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Posts Tagged ‘Nebula’

Review: Samyang 135 mm f/2 Astrograph

March 6, 2016 9 comments

IMG_2663

By calling the Samyang 135 mm f/2 lens an astrograph in the title, I’m giving away a bit of the conclusion, so let me just state the conclusions up front: I found this lens to be sharp from corner to corner with a reasonably flat field across a full-frame sensor. This is better performance than all but the best prime telephoto lenses, and also better than many telescopes I’ve owned claiming to be astrographs. Even more impressive is the fact that it accomplishes this at a focal ratio four to eight times faster than “fast” refractors. Finally, it’s hard to beat the price: currently just over $500.

While the performance was adequate at f/2, I found that stopping down the lens one full stop to f/2.8 improved sharpness. This is true of any lens, and even stopped to f/2.8, that’s still four times the light gathered per sensor area than an f/5.6 telescope. It’s easy to forget how fast this is, but my first night using the lens reminded me. My usual telescopes are two f/5 William Optics Star 71s and a Takahashi FSQ-106ED, also f/5. I usually shoot narrowband exposures of 20 minutes with these. So the combination of broadband and f/2.8 put me in the realm of 30 to 120 second exposures—anything longer at ISO 800 overexposed the stars.

The infinity focus point is about 2 mm left of the mark on the lens barrel, so you’ll have to carefully dial in focus. There isn’t much tolerance for error at such fast focal ratios, as the zone of focus is very narrow.

Vignetting is substantial in the corners, but it is more reasonable if you move slightly inward.  For very fast optics, this is typical, though it does lead to lower SNR toward the corners. I was able to keep the full frame images without cropping by using good flat frames, but this is essential.

Master Flat created from 33 pictures (Average)

Master Flat created from 33 pictures (Average)

The quick 99×1 minute image below of the Rosette Nebula area gives you a sense of how wide the view is with a Canon 6D. In the center is the Christmas Tree/Foxfur/Cone Nebula area, with huge dark nebula Barnard 37 prominent. This was taken without a CLS filter, so light pollution prevented me from adequately revealing the Foxfur nebula well. The Rosette Nebula shines brightly to the left, though. (Note that this image is reduced to 25% of the actual image resolution.)

Samyang 135 Rosette_widefield 25 percent size

As you can see from the full resolution close-ups below, the lens is impressively sharp across the Canon 6D’s entire field of view, with very minimal distortion even in the extreme corners.

Samyang 135 corner performance

The 9-blade diaphragm of the Samyang results in a pleasing radiant around bright stars, but the lens does exhibit some internal reflections.

Samyang 135 reflection

I look forward to using this lens as my (very) widefield astrograph. Depending on your sensor size, the ideal targets for this lens will vary, but I’m looking forward to shooting:

  • The Orion Molecular Cloud Complex
  • IC2177 and Thor’s Helmet area
  • The California Nebula to Pleiades area
  • Orion’s Head/ Meissa Nebula
  • Heart and Soul Nebulae area
  • The Rho Ophiuchi area
  • Cygnus
  • The IC405/IC410 area
  • Taurus Molecular Cloud
  • The Milky Way’s Pipe nebula region
  • Sagittarius

After complex mosaics and multi-night narrowband CCD projects, it’s a joy to throw a simple setup like this onto the mount to grab bright widefield images in a few hours.

Pros:

  • Fast focal ratio
  • Sharpness
  • Flatness of field
  • Price (currently ~$529 USD)

Cons:

  • Some internal reflections
  • Limited targets available for this focal length
  • Will require adapter to fit CCD cameras
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The Pleiades (M45)

January 10, 2016 Leave a comment

Somehow, I’ve never really captured an image of The Pleiades (M45). Such a bright target directly overhead, but I was mostly looking for narrowband objects instead, I suppose.

Pleiades final 8x10 crop

This image was processed entirely in PixInsight, except for the final rescaling and jpeg conversion.  I’m moving more in that direction. Frustrating and unforgiving it is, but powerful.  For such a bright object, the dust makes it more challenging to process than I’d expected.

Image data:

  • Exposures: 20×10 min L (1×1 binning), 8×10 min each R, G, B (2×2 binning) – total exposure time:  7h 20m
  • Telescopes: Two William Optics Star71s (360mm f/5)
  • Cameras: SBIG ST-8300M and QSI 583wsg
  • Mount: Takahashi EM200
  • Guiding: QHY 5L-II mono, guided using PHD2
  • Conditions:  fair transparency, calm winds
  • Processing: DeepSkyStacker -> PixInsight
  • Date: Jan 2, 2016

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.

The Heart Nebula, IC1805, in Narrowband

January 27, 2015 Leave a comment

This is one of my favorite deep sky objects, especially for narrowband.  It just fits on an KAF-8300 chip at 350 mm focal length.  The small cluster in the core is Melotte 15.

