Why can't I get PHD to lock onto stars?

[BlackWidow (Mardy)]

Well this is about night 3 of not getting anywhere. I am trying to get PHD to work with my SPC900nc as a guide scope.. I can get the cam working and find a star all ok but don't seem to be able to keep the scope locked onto a star. It does it's calibration and starts to guide all OK but the star slowly drifts up the screen and then the tracking is lost??

I can see the North, South and East West corrections being calculated at the bottom of the screen but after a few min the star seems to move out of the bok and the tracking is lost. I have been adjusting settings like working out a Rubiks Cube and still no luck.

Any ideas would be great. The only thing I can think of is that I am not polar aligned well enough. I am waiting for my key to use Alignmaster. I thought I was pretty near the mark..

Any tips would be great as I am at about frustration level 8.5 at this point.

Regards
Mardy

[[1ponders] (Paul)]

First thing I'd suggest is to check you balance Mardy. Which direction is up? RA or Dec?

[BlackWidow (Mardy)]

Thanks Paul.. But dosn't PHD adjust camra orientation and does not care. I ahve tested the camera on a grid to make sure it is inline in the eypiece. I have also tried diff orientations as well.. Is this what you are advising or am I missing something?

Mardy

[[1ponders] (Paul)]

It does adjust, but knowing which direction is RA and which is dec can help determine which axis may be out of balance.

As an aside when setting up for autoguiding I normally set the camera so that when i press the up dec button the star moves up. It just helps me to know which way a star is going to move when I press a button. Helps to simplify and standardize things for me.

[mithrandir (Andrew)]

What version of PHD is it? The are some differences in behaviour between versions.

Check the brain settings.

You don't have "Disable guide output" ticked?
You don't have "Dec guide mode" set to "Off"?

How many steps does it take to do the calibration? You want it to take something around 15 in each direction. If it is less, reduce the calibration step size. If more increase it. For a scope like your Vixen (1050mm f/11) it should be something in the 750-1000 range.

What are the max duration settings? If they are too small PHD may not be able to keep up with drift from poor polar alignment. There is no real issues with making it too big as PHD will only request the step it thinks it needs. 2000 is probably overkill, but you never know.

There were posts about using PHD to do drift alignment recently. This one and this one in particular. If you can make sense of them you may not need Alignmaster.

Andrew

[BlackWidow (Mardy)]

Thanks Andrew. I think your help with settings has done the trick. It seems now to be holding the guide star. I have been trying some 3 -4 min exposures to have a look at shortly. It des seem to be guiding and only drops the odd frame.. Thank you both for you help as it has got me up and running..


Regards
Mardy