Celestron Advanced GT

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Astrophotography: Constellation Cygnus the Swan

Posted by Snob on June 15, 2016
Posted in: Astrophotography, Nature. Tagged: , , , , , , , , , , , . Leave a comment
2016_Astrophotography_ConstellationCygnus

Constellation Cygnus the Swan – Canon 5DsR + EF 24-70mm f/2.8L II @70mm

I have tried my hand at many a genre of photography but none have humbled me the way astrophotography has. A few weekends ago I happened to be free the same time we had a New Moon. This meant that I could actually have a care-free 24 hours to pack up all my gear and run away somewhere with less light pollution than my backyard. I opted for my good friend Ethan’s place in Auburn. An amazing artist himself, it was refreshing just to catch up with him. Another friend Jeremy came out at the last minute. He’d always wanted to explore Astrophotography so I figured this would be a good opportunity to share what I’ve learned so far.

I stuffed my car full of everything I could think of – my entire telescope and mount setup (read more about that here) as well as my entire photography kit – and headed up the Auburn Hills to Grass Valley. I figured if it turned out to be a good showing, I wanted to be prepared. It was mostly cloudy but the forecast said it should clear up by 10pm, right when the sunset really ends, so I took my chance. Unfortunately the clouds and haze lingered all night especially in the Northern sky where it was darkest. The light pollution from the Sacramento valley was also much worse than anticipated. Combined with the haze it overpowered all but a few of the brightest stars.

Finally around midnight the North Eastern quadrant of the sky cleared up. Due to the weather conditions I was only able to perform a very loose polar alignment as well as a poor 2-star alignment of the Celestron Advanced GT German Equatorial (GE) Mount. This resulted in poor tracking. However poor tracking on a GE mount is always better than a simple tripod. To compensate for this I chose to use the Canon 5D Mark III for its excellent high ISO low noise capabilities. I mounted it (piggy-back) on the telescope and aimed at the clear part of the sky – the Constellation Cygnus. After just a handful of shots I realized that even with the poor alignment, I was still able to do 3 minute (180 second) exposures at ISO-400 without the stars trailing. I knew this was well within the capabilities of the higher pixel density sensor cameras such as the 7D Mark II or even better, the 5DsR. Both just happened to be laying idle in my bag.

I had never tried the 5DsR at astrophotography and very much wanted to see how it performed. I liked how the 7D Mark II did and knew the 5DsR would at least match or exceed it since they have very similar pixel densities. Accounting for about 1 stop exposure difference from the 5D Mark III, I bumped the ISO to 800. Exposure stayed the same at 3 minutes. I was also shooting with the Canon EF 24-70mm f/2.8L II which I recently added to my kit. I knew it was tack sharp and would be able to keep up with the 50 megapixel body. Nothing prepared me for what I saw. I only took 4 shots and decided it was good enough.

What you are looking at above is a single 3 minute exposure. Processed from a RAW file with no noise reduction, some color temperature and curve adjustments and a final light mask to help reduce the atmospheric haze. Nothing fancy not even lens correction (you can see some vignetting). The shot has bee downsized to about 1/12th it’s original size. At 70mm the detail is astounding. The light “clouds” are easily revealed to be individual stars. Mind-boggling scale and detail. It’s one thing to see images from the Hubble telescope, but an entirely different experience to see it for yourself.

I’m not sure what took me so long, but it’s safe to say I will be spending several sleepless nights shooting the stars out in the middle of nowhere this summer.

Review: Canon 300mm f/2.8 vs 400mm f/2.8 – Part 3

Posted by Snob on May 1, 2015
Posted in: Astrophotography, Canon 7D Mark II, Nature, Reviews. Tagged: , , , , , , , , , , , , . 3 Comments

Astrophotography

Also in this series: Canon 300mm f/2.8 vs 400mm f/2.8

Part 1 – Landscape Photography
Part 2 – Fashion and Portrait Photography
Part 3 – Astrophotography

Continuing from: Review: Canon 300mm f/2.8 vs 400mm f/2.8 – Part 2

Canon 7D Mark II + Canon EF 400mm f/2.8L IS II USM
Tracking M42 on Celestron Advanced GT mount

The last step in my evaluation of each lens was to see if I could successfully photograph a DSO (Deep Sky Object) from my backyard. The urban location presented some major challenges in the form of light pollution, smog and haze. This meant that I had a very limited window of opportunity. There simply weren’t that many clear winter nights with great visibility. Wind conditions also posed a major challenge to keeping the camera system steady during extended exposures.

After putting each lens through it’s paces and getting nothing but absolute uncompromising perfection from both lenses, I was beginning to see a stale mate. The whole purpose of this exercise was to determine which of these lenses I should consider adding to my kit down the road. Up until this point it was looking like I may be stuck with the idea that I have to own both. An investment I may very well not be able to justify.

