My first Guided Image & First M51

[dazza1639]

Here is my first attempt at M51 which is also my first guided image. it is made up from 10 3min exposures and 16 5min exposures totalling 1h50m exposure all taken with the EOS 1000d at f10 through the NS8GPS.

I seem to have a problem with some sort of image shake as on most of the raws the stars are dumbbell shaped with a main bright star and a fainter version of the star just to one side connected with a brighter wisp. I have ruled out flex and guiding errors so I'm a bit stuck. I think it may be a problem with my RA worm gear as I've had the same problem with unguided images. I'm going to have another go but alter the balance with the weight shifted in RA towards the east putting pressure on the gear.

Any suggestions would be welcomed on both how to improve the image and tips on guiding and setting up the NS8GPS on a wedge.

[ollypenrice]

You've ruled out guiding errors? How did you do that?

What you describe on the individual subs is absolutely classic backlash. The scope oscillates between one side of the worm mesh and the other. (It falls away to the west then rocks back to the east etc) The cure is indeed to load it to run east heavy so the drive pinion is always pushing the worm. It may also help to adjust the backlash compensation and/or aggressivity in the guide software parameters.

Looking at SkyMap Pro and your location I guess you had the camera mounted orthogonally, square ont to RA and Dec so the error we see is in RA. This sits well with the backlash hypothesis.

Curiously, in the stack we see the opposite, a good bright star in the centre with fainter trails each side. I can't explain that, but maybe it comes from the stacking procedure.

Anyway well done. Apart from the guiding gremlin you have got things working nicely and guiding at 2 metres is never easy.

Olly

[dazza1639]

cheers Olly

The 5 min exposures where taken on 2 nights at different times. the exposures taken on the friday where at about 1 am is so M51 was west of the meridian and the images taken in the sunday where taken about 11pm so M51 was east of the meridian. So when the images where stacked I got the Saturn shaped stars.

[ollypenrice]

cheers Olly

The 5 min exposures where taken on 2 nights at different times. the exposures taken on the friday where at about 1 am is so M51 was west of the meridian and the images taken in the sunday where taken about 11pm so M51 was east of the meridian. So when the images where stacked I got the Saturn shaped stars.

Aha! Then backlash apart, I think you have good underlying tracking.

Oly