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kens

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About kens

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    Star Forming
  • Birthday 08/05/61

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    Deep sky, fly fishing, cycling
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    Melbourne, Australia
  1. If you look closely at the calibration graph you can see that the eastbound leg overshoots by a long way and also that the first few readings on the westbound leg are very close together before they spread out to a more normal, even spacing. Tht accounts for why it takes 18 steps for RA and only 13 for Dec. My guess is that you had slewed the scope eastwards to the calibration position which introduced backlash into the RA axis. So it took a while to get moving westwards. Either that or the worm was binding or you had stiction or an imbalance that caused a lag at the start of the westbound leg.
  2. The luminance filter provides the detail in the image so it is very important.
  3. You need to be able to find a decent guide star near the object you ar eimaging. If you are imaging small galaxies, a bright star can be hard to find and more aperture can help. Typical aperatures for a guidescope range from 50 to 80mm. You can also use an off axis guider (OAG) which is an attachment on the focuser that lets you attach both your imaging camera and guide camera so you don't need a guide scope. The OAG uses a small prism to pick off some of the light coming through the focuser and send it to the the guide camera.
  4. That depends on your imaging scope. Autoguiding software like PHD2 http://openphdguiding.org/ can resolve down to around 0.1 pixels. As a simpe rule of thumb, a guidescope should have a focal length in the order of 1/4 the focal length of your imaging scope. Many people adapt a finderscope for the purpose.
  5. I have some code that enabled auto-guiding on my Super Polaris mount but that was using unipolar steppers. I'm happy to share that FWIW. Auto-guiding will help to overcome periodic error in the RA drive train. Periodic error exists to some degree in every mount due to slight imperfections. It causes tracking to speed up and slow down slightly - enough to cause problems with astrophotography. Autoguiding uses a second scope and camera to track a guide tar and send corrections to the RA motor that keep the star stationary. When you get your camera, aim at a star and take a long exposure (5 minutes or more). That will show you graphically the effects of periodic error and polar alignment.
  6. Now that you have an Arduino controller it would not be hard to code it to do guiding pulses so you can autoguide.
  7. I just ordered a 0.965 to 1.25 adapter on eBay for other purposes. http://www.ebay.co.uk/itm/Black-Metal-0-965-to-1-25-Telescope-Eyepiece-Adapter-24-5mm-to-31-7mmAdapterES-/272474471611 Depending on the thread on the focuser you may be able to get a screw fitting instead. For my Vixen scope with a 36.4mm thread I was able to get a screw in 1.25" eyepeice holder and a 36.4mm to T thread adapter. Basically - there are plenty of options
  8. Displaying in arc-sec is good practice, but providing the pixel scale shown is correct, the guiding looks good. That suggests differential flexure is the problem. However, the RMS values don't correlate with what is showing on the screen shot. Please attach the guide log as it is hard to analyse screen shots in any depth.
  9. 0.9 x 0.6 should be plenty as long as you have the appropriate index files. I plate solve my imaging scope which is only 0.63 x 0.48 and it solves fine. The fact that it resolves each frame to a different location could be a clue. That could be due to the amount of drift. You could try having guiding on whilst running SharpCap. Best to turn it on only in Dec whilst pointing at the pole. That should not affect the SharpCap routine. If that does not work, try the QPPA method I linked to.
  10. Curiouser and curiouser. The drift in each of the unguided graphs tallies with what PHD2 reports at PA error. The drift is consistent at around -0.1" per second. Even loading the guided graphs under PEMPro log viewer shows a similar level of drift when guiding pulses are removed - of course in opposite directions on each side of the pier. What happens when you adjust the altitude bolt? I wonder if altitude PA error is swamping everything else?
  11. This certainly an interesting conundrum. Everything looks fine. Calibration looks good even with the smaller steps. It is slightly odd that the brain calculator does not give the right step size so double check the parameters. A recent guide log may be informative - especially if it contains the calibration and drift alignment sequences. One possibility, although it seems unlikely, is that you are not aligning on Polaris. Or that the inverted image is not being taken into account. There is a tutorial on the EQMOD Polar Alignment at http://www.myastroscience.com/eqmodpa You could also try other methods like SharpCap (which uses plate solving) or QPPA http://www.astronomyforum.net/telescope-mounts-forum/228041-free-polar-alignment-program-qppa2-new-easier-use-version.html
  12. You mean celestial equator don't you? That is Declination 0 degrees. If you change your polar alignment by a substantial amount you should recalibrate and check with another drift alignment. You don't really need to recalibrate in the middle of a drift alignment.
  13. Did you rotate the mount so that Polaris was in the right position on the circle?
  14. It is unrelated to the drift problem. Assuming what we can see of your guide log is representative, PHD2 is keeping the guide star centred so there is no major problem there. So if the stars in the image are moving the most likely reason is differential flexure. If you could attach your PHD2 guide log it would really help the analysis of your problem by removing a lot of guessing and assumptions.
  15. I've also been chasing down a differential flexure problem with similar symptoms. The guide graph shows that for half the time at least the guide star was centred, yet the stars in the image are moving. By the way, screen shots are pretty useless for analysis - you need to attach the guide log itself. Attached file shows the images from the session stacked without alignment so the movement is clearly shown. I think one of those hockey sticks is the guide star but can't be sure. The guide star was kept centred in the guide scope the whole time. To home in on the problem I pointed at the pole and took a series of images from both guide camera and imaging camera as I rotated the mount 90 degrees in RA East and West. I did this by running two PHD2 sessions as I described earlier and File | Save As at each point. The combined traces are attached. For a bit of fun I edited in lines showing the movement of BQOct. The plots clearly showed a problem with the imaging scope as the trace should have been circular in both cases. So at least I could eliminate at least half the possibilities. Two possibe causes came to mind: the dovetail mount and the camera attachment. Some preliminary adjustments to the dovetail have been promising - an after shot had a circular trace but I'm not sure it will stay that way. In short - there is no easy solution without gathering diagnostic data. Hope this technique may help you. Its work in the southern hemisphere as there are some nice bright stars near the pole TEST-all-30s.tif