[Shiraz (Ray)]

Originally Posted by MelD

"You don't have to open the mount to adjust the worm backlash - it can be done easily with the mount in one piece."

Hi Ray, would you care to explain this for us please?

Regards,
Mel

Hi Mel - sorry I missed your post. this shows how: http://www.astro-baby.com/heq5-rebuild/heq5-we1.htm

Originally Posted by konstantinos75

Hi

I have found some time to experiment more with my equipment and my problem with the elongated stars.

To remind you this is my equipment
- Vixen VC200L operating at f/6.4
- SBIG ST2000xm dual chip camera
- Skywatcher HEQ5 synscan pro mount
- Skywatcher 9x50 finderscope with focal length 180mm


I have performed the following tests

test1)


point the telescope to the East - target star Vega

- take 1 sec exposure without guiding; as you can see the stars are round so this excludes problem with collimation of the telescope optics.
- start autoguiding, guiding scope is 9x50 finderscope, PHD guiding software is used
take 1 min and 2 min exposures of Vega; as you can see the stars are elongated in both images.
Please find attached the PHD logs
Also have a look at image1.JPG, this is the PHD lab output after inserting the PHD logs



test2)


point the telescope to Zenith - target star Mizar

- take 1 sec exposure without guiding; as you can see the stars are round so this excludes problem with collimation of the telescope optics.
- start autoguiding, guiding scope is 9x50 finderscope, PHD guiding software is used
take 1 min, 5 min, 10 min exposure of Mizar; as you can see the stars are almost round in all images.
Please find attached the PHD logs
Also have a look at image2.JPG, this is the PHD lab output after inserting the PHD logs




test3)


point the telescope to the East - target star Vega

- start autoguiding, guiding scope is VC200L, guiding camera is SBIG ST2000XM with dual chip ST237, MaximDL is used as a guiding software
take 2 min, 5 min, 15 min exposure of Vega; as you can see the stars are elongated in all images.
Please find attached the MaximDL logs
Also have a look at image3.JPG, this is the MaximDL graph output




test4)


point the telescope to Zenith - target star Alkaid

- start autoguiding, guiding scope is VC200L, guiding camera is SBIG ST2000XM with dual chip ST237, MaximDL is used as a guiding software
take 2 min, 15 min exposure of Alkaid; as you can see the stars are almost round in all images.
Please find attached the MaximDL logs
Also have a look at image4.JPG, this is the MaximDL graph output



You can download all the files here
http://www.albireo.gr/tmp/all.rar


So judging from these test results I have come to the conclusion that my problem can be caused by
(a) flexure by the VC200L focuser since a heavy camera SBIG ST2000xm is connected to this focuser
(b) HEQ5 mount has problem with RA motor; backlash present in RA; mount needs adjustment

I would like to hear your opinion also about my conclusion.

Thank you
Konstantinos
www.albireo.gr
Greece

Hi Konstantinos.

You have established that there is not an optics problem - that's good.

Since your guiding chip is in the same body as the imager, I think that it is unlikely that flexure of the focuser is the problem (it would affect both chips and be guided out). The most likely problem with the mount is backlash - try adjusting both axes to get rid of as much as possible without binding. It is also worthwhile unbalancing the scope slightly in both axes so that the offset weight ensures that the worms and gears remain in close contact when the scope is buffeted by minor wind turbulence.