Focusing Aid

The Focusing Aid is accessible from Tools tab
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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. It is advisable to relay on HFD instead of FWHM, because the first is more stable against the atmosphere turbulence. HFD works with the whole star area while FWHM works only with the line of the star profile.
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. In DSLR mode also switch to 1:1 Preview Mode.
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
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.

Star Profile

2. Star Profile
Shows the star profile.

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.

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.

Reset Best

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

Auto track star

6. Auto track star
When enabled moving the Focus Aid window will be moved in ordet to center the focusing star it there is movement during the focusing.

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
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.