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ngc 691 in Aries


wimvb

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Started on this image a week ago, but work interfered (trip with my class to Prague for concerts)

Red: sloan-r 39 frames of varying exposure times (about 90 secs)

Green: Bessel-V 21 frames

Blue: Bessel-B 19 frames

Data from the Liverpool telescope on La Palma (2 m f/10, 0.3 "/p)

The blue and green masters were made up of fewer subs, and especially the blue master was very noisy (probably also due to the lower QE for blue light).

After channel combination, colour calibration and deconvolution, I did noise reduction (TGVDenoise) on the individual R, G, and B channels. Then recombined for further processing.

The light streak in the lower left corner is due to a nearby star.

This rendering shows more colour in the core than @gorann's version. Probably due to different colour calibration methods.

As usual, processed in PixInsight.

ngc691_1.thumb.jpg.9867f3b76af49c07446df47569a85771.jpg

 

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Nice Wim,

you also managed to suppress the noise a bit better than me - I should have done more of that on the blue channel before I combined them. As you say the blue is usually the noisiest one in the LT data. I live and learn...

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6 minutes ago, gorann said:

Nice Wim,

you also managed to suppress the noise a bit better than me - I should have done more of that on the blue channel before I combined them. As you say the blue is usually the noisiest one in the LT data. I live and learn...

Isn't that why we do these exercises? :icon_biggrin:

BTW, the published version of this image shows a very weak reflection of the mirror around the double star left of the galaxy. It's almost the width of the galaxy. I have never seen this reflection before in LT data.

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Sorry, I mean the version shown here and on astrobin, as compared to the xisf (pixinsight) file on my computer. It seems that the jpeg conversion and server software enhance this.

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Aha, do you mean that additional weak outer blue ring around the double star? Blue is certainly the most troublesome in LT data both with regard to noise and reflections. I also often experience that downloading images onto SGL can be very revealing on small things like this and gradients that I do not notice on my screen while processing. Would be nice if SGL put in some filter that instead made the images look better after posting.....

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9 minutes ago, gorann said:

Aha, do you mean that additional weak outer blue ring around the double star? Blue is certainly the most troublesome in LT data both with regard to noise and reflections. I also often experience that downloading images onto SGL can be very revealing on small things like this and gradients that I do not notice on my screen while processing. Would be nice if SGL put in some filter that instead made the images look better after posting.....

Yes, that's the one.

You mean like the one in the bottom of a beer bottle? :grin:

 

Ha det bra.

(Nu måste jag söka i LT arkivet efter en ny utmaning)

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1 minute ago, wimvb said:

 

Yes, that's the one.

You mean like the one in the bottom of a beer bottle? :grin:

 

Ha det bra.

(Nu måste jag söka i LT arkivet efter en ny utmaning)

If you tell me which one you go for next we may not have to duplicate our efforts and maybe do the whole archive until astro-dark arrives up here again.

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Ngc 5566 is the subject of my next image. Having duplicates of images helps us compare, but I agree that we shouldn't duplicate too much. But sometimes our different approach results in very different outcome, which I find fascinating.

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58 minutes ago, wimvb said:

Ngc 5566 is the subject of my next image. Having duplicates of images helps us compare, but I agree that we shouldn't duplicate too much. But sometimes our different approach results in very different outcome, which I find fascinating.

...and in the one instance we combined our efforts we won an IotD. NGC 5566 is an interesting looking object(s)  - I did look at the data for that one some days ago but moved on since I worried it was a bit thin in data (but then somehow ended up doing the Egg nebula with almost no data).

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In a dark sky, the aperture should be ok. But it's a small one, only 3.4' x 2.5'. If you have a resolution of 1"/pixel, the galaxy will be only 200x150 pixels. To get any reasonable detail, the resolution should be better than this. (The Liverpool telescope has 0.3"/pixel.) The image will also be limited by seeing, unless you have a high mountain top nearby.

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33 minutes ago, wimvb said:

In a dark sky, the aperture should be ok. But it's a small one, only 3.4' x 2.5'. If you have a resolution of 1"/pixel, the galaxy will be only 200x150 pixels. To get any reasonable detail, the resolution should be better than this. (The Liverpool telescope has 0.3"/pixel.) The image will also be limited by seeing, unless you have a high mountain top nearby.

Without the reducer I'm at .4 , with the reducer .57.  Sounds doable! esp. at F10 (never shot at F10 though).

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3 hours ago, cfpendock said:

Go for it!  I for one will would be very interested to see the result.

Chris

I'll put it on my list--though I need to get in better with the man upstairs--2 months and counting of cloudy weather.  Really hoping for a change

Rodd

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15 hours ago, wimvb said:

Thanks, Rodd.

The background is an easy fix. It shows slightly lighter here than the original image on my laptop.

Did you crop this image at all?  Just wondering as I noticed a really nice barred spiral face on just off the upper left corner of your image in the FOV calculator.  Its smaller than 691, but clear.  It would make for a nice target for that telescope.

Rodd

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+1 for "Go for it". It would be nice to see an amateur version (in terms of equipment, not effort) of this target. Even with clear skies, you still need to have good seeing as well.

I didn't crop more than necessary to get the stacking edges clean. LT images are 2048 x 2056 pixels in 2x2 binned mode (with 15 micrometer pixels, that translates to a 60 x 60 mm sensor, or medium format in film terms).

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