I took three nights of exposures, which were spread over 41 days due to poor weather and holiday trips.  Maybe next year when Cassiopeia swings into view, I’ll make a similar project of the Soul Nebula nearby.

The Heart Nebula (IC1805)

The Heart Nebula (IC1805)

Image data:

  • Exposures: 32 hours total: 96 x 10 min Ha, 43 x 10 min OIII, 53 x 10 min SII
  • Telescopes: Two William Optics Star 71s (360mm f/5)
  • Cameras: SBIG ST-8300M and QSI 583wsg, 2×2 binned
  • Mount: CGEM
  • Guiding: QHY 5L-II mono, guided using PHD2
  • Conditions:  mild winds on two nights
  • Processing: DeepSkyStacker -> PixInsight -> Photoshop
  • Date: Nov 21 2014, Dec 31 2014, and Jan 1 2015

The Cone Nebula/Fox Fur Nebula/NGC2264 Area

January 24, 2015 Leave a comment

Between snow storms, I’ve been able to squeeze in the occasional night of imaging.  It was a less than ideal night–poor seeing and all sorts of polar alignment issues plagued me–but I’m please to finally have an image of the Cone Nebula… or Fox Fur Nebula if you prefer…or Christmas Tree Cluster.  Whatever you call it, putting NGC2264 (the cluster) into your goto mount will get you there.

Somehow, I’ve never captured this one before.  That region of the sky has so many highlights (M42, IC2177, The Rosette, Horsehead…) it takes several years to get to them all.

Cone Nebula Widefield in H-alpha

Cone Nebula Widefield in H-alpha

Image data:

  • Exposures: 39 x 10 min H-alpha exposures
  • Telescopes: William Optics Star 71 (360mm f/5)
  • Cameras: SBIG ST-8300M, 2×2 binned
  • Mount: CGEM
  • Guiding: QHY 5L-II mono, guided using PHD2
  • Conditions:  calm, but damp
  • Processing: DeepSkyStacker -> PixInsight -> Photoshop
  • Date: Jan 22, 2015

The Bubble and the Lobster Claw

January 10, 2015 Leave a comment

There is an area on the border of Cassiopeia and Cephus that’s packed with deep-sky objects, including the assortment shown here.  The main nebula here is the Lobster Claw, Sh2-157.  Above it and to the right is the famous Bubble Nebula, NGC7635. In the upper right is the cluster M52.  The nebulae at middle right and lower right are Sh2-159 and NGC7538, respectively.  The very dim nebula the goes off the right edge of the image is Sh2-161, and the little star cluster at middle bottom is NGC7510. So that’s at least five distinct nebulae and two star clusters (there would be more if we considered how other catalogs, like the LBN and IC, define the objects).

The Bubble and Lobster Claw NebulaeWith all of that said, this is the second year I’ve imaged this area, and I haven’t been happy with either result.  The Lobster Claw is not particularly photogenic, and it’s fairly hard to process well.  Given the chance to do it again, I’d probably either use a longer scope to focus on the Bubble Nebula alone, or go even wider with a telephoto to capture the sea of nebulosity in the whole area.

Image data:

  • Exposures: 60 x 10 min Ha, 33 x 10 min OIII, 27 x 10 min SII
  • Telescopes: Two William Optics Star 71s (360mm f/5)
  • Cameras: SBIG ST-8300M and QSI 583wsg, 2×2 binned
  • Mount: CGEM
  • Guiding: QHY 5L-II mono, guided using PHD2
  • Conditions:  strong wind gusts
  • Processing: DeepSkyStacker -> PixInsight -> Photoshop
  • Date: Nov 18 and 20, 2014

The Cave Nebula (Sh2-155)

November 22, 2014 Leave a comment

The Cave Nebula is probably better suited for 600 mm of focal length, but I thought I’d try a wide field view of the area.  The whole nebula is fainter than I expected, especially the diffuse OIII spread about the region.  20- or 30-minute sub-exposures would do a much better job of revealing it, but because it was so windy, I wanted to keep the subs at 10 minutes, so I really had to fight a lot of noise in the blue channel.

The Cave Nebula (Sh2-155) in narrowband SHO palette

The Cave Nebula (Sh2-155) in narrowband SHO palette

Image data:

  • Exposures: 55 x 10 min Ha, 28 x 10 min OIII, 28 x 10 min SII
  • Telescopes: Two William Optics Star 71s (360mm f/5)
  • Cameras: SBIG ST-8300M and QSI 583wsg, 2×2 binned
  • Mount: CGEM
  • Guiding: QHY 5L-II mono, guided using PHD2
  • Conditions:  gusting winds
  • Processing: DeepSkyStacker -> PixInsight -> Photoshop
  • Date: Nov 9-10, 2014
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