Dwarf Mini and RISC OS
The Dwarf Mini is an ultra-portable “smart telescope”, suitable for photographing deep-sky objects like nebulae and galaxies. It can also be used to image the sun and moon, but isn’t suitable for planetary imaging as the magnification is too small. It’s also useful for terrestrial imaging.
There is no eyepiece — you don’t look through it — and all operations are controlled via a tablet or smartphone, in our case a Pixel 6a. It’s motorised and can track astronomical objects automatically, either by just plonking it down on a flat surface or, for more accuracy in longer exposures, setting up an equatorial mount: just attach it to a tripod and align the scope to the pole star. There are built-in filters for deep-sky objects, a magnetically attached solar filter, and the device can take many images and stack them to increase the quality.
There are two cameras, wide-field and telephoto. The scope communicates with your phone using NFC, Bluetooth or wifi, giving a live display. The wifi can connect over your home LAN or directly, using its own server. All operations are controlled remotely, so (given adequate wifi range) you can do an observing session from inside your own home — a distinct advantage on cold winter nights. There’s a built-in comprehensive sky atlas and the app has a help system, and there’s a full manual online, also available as a PDF.
An example
So what do the images look like? We’ve had terrible weather recently, but today was our first clear day for ages. And here’s the sun at 8:30 this morning.
There are three small sunspots visible, confirmed via the SpaceWeather site. It’s a stack of 20 photos, each with 1/200sec exposure. Tracking was perfect — all I needed to do was point it at the sun and the rest was automatic.
And just to show it can do more, here are some starlings, photographed a few hours later. All shots were taken through an open window.
Accessing the files
While the phone is connected to the Mini, you can download the final stacked image to your phone as a standard JPEG, and then transfer it to your NAS or computer for perusal and editing. But to access the full uncompressed data — which consists of a number of raw images in FITS or TIFF format along with shooting data, calibration images and a PNG file of the stacked result — you need a different connection.
The manual for the scope claims that you can access the full images via a USB C-C cable, also used for charging the scope’s battery. But I’ve not been able to get that to work with any of our devices/computers — for example, if we plug the scope into our phone using the supplied cable it just starts charging the scope’s battery from the phone. I’m not alone in this; a number of other users report the same problem.
Fortunately, the Dwarf Mini has a built-in wifi server, and this method works perfectly, giving access to the full data over FTP. And RISC OS will happily connect to it so you can download images:
- Power on the Dwarf Mini
- Wait until the Mini’s indicator is a circling green light
- On RISC OS, select the device from wifi networks
- Enter the wifi password (the default is in the manual)
- Wait until the iconbar connection icon is green
- Now you can use FTPc to connect:
Host: 192.168.88.1
Security: 0 - None…
Passive: On
Add this connection to FTPc’s user menu with an appropriate name. For reference, I’m using a 4te2 running RISC OS 5.31.
Once you’re connected, you should see see a filer-like display, as right. You can navigate this like a filer window and copy files by drag-and-drop.
Note that my main internet connection is via an ethernet cable. This operates concurrently with the wifi, so I’m able to copy files straight over to our NAS. Also note that if the scope isn’t connected to a phone, it will power down after 10 minutes or so — the ftp connection does not override this.
The Astronomy directory will contain a number of subdirectories containing the actual data. The names of these contain useful information — for instance, the data for the sun picture above is inside:
DWARF_RAW_TELE_Sun_EXP_0.005_GAIN_10_2026-02-14-08-36-33-624
This tells you which lens was used (TELE), the target (Sun), the exposure times (0.005sec), the gain used (10 — this is roughly like the ISO setting in a camera), and the date and time (YYYY-MM-DD-hh-mm-ss-mss). It’s unfortunate that FTPc’s display can’t be made wider; you have to navigate the menu to Info to see the full name.
