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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

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

IC 2177, The Seagull Nebula

April 16, 2012 Leave a comment

This is a narrowband image of the nebula IC 2177, known as the Seagull Nebula.  Frankly, I think it looks a lot more like a parrot, even a phoenix (which would be a more dramatic name), but it’s hard to deny that it looks like a bird of some kind. It’s just a terrifically photogenic deep-sky object.

Also going for it is the fact that it was discovered by an amateur, Isaac Roberts, who published what Wikipedia calls ” the first popular account of celestial photography of the deep sky” in 1893.  I was going to complain that it took me four nights to collect the data for this image, but I’m sure Mr. Roberts had it a lot tougher than me back in the day.

Click to enlarge

Image data:

Exposures:  28 x 600s Ha , 23 x 900s O-III, 17 x 900s S-II (14h 40m total), all binned 2×2

Software:  guiding by PHD, stacking in DeepSkyStacker, processing in Photoshop CS3

Telescope:  Borg 77EDII 330mm f/4.3

Camera:  SBIG ST-8300M with Baader standard narrowband filters

Mount:  CGEM

Taken March 17, 18, 19, and 22, 2012 from Whitehouse Station, NJ.

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