OS/IS equivalent

[Hysteria_UK]

I'm sure this has been asked before but I didnt know what to search.

I had the dilema last night of either the Nikon 35mm 1.8 or the Sigma 18-50mm 2.8-4.5 OS HSM. I may still get the Nikon at a later date but decided on the Sigma as its more of a walk about lens. I wanted something wider than the 28-100mm I currently have as on my camera I've found a few times its not wide enough and also that I needed something that dealt with low light a little better. This was what swayed me.

So my question is, what would be the equivalent aperture of the sigma 2.8 with the OS turned on? would it be nearly as good as the Nikon 1.8 in low light situations?

 

[a1ex2001]

So my question is, what would be the equivalent aperture of the sigma 2.8 with the OS turned on? would it be nearly as good as the Nikon 1.8 in low light situations?

there is no equivalent, the effect of OS depends entirely on what you are shooting, OS will generally speaking give you a couple of stops advantage if shooting a stationary subject.