Focusing

Take a Focus Frame

1. Select a star field in the upper half of the PT Target Selection window with the middle mouse button. A primary field near the zenith will do.
2. Hit the "Focus next" button in the PT Target Selection window. A window will prompt for the starting focus value (base value).
3. Enter the desired starting focus, generally two greater than your best guess for the correct focus value. For example, if you enter 1710 you will test at 1710, 1709, 1708, 1707, and 1706. You need to hit return in the entry box or the "okay" button to start the focus exposure.

Examine the Focus Frame

1. Select the focus image number in the PT Log window and display it by clicking on the "display selected image" button in the upper right corner. Adjust the display ("histeq" scaling is good).
2. Choose the "cursor" button in the saoDisplay
3. Left-click on the star images and their FWHM will be reported in the MOP xterm window. The "arcseconds" conversions are not for the PT so don't get too excited (PT pixels are 1.15 arc seconds across).
4. The wide space is between the last and next to last exposures are the smallest and next smallest focus values

Set the Focus

1. In the "PT telescope control" window edit the Focus field and press enter with the cursor in the field. The focus will be set to your new value (watch it change in the TCS display).
2. The focus routine first sends the secondary mirror to ten greater than its target before backing up to its final value. This is done to avoid backlash. This means you shouldn't adjust focus during an exposure.

Turn on Autofocus

1. If you want MOP to check and adjust focus after every sequence of exposures, type "setAutoFocus -on" in the MOP xterm window where you typed the ptConnect command.

Focus Alarms

1. MOP regularly checks focus (whether or not autofocus is turned on) and will occasionally pop up a window with a "No (in focus) stars in field!" message. Most likely you are far out of focus and you should examine an image to check. It might also be cloudy.
2. The autofocus feature does not operate if a focus alarm has occurred. You'll need to adjust the focus manually. Autofocus will resume after the next sequence is finished.

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