The Great Hercules Glob


Posted by crw816 on Tue Jun 09, 2015 9:34 am

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Image
Canon T5i (Modified), Canon 300mm f2.8is II + 2.0xTC III, f5.6, 60 second exposures (107 minutes total exposure), ISO 1600, Astrotrac, Dark, Flat and Bias Frames used for calibration, Pixinsight, Photoshop, Lightroom.

Please view in shadowbox. 


Messier 13- The Great Globular Star Cluster of Hercules.

We just had our first clear night in over three weeks and it happened to coincide with a full moon.  Not wanting to miss out an opportunity, I decided to photograph a Globular Star Cluster, as it would be least impacted by the full moon than other objects such as galaxies and nebulae.

I started imaging at around 11pm, and the almost full moon rose at midnight.  I continued to image until close to 2:30am so from start to finish there was a wide range of exposure of sky background.

This cluster only has an apparent size of about 2/3 of the full moon, so I decided to push my Astrotrac beyond its limits and shot at 600mm focal length.  Due to the smaller aperture I had to shoot 60 second exposures to achieve ideal exposure.  This did result in some tracking and focus error, and out of about 200 exposures I kept 107 that were tack sharp.

Also of interest in this image are two tiny galaxies located to the right and slightly above this cluster.

You can read more about it here:
http://www.whitephotogallery.com/index. ... essier-13/

 
Chris White
www.whitephotogallery.com

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by Diane Miller on Tue Jun 09, 2015 2:40 pm
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This is a wonderful capture of a small object! Even more amazing that you were able to shoot it with light pollution from the full moon. You are getting wonderful results with the Astrotrac.

The larger image shows even better on your web site.
 

by E.J. Peiker on Thu Jun 11, 2015 6:00 am
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Super cool!!!
 

by Diane Miller on Thu Jun 11, 2015 7:58 am
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An elegant detail about this image is how Chris captured detail over the range of brightness into the center of the cluster.

You must have had remarkably clear air!
 

by crw816 on Thu Jun 11, 2015 8:09 am
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Diane Miller wrote:An elegant detail about this image is how Chris captured detail over the range of brightness into the center of the cluster.

You must have had remarkably clear air!
Thank you for your comments Diane!  My first attempt at this one was a few nights earlier.  We had about an hour of clear skies.  I overexposed just a tiny bit and lost the color in the core stars.  This time I was more careful to expose more to the left and was fortunate to retain the color and details. 

My skies are really not that great.  Even on a new moon I contend with the light pollution of Burlington Vermont (only 5 miles away) and a supermarket about half mile away.  My skies are yellow/orange with Red nearby.  About an hour drive I can get into pretty dark sky territory, but its just so much more convenient to shoot in the back yard!!!
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by Diane Miller on Thu Jun 11, 2015 8:21 am
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Have you tried a light pollution filter for the contribution from the tungsten/halogen lights? I got one and have mixed reviews. Shoot the flats with it in place -- it vignettes on the bottom and left edges. And I haven't mastered good color correction for it.
 

by crw816 on Thu Jun 11, 2015 9:59 am
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Diane Miller wrote:Have you tried a light pollution filter for the contribution from the tungsten/halogen lights?  I got one and have mixed reviews.  Shoot the flats with it in place -- it vignettes on the bottom and left edges.  And I haven't mastered good color correction for it.

Diane,

I have an Astronomik clip in light pollution filter which works exceptionally well for me with certain targets.  I don't use it when shooting star clusters or reflection nebula as it filters out some of what I want.  It was not used in the example above, and not particulary effective at filtering out illumination from the moon.   It is particularly useful for emission nebula where the red wavelengths get mixed in with the glow from sodium lamps.  With the clip in filter the vignetting is apparent, but minimal on a crop sensor, and calibrating with flat frames removes it entirely.

What are you using for color correction?  I now use PixInsight which effortlessly achieves excellent and accurate color whether I am using a LPS or not.  Previously I was using ImagesPlus and Photoshop, which I found to produce lackluster results. 

Have you tried PixInsight?  It is the most complete astrophotography editing platform available.  A little bit of a learning curve, but the effort is well worth it when you start to realize what it is capable of. 
Chris White
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by Diane Miller on Thu Jun 11, 2015 11:02 am
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Chris, thanks for the information. PI has been highly recommended but I've been hesitant about the learning curve and price, although having gotten this far with this hobby, there is no justification for thinking about either.

I have Nebulosity but have been trying Roger Clark's method which seems to work very well for the 7D2 and Lightroom/ACR processing. Darks and biases not needed, but flats probably a good idea for the LP filter. Take a flat and push Levels way up in Photoshop and you see the vignetting with color differences. But most objects are cropped enough it may not be a factor.

But I haven't figured out the best way to deal with color correction with confidence. (Also have the Astronomik.)

I should make time and tackle PI. Haven't even gotten very far with Nebulosity. Had some issues focusing with it but now upgraded to the latest v3, which I haven't tried yet. Have been using Helicon Remote to focus and frame, shooting with the intervalometer and dumping the files to the laptop with Lightroom's tethered capture to keep an eye on things. (Had to upgrade to LR 5/CC for tethered capture to work with the 7D2.) Then processing the raw files in LR/ACR. Stacking and aligning works very well in PS, then I do Median mode on the smart object stack. PS and LR from there to stretch to pull out detail.

It looks dark and clear here for the next week!
 

by crw816 on Thu Jun 11, 2015 11:44 am
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Diane,

Check out Harry's tutorials. He does a fantastic job walking you through some of the pixinsight tools. They are free to view and super informative. Just google Harry's astro tutorials.

Also, pixinsight trial version is avail for 45 days free.
Chris White
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by Diane Miller on Thu Jun 11, 2015 12:07 pm
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Thanks -- will do!
 

by Carol Clarke on Thu Jun 11, 2015 2:36 pm
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You're taking us on a real roller coaster ride around the heavens Chris!
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the world will know peace"....Jimi Hendrix.

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by John Labrenz on Fri Jun 12, 2015 1:01 am
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Chris;
Hats off to your dedication in obtaining these amazing images.
Off to read your blog.
 

by Jens Peermann on Fri Jun 12, 2015 7:21 am
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Amazing shot, although I might prefer the subject a little off center.
A great photograph is absorbed by the eyes and stored in the heart.
 

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