Ha Calibration Woes . . .

[bulrichl]

Regarding the flipped notation. That puzzled me as it was my intent to upload a file as it came from the camera.
I am imaging as I write this and it seems all my subs, as they come from the STL, now have Flipped=T! I went back and looked at some from a couple of years ago and they had Flipped=F.
When this happened, I have no idea. And I have no idea as to why it happened either. Or if I should do anything about it?

I am also puzzled and interested in the cause.

Indeed the representation of your image (m82Feb11_2019_1800sec_1x1_HA_frame1.fit) in PixInsight IS mirrored, I checked it versus an image of mine.

The FITS keyword 'FLIPPED' is created by the capturing software, which is SGP in your case. The plate solving software is detecting whether the image is mirrored or not. SGP then passes this information from the plate solving software to the FITS header, see this discussion: https://forum.mainsequencesoftware.com/t/center-here-is-ok-in-dec-flipped-for-ra/3102.

I really cannot understand why this issue would appear suddenly. If there is no mirror or an even number of mirrors in the optical path, the resulting 'FLIPPED' value must be "F", otherwise "T". So a change could only happen when you change the telescope type, e.g. from a refractor to a hyperstar system.

I noticed that you use an outdated version of SGP. Perhaps it is worthwhile updating to the current version (hoping that the issue is related to the SGP version)?

'FLIPPED' is not a standard FITS keyword (indeed I was not able to find it in a search for "FITS keywords"!). So it is very unlikely that PI will ever evaluate this keyword and automatically mirror FITS images if the value of 'FLIPPED' is "T".

Bernd

[Terry Danks]

Thanks, Bernd and Adam. I remain mystified as to the reason for the change from F to T for the flipped keyword in ALL my images now . I have seen Bernd's post to the SGP forum as well.

I am using the latest version of SGP, BTW. Just that those subs were not taken since my last update. The latest version is still giving me FLIPPED=T, for no reason I can ascertain. This includes subs taken in the past 12 hours from SGP v. 3.0.3.169
And I remain unclear as to whether this flipped business can be the source of my lousy Ha calibrations of late and my need to add a pedestal while calibrating. I gather from Bernd's latest post, likely not.

All hardware remains the same other than going to a newer Win10 laptop for data acquisition.

[pfile]

do you have darks and lights taken with very old versions of SGP that you can compare with the newer ones? you should be able to tell if the older darks are rotated/flipped/whatever vs. the newer ones by looking at the column defects/gradients. i think the version number of SGP is written into the fits header, so you can know that definitively without guessing based on when the frames were acquired.

since the FLIPPED=T thing seems to be related to platesolving, did you happen to change platesolvers in SGP recently?

rob

[Terry Danks]

Only in the almost vanishingly rare cases when PS2 fails do I go to the failover astrometry plate solver. That cannot be the source of my subs going from FLIPPED=F to FLIPPED=T as I've just used PS2 since it became avaliable in SGP.

It will take some work on my part to determine the date when this strange change from F to T took place. OK. Did it.
All my subs taken on and prior to Mar 26, 2016 are "FLIPPED F."
All taken subsequent to that date are "FLIPPED T."
The break occurred between sessions on Mar. 26, 2016 and April 5, 2016. It occurred despite both sessions being SGP v.2.4.2.10. I can think of no change in routine, software or hardware that would account for the change. It seems curious, but irrelevant to the calibration problem recently encountered.

Yes, I should be able to come up with master darks created several years ago but only the master. I will not have the individual dark subs from which the old masters were integrated.

[pfile]

i guess all that's left is the SBIG drivers/firmware... but yeah i don't think the FLIPPED thing is necessarily related. i guess it could be if the SBIG driver suddenly started writing out the images with the opposite direction, but since this particular problem with the darks seems to have manifested just the other day it's probably not related to whatever change happened in 2016.

rob