Hi,
It's nice to hear that the Bathinov Mask Focus Assistant Tool is used. Here a detailed description on how I use this tool without an auto-focuser.
I don't have an auto-focuser too, so it is definitly possible. The steps are as follows:
- Point your telescope to a bright enough star to be able to use your bathinov mask
- Place your bathinov mask
- Go to the kstars-ekos focus assistant tool
- Set the correct exposure time and select detection mode 'Bahtinov'
- Take a first shot by clicking the small camera icon next to the stop button to take a single shot
- A shot is taken and (only the first time after starting kstars) the message window shows a message to select the star to focus on
- Click in the photo on the star that you want to focus on
- After you have clicked the star to focus on a new shot is taken automatically and the bathinov pattern recognition is executed and shown as overlay on the photo
- Increase the 'box size' so it will contain about 60-80% of the whole bahtinov diffraction pattern. If you choose it too small or too big it will have difficulty detecting the diffraction pattern lines.
- Verify that the lines of the bahtinov pattern are overlapping the diffraction pattern in your photo, if this is not the case, increase or decrease the 'number of rows' value and take another photo (the 'number of rows' values is used to in a similar way as binning. it groups several rows of pixels in the image to get a better detection of where the diffraction lines are in the image (higher resolution images or a more bold diffraction pattern required a higher 'number of rows'.
- Note the two circles with a line in between in the overlay, they are an amplified graphical representation of the HFR. At the bottom of the focus tool the HFR value is shown
Strive for the smallest HFR possible, preferably less the 1. I usually try to reach values of less then 0.5. Note that an HFR of 0 is almost impossible, that would mean perfect focus, which is hard to do when you are on earth with a thick atmosphere above you
- Manually turn your focus knob a little to one direction
Remember the direction, if the focus becomes worse, the next step you need to turn to the other direction
- Press the small camera icon to take another photo
The bahtinov pattern recognition overlay is shown and the HFR is updated
- See if the HFR value has gone down and the distance between the two circles has become smaller
If the HFR value has gone up, you need to turn the focus knob the other way and repeat the steps starting from step 7
- Repeat the steps starting from step 7 until you have reached the smallest HFR value
- If you are in focus (reached the smallest HFR), tighten your focus lock screw gentle (if you have one) to prevent your focus from slipping
- Take another photo to verify if the focus has not moved when tightening the focus lock screw
- if ok, then you are done
- if not ok loossen the focus lock screw a little and repeat the steps starting from step 7 to get back in focus
Note 1: Due to for instance atmospherical turbulence the value of HFR can vary from one shot to anoter. So to be more accurate you can take multiple shots to see how stable the HFR value is. I don't know (haven't tried yet) if the 'Average over number of frames' will do the same. If so, that would be a nice feature
Note 2: When you are using manual focus (pressing the capture single shot button) the HFR graph won't be updated. This is also not the case for any other detection method when using the capture single shot button)
Sometime I do want to use the graph, in that case I press the start capture button (button right of the small camera button). That will take photos continuesly, so you have only a very small time to adjust the focus knob. Since I have an old camera which takes about 5 seconds to download a photo, i have about 5 seconds to turn the focus knob. Another alternative to gain extra time with an DSLR is to increase the mirror lock timeout to about 5 seconds. That will flip up the mirror in your DSLR and wait 5 seconds before taking the shot. Unfortunately that won't work for mirror-less cameras.
I hope this description is clear enough. If you have any questions, don't hasitate to ask. Also improvement suggestions are welcome.
Clear skies!
AstroRunner