Fstop and zoom

[Lee_Maryland]

I have set my F stop to 3.5 on my Kit lens, but once I have zoom to 100 then the F-stop will change automatically to F5.5. I am assuming the kit lens is not able to shoot F3.5 at max zoom? Why is that? Anyone know?

 

[eric-holmes]

You assumed correctly. It has a max aperture of 3.5 at 18mm and 5.6 at 105mm.

 

[480sparky67 66]

Why is that? Anyone know?

In order to make the lens smaller, lighter and less expensive.

 

[ulrichsd]

Its a variable aperture lens, not a fixed aperture lens