Inside the directory there’ll be a number of files like this:
Sun_0.005s10_Astro_20260214-083640954_25C.fits
…which is a FITS file. Again, there’s useful information here: the target (Sun), exposure time (0.005sec), the gain (10), the internal filter in use (Astro), and the date and time (YYYYMMDD-hhmmssmss). And lastly, 25C is the sensor temperature.
There’ll also be a file called shotsinfo.json, which can be opened as a text file:
{
”DEC”: 0.0,
”RA”: 0.0,
”binning”: ”1*1”,
”exp”: ”1/200”,
”format”: ”FITS”,
”gain”: 10,
”ir”: ”Astro”,
”maxTemp”: 25,
”minTemp”: 25,
”shotsStacked”: 20,
”shotsTaken”: 20,
”shotsToTake”: 20,
”target”: ”Sun”
}
DEC and RA are the celestial coordinates of the target. For the sun and moon this is not set, as the device tracks the target using the image itself, rather than knowing its position in the sky. For other objects, when you request a target the scope will analyse the star pattern it sees, and work out exactly where in the sky it’s pointing — an impressive process known as plate solving. The scope can then slew to the target’s position.
The stacked.jpg file is the one you can access on the phone, and there are also stacked versions as a 16-bit png and a 16-bit FITS file.
If you look at one of the FITS files in a text editor (double-click and hold), there’s a header like this:
SIMPLE = T / file does conform to FITS standard BITPIX = 16 / number of bits per data pixel NAXIS = 2 / number of data axes NAXIS1 = 1280 / length of data axis 1 NAXIS2 = 720 / length of data axis 2 EXTEND = T / FITS dataset may contain extensions BZERO = 32768 / offset data range to that of unsigned short BSCALE = 1 / default scaling factor DATE-OBS= ’2026-02-14T08:36:40.944′ / Time end of exposure EXPTIME = 0.005 / [s] Exposure Time GAIN = 10 / Gain RESTACK = 0 / is Mega Stack XBINNING= 1 / binning factor used on X axis YBINNING= 1 / binning factor used on Y axis FILTER = ’Astro ’ / selected filter CAMERA = ’TELE ’ / shooting camera XPIXSZ = 2.9 / [um] pixel size in microns (with binning) YPIXSZ = 2.9 / [um] pixel size in microns (with binning) FOCALLEN= 150. / [mm] Focal length of telescope in mm DET-TEMP= 25 / Detector temperature in C RA = 0. / [deg] Observe object RA coordinate (J2000) DEC = 0. / [deg] Observe object DEC coordinate (J2000) OBJECT = ’Sun ’ / Observe object BAYERPAT= ’RGGB ’ / Bayer pattern EQMODE = 0 / Equatorial mode FIRMWARE= ’1.0.22.1′ / telescope firmware version MACADDR = ’xxxxxxxxxxxx’ / telescope MAC address TELESCOP= ’DWARF mini’ / DWARFLAB telescope INSTRUME= ’DWARF mini’ / DWARFLAB instrument ORIGIN = ’DWARFLAB’ / DWARFLAB TEAM END
Solar and lunar photography has a resolution of 1280×720, while everything else is 1920×1080. The raw data is 16-bit graphics — just to be clear, that’s 16-bits per channel. And here’s where RISC OS will have problems: there is little software that can process 16-bit graphics files.
PhotoDesk will load the 16-bit PNG. I haven’t played around much, but on a star field image, the Increase contrast setting of Image processing>Gamma does a good job of reducing colour noise.
ChangeFSI can sort-of handle FITS files. But with limitations: you’re losing data (and low-level light data is very important in astronomical imaging), and you’ll get a greenish tinge which needs to be processed out. This is due to the RGGB Bayer pattern of the detector, which is quite standard.
I’ll be investigating this further, and will report on results here. Let’s hope for … clear skies! Which we had briefly last night, enough to get a first attempt at a random star field:
Well, I say random — it’s actually centred on the star HIP 80364, which, if you google it, turns out to be a star in the game Elite: Dangerous. So, a RISC OS connection…