Pretty complicated problem on Nikon D40

[PinkyTheGreat]

Hi...

I have a problem with my Nikon D40 - when the lens is zoomed all the way in, the view in the viewfinder darkens and the camera can't auto-focus.
Is it the lens? How to fix that? (I don't have another lens to test)

I hope there is some easy/cheap solution.
Thanks in advance.

 

[480sparky]

What lens?

And is it (the amount of ambient light) rather dark when this happens?

 

[PinkyTheGreat]

It's 18-55mm.
The problem occurs always (on any amount of light).

 

[480sparky]

The viewfinder darkens because it's a variable max. aperture. At 18mm, it's f/3.5, at 55mm it's f/5.6. That's more than one full stop.

As for AF, maybe you've got something in the in-camera AF settings changed.

 

[Destin]

The viewfinder darkens because it's a variable max. aperture. At 18mm, it's f/3.5, at 55mm it's f/5.6. That's more than one full stop.

As for AF, maybe you've got something in the in-camera AF settings changed.

The smaller the max aperture, the more the AF will struggle. The sub-par AF of the d40 can't cope with f5.6 in anything but direct sunlight. You need a faster lens.

 

[PinkyTheGreat]

Thanks to both of you for the explanation! I'm a newbie in DSLRs, but it's much more clear now.