Astrophotography is a highly technical/scientific endeavor that requires you to push every single piece of equipment to it’s maximum regardless of compromises. It turns most conventional wisdom in photography on it’s head. The result is a genre of photography who’s prime objective is to first highlight all the flaws in your camera system so that you can quickly and effectively apply yourself to the challenges of working around or compensating for those flaws with the goal of generating as clear a picture as possible of celestial bodies and DSOs.

I chose the Orion Nebula (also known as Messier 42, M42, or NGC 1976) as my test subject because it is readily visible in the winter night sky with the naked eye. You can see its very faint glow in the second photo of the night sky above.

The EF 400mm f/2.8L IS II USM
In each of my tests, this lens’ performance wide open at f/2.8 is perhaps the most important property I observed with the highest level of scrutiny. My reasoning was if this is the the single biggest differentiating feature of this lens, it should and must be able to deliver on every expectation, because Canon does make several alternatives to this lens at smaller apertures and they all deliver impressive results for orders of magnitude less in cost.

The EF 400mm f/2.8L IS II USM failed my astrophotography test. Why? Because my first shot of the Orion Nebula wide open at f/2.8 showed some really serious coma optical aberration, even in the center of the frame as shown in the composite below. I had to stop the aperture down to f/8 in order get a respectable image. This obviously severely restricted the lens’ light gathering ability and at f/8, I would sooner use any of the other 400mm f/4 or f/5.6 alternatives that don’t have this aberration. This also means that any attempt to photograph cityscapes and night scenes after dusk will quickly go sour. You can’t just filter or process coma out of your shots.

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Orion Nebula – Canon 7D Mark II + Canon EF 400mm f/2.8L IS II USM

As you can tell, in order to shoot at the coma reducing f/8 aperture, I had to extend my exposure, but as I extended the individual exposure, I had to drop my ISO in order to keep the noise from overwhelming the image detail. A drop in ISO meant yet another increase in exposure. This feedback loop finally settled at 15 seconds and ISO-400. At this stage there would not be enough observation time to get enough frames for a proper stacking. I only had a few hours of clear winter sky during the entire evaluation period so I settled for a quick and dirty 15 frame stack with DeepSky Stacker (DSS).

2015_400mm_5I should also mention that because of the forbiddingly long exposures needed when using this lens coupled with it’s narrow field of view, a properly aligned computerized tracking mount is all but required. In this case, I used a Celestron Advanced GT German Equatorial Mount. I had to fabricate a custom mounting bracket adapter for the mount. If you have ever tried to observe celestial bodies, you must know how fast they are moving across the sky. On this particular night I happened to get a proper polar alignment and good tracking. I kept thinking if this lens was flawless wide open at f/2.8, imagine how much more light and detail I could collect over a 15 second exposure at ISO-100. If Canon can fix the coma aberration in this lens, it would be hands down, unequivocally, the absolute best, most amazing lens ever made.

Despite the coma, the sharpness and clarity is impressive. I was able to make out four stars at the center of the nebula as well as other gas cloud details. Images should be even more spectacular with a 100+ light frame stack in DSS, however once again the coma should also become more apparent the more you stack. This was the least expected deal breaker for The EF 400mm f/2.8L IS II USM. I expected it to trample any challenge I could possibly come up with in this category.

The EF 300mm f/2.8L IS II USM
This lens was up against greater odds in this category. There were no clear skies that week except for the night after my Photo shoot with Charis. Upon my return I decided to stop for a little wine with a friend. I immediately noticed the skies had cleared up for a brief moment at which point I decided to get a few very quick and casual shots for evaluation later. My very first shot hand held led me immediately to my conclusion. I was able to get a clear shot of the Orion Nebula hand held, at f/2.8 with no coma and no discernible chromatic aberration. Unlike the EF 400mm f/2.8L IS II USM, I did not have my German Equatorial tracking mount with me.

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Orion Nebula – Canon 7D Mark II + Canon EF 300mm f/2.8L IS II USM

While the above composite may not seem as good as that from the EF 400mm f/2.8L IS II USM, the devil is in the details. I did not have the benefit of a tracking mount. I had much less time to acquire my frames than I did with the EF 400mm f/2.8L IS II USM. I could shoot wide open at f/2.8 aperture, ensuring that after traveling 1,344 light years, as few photons as possible were wasted. I look forward to making more detailed observations with the EF 300mm f/2.8L IS II USM mounted to a tracking mount and at a more ideal location for star gazing.

It is at this point where I realized the EF 300mm f/2.8L IS II USM was in fact the better lens of the two. It was not only more versatile as a result of its more manageable size and weight but its optics were the most true of both lenses. It obviously does not hurt that it costs almost half the price of the EF 400mm f/2.8L IS II USM. This outcome was most unexpected, and I have since gone back several times to double check and question my results.