If you are shooting with a diagonal, or if your scope has an odd number of mirrors, your image will be mirror reversed and you should correct this. Some software, like AviStack, outputs mirror-reversed images also.

Imagine you have taken a normal daytime image of famous right-handed baseball pitcher Nolan Ryan and the image is mirror reversed. In the image he would look like he was pitching left handed! Not only that, but you would not be able to read his team's name on the front of his jersey because that would be mirror reversed also. This is simply wrong. It needs to be corrected.

Mirror reversal, however, cannot be corrected by simple rotation. Luckily most image processing programs also have a command that will flip an image horizontally or vertically to correct for mirror reversal.

This image of the lunar crater Clavius is mirror reversed after processing in AviStack.

• Under Photoshop's Image pull-down menu, select Image Rotation > Flip Canvas Vertical.

• Depending on the image's orientation, you may need to select Flip Canvas Horizontal.

This image of the lunar crater Clavius is corrected for mirror reversal.