That means that each millimeter is 118 pixels long. Half that height, 1,416 pixels, represents 12mm. I used a Sony A7S II, which has a vertical pixel height of 2,832 pixels. The dashes will vary by your camera's sensor resolution. Place a line from the zenith to the image circle's perimeter, anywhere, and then create dashes for measurement. Step 2: Use Pixel Counts to Create a Radius Line Snapping the end of a measuring line to the intersection ensure accurate zenith measurements. One-point lines (approximately five pixels) aligned to the image center help identify the exact center. These two givens, level image with a horizon around the perimeter and the image circle size, let us start to work on our calculations. We also need to know that the image circle is 24mm across on the film or your full-frame sensor. For the purposes of this article, this photo of a very-stern Abe Lincoln at the Lincoln Highway Memorial near Laramie, Wyoming, works. So, let's dive in: How do we do this? First, we need a photo taken with the lens pointed, level, directly at the sky. Let's imagine that we've discovered a meteor heading toward Earth and we want to track its progress. Cloud size could be measured for estimating the water volume they contain. Knowing the geometry behind this lens' scientific use opens a number of doors for interesting and creative projects. The orbits of planets could be plotted against the zenith to study their rotation around the sun. Tree canopies could be recorded from the same location to measure growth over months or years. Satellites could be recorded over a span of minutes for the same purpose. For instance, a comet could be tracked for many nights to calculate trajectory, speed, and direction. Nikon 8mm f/8 Fish-eye Nikkor: Scientific Useīut why? What use does the following process have? This process can be used to help measure object movement through space. These technical corrections make measurements with this lens possible. The Nikon 8mm from the early 1960s has exceptional correction to eliminate magnification shift over the image field and to provide exceptional radial symmetry from the lens' optical center, as the data we'll review show. Not all circular fisheyes can be used this way, and even those that can, the calculation tables provided by Nikon for this lens are specific to it. This article examines, in depth, how to use this lens for object measurement along radial lines emanating from the sky's zenith. This capability of this lens, specifically, means that the Nikon 8mm f/8 Fish-eye Nikkor has measurement capabilities for the placement of objects within the sky. 2X is one stop 6X is 2.5 stops.The video below shows how proper lens alignment allows the whole sky to be in frame with the horizon along the image's perimeter. Note that the EV compensation is a factor and needs to be converted to stops. Reproduced from data in the Nikon manual, this table also provides some added detail that I input from experience.
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