First go with PHD guiding + EQMOD

[Carl M]

Hi guys,

Well I didn't expect it to go perfect first time so I'm wondering if anyone has any tips/pointers as to what happened and why. Unfortunately I didn't get a screengrab of the graph at the time but I can explain it - It looked like both RA and DEC were over correcting themselves every so often and then there would be a sudden drop in both axes? I'm also having trouble using stellarium as the GOTO of the setup, It slewed to roughly the right place but not exactly, do you need to do the star alignment when using the synscan handset as the interface?

Attached is a 5 minute sub of M45 showing the over corrections (not the best object to image when the moon is just over half way) The other is showing the PHD settings.

As you can see some of the stars are doubling all in the same direction, so I guess it is over correcting? Hopefully the settings in the attachment will explain why it's doing that.

Thanks in advance,

Carl

Edit: Forgot to add equipment,

It was a 200P on an EQ6 guided with an ST80 and SPC900 webcam

[Freddie]

Doesn't look like there is anything odd about your settings. Do you know which direction (RA or Dec) you are getting the double image of the stars?

[Carl M]

I think it could be Dec, if I remember correctly the graph showed Dec falling in quite a sharp V. RA wasn't as bad but it did drop significantly along with Dec albeit very quickly and it only did it once when I was taking the 5 min exposure which I assume would have caused the duplication of the stars.

[Spikey]

You could try lowering the calibartion steps to about 1500 it seems quite large and see if that makes much difference.

[Carl M]

Thanks Spikey, I saw on a thread previously that it should be 2500ms which is why I put it so high but will lower it to 1500ms tomorrow providing it's clear, no knowing with the metoffice. Hopefully will be able to get 10 minute subs once I can get guiding sorted before the moon starts to destroy the image. Typical that the moon is up when it's a good week with a few clear nights

[ThomasBR]

Could it be a balance issue? I recently started guiding and sometimes get a similar picture as above. I can get rid of it by first balancing the setup (with all equipment on) in both RA and DEC. Next I skew balance slightly (by moving one of the counter weights) so that the setup is "too light" on the west facing side i.e. if the counter weight shaft is post in a westernly direction I move one cw up the shaft (and vice verse.

I read several places that this ensures constant contact in the gears so the scope will not "fall" from one position to antoher creating a slight shift in the sub you are taking.

Since I am fairly new to astrophotography I hope I got this right (if not please correct me).

Th

[Freddie]

Carl, to help diagnose this it would useful to know based on the picture and camera orientation (rather than the PHD graph) if the double stars are aligned in Dec or RA.

[Carl M]

Just a quick follow up from this thread, I think I've got it sorted now. Ensured balance was good and tweaked the PHD settings a little - changed RA aggressiveness to 110 and Dec Duration to 200ms and the graph had calmed down Here is another 5min sub with no star duplicates this time!

Stars look a little pinched because (don't laugh) I've not collimated my scope ever since I got it in Dec 2010 Next thing on the cards is a Laser collimator and Baader Coma Corrector and I will hopefully be well on my way.

Thanks all