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Focusing Aid

 
The Focusing Aid is accessible from Tools tab
or with Alt+F shortcut.
 
Focusing Aid allows achieving perfect focus using the HFD (Half Flux Diameter) and/or FWHM (Full Width Half Maximum) metrics to measure the focus quality. The lowest value is the best one.
 
Note: In CCD Mode you have to switch to 1:1 Preview Mode in order to use the raw FITS data for calculation of HFD/FWHM. Using the raw data gives much more accurate focus quality measurements that the values calculated on screen data.
 
The Focusing Aid use the common aid behavior in APT- dragging the window and placing the Source frame over the image part that you want to use.
 
Focusing Aid
 
 
1

Source

1. Source
 
It is a "transparent" window that shows the image under the Focusing Aid and defines what is the source to be used in the Aid. It automatically detects the brightest star in the frame and analyze it.
 
2

Star Profile

2. Star Profile
 
Shows the star profile.
 
3

Focus Quality

3. Focus Quality
 
In left are the FWHM and HFD values for the current image. In right are the best measured values since last reset. The best values are reset if Reset Best button is used or when Auto Reset Best is enabled if you move the window.
 
4

Star Quality

4. Star Quality
 
Peak shows the brightest pixels value in the selected stars (8bits value). Sat means saturation and shows how many pixels has the brightest value.
 
For focusing is good to use stars with saturation 1-2 and peak bigger than 40.
 
5

Reset Best

5. Reset Best
 
Reset the best values for FWHM, HFD and clears the graph.
 
6

Auto Reset Best

6. Auto Reset Best
 
When enabled moving the Focus Aid window makes the same as clicking on Reset Best button.
 
7

LiveView Stacking

7. LiveView Stacking
 
Used in EOS mode when LiveView is activated. Defines how many images from the LiveView stream to stack before the star quality analysis. Bigger value reduces the influence of the atmosphere turbulence and the image noise, but requires giving time after focus change before you can see the actual effect - stacking leads to less "live" image. 
 
8

Graph

8.  Graph
 
Shows graph of the FWHM or HFD value changes. It is valuable to see if you are tuning the focus in the right direction or if the focus point is passed. Lowering graph means that you are moving in the right direction.
 
Double click on the graph to switch between FWHM or HFD metrics.