What is Dithering?
Dithering is the process of moving the image’s location across images. The result is that the noise generated by the camera will be in different location for ALL of your images. When you stack your images, the noise will be taken out more efficiently because it's never at the same location. Without dithering, you end up stacking your noise and dark subtraction can only do so much.
BackyardEOS/BackyardNIKON sends a signal to PHD to tell it to move the “lock position” (the position of the crosshairs in PHD) by a small, random amount. Once PHD has moved the star and reestablished stable guiding in the new location, BackyardEOS/BackyardNIKON will resume imaging.
Please see this thread on how to configure dithering.
What are all those numbers from 0 to 2.55 for?
The number you see in the progress wheel during dithering is the distance PHD is reporting and is indicative of where PHD is from its new location (chosen at random by PHD). The values are from 2.55 to 0.00. At 2.55 PHD is reporting that it is still at its original location of the guide star… at 0.00 PHD is at the new location.
In reality however, PHD will almost never hit the new intended target dead-on… this is where the 'Settleditherat' variable comes into play. If set at 0.20, the dithering process will terminate successfully when the new location reaches a distance of 0.20 away from the new location. Because everything here is random anyway, the fact that PHD rarely settle to its absolute intended new location is irrelevant… because the selection of the new location was random too ~ so all is good here.
PHD moves the guide star once per interval, so if you are guiding at 0.5 versus 2 or 3 second interval then the amount of time it takes to dither will vary greatly; 1 minute is not abnormal at all.
Can I change some Dither settings?
Yes you can. See the setting dialog in BackyardEOS/BackyardNIKON
PHD dither on start-up: This parameter will automatically turn ON (or OFF) the BackyardEOS/BackyardNIKON dither feature each time you start BackyardEOS/BackyardNIKON. You still need to check the ‘Enable Server’ in PHD.
Dither aggressiveness: The dither sent will be a random number of pixels in X and Y, scaled by the level you set here. In the lowest level, the random numbers will vary from -0.5 to 0.5 pixels and in the highest they will vary from -1.5 to 1.5 pixels in the guide frame. Since people typically guide at shorter focal lengths than they image at, this will usually have a much larger effect in your main images.
Settle dither at: This parameter specifies how far off the star can be from the lock position before Dithering is considered a success. Typical value is between 0.10 and 0.30.
Calm down period: A set number of seconds to pause between dithering and the next image capture. This is particularly useful to let PHD stabilize properly.
Dithering is the process of moving the image’s location across images. The result is that the noise generated by the camera will be in different location for ALL of your images. When you stack your images, the noise will be taken out more efficiently because it's never at the same location. Without dithering, you end up stacking your noise and dark subtraction can only do so much.
BackyardEOS/BackyardNIKON sends a signal to PHD to tell it to move the “lock position” (the position of the crosshairs in PHD) by a small, random amount. Once PHD has moved the star and reestablished stable guiding in the new location, BackyardEOS/BackyardNIKON will resume imaging.
Please see this thread on how to configure dithering.
What are all those numbers from 0 to 2.55 for?
The number you see in the progress wheel during dithering is the distance PHD is reporting and is indicative of where PHD is from its new location (chosen at random by PHD). The values are from 2.55 to 0.00. At 2.55 PHD is reporting that it is still at its original location of the guide star… at 0.00 PHD is at the new location.
In reality however, PHD will almost never hit the new intended target dead-on… this is where the 'Settleditherat' variable comes into play. If set at 0.20, the dithering process will terminate successfully when the new location reaches a distance of 0.20 away from the new location. Because everything here is random anyway, the fact that PHD rarely settle to its absolute intended new location is irrelevant… because the selection of the new location was random too ~ so all is good here.
PHD moves the guide star once per interval, so if you are guiding at 0.5 versus 2 or 3 second interval then the amount of time it takes to dither will vary greatly; 1 minute is not abnormal at all.
Can I change some Dither settings?
Yes you can. See the setting dialog in BackyardEOS/BackyardNIKON
PHD dither on start-up: This parameter will automatically turn ON (or OFF) the BackyardEOS/BackyardNIKON dither feature each time you start BackyardEOS/BackyardNIKON. You still need to check the ‘Enable Server’ in PHD.
Dither aggressiveness: The dither sent will be a random number of pixels in X and Y, scaled by the level you set here. In the lowest level, the random numbers will vary from -0.5 to 0.5 pixels and in the highest they will vary from -1.5 to 1.5 pixels in the guide frame. Since people typically guide at shorter focal lengths than they image at, this will usually have a much larger effect in your main images.
Settle dither at: This parameter specifies how far off the star can be from the lock position before Dithering is considered a success. Typical value is between 0.10 and 0.30.
Calm down period: A set number of seconds to pause between dithering and the next image capture. This is particularly useful to let PHD stabilize properly.
![Backyards Backyards](/uploads/1/2/5/7/125788750/706456528.jpg)
BackyardEOS to control the DSLR; PHD2 to handle autoguiding; Dithering switched on in BYE; Initial registration and stacking was handled by DeepSkyStacker. After that I saved the image as a TIF and imported that into PixInsight. All of the post processing was done in PixInsight – I really need to use it more, the results are worth the effort!