speckled wood

Another bit of confudion with many Digital SLRs is that the effective telephoto is not the same as on a 35mm camera for instance my canon eos300D 18 to 55 is about equivilent to how a 28 to 75 would be on a 35mm camera. This is down to sensor size I think.

This is called the crop factor and is a multiplication of the image size compared to a standard SLR format.

Canon use 1.3x on 1D MKII and 1.6x on most other models except the 5D and 1Ds MKII which are full frame.

Nikon use 1.5x

Olympus 2x

etc etc

So you multiply the lens focal length by the crop factor of the camera to get the actual focal length.

Digi

[Gaina]

Originally Posted by eeyore

The length of the lens refers to how far the lens element is from the film or sensor, thus an 18mm lens is 18mm from the sensor giving a wide angle , 55mm is further away giving a narrower angle of view and thus more magnification , 500mm is much further away giving greater mag still etc

(by the way if photo buff people reading this , I know this is oversimplified , and am aware of the complex science but am trying to put it in laymans terms)

Ok, that works for me! I can't take much more science on an empty stomach.

Thanks

[speckled wood]

Originally Posted by digi

This is called the crop factor and is a multiplication of the image size compared to a standard SLR format.

Canon use 1.3x on 1D MKII and 1.6x on most other models except the 5D and 1Ds MKII which are full frame.

So you multiply the lens focal length by the crop factor of the camera to get the actual focal length.

Digi

So in effect it makes the top end of my 90 - 300 something like a "pretend" 500.

[glsammy]

Originally Posted by speckled wood

So in effect it makes the top end of my 90 - 300 something like a "pretend" 500.

Yes, it makes it a 480mm if comparing with 35mm. (With a 20D for instance.) Of course the 500mm will be a pretend 800mm and so on!