I also have recently purchased a Rokinon 500-1000 mm telephoto lens with the 2x multiplier, however, when I attach it to my Nikon D3000 the camera still says "lens not attached" Is there something "special" I have to do for the camera to recognize it or should I contact the company because it broken?

Mount the multiplier onto the camera and then mount the lens onto the multipler. This assumes that by multiplier you really are referring to a tele-extender.

You need to shoot in the Manual mode by turning the mode dial to "M". You have to set the shutter speed and aperture yourself, without any help from the camera's light meter. You can review the photo afterward and adjust the exposure accordingly. The histogram will help in this.

Oh, and you also have to focus manually.

This lens does not have the electronics to communicate with the camera. You have to use the camera on the Manual exposure mode (turn the mode dial to M) and set the aperture and shutter speed yourself. You will not get any metering help from the camera's light meter, but you can use the histogram to fine-tune your exposure. You also have to focus the camera manually.

You'll want to use a tripod or other support, as the lens will magnify every bit of camera shake.

The filters go on the back of the lens (the end that connects to the camera). If you detach the lens and look inside, you'll see a threaded ring. Simply screw the filter on, similar to how you put filters on the front end of other lenses.

Due to the great magnification ratio of this lens, you absolutely need to have it on a tripod or other stable support. Even the slightest camera shake will be magnified.

The lens also has very little depth of field, so you must focus precisely. Since you're mounted on a tripod, you might want to activate the LiveView feature and zoom in the subject while you focus.

You don't. The Zeikos attaches to the front of lens with a 52mm filter thread, which then attaches to the D90. If you have the 18-55mm lens, for example, this will fit onto the front of that lens, effectively converting it to a 36-110mm lens. If you have the 18-105mm lens, this won't fit onto it.
This device is really intended for use with cameras that don't have interchangeable lenses. With your D90, you're much better off using another lens instead of putting this onto the front of another lens.

For Nikon AF and manual focus SLRs. The compatible T Mount System makes it possible to use most any single lens reflex camera in combination with various front camera attachments such as telescopes, mirror lenses and slide duplicators. The T Mount is a metal connector that screws onto the compatible front attachment and allows this combination to be coupled to the SLR camera lens mount.

Yes. The smaller sensor of the D3000 will make it the equivalent of about a 105-315mm lens on a 35mm film or full-frame digital camera. Also, the autofocus will not work with the D3000.

hi there, Nikon D3000 only support lenses with built-in motor
if you want to use this lens, you can only operate it manually while focusing on object
hope this reply will help

This is a mirror lens. Light enters the leans, ir reflected back to the front of the lens by a mirror and is then reflected back to the sensor by another mirror(behind the black circle in middle of lens). DO NOT REMOVE OR TRY TO. To do so will rendeer lens useless.Filters screw on front of lens, like any other lens.

All third-party lens makers make their lenses available with a Nikon mount.

Keep in mind that autofocus will only work if the lens has an internal focus motor.