Imaging through a flip - Forums

Topic starter

Dec 16, 2016

I currently use Backyard EOS for image capture and PHD to guide. Up until now I have started capture sessions when a target has just passed the meridian or stop imaging just before to avoid a mount flip in the middle of a session. If however, a target will cross the meridian in the middle of a session this poses a couple of problems and I'm wondering 2 things.

1. Can Pixinsight's Batch Preprocessing script handle some images one way up and some upside down?
2. Will PHD figure out that it's calibration settings need to be flipped when it sees stars moving in the wrong direction after the flip?

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Wei-Hao Wang

Dec 17, 2016

It's not rare for me to have a meridian flip in the middle of a imaging session. Sometimes I stack the images before/after the flip separately, and sometimes I just stack them all together. I don't remember a case where PI failed to stack those 180deg rotated images with the others, as long as the telescope pointing is still good. I do remember case of failures when there are both large pointing offset and large rotation, in combination of image distortion from the optics.

For PHD, someone may have more accurate answers, but I saw options related to the meridian flip in PHD2, meaning that it can do something to it. However, someone (or something) have to tell PHD2 it had been flipped. I am not sure how a user can tell PHD2 the flip had happened, but ASCOM may tell PHD2 such things. Personally, I always redo the calibration after the meridian flip. The different weight distribution after the flip may cause an overall tracking pattern change. A re-calibration generally improves tracking accuracy in my case.

Cheers,
Wei-Hao

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Adam Landefeld

Dec 17, 2016

Yes, and yes (as long as your mounts ASCOM driver reports what side the mount is on)

Wido's AstroForum

Dec 18, 2016

There is an option which I used in PhD that lets you flip your calibration data. It works very well for me.

Michael Southam

Topic starter

Dec 23, 2016

Thank you all for your advice. I was hoping to have the calibration flip happen automatically. I guess the only way to see if it will is to try. Great to know that PI will handle the flip without issue. Thanks again.

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astrofarm

Nov 2, 2017

PI Star Alignment takes care of it, although you may end up with some borders on the master that need to be cropped off.

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John Stiner

Nov 2, 2017

Sequence Generator Pro will do the flip for you. It also plays well with PHD.

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Greg Trotter

Nov 3, 2017

+1 for SGP handling meridian flips well. I didn't think BYEOS could do automated flips, but I honestly don't know for sure. I've integrated in DSS and PI with flipped images without issue. To my understanding it's only a problem if you rotate the camera after the flip - then the calibration subs need to match each pier side. Be sure to experiment or check with others for the correct PHD settings for flipped calibration - it varies with different mounts.

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HR_Maurer

IOTD Staff

Mar 5, 2019

Hi Michael,

as far as my experience concerns, PI registeres properly even if some of the frames are flipped by 180°. In some cases, manual flipping might be required, but i cant remember i ever had this in PI.
However, i think better re-calibrate your guiding after meridianflip. You have to re-frame anyway, if you're not off-axis guiding.
There's another possibility, at least for Synscan mounts. You can force a meridian flip. This command is valid only once, that means for the next operation. So you have to select "force flip" (in the setup menu), perform a one-star alignment, select "force flip" again, and drive to your object. You have to take care and stop the mount in case of possible collisions.

I also have some experience on image artifacts due to meridian flipping. After i had my mono CCD, i started doing my RGB images with this camera, too, using broadband filters. Sometimes, i had to meridian flip the mount after green and before blue. Due to a small misalignment in the telescope itself, stars werent perfectly round, and this issue rotated by 180° with the meridian flip, too. So i ended up with colorful seams around the stars, that were hard to deal with.

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Kevin Morefield

IOTD Staff

Mar 5, 2019 · Edited: Mar 5, 2019

I use CCDAutoPilot to manage my sessions and it will perform the flip, re-platesolve and adjust to match the prior framing with the precision I request. I believe I have it set to within 20 arc seconds if memory serves. Following the flip it will also reselect a guide star automatically. Quite seemless.

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Rick Stevenson

Mar 7, 2019

I treat meridian flipping as super dithering. It certainly helps to clean up bad columns. PI handles a mix of data from both sides of the sky very well.

