Sigma 10-20 vs Nikon 18-105 at 18mm

[batmura]

I have a question about focal lengths of two different lenses. At 18mm on my Sigma 10-20, I get a "wider" result than at 18mm on my Nikon 18-105. The 18mm on my Nikon produces "bigger" background subjects. Maybe it's just me, but shouldn't they be the same? Or does the Sigma produce different results because it's an ultra-wide angle lens?

 

[batmura]

Anyone?

 

[grafxman]

18mm to one manufacturer is possibly different to another manufacturer. I wouldn't be surprised to see a different result from some other lenses, even from Nikon or Sigma. BTW are you using the markings on the lens barrel or the exif data? The markings may be off a little. In any event it's not particularly important on an SLR because you're looking at what you're going to photograph so you just zoom to see what you want.