[probably] Yet another focal length question..

Hi,

I have been comparing focal lenghts of my Canon S90 and my K100d.

Can someone explain, or send me to a page that explains the different uses of focal length markings?

Now I understand that my K100d has a crop factor in relation to film, and that my 50mm prime has an 'effective'focal length of X1.5 equalling 75mm.

With all that in mind I have compared my Canon S90 with the K100d and 50mm prime and to acheive the same frame on the Canon it tells me it's focal length is 85mm.

S90 reviews refer to it's focal length as '35mm equivalent'

Is all this correct/does it make sense?

The reason I'm doiong all this is to try and work out the effective field of view that I will acheive if I get different primes for my K100d...

Is the Canon showing the 'correct' reading?

If I set the Canon to ~40mm will I get a similar field of view to the 24mm prime that I'm after for the Pentax?

Any help appreciated,

Andy

The crop factor varies between manufacturer and even body models and is dependent on te sensor used.

Pentax are 1.5 (nominally) whereas Canon are 1.6 on the 1000D and 1.3 on the 1D mk III

The S90 spec gives the following:

6.0 - 22.5 mm (35mm equivalent: 28-105mm) which means a factor of around 4.67

So, when you set your Pentax to 24mm you have a 36mm equivalent ...

Which means for the Canon 36/4.67 = 7.7 in the cameras native spec unless the display is calibrated in 35mm equivalents when you would select 36mm

Thank you. I'm learning more each day. 24mm is looking quite desirable!

Andy