Question about dithering settings in BYN

[dgold]

I have a specific question about dithering.  In the setup in BYN, there is a "dithering agressiveness" setting.  Mine is set to 2.  My question is, how do I relate that to the number of pixels it actually shifts the image.  I am using a modded D5300.  Adding that I am using the latest 32 bit version of BYN - 2.1.3

 

[s3igell]

Check out these two How-To threads:

• Debunking Dithering
• How to Setup BYE/BYN and PHD for Dithering

[dgold]

"Check out these two How-To threads:

• Debunking Dithering
• How to Setup BYE/BYN and PHD for Dithering"

I already have it working, that is easy and straightforward.  I was hoping, however, to determine without having to experiment with the settings during an image session, how to understand how the parameters in the BYN app effect the amount of shifting it does of the sensor during the dither.

[astroman133]

The Debunking Dithering link in the previous post describes the aggressiveness setting like this:

Quote

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.

I take that to mean that aggressiveness values from 1 to 5 change the movement factor between +/- 0.5 to +/-1.5. This would likely mean that an aggressiveness value of 3 would apply a factor of 1.0 which would mean that BYE would use the values just as they come from the guiding app.

The guiding software is dithering based on the guide camera images taken through the guide scope but you want the dithering to affect your light images taken through the main scope. The best value for you will depend on the guiding focal length in relation to the imaging focal length. Basically the greater the ratio between the two focal lengths (imaging scope to guide scope) the more you have to move the mount to affect your light images.

If there were a single best value then it would not be a user adjustable setting. I would start with a value of 3 and increase it as necessary. Whatever you set, you have to understand that it also has to work with the autoguide program, which may also have different aggressiveness settings.

I don't think that there is any way to avoid a test/evaluate/adjust/repeat scenario to get the best images for your equipment and conditions. I am reminded of an old saying -- "If it were easy everybody would do it". In this case it is apt for AP.

 

[dgold]

18 hours ago, astroman133 said:

I take that to mean that aggressiveness values from 1 to 5 change the movement factor between +/- 0.5 to +/-1.5. This would likely mean that an aggressiveness value of 3 would apply a factor of 1.0 which would mean that BYE would use the values just as they come from the guiding app

All of the above makes sense.  What I noticed in dithering at aggresiveness of 2 is that the vignetting I get in my Astro-Tech AT115EDT with it's 2 inch Flattener/Reducer is made worse by dithering once I calibrate, debayer and integrate frames in Pixinsight.  When I zoom into that integration, I can see the actual pattern of dithering and it definitely darkens the corners of the frame of the integration far more than any single frame.  All that said, I am thinking of backing it down to 1 and seeing if that helps.

FWIW, I use ASTAP for my plate solving and it does a pretty darn good job.  However, it would only have to be a few pixels off between imaging sessions to exacerbate this issue, (one more variable to consider).  lol

[astroman133]

Vignetting (darkening of the corners of an image) is not typically caused by dithering.

Vignetting is typically caused by the circle of light reaching the sensor is too small to illuminate the entire sensor. It is possible that this could be caused by the focal reducer that you are using.

I would also verify how you are processing your images in PI to make sure that your workflow and settings are appropriate.