At a look
Minimal system necessities
macOS: 2GHz Intel Core Duo or sooner, macOS Sierra (10.12), Excessive Sierra (10.13), Mojave (10.14) or Catalina (10.15) 512MB RAM, 64MB video RAM, 2.5GB disk house
Home windows: 1.5GHz or sooner, Intel Pentium 4, Pentium M, Pentium D or higher, or AMD Ok-8 (Athlon) or higher, Home windows 10, 512MB RAM, 128MB video RAM, 2.5GB disk house
Linux: A pc working 64-bit x86 Linux Ubuntu 12.04 LTS or later, Ubuntu GUI and OpenGL, 512MB RAM, 2GB minimal disc house
Raspberry Pi: Third-generation Raspberry Pi gadget (Raspberry Pi 3 Mannequin B or later) SanDisk Extremely PLUS 16GB microSDHC UHS-1 card, 2GB minimal free house, Effectively-ventilated mission case (fan not obligatory) Elective exterior 9-pin serial port
Last problem we assessed The Sky Imaging Version’s (TSIE’s) capabilities in making a exact pointing mannequin for equatorial mounts utilizing its TPoint module. This new version of The Sky comes with each TPoint and the Digital camera Add-on. The latter permits for the mixing of imaging cameras, autoguiders, filter-wheels, focusers and so forth to the planetarium software program used for controlling equatorial mounts and navigating across the sky. With a mannequin containing simply 61 stars, I used to be in a position to considerably enhance the accuracy of my Paramount ME equatorial mount.
Auto-focusing in TSIE
This problem, I’d wish to assess how effectively TSIE performs when autoguiding, in addition to judging its autofocusing accuracy. We’ll begin with the latter. Attaining sharp focus is extremely tough and is a make-or-break decider of picture high quality. It’s additionally important for any scientific imaging reminiscent of photometry. The purpose of greatest focus in an imaging system is called ‘important focus’. It is a zone of sharp focus that’s smaller in ‘quick’ optical techniques with steep mild cones, making quick telescopes tougher to focus. The important focus zone is calculated by multiplying the sq. of the focal ratio by 2.2, with the outcome delivered in microns.
Utilizing my GSO 254mm Ritchey–Chrétien telescope, geared up with a 0.67× focal reducer, I’ve an f-ratio of f/5.3 (and a focal size of 1,340mm). Inserting this into the calculation offers 5.32 × 2.2 = 61.8 microns.
It is a preposterously small focus zone. For people who choose ‘actual world’ figures, it equates to 0.0618mm. Because the f-ratio will increase, the important focus zone turns into wider. With my telescope imaging with out the focal reducer at f/8, the important focus zone enlarges to 0.14mm. Unsurprisingly, the usage of high quality digital focuser is required to acquire one of the best outcomes.
TSIE options some good instruments for attaining sharp focus. The primary, generally known as ‘@Focus2’, is a complete computerized focusing routine that slews to a star of applicable brightness, locations a small sub-frame across the star, computes an acceptable publicity time after which finds the important focus. I don’t suppose @Focus2 has modified a lot since my evaluate of an earlier version of The Sky in 2018, so I used to be ready to make use of the identical parameters as earlier than they usually labored extraordinarily effectively.
To arrange the focusing run, it’s worthwhile to click on on ‘Focus Instruments’ within the Digital camera menu. From right here there’s a alternative of utilizing two focusing aids, @Focus2 or a brand new addition, @Focus3 (extra of which shortly).
Determine 1 lists the parameters that I chosen to be used with my Moonlite focuser. ‘Samples’ is the entire variety of photos taken for either side of the optimum focus place and for this I selected eight (i.e. 4 all sides). ‘Averaging’ is the variety of photos taken per focus pattern, so for every of the eight samples I selected, the software program can take a number of photos earlier than shifting the focuser. The rationale for that is that if the seeing is poor, a number of photos may be averaged to provide a more true worth. I chosen two for this. ‘Focus Vary’ is a bit more advanced and requires some consumer enter to get one of the best outcomes with any explicit focuser. The consumer handbook (which could be very effectively written and complete, however barely outdated) states that greatest outcomes come from utilizing a worth that’s roughly 40× the scale of the important focus zone. For my arrange, that is 40 × 61.8 = 2,472. This quantity then needs to be divided by the distance-per-step determine of a specific focuser. Sadly, I used to be unable to recollect the step-size of my focuser, so I went on-line and located an analogous mannequin that had a step-size of 4.06 microns. Dividing 2,468 by 4.06 offers a worth of 608. I’d initially guessed a worth of 500 for the Focus Vary and it labored effectively.
