High resolution and high dynamic range view of M3

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timh
Posts: 515
Joined: Mon Aug 26, 2019 5:50 pm

High resolution and high dynamic range view of M3

#1

Post by timh »

Here a high dynamic range composition of M3 combining 10s, 20s and 40s exposures was built as described in viewtopic.php?p=20601#p20601. Then a high resolution "lucky image" of just the core ~ 9 x 7 arc min obtained by selecting and combining the best of many 130ms exposures from a SER file video capture and then merging the luminance of this into the corresponding part of the high dynamic range composition. This provided improved resolution of the core. The lucky imaging method to resolve the core of globular clusters and its development is described in this thread viewtopic.php?p=21725#p21725

High dynamic range composition

8 " SW PDS200 Newtonian , Baader flattener (F5.0) on an Ioptron CEM 70 mount , PHD2 guiding with an ASI 120 mm and 160 mm guidescope under Bortle 6 skies (near half moon)

ASI 294 MC PRO (osc version) at -10 C , 4.63 uM pixel --> image scale 0.95 arcsec/ pixel

3 stacks - 180 x 10s, 9 x 20s and 52 x 40s exposures all at gain 124 combined together as a high dynamic range composition in PixInsight (the program effectively uses concentric masks to vary the exposure in the final composition) then using a high dynamic range stretch to further flatten out the brightness at the centre.

Lucky imaging

10" SW 250 Newtonian Synscan Dobsonian, SW 0.9X reducer flattener (F4.2)

ASI 294 MM PRO (mono version) , 2.315 uM pixel --> image scale 0.44 arcsec/ pixel

7 minute 16 bit SER file at exposure 130 ms and at gain 336. 1280 x 1024 pixels. The best 284 frames (~7%) were selected using PixInsight subframe selector on the basis of the number of stars and their ellipticity and then registered, integrated and aligned with the high dynamic range composition. The luminance of this high resolution image was then merged into the corresponding RGB pixels of the high dynamic range composition.

Overall, quite a lot of work -two cameras and two telescopes for an image of a globular cluster. But quite a nice final effect that is somewhat similar to the view through a telescope using a wide field eyepiece --- i.e. the core looks to be highly in focus (where the resolution of the image is in fact higher) and the periphery somewhat more blurred?

TimH
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Menno555
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Re: High resolution and high dynamic range view of M3

#2

Post by Menno555 »

Verrry nice Tim!!
And yes, the core has a bit "weird" look with the larger image. A bit like a cluster inside a cluster?

Menno
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