If we shoot at too small of a focal length, an image may be small in the frame with a lot of wasted space around it (Figure 1). We may want to crop and cut off this wasted space to make the subject larger in the frame to give it more impact.

Figure 1 - Full frame image of the Moon occulting Antares taken with a telescope with 420mm of focal length.

• Select the Crop Tool from the Tool Palette and click and drag a crop box around the subject (Figure 2).

  Fill in the size that you want to crop the image to in the options bar at the top. If you fill in a specific size here, Photoshop will resample the image at the same time it crops it. If you leave the height and width blank, it will only crop the image and keep the resolution the same.

Figure 2 - Crop tool used in Photoshop.

• You can click and drag a corner of the crop box to resize it.

• You can click inside the crop box and hold down the left mouse button to drag it to move it.

• You can nudge the crop box in one pixel increments with the arrow keys on the keyboard.

• If you hold the mouse pointer just outside a corner of the crop box, the mouse pointer will turn into a curved double headed arrow and you can click and drag a corner to rotate the crop box.

• Once you have your crop selected, hit enter on your keyboard, or click on the check mark in the options bar to apply it.

Figure 3 - Resulting cropped image.

Now the Moon is much larger in the frame and we can even see Antares at about the 10 o'clock position, just about to be occulted by the Moon.