Determine 2 exhibits the outcomes of the primary focusing run. The graphs look a bit ragged however the ‘Most Pixel Worth Historical past’ and ‘Half Flux Diameter (HFD) Historical past’ are shifting in the fitting path. The ‘Focus V-Curve’ actually isn’t a clean ‘V’ form, however the level of greatest focus was fairly correct. I instantly shot a 30-second publicity of the main target star and utilizing the ‘Heuristic show mode’ I used to be in a position to verify that the star photos had been crisp and the lengthy diffraction spikes had been single. I ran the autofocus routine a number of occasions and usually it returned a really related outcome, though it additionally failed just a few occasions. If nothing else, this underlines that autofocusing is a sophisticated process.
Subsequent, I clicked on @Focus3. I couldn’t discover any details about this new characteristic within the consumer handbook, however I positioned a PDF on the Software program Bisque web site that defined how the routine works. Intriguingly, it doesn’t depend on a star’s half-flux diameter or FWHM measurement, however as an alternative makes a distinction/sharpness-based evaluation, which I presume is how fashionable auto-focus digicam lenses work. Even higher, it purports to have the ability to give attention to a subject of stars, galaxies, nebulae and Photo voltaic System objects (with filters). The benefit of that is you can stay in your imaging goal, refocus after which proceed. Astonishingly, you too can give attention to daytime targets.
The system is fairly effectively automated, however as soon as once more requires some consumer enter. Determine 3 exhibits the choices. I typed 5.3 within the ‘Focal Ratio’ subject. For ‘Focuser Step Measurement’, I clicked on the downward arrow and it opened a listing of focusers together with two Moonlite choices. Fortunately, considered one of them inserted a step-size of 4.0640 microns, which was the worth I’d used on the earlier take a look at. For ‘Digital camera Pixel Measurement’ I used to be ready to decide on my imaging sensor from the small checklist that opened, utilizing a worth of 5.4 microns. With these parameters, the software program computed a ‘Search Span’ of 26, that means that every transfer of the focuser was in increments of 26 steps. The ‘Samples’ choice permits extra photos to be taken at a particular focuser place (just like @Focus2) which, when averaged, give extra correct knowledge factors in poor seeing.
Because the digicam strikes out and in of focus, the sharpness of the star picture is plotted as a bell-shaped or ‘Gaussian’ curve. The highest level of the curve is the area of sharpest focus. Supplied that there are a minimal of 5 knowledge factors inside the curve, then the routine will work. I simply had to do this routine on a daytime goal, so within the afternoon I slewed the telescope onto a distant tree and, utilizing a hydrogen-alpha filter and a really quick publicity, I used to be in a position to get a useable picture. Determine 4 exhibits this inside the @Focus3 Management Centre. On this menu you may select an acceptable publicity time (@Focus3 will modify this if obligatory), binning and filter.
Clicking on ‘Take Pattern Photograph’ takes a picture utilizing your settings. On the high of the menu is a readout of the brightest star or pixel within the picture, as a way to make certain the main target star isn’t saturated. The ‘+’ or ‘–‘ zoom buttons at higher centre permit zooming in or out and, in the event you’ve zoomed in, clicking on ‘Set Subframe to Present View’ takes a brand new picture that’s sized on the zoom degree, rushing up obtain occasions.
On the backside of the menu is a graphical illustration of the process, with the info factors positioned alongside what we are able to name an ‘A-Curve’. Subsequent, I ran the focusing sequence a number of occasions with the digicam manually defocused beforehand to check whether or not the purpose of greatest focus was reproducible. The accompanying desk (above) lists the outcomes. I additionally adjusted the ‘Search Span’ determine and that is proven within the desk’s right-hand column.
The 2 X’s mark the place the main target routine failed. The primary was due to my focuser reaching the tip of journey. I’d needed to transfer the focuser by a number of thousand steps to get the tree in focus, so this wasn’t shocking. I’m unsure why the second failure occurred. Nevertheless, the purpose of greatest focus was fairly constant taking into account the nice and cozy afternoon sunshine and possible air currents. I discovered it to be very spectacular. I continued the take a look at by slewing onto a shiny star (in broad daylight) and working the routine from both facet of focus and it labored each time.
