Flats and meridian flips??

[Martin-Devon]

I don't have an obs, so am taking flats the morning after my nightly imaging session. I'm confused though what to do about taking flats if a meridian flip is involved. So what do folks do about taking flats when they image a target, and it's necessary to do a meridian flip half-way through? At the moment I turn my CCD 180 degrees after the flip so that I can align my target up identically on the chip as it was before the flip. However, now that the camera is turned like this when I take my flats, they are only relevant to the subs taken after the flip, not before. Since I'm not in an obs I cannot take a set of flats "on the fly" just before I do the meridian flip. I'd be interested to see how others cope with this.

I've tried not rotating the CCD 180 degrees as well after the meridian flip, and then flipping the subs in Maxim the next day - but I've had real headaches so far with this trying to get the Auto-Star Matching process in Maxim to work, it seems fussy and often fails unless everything is an exact mirror image on the chip post the flip - I don't find this easy to do under just a red torch, freezing cold, often around 1.00am in the morning.....

[Photosbykev]

If you rotate the scope AND ccd then the flats are valid before and after the flip. If you only move the ccd then you should take flats before and after the rotate, if you don't then the flats will only be valid for one set of images

[steppenwolf]

You'll be fine if you haven't rotated the CCD camera

[Digz]

If you rotate the scope AND ccd then the flats are valid before and after the flip....

Its been a long day but....is this right? If the CCD has been rotated then a new set of flats will be needed? ;-)

[Photosbykev]

Its been a long day but....is this right? If the CCD has been rotated then a new set of flats will be needed? ;-)

as long as the relative position of the scope and ccd remain unchanged then the flats remain valid. If the ccd is rotated relative to the scope then new flats are required.

[Digz]

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as long as the relative position of the scope and ccd remain unchanged then the flats remain valid. If the ccd is rotated relative to the scope then new flats are required.

Thats what I thought and I've just re-read your post and that's what it says......told you its been a long day

[ollypenrice]

Don't rotate the camera in the scope! When you need to re-frame after the flip just open a pre-flip image in another programme and rotate it 180. Use that as a reference to reframe your post flip image.

Olly

[Martin-Devon]

Thanks for the feedback - what I'll do now then is take a screenshot of my image before the flip, paste it into Powerpoint, rotate it 180 degrees on a slide and use this as Olly suggests as a guide to get the target framed up again properly on the CCD post the meridian flip - so I'll stop rotating my CCD from now on!

[pilkinn]

Depending on which method you're using, MaxIm should have no problem doing the alignment. Just rotate one set of images 180 degrees, save and then do the alignment.

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[Martin-Devon]

The worry I have is orthogonality in the imaging set-up. It seems it has to be just 100% perfect for the target to be on the cross-hairs and in exactly the right CCD orientation pre and post-meridian flip without touching anything. This is rarely the case, at least with my set-up. Some more head-scratching ahead I can see....