Clavius region 7-panel mosaic

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turfpit
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Clavius region 7-panel mosaic

#1

Post by turfpit »

Found during a disk tidy - overlooked when 2h lunar session created 200Gb of data. Captured 21st April around 22:00. 66% waxing at 55° elevation.
Celestron C8, Skyris 618m CCD camera, UV/IR-Cut/L filter, JMI motorised focuser. Each panel 1 minute @ 120fps = 7200 frames. SharpCap 4 - SER, MONO8, 640x480, exposure=0.9ms, gain=300/1000. Autostakkert stack best 40% with drizzle 1.5. Microsoft Image Composite Editor to stitch mosaic. Registax 6 wavelet slider 2 only and gamma. Final crop and contrast with GIMP.

Clavius-region-7-panel-mosaic.jpg
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Dave
timh
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Re: Clavius region 7-panel mosaic

#2

Post by timh »

Hi Dave,
Another nice detailed moon panorama. Thanks for the details on the methodology. Two questions ..

1) The terminator appears to move somewhat between the top and the bottom. Is that because of the time lag between taking different parts of the mosaic?

2) A basic question - apologies if it is well known but new to me. Is there a technical advantage to making up moon pictures as a mosaic rather than as a single take ? e.g. a single 1440 x 2040 image would be expected to offer inferior resolution to one that is made up of a mosaic of nine or more 640 x 480 individual images?

When I was experimenting with lucky imaging of the Epsilon Lyra double double I did notice that the best frames for the E1 pair were rarely (about 10%) the same frames as for the E2 pair. The separation of the two double star pairs is 3.5 arc min. So - translated to the moon - it would make sense I guess to stitch together smaller (< 2 arc minute images) rather than try and select best frames across say an entire half moon because the latter would always comprise a compromise selection and therefore be less sharp?

Tim
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turfpit
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Re: Clavius region 7-panel mosaic

#3

Post by turfpit »

Thanks Tim.

Answers:
1) 7 x 1 minute panels plus some slewing will mean that the image set takes around 10 minutes to capture. As the moon progresses the terminator angle does change. I suppose it all contributes. Even the illumination changes over 10 minutes as the exposure had to be adjusted to maintain a 60% histogram. Exposures for the panels were 0.9680ms, 0.8416ms, 0.8033ms, 0.9680ms, 0.9680ms, 0.9680ms, 0.8033ms in ascending capture time order. I traversed horizontally from the terminator at Clavius left to right then moved up and captured left to right. Maybe I should capture the terminator first? With 120fps I could capture 15s per image and still have 1800 frames to play with.

2) The Skyris 618m has a maximum capture area of 640x480. It really is a planetary camera https://s3.amazonaws.com/celestron-site ... ams_AN.pdf. It was a knock down £80 from an astro dealer clearing out their obsolete kit. In an ideal world (with wallet to match) I would probably go for a ZWO ASI174M or Imaging Source DMK 33UX174 which have 1920x1200 with 5.86um sensor. The 174 sensor does well on Astrobin for lunar Top Picks and IOTD's.

Larger frames will always be trading fps and lunar really does show up the variability of the atmospheric conditions. What works well one night is not necessarily going to give the same quality the next night. Early morning lunar (before sunrise) have got me my best results - steady atmosphere most likely.

The Baader UV/IR-Cut/L filter has given good results, producing good contrast of features and requiring less processing - for example only wavelet slider 2 was used for sharpening in Registax.

Dave
timh
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Re: Clavius region 7-panel mosaic

#4

Post by timh »

Thanks for the explanations Dave,

So the small tile mosaic approach is necessitated by the equipment. Getting such good results as yours from quite modest equipment is in itself a big win I think. Just maybe the approach also has some inherent advantage anyway ? i.e. if seeing were to vary significantly across a given area of visual field as well as in time - but probably not if the best pictures on Astrobin are with a sensor 4X as big?

Your comment on seeing conditions early morning is interesting. The same should hold for some of the 'lucky imaging' I have been attempting on bright deep sky objects.

Tim
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