This tool is to take a preview exposure for focusing or centering purpose.

Set the Exposure time and the Binning to use for the preview.
You can also change the Gain and Offset or the “ISO” if supported and activated in the options
The camera lens F-Stop when using a supported INDI DSLR.

This setting is totally independent of the Capture setting.

Click Preview for a single exposure or Loop to take exposure continuously until you stop it with the same button. The light change to green when the loop is active.

The Option on top let you select an action to do on every preview image.

• Astrometry , every preview image is solved and the current center coordinates are shown at the bottom of the preview tool:
  

• Image inspection , show the image inspection overlay.

• Stack , visible only if you activate the “stacking option” in the preferences
  When it is checked, every preview loop frame is added to the previous ones. If available the images are processed with Dark and BPM. If the option is activated the frames can be aligned.
  
  After you start the Loop, you see the object image to appear progressively in the screen as the number of frame increase. This function is often use in public demonstration.
  
  You can use the menu File/ Save FITS file... to record the stacked image after you stop the Loop.
  A new stack is started when you restart the Loop.

• Preprocessing , preprocess every image with the loaded dark and flat frames.