For a non-APO lens stacked with three teleconverter (1.4x + 2.0x + 75-300 lens + 1.7x), any lens defect will be taking a toll on the final image. This is what I found when I look at the image closely and studied the individual channels of red, green and blue light.
Original shot resized, looks alright in this low resolution version but trust me you will see blue halo if you looked closely.
So what went wrong with the blue channel? It is clearly out of focus and made of fuzzy blur stuff.
Two words..
Chromatic Aberration
Physics time here...
Well, we learn from optics that light bends when it goes between 2 materials of different refractive index. It turns out that the refractive index is different for different wavelength. Hence if you focus the red light, the blue will be out of focus. Now what you seen here in the moon are shot with manual focus. So I got the red light nailed but I totally lost the blue light in the focusing. Hence we get a fuzzy mess ball here instead.
Now for our everyday digital camera, 1/4 of the pixels are sensitive to blue, 1/4 to red and 1/2 to green (like our eyes are more sensitive to green than blue and red). The way this sensors are arranged to capture our image is in the form of a bayer pattern. So there is 3mp of red information, 3mp of blue information and 6mp of green stuff inside my camera.
So effectively, my 12 mp camera took only 9 mp of useful information. So after discarding the blue part away.. here's what I end up with (again with generous amount of sharpening applied)
Almost the same image but less the halo effect with a slightly sharper outlook as we don't have the blue part messing up the moon
0 comments:
Subscribe to:
Post Comments (Atom)
Posts
