Aperture won't open - Canon EF-S 17-85MM F/4-5.6 IS USM Lens

Make sure the subject is well lit. The autofocus relies on differences in contrast to determine proper focus. Move to a well lit area or add additional light and attempt again.

Make sure the aperture ring on the lens (if that lens has one on it) is set to minimum (highest number - f22 etc.) This value it often a different color ink than the others to help speed locating it. On most Nikon & compatible lenses, when the aperture is set to minimum, the camera's main & sub command (thumb and finger) dials will control the aperture and shutter speed. When the shutter is held down 1/2 way, the aperture will open fully (to allow the most light in and speed composition) and then automatically stop down to the commanded value when fully depressed for the exposure. If you have the aperture set on the lens to something different - it may be preventing sufficent light from entering and interfere with the autofocus function.

Good luck!

The aperture of a lens system is the opening between the actual lens elements, typically made of glass or plastic, and the camera's digital sensor that translates the light into image data. Aperture openings are referred to in terms of stops or f-stops that equate to the ratio of the lens focal length to the diameter of the opening. A lens system with a focal length of 50mm and an aperture opening that is 25mm in diameter would equate to an f-stop of 2, and would be known as a 50mm f2 lens. Some lenses have variable apertures that can be set to one of multiple f-stop values. Reducing the aperture size decreases the amount of light that makes it to the sensor as well as increases the amount of depth of field that the lens will provide.

When the camera is set to autofocus, let the camera do the focusing. If you want to focus manually, turn off the autofocus so you can turn the focusing ring.

On a film camera, the internel electronics determine the shutter speed and aperture. The camera computer figures out a higher shutter speed against the aperture speed. You have a lever on your lens that, when mounted on the camera, will keep the aperture open until you fire. That allows viewing in the brightest light. Then that aperture arm is allowed to close to what the exposure setting the camera determines when you click the shutter. You should be able to take off the lens and easily move the aperture arm and have it snap closed. If it takes a few seconds to close.. then the lens has oil on the aperture blades or the grease inside the lens is bad. These days, unless is it a very expensive lens it's replacement time. Canon lenses will fit any Canon (except Fd) film or digital camera.

This means that the lens doesn't have its aperture ring set to its smallest opening.
Turn the aperture ring to its smallest opening (largest f/fnumber) and lock it if the lens has an aperture ring lock. You control the aperture from the body, the same way as with a lens without an aperture ring.

Were you about to say it says FEE on any other setting? This is perfectly normal for a lens with an aperture ring. Leave it at f/22. You control the aperture from the camera body, the same way with a lens without an aperture ring.
If you need a manual, you may download a copy here.

This lens lacks the electronics to communicate with the camera. You need to set the aperture ring on the lens to its smallest opening (largest f/number). You control the aperture from the camera body, the same was as on a lens without an aperture ring.
For the camera, you need to set it to the Manual exposure mode and set the shutter speed and aperture yourself. You also won't get any metering assistance from the camera. You can review the pictures and/or use the histogram to get the proper exposure, or use a separate light meter.

Not realistically possible, due to the incompatible lens to focal plane distances. If you found one it would either not allow infinity focussing or would need to incorporate corrective optics which add cost and ruin image quality.

All such adapters mean that the AF won't work, and focussing and image composition must be done with the aperture fully open before manually closing the aperture down to the desired value for metering and shooting. With Nikon G lenses the aperture is fully electronic, so the lens would only be operable at its smallest aperture.

You can get an adapter to allow Nikon to Canon EOS though, but as both cameras have plenty of excellent quality new and used lenses and resale values are high it's a pointless exercise.

You must lock the aperture ring to f/22, so the camera can engage the aperture adjustment lever on the lens. Then, you can change the aperture with the command wheel.

When you change the aperture with the command wheel the aperture ring on the lens doesn't move when the camera actually adjusts the lens aperture.

Take the lens off and locate the aperture adjustment lever on the lens mount.

Unfortunately, this won't work with older AF lenses. So if you are using an older lens, the only thing you can do is change the camera setting to M (Manual) to adjust the aperture on the lens yourself.