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My astronomy project:
Building an astroserver with a Raspberry Pi4


  1. Introduction
  2. The passive cooler
  3. Formatting the microSD card and transfer of the mirror file
  4. Setup KStars and Ekos
  5. Setup INDI Control Panel 'Telescope simulator'
  6. Setup INDI Control Panel 'Canon DSLR'
  7. Battery test
  8. Indoor test of focus control
  9. Adding a GPS receiver
  10. First Light
  11. Setup as Hotspot controlled from a pad
  12. Setup drivers peripheral
  13. Good to know commands
  14. To be continued

Related projects:

  1. HEQ5 as portable mount
  2. Pentax 645 300 mm ED IF f/4 lens
  3. KStars / EKOS and Raspberry Pi4

I take no responsibility or liability for what are written here, you use the information on your own risk!

8, Indoor test of focus control:

With the KStars and Ekos there is a module that is used to control the focus of the camera. But can it also control the focus motor that are built in the lens of a DSLR camera as my Canon 6D lenses has ? In this case the lens is a Canon 50 mm f/1.8 stopped down to f/4. The focus button on the lens is set to automatic focus.

Canon DSLR, check mirror lock:

Indoor test of KStars and Ekos function Focus

Check the mirror lock delay, I have it set to three seconds. Don't forget to save under the Options tab. It's often I have to do this, the mirror lock delay disappears, I don't know why.

Canon DSLR setup:

Indoor test of KStars and Ekos function Focus

Before proceed to the focus setup, I set the exposure time to one second with one second delay between the images. Note: this is not the same delay as the mirror lockup. Do a test shot, it's the blue button at the lower arrow. A preview window will pop up. You can close it when you have found the correct exposure.

Canon DSLR, Focuser Settings:

Indoor test of KStars and Ekos function Focus

The Settings tab: Set 'Full Field' and 'Suspend Guiding', because there is no auto guider in this profile.

Indoor test of KStars and Ekos function Focus

The Process tab: Set 'Detection' to Gradient and 'Algorithm' to Polynomial. This is what I found worked best for me and my equipment, it could be different for you.

Indoor test of KStars and Ekos function Focus

The 'Mechanics' tab: I set the 'Initial Step size' to 500 ticks. Better with bigger steps than small when auto focusing. It will by automatic use smaller steps when closing in to perfect focus. Set 'Max Step size' to 1000 ticks. Set 'Max Travel' to 100'000. All these data are based on my equipment, for other cameras and lenses it could be different. The built in lens focuser is not an absolute focuser what I know, it has not a defined zero point. In Ekos it looks as it always start at 50'000 independent of where the focus was from the beginning.

First focus shot:

Indoor test of KStars and Ekos function Focus

No luck with clear sky here. Has to do this with a synthetic star on my monitor.

I think there is some bug in Ekos Focuser. After many hours struggling to get it to work, I found: The lens' motor focuser can't be moved in 'Normal' mode, only in 'Live view' mode. And even if the camera can be set in live mode with the Ekos 'CCD button' it doesn't move the focus motor when doing automatic focus, but it do when doing it manually with the up/down buttons.

I had to switch to 'Live view' direct on the camera with the Start/Stop button. And then click the Ekos' button 'Automatic focus'. That was bad because then there is no chance to have this focusing process totally automatic. I will wrote a note to Indi forum to hear if they have some idea about this.

I also did a test with the 'Mirror Lockup' in camera disabled, it didn't work in that case either. The Ekos' 'Force Lockup Mirror' was disabled too.

After I found it out I did this:
I have the camera's 'Start/Stop' button in 'Live view'. I did a test shot with the blue button where the arrow points. After when I got the image up in the viewer, it will take a while. Set to 'High contrast' and 'Zoom to fit', the two upper arrows point at these buttons.

Zoom in on a 'star':

Indoor test of KStars and Ekos function Focus

Click in the middle of a star, in this case a synthetic star on the screen. A green rectangle appear.

Activate 'Sub Frame':

Indoor test of KStars and Ekos function Focus

Select 'Sub Frame' and shrink the 'Box' until it enclosure the star. Click on the center of the star to center the green box around it. In my setup I zoom with the scroll wheel and pan with the sliders.

Start 'Auto Focus' process:

Indoor test of KStars and Ekos function Focus

Start the 'Auto Focus' process. Now Ekos start to taken photos with variation of the focus, it will last until it find the correct focus or stop if it fail.

Find the correct focus point:

Indoor test of KStars and Ekos function Focus

The polynomial adapt to the test points, with enough points it can calculate where the perfect focus is placed. Ekos crashed a couple of times in this mode.

When the camera is in Live view it get very hot. The cameras temperature in my case increased from 22 degrees Celsius to 32 degrees. It takes long time to cool it down again. Make the Live view as short as possibly. It drains the battery too.

USB-Focus V3 problems:

Normally I use the USB-Focus V3 motor focuser to my telescopes. Sometimes there is a problem to get it to work correctly.

I noticed some strange behavior of the focus position. When I moved to the new Pentax 645 300 mm lens I set the focuser position at infinity, the end stop, to 65500. I normally have perfect focus at 63900 and set the max position to 65000. Sometimes I could see in the focus windows when doing auto focus that it suddenly could jump to zero or nearby.

I sent a question to the Indi forum about this, I got the answer that this could happen if the focus is near the end scale of the 16-bit scale, 65550. I have set max position to 65000 but it looks that the focus controller can override this, what's looking to happen is that it do a wraparound. The recommendations I got was to get a better margin to the end stop by moving it mechanically. I look it over and did something similar. I offset the positions counter by moving to position 5000, push the OUT and IN button on the hand controller. Then it reset the focus position counter to position 0, save it in Ekos focuser driver. Then you must set a new max position, you don't want to runt into the end stop. This work for my USB-Focus V3, maybe not for other focusers. Now I have to run it an evening and see if this wraparound problem is gone too. More information at Indi Forum, USB-Focus V3.

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