Later that night I used to be in a position to take a look at @Focus3 on the night time sky. Determine 5 exhibits the outcome obtained through the use of a shiny star and a one-second publicity with a hydrogen-alpha filter. To verify the main target, I took longer take a look at exposures after each run they usually appeared fairly sharp. My subsequent take a look at concerned taking a brief publicity of M27, the Dumbbell Nebula, and working the auto-focus routine on the entire body reasonably than only a zoomed-in part. I used an publicity time of simply 5 seconds and binned the digicam 2 × 2 with a luminance filter. After just a few moments @Focus3 introduced that it had made a profitable focus (Determine 6 left-hand facet, overleaf) and I took a 30-second publicity (with a single darkish body however no flat subject), which is proven on the fitting of Determine 6 and appears completely wonderful.
I’ve to confess to being vastly impressed by each of those focusing routines. As soon as I turned accustomed to the user-parameters and methodology, I discovered that they each labored extraordinarily effectively – high marks!
Calibration and autoguiding
Autoguiding is a vital a part of long-exposure deep-sky imaging. For achievement, a calibration process should be carried out to match the information digicam with the monitoring mount. This normally entails centring an acceptable star on the guider and instructing the mount to maneuver in +x, –x, +y and –y instructions. By doing this process, the mount will know the way far to maneuver when making a guiding correction. TSIE helps autoguiding utilizing a relay cable between the information digicam and mount or through ‘pulse’ guiding with out a cable. Each situations require calibration to be accomplished first. The ‘Autoguide Setup’ menu is the place you set an acceptable calibration time. By this I imply the time that it takes to maneuver the information star an acceptable distance and never off the sting of the sensor. This menu is the place the kind of guiding is chosen (through a relay cable or pulse) and the ‘aggressiveness’ of the monitoring corrections (the default quantity, 10 being 100 per cent correction, however this may be lowered if the monitoring is over-correcting).
Determine 7 exhibits the Autoguide Setup menu. I carried out the primary guider calibration utilizing a relay cable and chosen calibration transfer occasions of 5 seconds. The left-hand pane of Determine 8 exhibits a profitable guider calibration. The inexperienced calibration vectors had been barely offset from the x and y axes, exhibiting that my Starlight Xpress Lodestar information digicam was not positioned orthogonally on the information digicam port of my QSI 683wsg CCD digicam. This wasn’t an issue as TSIE can information fortunately in any orientation. One factor to keep in mind, although, if you’re utilizing an uncooled information digicam that generates ‘sizzling’ pixels (faulty pixels which are saturated and so are very shiny) is that these rogues may be mistaken for the information star throughout each calibration and autoguiding. The way in which spherical that is to make sure that a darkish body is taken that data and subtracts the new pixels. I did this however discovered that the fiends had been nonetheless seen, so I had to decide on a a lot brighter information star. I additionally created a grasp darkish body from eight sub-exposures with the Lodestar information digicam and set it to mechanically calibrate each subsequent mild body used for guiding, which helped.
The appropriate-hand pane of Determine 8 exhibits the precise guiding errors. TSIE can present whether or not the information star is beginning to saturate utilizing crimson markers, and there are just a few proven right here as I used the identical calibration star for autoguiding. The graphs right here look jagged, suggesting poor guiding, however in truth numerous this jitter might be from atmospheric seeing. I’m utilizing an off-axis guider and it’s sampling the sky by a 1,340mm focal size telescope, so it’ll actually see some jitter. The vertical scale of this graph is in increments of 0.5 pixels and I’ve marked the primary ± 0.5 pixel line in yellow. You may see from this that the guiding corrections are very small and may produce nice star photos in lengthy exposures. Subsequent, I calibrated the mount utilizing ‘pulse’ guiding (with my Paramount ME it’s generally known as ‘Direct Information’). As talked about beforehand, this dispenses with a relay cable, and corrections are managed solely by the mount itself. Quite than selecting a calibration worth in seconds, Direct Information requires a measurement in arcseconds. The identical state of affairs applies as earlier, in that there should be sufficient motion seen with out driving the star off the sensor. I discovered that 120 arcseconds labored effectively, with the calibration vectors proven in inexperienced on the left-hand of Determine 9. The centre pane exhibits the guiding errors with the 0.5 pixel marker line highlighted in yellow. The appropriate-hand pane exhibits an RA versus Dec scatter plot with my yellow field exhibiting vertical and horizontal guiding errors contained inside the 0.5 pixel field. Completely satisfied days!
This concludes the reasonably intense second night time, however TSIE got here by with flying colors. Subsequent problem I’ll use every thing I’ve realized to this point to take some photos and look into some extra new options.
Nik Szymanek is an astro-imager primarily based in Essex and is the writer ofTaking pictures Stars andTaking pictures Stars II, whichare Astronomy Now books about fashionable astrophotography methods.