Pleiades with Astrotracer

The image of Pleiades Open Cluster (Messier 45) is a stack of 32 frames taken with Pentax K-1, Pentax SMC F* 300mm lens and Astrotracer.

Actually it is quite difficult to calibrate Astrotracer with 300mm lens. Only after several tries I was able to get 30 sec exposures. The stars are not round, but it is an effect of few worse frames which I did not exclude from stack. I think it is not bad, taking into account it was done without equatorial motorized mount, just regular tripod.

Comet C/2020 F3 (NEOWISE)

Image was taken with Pentax K-1 and vintage lens in Wisła, Poland on 23.07.2020.
The comet is barely visible with naked eye and is quite low over horizon.

Some technicalities

To achieve 1 minute exposure I used the Astrotracer - an exclusive Pentax feature.
The lens was AUTO CHINON 1:2.8 f=135mm with M42 mount. It is pretty sharp but has terrible purple fringing visible on bright stars. The lens is also vingetting a lot on full frame.

Piece of Orion

Here is a photo taken with Pentax K-1 and SMC Pentax-F 1:4.5 300m * lens.

It is stacked from 28 300s exposures at ISO 100. Of course the session was driven by AstroBox M4 :-) I was stacking the photos using SIRIL and then made some adjustments in Darktable. The biggest and still not solved problem is how to get rid of this huge gradient...

Half a year with NanoPI M4

After some time of using the AstroBox M4 - FriendlyElec NanoPi M4 - it is time for a little summary...

So far my the experience with the board has been great!

The AstroBox works well - finally this is a board which delivers enough power to drive what is needed. Quite a lot of stuff actually:

• INDI + Kstars with Ekos (compiled from source)
• Lin_guider (compiled from source)
• Celestron Nexstar mount
• Various scripts (bash, python)
• Relays controlled by GPIO
• Heater controlled by onboard PWM
• Canon cameras via gphoto2
• Pentax DSLRs via pktriggercord
• QHY5 guiding camera used directly by Lin_guider, but also via INDI...
• DreamFocuser via INDI
• Astrometry.net installed locally
• TurboVNC - by far the best VNC server! (compiled from source)

All the above runs in Armbian (Debian) and the entire Debian repository is available. I've choosen to compile INDI, Kstars and other software to have the latest versions. In some casese (e.g. TurboVNC) the software is not in the repositories.

Ekos functionality
I wanted to use more of Ekos and less of various scripts. Basically it is just working, however I did not ditch my scripts completely.

• Autofocus = DreamFocuser + Canon 400d =
• PROS: works and does the job automatically (stops guiding, finds the star, iterates to reach the best focus)
• CONS: I can achieve better focus using Bahtivov mask; sometimes it thinks a noise is a star and focus goes completely off (can't be left unattended)
• Platesolve to synchronize and to slew to your target = Nexstar + Canon 400d =
• PROS: works and achieves very good precision; just give it target name or even FITS file with your earlier photo; works offilne
• CONS: sometimes it does not work with FITS (some my files probably miss important data); with my mount it can try ten times until it achieves the target with good enough precision
• Autoguiding = QHY5 + Nexstar =
• PROS: all in one program and well integrated with other functions; can use external guider (Lin_guider or PHD2) and still integrate
• CONS: has tendency to loose the guiding star; external guiders allow more control over guiding parameters
• Driving the entire session - scheduler
• PROS: could potentially automate entire sesion
• CONS: needs a quality mount, quality cameras and telesope to work reliably; in my experience it is quite picky (e.g. autofocus failed -> entire session fails or autoguiding lost the star -> entire session fails etc.); still better to run individual tasks manually...

To summarize
The NanoPi M4 was one of the first SBCs withe enough horsepower to drive astrophoto sessions. IMHO it is currently the best! Only few months ago the RPi4 became available and now the solutions like Stellarmate for RPi4 start to appear. But NanoPi is still better: there is a lot of development around mainlinig the Rockchip boards. As a result NanoPi M4 currently can work with pure, open source Linux! No vendor lock-in. Runs 64bit (ARM64 aarch64) Linux - with the necessary software installed directly from repositories (few exceptions can be compiled - easy). I can use all 7 USB ports (4 are USB3). The onboard wifi and bluetooth work as well, without any special drivers. Performance wise it is equal or better than RPi4.

I bougth another such board, this time with 4GB memory. I will use it as tablet (with a touchscreen). I already installed Arch Linux on it and experiment with Panfrost drivers (open source 3d for ARM Mali)...

Next post: some pictures I made during this half year... Stay tuned ;-)

AstroBox M4 inside

Here are ugly internals:

• one relay module with four relay ports, used to gate power outlets for DLSRs and multipurpose 12V; one relay is used to control the shutter release of DSLR (NanoPi has only one serial port, used for telescope so I had to control shutter with GPIO&relay)
• two DC/DC voltage convertors, one from 12 to 5V for powering NanoPi M4 board, one from 12 to 7.4V for powering DSLR cameras
• one PWM module which takes as input the hardware PWM from NanoPI and 12V DC, output is modulated 12V, used to power dew heater
• one module to convert serial TTL levels to RS232, to control the telescope mount

AstroBox M4

A new toy: NanoPi M4,

brand new development board, similar to RPi but better(!) in quite a few areas. It has 2GB RAM, speed Rockchip Rk3399 processor and a lot of other goodies (WiFi, 1G ethernet, 4 USB3.0 and 3 USB2.0 ports, etc).

I decided to make a new AstroBox with it because the former built on OrangePi had not enough processor power and too little RAM. Now it is ready and runing great.
It is self contained with INDI, Kstars and Ekos. You have to connect to it to initiate the session, but while it is running (making photos, guiding, focusing), you can disconnect and it does not disrupt the session.

It provides the following conectivity to telescope and other astro devices:

• 2 x 7.4V switchable power outlets for DSLR cameras
• 1 x shutter release mini jack for Canon or Pentax DSLRs
• 1 x RS232 with RJ11 socket (for simple 1 to 1 connection to Celestron mount)
• 1 x 12V PWM for heater
• 2 x 12V switchable power outlets for other devices
• 4 x USB 3.0
• 2 x USB 2.0
• 1 x USB3 socket (but USB 2.0 speed only)
• 1 x 1G ethernet
• HDMI (not used)
• headphones (not used)

From the PC side, one can connect to it using VNC or RDP.

Basically it covers all the AstroBox v1 did, but just better...

Chainguard

A small DYI project
It is a parametrized OpenSCAD model of bicycle chainguard.
It is beased on the module done by enif. I added an ability to specify angle pro each screw hole.