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Processing Skills: What Difference Does A Year Make?

Over the past year, my career path changed, and so did my budget for gear, so I stopped buying it. What might seem like a downside for my toys turned into an upside for my processing skills. Here’s what I learned in a year.

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Building an Observatory, Prologue

One of my dreams since I was a kid was to have my own observatory. Now with a family of my own, including two rambunctious boys who love to explore and build things, I’ve decided to pursue that dream and document it as we go along. This new blog series is all about the trials and triumphs of the entire process, unfiltered and unabridged.

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Explore Scientific ED127CF Triplet APO + 0.7x Reducer/Corrector

The Explore Scientific ED127CF Triplet APO is the first refractor telescope I have ever owned. With a native focal length of 952mm and 127mm (5 inches) of aperture (F/7.5), it lives somewhere between the “wide field” 80mm refractors and the longer SCTs used for planetary imaging, both in terms of field of view and imaging “speed”. When coupled with Explore Scientific’s 0.7x Reducer/Corrector, the ED127CF widens to an equivalent focal length of 666mm and faster focal ratio of F/5.25. Here are some star quality tests shot with this scope/reducer combo.

Corner/Edge Performance

The following 100%-crop mosaics were made using a Canon 6D and a Canon 60Da to show the differences in corner/edge performance between Full-Frame and APS-C sensor sizes. No filters were used as the 0.7x Reducer/Corrector does not provide any means of attaching filters (although some have made modifications to do so).

Figure 1: Single exposure taken with a Canon EOS 6D (unmodified), 180 seconds, ISO400. Several dozen exposures, including this one, were stacked to create the star field background in the 2017 Total Solar Eclipse photo in Figure 5 below. The eclipse itself was also shot on the same ES ED127CF + 0.7x Reducer/Corrector with the same EOS 6D body.

 

Figure 2: Single 4-minute exposure taken with a Canon EOS 60Da, 240 seconds, ISO800. Several dozen 4-minute exposures, including this one, were stacked to create the image of the Pleiades in Figure 6 below.

In both of these images, some color fringing is present in high-contrast areas, but the amount of Chromatic Aberration present is nothing that can’t be dealt with in post (see sample images below to see how it can still be removed after heavy processing). What’s great about both of these mosaics is that there is very little elongation of stars at the corners, both for APS-C and Full Frame sensors. Coma and astigmatism are both very well-controlled, all the way to the edges.

Vignetting

Below are two contoured images created from flats produced with both the Canon EOS 6D and EOS 60Da. This is where the similarities in performance for both sensor sizes end.

Figure 3: Vignetting profile for the Canon EOS 6D.

 

Figure 4: Vignetting profile for the Canon EOS 60Da.

As you can see, the vignetting on the EOS 6D is severe with less than 30% of the light coming in at the center reaching the corners. This can result in unwanted processing artifacts appearing in the corners of your images as soon as you calibrate your subs. On the other hand, vignetting on the EOS 60Da is almost non-existent with nearly 90% of the light present in the center still reaching the corners.

Thoughts

The Explore Scientific ED127CF is a great piece of hardware for the money, yielding fantastic images given the right sensor size. While it’s unfortunate that the vignetting ends up being so severe for the extreme corners of full-frame sensors, APS-C sensors fare much better. Even so, great images can still be made with full-frame sensors, given the right observing conditions. One of my favorite full-frame images captured with this setup is my shot of the 2017 Solar Eclipse, shown below. Barring another Solar Eclipse outing, however, I think I’ll stick to APS-C sensors on this particular combo.

Sample Images

Figure 5: 2017 Total Solar Eclipse, taken near Douglas, WY, with a Canon EOS 6D. Prints available.

 

Figure 6: The Pleiades, captured with a Canon EOS 60Da. Prints available.

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Hoya Intensifier (Red Enhancer)

Sodium vapor lamps, which are used in street lights, cause much of the light pollution produced by cities. These lamps emit yellowish light with a wavelength around 589nm. Didymium is particularly good at blocking this wavelength and finds its way into many light pollution filters, including the Hoya Intensifier (also known as the Hoya Red Enhancer). Here are a few test results showing what the Hoya Intensifier can do to help reduce the effect of light pollution in your astro images.

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Canon EF 35mm F/1.4L USM + Hoya Intensifier

The Canon EF 35mm F/1.4L USM lens (first generation) has been around since 1998, but is still highly acclaimed for its overall image quality despite its age. This lens was my first prime with L glass and is probably my most used. Here are some star quality tests I shot with it using a Canon EOS 6D body and a Hoya Intensifier to mitigate the effects of light pollution where I live.

