Help with guiding please

[greenkat]

Ok, heres the problem ,

I think my polar allignment is pretty good, I can put a star on my cursor and it will stay put for about 3 -4 mins with a little wobbleing which I am presuming is periodic errorbefore starting to move off the cursor.

However, when it comes to taking exposures, I still get slight trailing with 1min subs, hence i'm stuck stuck on taking 42 sec subs.

I have PHD , and am using eqmod on HEQ5pro mount.

I gave it a try last night, but after going thru the west calibration thing it keeps saying calibration failed, star didnt move enough

Any help please

[SteveL]

To fix the PHD calibration failure, you need to tell it to move the mount more. In PHD, click on the brain, increase the "calibration step (ms)" value, try again. Basically, the star has to move at least 5% of the chip dimensions to qualify as being calibrarted. SHorter focal length scopes need higher calibration stepm value, and longer focal length scopes require shorter steps.

[Reggie]

what other kit are you using?

The usual setup for guiding is this:

Computer

Imaging camera

Guide camera

Mount

Guide camera is usually connected to the computer and sometimes the mount if the camera has a has a guide port. if it doesn't have a guide port then the computer usually controls the guiding either through some drivers (manufacturer supplied and/or ASCOM Usually) directly connected to the scope via a serial cable (or usb to serial adapter + cable) or something like a gp-usb box from shoestring astronomy.

If the star didn't move via the west calibration I would check all of your connections and make sure that you can communicate with the mount, PHD has various settings for controlling the guiding, make sure you have it set to the right type, (Ascom, serial, lpt or 'On mount' which is the dedicated guide port on some scopes/cameras).

hth.

[Reggie]

Further to what Steve has mentioned I would also check what guiderate the HEQ5 is set to, if its not high enough that may cause issues too. Set it to 1x (or 0.99x I think on the heq) its highest rate and work your way down from there using aggressiveness at first in PHD or if you have to drop the guiderate on the scope.

I ran through my guiding setup properly for the first time last night and I believe the key is getting the graph tool up and watching the OSC index once PHD has calibrated.

I started at the highest guid rate of the mount, and set aggressiveness to 100, hysterisis to 10, the calibration step size I have for my F7.5 80mm/qhy5 cmos guiding rig is 1250ms.

Watching the graph for the osc index I was hitting about 0.7, this is too high, so the guider is overshooting, it needs to be around 0.5 according to the manual, so I dropped off the aggressiveness to 75, this caused the osc index to drop to 0.38, so now undershooting, just a process of going back and forth, this time back up to 90 aggressiveness, too high again, down to 85, just too low, at 0.44, up to 86 now and osc index is now going between 0.49 and 0.51. I added a little to the hysterisis putting it to 12 to smooth out some of the commands as it was a little breezy last night.

I know that PHD is supposed to be 'push here dummy' simple and it does work fine without major tweaking but I'm guessing that getting the osc index closer to 0.5 has got to be worth the effort as its less work for the motors in the long run.

[greenkat]

Cheers for your help & advice,

I was initialy using my DSI III for testing, but after Steves advice on the star having to move 5% , I had a go with the old DSI 1, less pixels , and no more errors of no star movement , Thanks for the graph info Reggie, I had the OSC hovering around 4.5 before having to pack up ang go to bed ,

Tried a test exposure and got up to two mins with only slight trail, a bit of tweaking and I might get there.

Would you have to go through this routine with every scope?

I am hoping to guide using the DSI-1 attatched to my old little ETX70 piggybacked on the ED80Pro & also on an Orion optics 150mm f/6 reflector. Does that sound feasable?

I have the EQmod serial to usb from Opticstar eliminating the handset.

Any more advice welcome

Cheers again

[Reggie]

Now you've got the osc about right I probably wouldn't worry too much about it, as long as its not getting to low or too high then it should be fine anywhere between 0.3 to 0.7. Watching it every now and again will tell you whether there is anything untoward going on with the system, just useful to know what its doing and how it will react if you need to tweak stuff.

I'm slightly worried that you only managed 2mins without trailing on the heq5 pro, my last session out I was doing 7min subs without any issue. How tight was your polar alignment and which scope was your guidescope?

You certainly have a lot of options there as to what you can do, any of the scopes you have mentioned could easily be a guide scope or an imaging scope You may want to consider a dual mount bar, it mounts the scopes side by side, instead of piggybacking, as this will give you a lot more options as to what you can mount with what.

[greenkat]

Thanks for your help guys, managed to guide last night for the first time

The OCS was reading around 2.9 but I was getting 5 mins without any hint of trailing and could probably have got longer, managed to get 15 4 min subs of m51 before bedtime.

Am posting pic in deepsky section now

Cheers again

[Reggie]

Great stuff, glad you got it going GreenKat