Posts Tagged ‘galaxy’

The Astrophotography Sky Atlas

November 22, 2015 Leave a comment

TASA Cover 500px

The Astrophotography Sky Atlas is now available at Amazon!

I spent two years coding, researching, and writing this book with a simple goal:  to create a compact, reasonably-priced atlas designed for the imager. Over 2000 deep-sky objects are plotted in their correct size and shape, including many faint nebulae not shown in other atlases. Stars are shown down to 9th magnitude.  The entire sky is covered in 70 full-color charts.

A tabular index contains important details on each object, including a description, the best time of year to capture it, and the required field of view.

What’s shown:

  • 416 emission nebulae and supernova remnants, including the complete Sharpless (Sh2) and RCW catalogs.
  • 171 reflection nebulae, including the complete van den Bergh (vdB) catalog.
  • 146 planetary nebulae, including the complete Abell catalog
  • 52 dark nebulae and molecular clouds
  • 792 galaxies (larger than 3 arcminutes)
  • 38 galaxy groups from the Abell and Hickson catalogs
  • 108 globular clusters (larger than 5 arcminutes)
  • 309 open clusters (larger than 5 arcminutes)

Keeping a focus on what is important to imaging, sparse open clusters and galaxies smaller than 3 arcminutes (unless part of a group) were left off the maps.

With information on nearly every possible photographic object in the night sky, The Astrophotography Sky Atlas will help you choose your targets and plan your imaging.


Testing out the Takahashi FSQ 0.73 focal reducer on the Virgo Cluster

May 31, 2014 3 comments

I recently purchased the 0.73 focal reducer “QE”for my Tak 106ED. It promises to turn it from a speedy f/5 to a ridiculous f/3.7 while still filling a full frame sensor. In fact, with the full frame sensor of the STL-11000M, we’re looking at a field of view of 5.3 x 3.5 degrees.

Of course any new purchase like this causes days of clouds and rain, but that’s been the case for about six months anyway. It gave me time to order the insanely priced adapter required to mate it with the STL camera. Once I had a clear night, I seized it, even though it was a full moon. Because of this, the image you’ll see below is far from optimal. Consider it a test image more than a aesthetic image (though the effect is still pretty cool). I fought a valiant battle with gradients in PixInsight, but for the most part they got the best of me.

Wide Field of the Virgo Cluster of Galaxies

Wide Field of the Virgo Cluster of Galaxies

Even after cropping a little, that’s a WIIIIDE field. Looking in detail at the extreme corners, the left side showed a little distortion, but that could potentially be due to some non-orthogonality in the connections.

Extreme corners of the image

Extreme corners of the image

Overall, the image is very sharp, and it’s a pleasure to capture a field that would normally require a mosaic. I look forward to the beginning of narrowband season to really give this new system a try.

Why Spring is Galaxy Season

February 28, 2014 2 comments

I’ve been hard at work on the second edition of The Deep-sky Imaging Primer, which is the main reason I haven’t posted anything new in such a long time. (The other reason is that we have had a very long stretch of astronomically unfriendly weather here in NJ.)

In the second edition, I am adding some sky maps focused on imaging-worthy objects. After many hours of programming and data munging, I have some useful charts. One of these is a simple plot that clearly explains why we call spring “Galaxy Season.”

Imaging-worthy galaxy locations by optimal viewing date

Imaging-worthy galaxy locations by optimal viewing date

So what are we looking at here? On the X-axis is declination. Up at the top you can see a distorted little dipper, because this is an Mercator-like projection (orthographic, if you really want to know). On the Y-axis, instead of hours of right ascension, I’ve marked the map by the date of ideal viewing–that is, the night that that particular line of RA is directly overhead at solar midnight. In other words, these are the objects that will spend their maximum time in the night sky on the date at the bottom.

And what is plotted in red? Those are galaxies that I’ve deemed to be at least remotely “imaging-worthy.” They don’t have to be pretty, they just have to be at least 5 arcminutes across their longest axis. Pretty simple, huh?

Because our own galaxy blocks our view of other galaxies, the time of year we can see the most galaxies in the night sky is when we see the least of our own. This is in the spring and fall, and particularly in the northern hemisphere spring. In fact, you could probably estimate that the absolute peak for galaxy viewing and imaging is sometime in late March for those of us in the north, as this is when the Virgo and Coma groups are in prime position. So get your long focal length scope ready and cross your fingers for good weather, as Galaxy Season is upon us!

M31 – The Andromeda Galaxy

November 14, 2012 Leave a comment

After taking the luminance exposures that were intended to be a test for the new STL-11000M, I couldn’t help but dig up some old DSLR exposures of M31 and merge their color data into the image.
This is 18×10 min luminance with an SBIG STL -11000M through an NP-101 at the native f/5.3 combined with color data from 169×4 min (11+ hrs!) taken with a Canon 450D through an 80 mm refractor at f/6 last November.

A quick evaluation of the NP-101 for use with the SBIG STL-11000

November 10, 2012 Leave a comment

I recently purchased an SBIG STL-11000, and my biggest concern was whether buying a camera with such a large sensor was going to require me to buy a new telescope to cover that sensor.  My main scope is a Televue NP-101 (the non-is version), which means I have to shoot through the 2″ focuser.  While I’d trade up to the NP101-is or even a Tak FSQ-106 at the right price, let’s face it:  those are very expensive upgrades.

Last night was first light with the new camera, and I’m posting this information to help others make a similar decision.  Two important caveats here:

  1. Focus was a little off.  I think I need to recalibrate FocusMax, and this was just meant to be a “first light” test of the camera. So compare the relative sharpness of the corners, not the overall sharpness.
  2. No polar alignment was done, so there is a little field rotation evident.

First is the question of whether the NP-101 can deliver sharp stars all the way out to the corners.  Let’s have a look at the full image first.

This is 18 10-minute exposures taken through a luminance filter, synthesized in DeepSkyStacker.  When I loaded up the files in Photoshop, it was impressive to see their scale:  4000 pixels across!  Now, let’s look at the corners:

This is sharp enough for me, especially with the field rotation evident.  I am really impressed with the edge performance of the NP-101.  At this point, I’m not seeing a need to upgrade to the FSQ or 101-is.

Second, we have to consider the light fall-off.  I braced myself for considerable vignetting.  Here is the master flat with levels on an 8-bit scale marked in green:

Again, to me this is acceptable performance, though less than ideal.  There is about a third reduction in light at the corners versus the center.  That’s a lot, but it’s not nearly as bad when you move just a little bit inward.  I figure with the usual cropping and overlapping of frames that happens, this won’t be much of an issue.  It’s almost the same levels of vignetting I’ve seen on the ST-8300’s chip when using this scope at f/4.3 via the reducer.  Careful processing there proved that the vignetting wasn’t a problem.

So what’s the verdict?  The NP-101 is perfectly acceptable for use with the STL-11000.  My guess is that the -is version with its larger focuser would perform better, but until I see a deal on one of those, I think I can happily image with this combination.  If anyone has similar information for the STL-11000 with either of the Televue -is scopes or the Tak FSQ scopes, please post a comment for comparison.

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