Lucky imaging is not magic, but effective. I am using short exposures times, often in the range of 500 ms to 2 seconds per sub.
This has some advantages over more traditional deepsky imaging techniques... with short exposures you do not need an expensive mount,
auto-guiding is also not needed and the frames you take are often sharper than their long exposure counterparts.
With recent camera advancements - with low read noise and high quantum efficiency (QE) - this can work really well
to produce high resolution deepsky images with more details.
What you can see here and above are effects of seeing. Better seeing, sharper stars and more structures and details in objects, poorer seeing, larger stars and washed out structures.
Particularly, local seeing conditions have a negative effect at long focal lengths. Therefore, the useful selection or a usage rate decides on more or less details in objects.
First, choose the right exposure time... for example, better seeing = short exposure times, bad seeing = longer exposure times. Second, analyze the results e.g. with the
frame selector tool from pixinsight and after it consistently take out images with bad FWHM values. Third, processes (stacking) the images with the best FWHM values.
For short focal lengths, I'm thinking, this procedure is not so important. But if you want to do high resolution astrophotography with long focal lengths, in any case...
Short Exposure Techniques
Short Exposure Techniques
First of all, the mount must be aligned to Polaris. Then the observation object is approached via mount control and centered on the camera sensor. The exposure time and the other camera parameters like gain value are set in the capture software, e.g. SharpCap or FireCapture.
For the gain value, you can orientate yourself e.g. on the unity-gain of the camera manufacturer. For the ASI533MC, the recommendation is a gain of 100.
In the example on the left, I have given the sequence 60 x 10 seconds exposure time. In contrast to lucky imaging, the exposure time can be a bit longer
range of 5 to 10 or 20 seconds per sub. This has some advantages over more traditional deepsky imaging techniques... with short exposures you do not need an expensive mount, auto-guiding is also not needed. With recent camera
advancements - with low read noise and high quantum efficiency (QE) - this can work really well to produce no autoguided deep sky images that show a amount of details.
If the object slowly moves out of the center of the image, the object can be brought back to the center of the image using the camera control software, mount control or via platesolving. After that you can start the next sequence.
The first M 51 example on the left shows a single exposure in RASA C8 of 10 seconds, after that the example shows sequences of 10x10, 10x100 and 10x1000 seconds.
Short exposures works well with the fast scopes in even mildly light polluted skies, especially with a low read noise CMOS camera. My standard exposure (Bortle 7) is 10 seconds, has been ever since I got the RASA.
10 secondes are long enough I won't have to worry about guiding, and the data volume and the processing time remains manageable.
Sharpcap is my camera control software that I use to set up the image sequences and camera parameters, save, focus, use platesolving, and for live viewing of the images.
Autostakkert (AS!3) is the fastest stacking software and is used to pre-stack the sequences, for example 60x 10 s. is one sequence.
The image post-processing is done as usual with programs like Photoshop, Fitswork or PixInsight. My final image, post-processed with PixInsigth,
consists of about 18 sequences, each (60x10 secondes).
Improve resolution of your images
You can further improve resolution of your images by improving your FWHM (Full Width at Half Maximum) - better guiding, making sure you image when seeing is exceptional, using larger aperture, or using some advanced stacking algorithms. As you have noticed, there is deviation between FWHM values in different frames. Use the subs with low(er) FWHM values for further processing. You can give it a try with some smaller pixel camera (like ASI183 - low readout noise, quite high QE). CMOS cameras are also better suited to short exposure subframes, normal CCD Cameras
for long exposures. You can try a drizzle + deconvolution combo with your current setup. I used PixInsight Drizzle Integration and then Deconvolution with PSF model and mask.
Drizzle integration makes sense if you think that image is undersampled.
The most successful type of data collection by the amateur is the transit method. As a planet passes over the portion of the star facing us, the light curve of the star drops for a time. As the planet passes through, the light curve returns to normal.
Taking a series of images of the field surrounding the host star of an exoplanet before, during, and after the predicted times of the exoplanet transit across the face of its host star. The transit method has been very useful for detecting a - hot Jupiter-, namely a large planet whose orbit is close to its host star and where the planet passes directly in front of the star from the perspective of an observer on Earth. Exoplanet transits are typically 2-4 hours long. However, conducting an exoplanet observation also involves beginning the imaging session at least 30 minutes prior to
the predicted beginning of transit and continuing for at least 30 minutes after the expected transit. Thus, it is not unusual for an exoplanet observing session to be 3 - 5 hours in length.
Light curve of Wasp-12, generated with AstroImageJ, an image analysis tool for astronomy. A technique called differential photometry is used to determine the changes in brightness (flux) of the exoplanets host star that might indicate an exoplanet transit. This technique compares the relative difference between the host star and one or more (assumed to be non-variable) comparison or comp stars during the imaging session. Since the difference in brightness of the host star and comp star(s) are equally influenced by common factors such as thin overhead clouds, moon glow, light pollution, etc.,
a change in this difference would be a measure of the effects of the drop in brightness of the host star due to an exoplanet transiting in front of it.