getting focus with PHD2

[oldpink]

I got my SW ED80 today so I swapped my 200p off the NEQ6 and mounted the ED with my ST 80 guidescope
up till now the ST guide has been fine but tonight PHD just said high SN rate star lost
I suspect it is a focus issue though I was careful to try not to move the focus in the swapover

is there an easy way to set the focus as the ST is a guide scope and only ever connected to the ASI cam
I'm currently imaging M31 but no matter what I can't get PHD2 to see the stars never mind track them

[Leveye]

Ever slightly defocusing the guide scope actually helps in guiding.  Try it.

[oldpink]

I can see why that would help as it would bloat the star making it appear bigger
but I can't get it to see a star far less focus or track

[glowingturnip]

have you got an eyepiece you can make parfocal with the guidecam during the daytime ?

[D4N]

Try and get good focus on something bright like the moon or Cappella first, then don't touch it

Use a planetary capture program like firecap to do this as PHD does all sorts of things to the image before it displays it.

TSED70Q, iOptron Smart EQ pro, ASI-120MM, Finepix S5 pro.

[Tinker1947]

Here is the spacing on my ST-80 the CCD a Lodestar has a  "C" extension  so the lodestar sensor is very close to the end of the extension tubes on the ST-80, this is the distance i need to get to the focal point...

[oldpink]

tinker its not a spacing issue, I have an extension tube and it was working fine when it was mounted on the 200p
I think the focus got knocked off when I mounted it on the 80

I got it focused on the sun this morning so it shouldnt be far off now but the weather is not good for the next few days

[rwg]

I can see why that would help as it would bloat the star making it appear bigger

but I can't get it to see a star far less focus or track

PHD works out the position of the 'center of mass' of the star by averaging all the bright pixels associated with the star. That lets it work out the position to accuracy of better than 1 pixel, and so makes guiding more effective because you aren't limited to the pixel resolution of your guiding camera.

That all goes wrong if any of the pixels in the star are saturated (ie hit the max value of 255 or whatever it is for the camera). When that happens the averaging is not going to be accurate as some of the brightness in the saturated pixels is lost. Defocusing slightly reduces the brightness of the core of the star image and reduces the chance of pixel saturation causing problems. Because PHD is calculating the average position by the center of mass formula, spreading the light out a bit more doesn't affect the result it calculates.

cheers,

Robin