I am considering making use of the direct mount guiding so that I can dither my mount in order to get rid of the “walking noise” patterns. I am not using auto guiding via PHD.
My mount is a tracking mount (Fornax Lightrack ii) and I can only dither in RA. I am shooting with a Nikon 180mm ed f/2.8 lens and ASI1600MM-Cool in LRGB.
I tried connecting it last night and I run a series of light frames but I am not able to tell if is indeed dithering. How can I tell?
Also, is medium scale aggressive enough?
Also, I see that there is a settling option. I would prefer to set this to about 5 seconds or so as my computer takes about 8 seconds to download in between frames. That being, said, I did not see an extra 5 seconds in added to the acquisition time…
Finally, anything I should consider when it comes to the filter wheel and refocusing? I am not sure if I should also consider the filter switch and refocusing in the equation as how everything communicates with each other.
I am using dither by mount for a similar focal length system (200 mm) and it works fine. The difference is that my system is a higher end mount (Paramount - it is one of three imaging systems on the mount - the other two are scopes) so it dithers in both axes. You will need to use the largest dither (extreme) to get enough at that focal length. If you have PixInsight you can check the dither by loading all the images into a “blink”.
I have my settling set to 10 seconds which works fine for me but then it is also a more precise mount.
I am not sure what you mean by the last question or why that would even be a concern. Are you just trying to get an estimate of total time?
I really like using the system and it is great for iffy seeing conditions. It is also very fast since you do not have to wait for PhD related items. I have found that with the Paramount and a large model and pro-track, I can take up to 30 minute subs with nice round stars.
Finally, I am not sure if you are running the system at f2.8 but I would not suggest it since no camera lens is going to give good edge stars on a chip of any real size. You will almost surely need to stop the lens, probably to f 4.5 or better (my tests show f5 is the best mine can do w/o edge star distortion that is greater than I am willing to accept). You should test at various apertures and examine edge stars. When you stop the lens you will get diffraction spikes from the iris. To eliminate those, I run the lens wide open but machined an aperture stop from a screw-on aluminum lens cap to create f5.
Picture of my system (note guider is available but seldom used):
So besides looking at the individual frames in Blink of PI, there is no way to tell if dithering is on while you are imaging…correct?
In my second question I am basically trying to understand if dithering has to be in sync with other processes while imaging which may affect the running of the settling…I am not sure.
I am imaging with a Nikkor 180mm f2:8 ed lens. I always stop it down to f/4 which I have found it to be the best compromise for speed and aberrations.
There are other programs that do an animation or blink as well but I use PI since I have it. You could also measure the centroid position of the star in multiple images - tedious but will work.
Yes, dither does need to be done while the image is not integrating, of course, but SGP will take care of that. Settling is really just a mount factor when doing dither by mount, unlike with guided imaging where the guider has to settle on the new position, dither by mount just bumps the mount a tad so settles very fast (really just resumes sidereal rate tracking). I use 10 seconds but could probably use much less, I just use that since it is the default and not long enough to affect overall time spent imaging.