Quote:
Originally Posted by Logieberra
Also, did you collect data with the same equipment on each run? Same Autoguider binning, barlow - the same image scales etc?
Something I've just bumped into -- my Kendrick dew heater settings have a bearing on my FWHM focus results! Until recently, I only ever saw 4s and 5s. Bumping Mr Kendrick down to 40% power, I now see high 1s and 2s. This no doubt would affect my PEC collection readings. I'll only measure PEC with Kendrick OFF from now on...
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That is a most interesting observation! You'd need to assume the dew heater was setting up some sort of convection over the lens, no? Perhaps you've got it located in a bad spot. I will need to also experiment with this one.
As for your first post I would find it odd if seeing wasn't somehow factored out in the PEC calculation when the curve was fitted. I have actually seen the opposite of what you report; namely that the PE measure without correction is pretty stable from night to night. If it wasn't stable and you generated a PEC curve from that data then your correction amount would also be all over the place and dependant on the seeing being the same as when you measured it. On the other hand I do agree with you that measuring the correction is quite seeing limited, but again I think the seeing is somehow mathematically supposed to be removed from the calculated amount.
Anyway, I'm not too sure about this so it might be a factor. The thing about my curves are that they are partly the same but with 2 areas of large difference. I don't see how that can be seeing.
No, the two runs were not done even with the same camera, but the camera angle and resolution for both runs was carefully noted, and both image scales differed by only .1 arcsec. One ought to get very similar results...and in fact a comparison of the two curves 5 months apart show pretty much the same shape...and both curves have worked, one now and one back then. I guess what I'm saying is the new curve has got to be valid or it wouldn't work.
The belt tension seems good, though perhaps it is fractionally looser than it was. I could try tightening it up a tad. Maybe that's all it is!
Thanks,
Peter