Also in this series: Canon 300mm f/2.8 vs 400mm f/2.8
Continuing from: Review: Canon 300mm f/2.8 vs 400mm f/2.8 – Part 2
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.
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).
I 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.
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.