Cheers,
Rick.

Steve Milne

Mar 7, 2019

As the object crosses the meridian, it is usually (maybe always) at it’s highest sky altitude. As such this is the best time to image it - especially blues - since you are looking through the minimum thickness of aperture. In other words, you certainly don’t want to avoid the meridian.

I use SGP and PHD2, which handles everything well, so long as you are using pulse guiding and not ST-4. But these programs are not the only show in town. You don’t need to worry about StarAlignment and you don’t need any additional calibration frames - everything flips so your flats are all just fine either side.

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Kevin Morefield

IOTD Staff

Mar 7, 2019 · Edited: Mar 8, 2019

Rick Stevenson:
I treat meridian flipping as super dithering. It certainly helps to clean up bad columns. PI handles a mix of data from both sides of the sky very well.Cheers,
Rick.

Rick, curious if your Bias and Flats don’t clean up the bad columns in calibration? I have several bad columns on my 16803 and whenever I get a new one I update my bias and darks. But there was this odd half a bad column I had for a month that went away...

kevin

Michael Juliano

Mar 8, 2019 · Edited: Mar 8, 2019

I'm still pretty new to guided imaging w/ an EQ mount. I've have my mount flip on me a few times during imaging and it scared the hell out of me the first time. It didn't quite line up right after the flip, either, and I got frustrated with it so I turned off the flip on my mount, so it images through the meridian without flipping. Are there any cons to this, given that my imaging time is relatively short per session? Generally, how do the more experienced imagers handle flips? Do you pause your subs to flip, re-center, and recalibrate, or can you image right through it with only 1 or 2 bad subs? I don't think my mount is accurate enough to do a flip without re-centering; hopefully I can afford to upgrade soon. (donations accepted via paypal

)

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Kevin Morefield

IOTD Staff

Mar 8, 2019

Michael Juliano:
I'm still pretty new to guided imaging w/ an EQ mount. I've have my mount flip on me a few times during imaging and it scared the hell out of me the first time. It didn't quite line up right after the flip, either, and I got frustrated with it so I turned off the flip on my mount, so it images through the meridian without flipping. Are there any cons to this, given that my imaging time is relatively short per session? Generally, how do the more experienced imagers handle flips? Do you pause your subs to flip, re-center, and recalibrate, or can you image right through it with only 1 or 2 bad subs? I don't think my mount is accurate enough to do a flip without re-centering; hopefully I can afford to upgrade soon. (donations accepted via paypal ;) )

Even with a very accurate mount re-centering or correcting the pointing location is still needed/desired. The good news is you only need to use software to do that rather than more expensive hardware. CCDAutopilot, Sequence Generator Pro, ACP or other other software will know when you need to flip, instruct the mount to do so, then take a short picture to verify the location, make the correction, and re-start your imaging session. That takes about 5 minutes with my mount.

In addition to the one of these session control programs I mentioned, you will need to have a planetarium program like TheSky or Pinpoint that the session control program calls to do the platesolving.

These programs are so worth the cost if you are a regular imager. With them you can turn on your mount and go to bed (if you want).

http://www.ccdware.com/products/ccdap5/
http://mainsequencesoftware.com/Products/SGPro

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Rick Stevenson

Mar 10, 2019

Kevin Morefield:
Rick Stevenson:
I treat meridian flipping as super dithering. It certainly helps to clean up bad columns. PI handles a mix of data from both sides of the sky very well.Cheers,Rick.

Rick, curious if your Bias and Flats don’t clean up the bad columns in calibration? I have several bad columns on my 16803 and whenever I get a new one I update my bias and darks. But there was this odd half a bad column I had for a month that went away...

kevin

Hi Kevin,

KAF-16803 cameras seem to develop a lot of dodgy columns as they age. They aren't that noticeable with LRGB but dim narrowband targets show them if you push the data hard and they don't all calibrate out cleanly for me. There's also a degree of inconsistency with some that pop up and go away as you suggest. It's manageable but requires some work.

Cheers,
Rick.

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