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October 27, 2014 Auroras
Peterson Road Bog, Grand Rapids, MN
As opposed to the previous night, solar wind conditions did appear to be somewhat enhanced with speeds between 400 and 450 km/s, density around 5/cc, and Bz varying between -3 nT and -5 nT.
Milky Way, black spruce, and auroras shot with the Sony a7s at ISO 1600, 24 mm, f1.4, 15s.
Canon 5d Mk III and Sony a7s Comparison (Second Night)
My main purpose of shooting this evening was to do a comparison between the Sony a7s (which I rented) and the Canon 5d Mk III (which I own). I was mainly interested in comparing the sensitivity of the sensors, primarily with regard to how quickly the images degraded as the ISO was increased. I was mainly interested in the noise as opposed to any crispness, brightness, or color saturation. Upon seeing the results of the last test, I decided to repeat it. Because I wanted to take the images simultaneously, and I don't have identical lenses to put on the cameras, I could not do a test that isolated the effect of the sensor on the resulting images. Thus, I swapped the lenses tonight, and this time, the Canon 5d Mk III had a Canon 24mm f1.4 lens, and the Sony a7s had the Samyang f1.4 24mm lens. Each of these lenses has its strengths and weaknesses, and it's possible I achieved a better focus with one than with the other. I wanted to see if the lenses affected the results, and I also wanted to try focusing again. Generally, I have noted that the images with the Canon lens are a little sharper than with the Samyang, but the Canon lens definitely has more coma effect around the edges of the picture. This time, in order to minimize the effect of coma and differences in lens coatings, I shot at f2.8 rather than f1.4.
The first round of tests is a simple side-by-side comparison of resized full images. I took the shot from each camera (at the same time), then brought the images into Adobe Camera Raw, and changed the white balance to a color temperature of 4400 K and a tint of +5. All other settings I left untouched and saved the images at 1200x800 pixels.
In the series of images below (at 1200x800 resolution), you'll notice that the noise difference is not dramatic until you get to ISO 51,200. At that ISO, the Canon 5d Mk III is outside its native range, and you must set the ISO to the extended range to go higher. At lower ISO, you can see a slight advantage to the Sony a7s, but it's not terribly dramatic. As a Canon 5d Mk III owner, I feared it might be much worse, but it wasn't.
What the Sony a7s might have done a little better, however, is pick up the vegetation on the trail in the foreground (lowest 1/4 of the image). In the first round of tests, the Canon pictures were a little darker than the Sony pictures, but this time, I did not see such a difference. In fact, the Sony pictures were probably a little darker this time, so I think the lens made the primary difference in luminance. I left the exposures unchanged so that you can simply see any difference in luminance.
Auroras shot with the Canon 5d Mk III at ISO 800, 20 secs (f1.4 on this image, the rest are f2.8).
Auroras shot with the Sony a7s at ISO 800, 20 secs (f1.4 on this image, the rest are f2.8).
Auroras shot with the Canon 5d Mk III at ISO 1600, 30 secs.
Auroras shot with the Sony a7s at ISO 1600, 30 secs.
Auroras shot with the Canon 5d Mk III at ISO 3200, 15 secs.
Auroras shot with the Sony a7s at ISO 3200, 15 secs.
Auroras shot with the Canon 5d Mk III at ISO 6400, 8 secs.
Auroras shot with the Sony a7s at ISO 6400, 8 secs.
Auroras shot with the Canon 5d Mk III at ISO 12,800, 4 secs.
Auroras shot with the Sony a7s at ISO 12,800, 4 secs.
Auroras shot with the Canon 5d Mk III at ISO 25,600, 2 secs.
Auroras shot with the Sony a7s at ISO 25,600, 2 secs.
Auroras shot with the Canon 5d Mk III at ISO 51,200 1 sec.
Auroras shot with the Sony a7s at ISO 51,200, 1 sec.
Auroras shot with the Canon 5d Mk III at ISO 102,400, 0.5 sec.
