SharpCap and PHD2

[sonata31]

Hello
I'm having trouble understanding the relationship between these various parameters.
- "Max dither step" in <SharpCap Settings>-<Guiding>
- "Scale" in PHD2-<Advanced Settings>-<Global Settings>
I have the following samples
- Imager: 2.01"/pixel
- Guider: 3"/pixel
Thanks for your help
Louis

[admin]

Hi,

the max dither step used by SharpCap is measured in guide camera pixels, so if you use 10 then SharpCap will ask PHD2 to dither up to 10 pixels (PHD2 picks a random amount up to the maximum). That will work out to be a dither of up to 30 arc seconds given your pixel scale.

I think the scale option in PHD2 adjusts the maximum sent from SharpCap, so if you set scale=2.0 and leave SharpCap at 10 pixels, SharpCap will send 10 to PHD2, PHD2 will multiply that by 2 and do a dither of up to 20 pixels (60 arc sec). I guess the scale option is there to allow you to adjust things if the imaging application doesn't give you a dither step size option. I don't think you need to use both.

cheers,

Robin

[sonata31]

Hello Robin
Thank you very much for those explanations
Louis

[sonata31]

Hello Robin
How to determine the optimal values for these parameters?

dithering-1.png (91.31 KiB) Viewed 560 times

Thanks for your help
Louis

[sonata31]

Hello Robin
By reading the PHD2 documentation I think that there is a correspondence between the following parameters:
- Max dither step (SC) = PT (PHD2)
- Settle threshold (SC) = ?
- Minimum settle time (SC) = ET (PHD2)
- Maximum settle time (SC) = TO (PHD2)
Is this correct?
Thanks for your help
Louis

[admin]

Hi,

I'm afraid I'm not familiar with those abbreviations for PHD2 parameters, but you can find the documentation that relates to SharpCap sending dither commands to PHD2 on this page - https://github.com/OpenPHDGuiding/phd2/ ... Monitoring . In particular, see the 'dither' command and the definition of the 'settle parameter', both in this section and just below : https://github.com/OpenPHDGuiding/phd2/ ... le-methods

cheers,

Robin

[sonata31]

Hello
Thanks for the links, I'll look at them
Abbreviations are those from the PHD2 documentation
Louis

[sonata31]

Are these settings?
-------------------------
Settle parameter

The SETTLE parameter is used by the guide and dither commands to specify when PHD2 should consider guiding to be stable enough for imaging. SETTLE is an object with the following attributes:

pixels - maximum guide distance for guiding to be considered stable or "in-range"
time - minimum time to be in-range before considering guiding to be stable
timeout - time limit before settling is considered to have failed
----------------------

- Max dither step = pixels
- Minimum settle time = time
- Maximum settle time = timeout

Is the match exact?
On the other hand, I don't see the correspondence of the "Settle threshold" parameter

Otherwise how can we determine the correct values for these parameters?

Thanks for your help
Louis

[admin]

Hi Louis,

the 'settle threshold' corresponds to the 'pixels' parameter which is basically a 'how close is close enough' threshold for deciding when the dither has reached the target position - otherwise the mapping is pretty much exact.

There are no real 'correct' settings for these parameters - the defaults will usually work well, but in some cases you may determine (usually by trial and error) that changes are required. For instance, if you see the image still shift after the dithering is 'complete' and the next image capture has begun then a longer time for the minimum settle time or a smaller threshold may help.

cheers,

Robin

[sonata31]

Hello Robin
Thank you for your reply
Louis