Nikon Teleconverter Which teleconverter would I need to add to a 70mm - 300mm telephoto lens to get more distant photos

Nikon Imaging Products NIKKOR Lenses
I am not an expert hence adding a recent review from B&H
http://www.bhphotovideo.com/explora/photography/buying-guide/best-2015-nikon-lenses

You can order the Tamron 2x teleconverter here. Be aware that not all lenses are compatible with teleconverters, and you can actually damage some lenses by trying to use them with a teleconverter.

Teleconverter loses maximum lens speed.
With 2X teleconverter, your 90mm-300mm f4.5~5.6 will become something like f8~f11. Most SLR AF cameras need maximum aperture of f5.6 to autofocus so by using the 2X teleconverter on this zoom lens, it will not autofocus, because the lens's light gathering became too low.
Here is more information about using teleconverters.
http://tinyurl.com/29s5osk

Attaching the lens will make no difference.
It sounds like the release button on the camera may be faulty.

The SX1 has an amazing 20X optical zoom. The teleconverter will allow to get pictures if the camera zoom is not fully on 20X. It means that you can't get a full 40X zoom images, but a 30X maybe. I don't why canon has this problem.

When using a TC, as the perceived focal length increases and the aperture falls off, AF struggles to work except in very bright light.

This is a lens for Sony/Minolta cameras. It is not compatible with the Nikon D90. Hence a Teleconverter for Nikon will not work on this lens to mount it to a Nikon D90.

Teleconverters are not recommended with variable aperture and slow zoom lenses. Since there is an additional element, the effective max. aperture will get reduced to about f/8-11. So it is not worth the money.

Canon currently makes super Telephoto lenses from 300mm to 800mm and a number of zoom Telephoto lenses from 28-300 to 100-400. You can also special order a 1200mm lens from Canon at a cost of $99k! (There are only about 20 such lenses made so far.)

You can also get a 1.4 or 2x teleconverter to further increase the power of a telephoto lens. However, the cameras are unable to auto-focus when the minimum f-stop exceeds f/8, which can happen when you use one (or both) of the teleconverters on these longer lenses, so you have to manually focus the lens.

You can also get telephoto lenses from other manufacturers such as Tamron and Sigma that are built to work with Canon cameras. However, the Canon lenses are generally regarded as the best quality.

Having a 'DG' in the name of the converter tells me, Yes...