Question: I am trying to get DOF portraits of my daughter with my Nikon d7000, as per my [previous post](https://photo.stackexchange.com/questions/5971/can-i-get-dof-using-nikon-d7000-kit-lens-18-105-f3-5-5-6).

I have zoomed in to 100mm or so and tried to get a large aperture but as I zoom, the camera decreases f# to about 6.

I have also tried in aperture priority mode and still have the same problem lowering the f#.

What am I doing wrong?

Answer: 
The aperture range on your lens indicates the maximum aperture at the shortest end to the maximum aperture at the longest end. So, at 18mm you can have f/3.5 but at 105mm you can only have f/5.6. That's pretty typical for a kit lens, the much more expensive zooms will offer a constant aperture across the entire range.
It all depends on the lens, not so much the camera. My suggestion, buy a better lens, there's several that'll do the trick for only a small amount of cash. Take a look at [Nikon's Lens](http://www.nikonusa.com/Nikon-Products/Camera-Lenses/index.page), and here's a few specific ones that might catch your attention. Sorry, I'm a bit more familiar with Canon's line-up, but they seem to be adequate.

* [Nikon 105mm f/2.8G](http://rads.stackoverflow.com/amzn/click/B000EOSHGQ)
* [Nikon 80-200mm f/2.8D](http://rads.stackoverflow.com/amzn/click/B00005LEOH)
* [AF NIKKOR 85mm f/1.8D](http://rads.stackoverflow.com/amzn/click/B00005LE75)
* [Nikon 50mm f/1.8D](http://rads.stackoverflow.com/amzn/click/B00005LEN4)
* [Nikon 35mm f/1.8G](http://rads.stackoverflow.com/amzn/click/B001S2PPT0)