Auroras shot with the Sony a7s at ISO 102,400, 0.5 sec.
Sony a7s at ISO 204,800, 1/4 sec.
Sony a7s at ISO 405,600, 1/8 sec.
Full Resolution Comparison (Cropped)
On this next set of tests, I took the same raw images above and cropped to the same part of the scene at 100 percent native resolution, and I saved them at 862x575 pixels for the a7s. Since the a7s is a 12 MP camera, and the 5d Mk III is a 23 MP camera, the 5d Mk III produces larger, higher resolution images (1170x780 px here). However, I left the difference as is. With a larger number of megapixels, you can make a larger print. Note: the images are still not full size on this page. You'll have to click on each image to get its full resolution.
I did not have a shutter release cable for the a7s, so I had to hit the button manually. On the previous test, the force required to activate the shutter on the a7s, as well as how firmly I had the tripod set up, caused the camera to move a bit, but that did not seem to affect this test. Additionally, I had different 24 mm lenses on the cameras. Last time, I had noticed a difference in image sharpness, but I refocused this time, and it appears that was a result of me not having focused the Samyang lens well enough so I don't think any sharpness differences (other than MP resolution) were due to the sensor. On the Sony, I had the Samyang 24 mm f1.4 lens, which has a lens coating that reduces coma around the periphery of the shot, but it is not as sharp in the middle as the Canon lens (see the first pair of images below). For all images other than the first, I used f2.8 aperture setting here, so the lens sharpness and coma differences are reduced from what they were on the previous test. I took the cuts from near the center of the image. As far as focusing is concerned, one of the advantage of the a7s is that the sensitivity is so high and the viewfinder so bright that it's easier to focus on stars than it is with the Canon. The downside of the bright LCD and live view on the Sony, however, is that it is very bright for aurora shooting. It almost blinds you like the headlights of an oncoming car if your eyes are adjusted to a moonless night.
One difference that I had really noticed on the previous test was that I had to add +0.5 EV to the Canon images to get the same luminance as the Sony images, but this time, it's the Canon images that were brighter, so there may be a difference between the Canon and Samyang 24mm f1.4 lenses. Having now done the test with the lenses swapped, I can't think of any other reason for the differences in the luminance.
Auroras shot with the Canon 5d Mk III at ISO 800 (f1.4 on this image, the rest are f2.8).
Auroras shot with the Sony a7s at ISO 800 (f1.4 on this image, the rest are f2.8).
Canon 5d Mk III at ISO 1600.
Sony a7s at ISO 1600.
Canon 5d Mk III at ISO 3200.
Sony a7s at ISO 3200.
Canon 5d Mk III at ISO 6400.
Sony a7s at ISO 6400.
Canon 5d Mk III at ISO 12,800.
Sony a7s at ISO 12,800.
Canon 5d Mk III at ISO 25,600.
Sony a7s at ISO 25,600.
Canon 5d Mk III at ISO 51,200.
Sony a7s at ISO 51,200.
Canon 5d Mk III at ISO 102,400.
Sony a7s at ISO 102,400.
Sony a7s at ISO 204,800.
Sony a7s at ISO 405,600.
Full/Matched Resolution Comparison (Cropped and Matched)
On of my main questions with a test like this is, "What if I just stayed with the Canon and downscaled the images to 12MP? Would the noise become equivalent to the a7s?" On the final pairings below, I simply repeated the ones above but with the Canon images resized to the equivalent resolution of a 12 MP image, so that both the Sony and Canon images are 862x575.
On the previous test, I added +0.5 EV of exposure to the Canon images to try to make them match as closely as possible, but it was clear here this time that the canon images are brighter. The Sony images had a slightly different color balance, even though I tried to set both images to the same color temperature and tint.
Auroras shot with the Canon 5d Mk III at ISO 800 (f1.4 on this image, the rest are f2.8).
Auroras shot with the Sony a7s at ISO 800 (f1.4 on this image, the rest are f2.8).
