Dithering with PHD2 and Sharpcap

Somewhere to ask questions about the best way to use SharpCap
Forum rules


If you have a problem or question, please check the FAQ to see if it already has an answer : https://www.sharpcap.co.uk/sharpcap-faqs
Post Reply
Moorefam
Posts: 47
Joined: Thu Nov 26, 2020 11:46 am

Dithering with PHD2 and Sharpcap

#1

Post by Moorefam »

I have just bought a CMOS camera and need to relearn lots of things as my experience so far has been with DSLR's and the Lacerta MGEN-3 for guiding dithering. Unfortunately so far for me at least it won't guide or dither with Sharpcap.
I want to take lots of say 2 min subs with dithering using Sharpcap. Am I right in thinking I need to use live stacking to enable PHD2 guiding and dithering? Is that the only way?
Also what min and max settle time should I use or how should I decide? How does PHD2 communicate with Sharpcap? Does the last exposure end, then a new short exposure start with dithering, add on a settle time and the sequence is repeated, so if I dithered every 4 image I would have 1 in 4 short exposures to delete? Why the need to create a short exposure for dithering if there is full control between Sharpcap and PHD2?
User avatar
admin
Site Admin
Posts: 13173
Joined: Sat Feb 11, 2017 3:52 pm
Location: Vale of the White Horse, UK
Contact:

Re: Dithering with PHD2 and Sharpcap

#2

Post by admin »

Hi,

SharpCap 3.2 really works like a video camera – it always takes images continuously on whatever camera you have selected. This means that when you want to use the dithering functionality inside live stacking, the best option to avoid wasting exposure time is to automatically reduce the exposure length to 1 second during the dinner interval and then increase it back to the correct value when the dither is completed. These one second frames are not saved and are not added to the live stack – the reduction of exposure is just a convenient trick to improve the efficiency and reduce the amount of time wasted for each dither.

SharpCap communicates with PHD2 via the PHD 'Enable Server' option which can be found in the Tools menu of PHD - when this option is enabled PHD listens for communication on a network port, which SharpCap uses to both query the status and send dither commands to PHD.

SharpCap 3.3 is a bit different – firstly it has a still camera mode which means that it doesn't need to take images all the time. Secondly, the sequencer tool that is one of the new features of SharpCap 3.3 can work with PHD to dither intermittently without needing to use live stacking. Finally the most recent versions of SharpCap 3.3 can also talk to the MGEN3 auto guide if it is plugged into the computer via the USB socket – in that case you don't need PHD at all (note that the support of MGEN3 is fairly new – there may be bugs and I would definitely appreciate feedback on whether it works properly or not. MGEN2 is not currently supported).

Cheers, Robin
Moorefam
Posts: 47
Joined: Thu Nov 26, 2020 11:46 am

Re: Dithering with PHD2 and Sharpcap

#3

Post by Moorefam »

Robin,
I dither with MGEN-3 and the latest version of Sharpcap. The dithering is always in one direction so the frame is slowly and incrementally moving away from where I want it to be. DSS offsets confirm this. I would much prefer a random motion dithering biased about a central point.

Regards,

David
User avatar
admin
Site Admin
Posts: 13173
Joined: Sat Feb 11, 2017 3:52 pm
Location: Vale of the White Horse, UK
Contact:

Re: Dithering with PHD2 and Sharpcap

#4

Post by admin »

Hi David,

that's interesting, particularly since SharpCap doesn't get to specify the direction of dithering when making the request to the MGEN device - I just get to specify the radius (the maximum dither distance), the period between dithers (I set 9999 seconds, because I run all the dithering operations manually) and whether dithering is on or off.

Can I just check that you have the latest firmware on your MGEN? If you are up to date then I will have a chat with the manufacturers about this to see if they can explain it.

cheers,

Robin
Moorefam
Posts: 47
Joined: Thu Nov 26, 2020 11:46 am

Re: Dithering with PHD2 and Sharpcap

#5

Post by Moorefam »

Robin,
I have put MGEN to one side for now as I can't use MGEN3 and see it as a virtual instrument in Sharpcap with a ZWI ASI 2600 with gain >100. Also I cannot balance G and B colours as I can if I choose the ZWO as the camera and not MGEN.
I have bought a ZWO guide camera and now want to use phd guiding and dithering. Do I need to use the sequencer for dithering, which I would prefer to avoid, as I don't use the sequencer at all at present? If I do can you suggest the simplest way I can use it? At the moment I just set exposure time and gain with the No of images to be taken and off it goes. I must admit that to get it to auto focus every hour with the sequencer would be an advantage if I have to use the sequencer.
User avatar
admin
Site Admin
Posts: 13173
Joined: Sat Feb 11, 2017 3:52 pm
Location: Vale of the White Horse, UK
Contact:

Re: Dithering with PHD2 and Sharpcap

#6

Post by admin »

Hi,

the two ways to get dithering to happen with PHD2 in SharpCap are

1) Live stacking - this has dithering options built in. If you want to process the individual frames yourself then just make sure to set the 'Raw Frames' saving option to 'Save except when paused/dithering' - this will save all the unprocessed images that go into the stack to allow you to process them later

2) The sequencer or deep sky sequence planner. The deep sky planner is the user-friendly way to do this, but the full sequence editor offers more flexibility.

cheers,

Robin
Post Reply