Distortion Correction for Samyang 8mm, f/2.8 Fisheye Lens

Started Oct 14, 2012 | Discussions thread
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RustierOne
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Distortion Correction for Samyang 8mm, f/2.8 Fisheye Lens
Oct 14, 2012

Hi All,

I thought I'd post some images showing distortion correction applied to the new Samyang 8mm, f/2.8 fisheye lens.

First is a 4 X 15 crop from a 4 X 6 original (similar to the second image below). I'm sorry the image is 180° flipped from the others.

Samyang 8mm, f/2.8, NEX-5N, ISO 1600, ~2-1/2 minute exposure w/ tracking, no distortion correction

The Samyang lens is noted for having much lower distortion (compared to many other fisheye lenses) by its use of a patented stereographic projection (versus equal-area projection used by many other lenses of this type). Still it does benefit from distortion correction. The following pair of images shows the effect of using Fisheye Hemi, a $30 US plug-in for Photoshop.

Samyang 8mm, f/2.8, NEX-5N, ISO 1600, ~2-1/2 minute exposure w/ tracking, no distortion correction

I assumed the trails (satellite or airplanes) should be straight. That assumption may not be valid, but for purposes of demonstrating the plug-in, its what I used. The program has 3 filters (called Hemi-1, -2 & -3 of decreasing power) that fit many common camera configurations. It has the ability to custom process to adjust power of the correction to be between any 2 of the standard corrections. I just adjusted the correction to be between Hemi-1 and -2 to achieve the nearly straight line trails as shown on the following image.

Samyang 8mm, f/2.8, NEX-5N, ISO 1600, ~2-1/2 minute exposure w/ tracking, Fisheye-Hemi applied

You can see how the plug-in was able to correct much of the distortion in the trails. Its also clear that some of the image has been cropped away. This plug-in may be of limited utility for astro-photography. So I'll show how it works with a daytime scene.

Samyang 8mm, f/2.8, NEX-5N

Notice the distortion in the outer part of this image. The following shot shows the effect of using Fisheye Hemi.

Samyang 8mm f/2.8, NEX-5N

Again some of the image has been cropped away, but distortion is well-controlled.The driveway edges are not as distorted as they look since the drive is steeper in the foreground and of gentler grade near the garage. As with the corrected Milky Way image, features in the middle of the frame are reduced in size compared to the uncorrected image. Notice the size of the garage above. The original image is 180° from corner to corner. So I estimate that the corrected image is around 140° side to side. For that width of coverage, the distortion is quite acceptable. I have not investigated if the plug-in has affected image resolution. But a close examination of the star images should reveal if there is much degradation.

Best Regards,
Russ

 RustierOne's gear list:RustierOne's gear list
Sony Alpha NEX-5N Sony Alpha NEX-7 Sony E 18-55mm F3.5-5.6 OSS Sigma 19mm F2.8 EX DN Samyang 8mm F2.8 UMC Fisheye +3 more
Sony Alpha NEX-5N
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