What lens should I use for astrophotography?

I want to take pictures through my telescope and I was wondering which lens to use?
I'm mainly interested in taking pictures of the moon and planets and maybe the sun "using a solar filter of course"

In case it's relevant… I'm using a nikon d-3200 and an orion xt8

I don't need any lens to take picture through your telescope…'cose your telescope is a lens itself ;-)

There are several ways to mount a camera to your telescope. First you need to know that a camera with a 50mm is deemed to image at magnification 1 in the astrophotography world. Also, your scope accepts eyepieces with a diameter tube. You can buy an adapter tube that mounts your camera and terminates with tube that slips into your telescope. This places the camera at the "prime focus" of your T8. Thus your camera with no lens, in this application delivers magnification 1200 (your scope's focal length) 50 = 24. In other words your camera at the prime focus delivers 24X magnification. This will be perfect for shots of the moon and sun with sun filter.

At the prime focus your system's aperture is 8 inches. With a 1200mm focal length the effective f/# is 1200mm 8 inches = 1200mm (8 x 25.4) = 1200 203 = f/6. This will prove to be an OK set-up.

Now if you think working at only 24X (magnification) is not your thing, you can purchase a more elaborate camera adapter that allows one of your telescope eyepieces ahead of your camera. Again, no camera lens is used. This is called eyepiece projection. This method allows high magnifications. This is super difficult to do because lots of light is lost in the set-up, and exposures become long. You need a motorized telescope mount and the knowledge to align and track celestial bodies using super long exposures -- again a formidable task.

You can just hold your camera up to the telescope's eyepiece and snap a picture. To accomplish this you use your camera with its lens mounted in the usual way. This is called afocal photography. You can buy a camera-to-scope mounts that hold the camera in the afocal position, or you can handhold on moon or sun. You can't handhold on planets or stars, as the exposure will be long and now you need a motorized mount.

Best for now, use the handheld afocal position or buy an inexpensive (no lens) mount for your camera and slip it into the scope's eyepiece holder.

You don't need a lens you need a T-mount. It attaches to the front of your camera and allows your camera to slide over the eyepiece of your telescope.

You will however need a special tripod if you want to take pictures of anything other than the moon and sun. The smart thing to do is google the phone number to the company who made your telescope and ask them if they have a specific brand T mount they recommend.

There are two "simple" ways to do this (although it will cost some money).

You can buy a mount to hold your camera with its 50mm lens attached right over the eyepiece (the afocal method). You will also have to rig up some weights to balance the telescope.

You will probably get better results with a dedicated astrophotography cam---> http://www.telescope.com/...c/4/58.uts Theses cams shoot thousands of shots of the target and software on your computer averages out the exposures for the best detail - don't know if you have used your telescope much but if you do you will notice the image of the planets wobble all over the place due to atmospheric turbulence, you have to shoot thousands of images and use image averaging software for the best results.

Doing the second method may require a clock driven telescope… So you may find you have the wrong camera and the wrong telescope for what you want to do.