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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 "Settle dither at" 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.
Although there are no plan to support the MGEN autoguider (at least in March 2015; see Mick's post on 02 March 2015 - 06:30 PM) you should consider to develop a dithering feature for the Lacerta MGEN autoguider (which is quite popular in Europe because of its great autoguiding performance). I'm quite sure that all the MGEN enthusiasts will applaud and make BackyardEOS their preferred astro imaging software ;-) And no, I do not get any commission by Lacerta ;-) (But I'm very much convinced of that product as of backyardEOS). Thanks for considering Uwe
I've been successfully using BYE and PHD2 in concert for Guiding and Dithering since early BYE v2 and PHDv1.12, and with BYE v3.12 and PHD2 v2.4 I've successfully imaged and Guided two separate Mounts simultaneously, so I know that it all DOES WORK. But, I've been using the recently released PHDLogView App to review many of these successful Sessions, and I'm perplexed... According to the Dither setting for SettleAt (defaulted to 0.25), many of my BYE Sessions would have NEVER resumed Imaging after most of the Dithers as per the PHDLogViewer (using the Settings/Exclude Settling Parametrically and the Exclude Frames Settling settings that match those used in BYE) the Excluded-for-Settling portion often runs for several minutes at "0.25 pixels". So, that leads me to ask: Does BYE implement the two components of "Settle" sequentially (as indicated in the "Debunking Dithering" HowTo) or are they evaluated simultaneously ?? All my experience sitting in front of BYE for whole Nights at at time say they are evaluated sequentially. But then, the PHDLogViewer App was written by one of the lead OpenPHD Devs, and we'd assume that it is also correctly interpretting the evidence in the Log Files. And that indicates otherwise... So, can you confirm which PHD API Property/Value is being evaluated for the Settle Distance ?? (I've posted an equivalent question on the OpenPHD forum in this Thread... )
Follow these steps to configure both BackyardEOS/BackyardNIKON and PHD for dithering. In PHD... Start PHD. Go to tools menu and check "Enable Server". Restart PHD. Accept all Windows Firewall warning. Start Guiding as you normally would. In BackyardEOS or BackyardNIKON Start BackyardEOS or BackyardNIKON. Click the "PHD" button, just right on the Camera Information Centre. This is a toggle ON/OFF button. Start an image capture plan as you normally would. You are now dithering between each image. Please see this Debunking dithering! thread for more information if you which to learn more on what dithering means and what it can do. Thank you