PEC or No PEC with PHD Guiding

BlackWidow (Mardy) · #1 28-08-2011, 04:26 PM

I have been having some trouble getting good guiding on my LX2ooGPS. I have been using PHD but have found my stars are not round and also have had some image shift between shots. My overall result when stacked is poor to say the least.. I have been playing with PHD settings with some improvement. I also noticed that PEC was turned on in the LX200 so I have now turned it off. I also noticed that the backlash in the Telescope was set to 91. I have now reduced that to 50 and will try again on the next clear night.

I would love some impute from other LX200 users on the settings I have changed. I really an not sure if I should even use PEC in the telescope at all? What is the best starting point also for Backlash? I think I am getting very close to sorting things out, but need some fine tune help.. I have been imaging around 5 - 7 mins.

Any advice would help guide me in the right direction...

Greatly appreciated
Mardy

Alchemy (Clive) · #2 28-08-2011, 05:34 PM

Image shift between shots is usually the result of drift from differential movement with a side by side setup or mirror flop/shift.

Out of round stars can be because of backlash and mount integrity, it can also be because of over aggressive settings in phd, I tend to under guide slightly and catch up rather than overshoot, so I have my guiding at 1 sec intervals and use 10% aggressiveness.

This may not be the causes, but worth considering.

Really poor polar alignment can also cause drift in a side by side setup

BlackWidow (Mardy) · #3 28-08-2011, 05:41 PM

Thanks Clive for the info... I am guiding with a Vixen 95L scope attached to the top of the LX200. I have really strong ADM mounts so I have no flexing. I am using a DSI11 pro as the guide camera and I have the mirror locked on the LX200. The only thing I have not considered is if the thier is any mirror shift in the Vixen guide scope (I don't thinks so).

I will try changing the aggressiveness settings as you have mentioned. I have tried 1 sec tracking and 1.5 without a great deal of change. I have reduced all the settings in PHD to default and that fixed alot of the problems, but still not good enough.. Thanks again, I will try you advice..

regards
Mardy

Alchemy (Clive) · #4 28-08-2011, 07:14 PM

Flexure can be one of those really nasty things to overcome, I don't know how much shift you have but considering a pixel can be 5-9 microns it doesn't take much.
If all your mounting points are rock solid, you still have other points, Rigidity of the focuser, particularly if extensions are used, down to the tightness of any compression rings etc..... ANY point of potential movement MUST be checked.

I had a 12 inch newt and it drove me nuts.

NorthernLight (Max) · #5 31-08-2011, 11:39 PM

i saw that you are using a wedge. can you exlude an elevation angle or tripod level error?
your phenomenon actually sounds like field rotation.

Tandum (Robin) · #6 01-09-2011, 01:50 AM

You can also try stacking a set of subs without registering them.
That should show if the subs are marching or rotating.