How to do long exposure Nikon D750. I'm trying to do astrophotography?

How to do long exposure Nikon D750. I'm trying to do astrophotography? - 1

Added (1). What on the Nikon D750 is the option to have your lens open for 10-20-30 secs?

There used to be a small plastic coated cardboard reference for exposure times for night photography, so it varies by the available light

Please read manual. To get the stars to be "still", it is frequently necessary to get a motorized mount on a tripod.

In Manual mode, you can set the shutter speed for "10-20-30 secs" or if you would need longer than 30 sec you have an option called "bulb" which is the next setting after 30 sec. When set to "bulb," the shutter will stay open as long as the shutter button is pressed. Look for tutorials about astrophotography.

Choose a dark clear night away from light pollution and preferably with no moon
Camera on a tripod
Point the camera at the area of sky where your interest lies
OPen the aperture to maximum
Manually focus at infinity
Set ISO to 800
Try an exposure of 15 seconds for starters. Use a cable release if you have one otherwise use the timer delay so any camera shake has dissipated by the time the shutter fires.
Look at the result and adjust ISO and exposure time as appropriate.

Depends on what you're doing.
Are you trying to get star trails? If so, look up stacking.
If you're after no-streaked star images, then bulb mode (discussed in your camera manual). Your camera also supports shutter speeds as slow as 30 seconds, but you'll need to use an ultra wide angle lens if you don't have a tracking mount. You may need to get a tracking mount (or piggyback on to a telescope with a tracking mount). Stacking is still required.

If you're just starting out, StarStax is a free and easy to use stacking program. I use Hugin for stacking (uses the enfuse program). There are better stacking programs out there.

Learn to set your camera so it saves images in raw format. Convert them to 16-bit/color TIFF.

Camera setup

* Mount the camera on a tripod and frame your shot
* Place the lens in the manual mode and focus the stars
* Set the white balance to Daylight
* Place the camera in the manual mode and use the 30 second exposure time.
* Lock the mirror up.
* Turn the VR on your lens
* Make sure that you are at least 50 miles away from any civilization (which causes light pollution)

You also need to make sure that ANY of the noise reduction features are turned off.

Here is a link to a much more intense discussion of using a digital SLR to shoot the night sky; It is a rather long (1:45) and you may want to take notes as the video continues.

Starting a 1:00 in the video ending at about 1:06, there's a discussion about usable ISO settings and how to setup your camera for shooting wide field astrophotography

The second link describes how to process your RAW deep sky photos

Set shutter speed to B or Bulb.