Corner/Edge Performance

The following mosaics were made from 100% crops using light frames shot at ISO1600 from a red zone. Exposure times started at 4 seconds at F/1.4 and doubled with each successive aperture stop, all the way through F/5.6. A Hoya Intensifier LPS filter was used to reduce the effects of light pollution, as well as some very light curves work in post. Use the gallery below to cycle through light frames gathered at different apertures (click to view full-sized images). Coma and Chromatic Aberration remain strong at apertures wider than F/2.8, then all but disappears at F/2.8 and narrower. Some is still present in the extreme FF corners, but slight cropping of images is enough to get rid of it.

Vignetting

Vignetting is fairly strong wide open on a full-frame sensor, but improves dramatically by F/2.0 and is mostly gone by F/4.0. APS-C users will see great vignetting performance from F/2.0 and narrower.

Thoughts

There seems to be a sweet spot at F/2.8 for this lens, as far as astrophotography is concerned. Vignetting is well-controlled, as well as Comatic and Chromatic Aberration. It’s a great focal length for stitching wide landscape shots. It’s also possible to shoot deeper stacks with this lens, but you’ll need wide-open skies; plan to deal with gradients in post, as this lens covers a lot of sky!

Sample Images

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Canon EF 50mm F/1.8 II STM + Hoya Intensifier

Cheaper than many fully-manual budget lenses, the Canon EF 50mm F/1.8 II STM (and its variants) is fairly ubiquitous. Below are some evaluation images I shot using this lens on a Canon EOS 6D. A Hoya Intensifier filter was also used to help lessen the light pollution effects from the red zone I live in.

Corner/Edge Performance

The following mosaics were made from 100% crops using light frames shot on a Canon EOS 6D body (unmodified) at ISO1600 from a red zone. Exposure times started at 3.2 seconds at F/1.8, 4 seconds at F/2.0, and then doubled with each successive aperture stop after that. A Hoya Intensifier LPS filter was used to reduce the effects of light pollution. Use the gallery below to cycle through light frames gathered at different apertures (click to view full-sized images).

Vignetting

Full-frame users may be disappointed by the vignetting performance of this lens. Vignetting remains strong even through f/2.8 and doesn’t much better unil f/4.0. APS-C users will be much happier, with decent vignetting around f/2.0 and becoming very good by f/2.8.

 

Sample Images

Figure 1: Taurus and the Pleiades, Canon EOS 70D, 80x180sec stack, ISO1600, f/3.2, Prints Available. Read more about how this image was created here.

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Rokinon 85mm F/1.4 AS IF UMC + Hoya Intensifier

Falling well within the “budget lens” category is the Rokinon 85mm F/1.4 AS IF UMC lens ($299 new at the time of this writing). Below are some evaluation images I shot using this lens on a Canon EOS 6D. A Hoya Intensifier filter was also used to help lessen the light pollution effects of the red zone I live in.

Corner/Edge Performance

The following mosaics were made from 100% crops using light frames shot on a Canon EOS 6D body (unmodified) at ISO1600 from a red zone. Exposure times started at 2 seconds at F/1.4 and doubled with each successive aperture stop. A Hoya Intensifier LPS filter was used to reduce the effects of light pollution. Use the gallery below to cycle through light frames gathered at different apertures (click to view full-sized images).

The Rokinon 85mm F/1.4 AS IF USM lens exhibits reasonably good corner/edge performance at f/2.8 and above. Coma is still an issue at F/2.8 in the Full-Frame edges, and astigmatism is always present in the far Full-Frame corners. Chromatic aberration is pretty harsh until F/4.0 and mostly gone by F/5.6.  It’s probably best if this lens is stopped down to F/4.0, and perhaps better on an APS-C body.

Vignetting

Vignetting is very strong at F/1.4 but improves at F/2.0 and is much better at F/2.8 and higher. These images were shot using the same body and settings as the light frames above.

Sample Images

Figure 1: Deneb shines left of center in front of several emission nebulae, including Gamma Cygni, North American, and the Pelican Nebula. Unmodified Canon EOS 6D, ISO1600, F/4, 60x60sec calibrated stack. Prints available.

 

Figure 2: Orion and Monoceros region, Canon EOS 6D, ISO1600, f/2.8, 29x120sec calibrated stack. Prints available.