Sigma 20mm Prime

gman

gman

Suspended / Banned
Messages
11,100
Name
Graham
Edit My Images
Yes
Bought a Sigma 20mm Prime last week but the lady told me that I wouldn't actually be getting 20mm because of my camera, EOS 400D.

Still bought it as after testing it seemed to do what I need it to do but was wondering if anyone could confirm what the lady said and perhaps let me know what equivalent I'm getting? (something to do with cropped sensor I think?)

Also wonder is this just relevant to this lens, like are there lenses that will actually correspond to the camera (EF-S lenses?)


Cheers
G
 
On a full frame camera (5D/1DS etc) the lens would function at 20mm. On the 400D which has a 1.6 crop sensor it will give the equivalent of 32mm;)

Simple equation: Focal length X 1.6
 
EF-S lens just means it is only suitable for cameras with the smaller sensors (eg 20D, 350D and 400D) but not 5D or 1D.

As the sensor is smaller you only get an image for the centre part of the frame (when compared to a 35mm frame). This is at a factor of 1.6x.

So if you were to compare say a 10-22mm lens on a 400D, it would be equivalent to using a 16-35 lens on a conventional 35mm camera (or a 1Ds)
 
Thanks for the replies, I think I'm getting there!

Still a little confused though because the kit lens (Canon EF-S 18-55mm Lens) seems to let me go more wideangle, more than I would have though with the extra 2mm. It feels like the Sigma definitely isn't going to 20mm but the Canon lens is?!!? :thinking:

Is there something else I'm missing?
 
The smaller the number, the wider it is, so the 18-55 will be wider than your 20mm.

This is the problem with crop factor bodies, it's hard to go seriously wide (10-20 Sigma is your best option I reckon).

Cheers,
James
 
What I mean though is that the 18-55mm Lens doesn't seem like an equivalent 29mm at its widest when compared to the Sigma.

Are some of the lenses designed specifically for crop sensors so that a 20mm will actually be 20mm? Or am I way off track here? lol
 
No all lenses refer to the focal length before any factor is added for the crop factor.

The focal length is still 20mm regardless of what size the sensor is. The 1.6x factor is purely to help people compare.
 
Cool thanks. It's finally clicked! lol
 
You must log in or register to reply here.
Back
Top