Plate solving or Astrometric calibration of an image was done before modern times by the careful measurement of photograph glass plates of star-fields; now, of course it is done by computer software. Nicola has implemented in AstroDMx Capture, two methods of plate solving the field of view in order to determine how to automatically move the mount so that the required object is placed in the centre of the field of view.
The first method is a local plate solving solution using ASTAP and the second method, which requires an internet connection, does the plate solving in the cloud using Astrometry.net.
Sometimes, particularly if the field of view is quite small, a local plate solver can struggle to find a solution, although this can often be resolved by increasing the exposure. If the local plate solver fails to find a solution and the user has an internet connection, the plate solving can be done in the cloud by Astrometry.net, which is more likely to be successful. AstroDMx Capture makes the plate solving transparent to the user who only has to select the method to be used. In the experiments done here with a Skymax 127 Maksutov, a local plate solver may struggle due to the accuracy of the field of view and focal length, which varies with a Maksutov in which focusing is achieved by moving the primary mirror. This is no problem for Astrometry.net plate solving in the cloud.
We did experiments including a slightly different approach that facilitates working with lunar and planetary imaging in addition to deep sky imaging.
An SV605CC 14 bit CMOS camera was mounted at the focus of the Skymax 127 Maksutov telescope and an SV305 CMOS camera was mounted at the focus of an F=190mm, 50mm guidescope. Two instances of AstroDMx Capture were run on separate virtual desktops of a Fedora Linux computer. One instance streamed data from the Skymax 127 and the other streamed data from the guidescope. AstroDMx Capture was used to send the mount/scopes to the Moon.
The imaging scope and the guidescope were co-aligned so that the moon appeared in approximately the same place in the field of view of each scope.
Screenshot showing the imaging scope data stream at the top left and the guide-scope data stream at the top right.
Whilst on the Moon, AstroDMx Capture was used to capture three overlapping fields of view to cover the whole of the visible Moon. 1000-frame SER files were captured.
The best 95% of the frames in each SER file were stacked in Autostakkert running in Wine and the resulting images were combined into a single image using Photopad running in Wine.
Photopad is a useful alternative to Hugin or Microsoft ICE and works with relatively small amounts of vertical displacement and if the images are arranged correctly horizontally.
Mosaic Lunar image in Photopad
The mosaic image was wavelet processed by Registax 5.1 running in Wine and post-processed in the Gimp 2.10. Alternative wavelet processors such as waveSharp or IRIS could have been used.
85% waxing, gibbous Moon
Having imaged the Moon, attention then changed to deep sky imaging despite the bright moonlight.
AstroDMx Capture sent the mount/scopes to Regulus and Regulus was nudged to the centre of the field of view of the Maksutov imaging scope.
Regulus was focused in the guide-scope using a Bahtinov mask.
Well focused stars would produce optimal stars for PHD2 auto-guiding.
Using the guide-scope adjustment rings, Regulus was brought to the centre of the field of view of the guide-scope
Contrary to usual practice, Plate solving was done on the guide scope image using Cloud plate solving to refine the position of Regulus.
This just showed that it could be done if there were too few stars in the Imaging scope field of view.
From here on, in this session, all plate solving was done in the cloud on the imaging scope field of view.
When using a scope with such a long focal length and small field of view, it is best to start autoguiding for plate solving and only turn guiding off briefly during slewing. Nicola plans to implement PHD2 control within AstroDMx Capture to automate stopping and starting of the guiding routines when slewing is required.
Screenshot of PHD2 auto-guiding during this session.
AstroDMx Capture sent the scope/mount to M13, plate solved in the cloud and centred M13 in the field of view. (M13 can also be seen in the centre of the field of view of the guide scope in the above image).
Screenshot of AstroDMx Capture capturing 32 x 2 minute FITS images of M13
Matching dark frames were also captured.
The best 50 minutes worth of data were calibrated with dark frames and flat fields and partly processed in Siril and post-processed in the Gimp 2.10, Fitswork and Neat Image.
M13
AstroDMx Capture capturing 3 minute FITS exposures of the Sunflower galaxy
Only 15 minutes worth of exposures were captured before clouds prevented further imaging.
Matching dark frames were also captured. The data were calibrated and stacked and partly processed in Siril and post processed in the Gimp 2.10, Fitswork and Neat Image.
The Sunflower galaxy M63
It is regrettable that more data could not be collected on this object at the time; but this image serves the purpose of demonstrating the imaging capabilities of the Skymax 127 in conjunction with an SV605CC camera.
This session succeeded in all of its aims:
- To co-align accurately the Skymax 127 and the guide scope.
- To position the Moon in the imaging scope with the aid of a second instance of AstroDMx Capture running on a different virtual desktop.
- To capture lunar SER files and to process them in various software into a single mosaic image, and point out alternative software that could be used.
- To demonstrate AstroDMx Capture plate solving in the cloud with Astrometry.net in a new GUI that is identical for the local ASTAP plate solver.
- To plate solve in the cloud using the guide scope image stream as well as plate solving in the cloud with the imaging scope and camera.
- To auto-guide the Skymax 127 using PHD2 and to capture image data on two deep sky objects.
The control of PHD2 by AstroDMx Capture for the purpose of automatically turning off guiding during slewing and turning it back on after slewing completes was recognised as a requirement for implementation, and Nicola will be implementing it for a future release of AstroDMx Capture.
The cloud plate solving will be present in the next release of AstroDMx Capture which Nicola will make soon, and instructions on how to set it up will be provided.
AstroDMx Capture for all operating systems can be downloaded HERE.
