Naked eye view

We have all been told many times: “it is impossible to render with images what eclipse really look like”.

The two main reasons are because of the limited brightness of monitors and because of their number of shades limited to 8 bits. But those two reasons can be somehow worked around:

• the limited brightness range of the monitor can be overcome by putting oneself in a dark environment, with monitor brightness set at maximum value.
• the limited number of bits of display, which creates “steps” in a continuous gradation of the solar corona, can be overcome with the addition of an appropriate noise distribution to render the appearance of a continuous, smooth shading.

Top: a continuous light variation, from black to white, rendered with a finite number of tones shows steps (16 levels here, 256 levels on 8 bits monitors) . Bottom: with the addition of an appropriate noise distribution, it is possible to create the impression of a continuous light variation distribution while only using the same 16 levels as on top.

In order to recreate the naked eye view of the eclipse, I used this strategy on the HDR composites of the eclipse I created, without adding any enhancement of the coronal structures. I just used a simple curve modification on the raw HDR to slightly boost the darkest shades. And I find that the resulting image, when looked in a dark environment, render pretty accurately what I could see with my naked eye.

Here is a nice blog review of my work to recreate the visual appearance of the eclipse.

Visual appearance of the eclipse with the naked eye

I used the composite image created with my large FOV setup to render the naked eye visual appearance of the eclipse. The result is surprisingly close to what i could see: the silvery “Y” of the coronal streamers, on the blue sky background, with the bright ring of light of the inner corona around the “black sun”.

It is interesting to see that the image renders well this “black sun” illusion, while when looking at the actual pixel values, the moon surface was definitely brighter than the sky background.

Visual appearance of the 2017 Eclipse. In order to render the visual appearance of the eclipse, download the image here, open it in full screen on your computer, adjust your monitor brightness at max value and place yourself in a dark environment, at the right distance from the screen. In those condition, the results are really close to what could be seen visually. You can try to spot Regulus and Mars in the image. 

The “black sun” illusion is well rendered while the lunar surface is actually brighter than the sky background.

Visual appearance of the eclipse with a scope

While the unaided eye appearance of the eclipse is supposed to similar for everyone with good eyesight, the visual appearance of the eclipse with a telescope depends on several parameters like the magnification, and the exit pupil diameter.

For instance, I observed the eclipse with a 65mm diameter spotting scope, equipped with a zoom eyepiece that could provide magnification from 16x (4mm exit pupil) to 48x (1.3mm exit pupil). And the view of the eclipsed sun was highly dependent on the magnification. At 16x, the corona was very large, with streamers being visible at more than 3 solar radii. At this magnification, I did not notice the prominences that were hidden by the general glare of the corona. On the other hand, at 48x, the prominences were the most eye catching feature because if their brightness and color. The inner corona was still well visible but the outer corona wasn’t.

It is thus impossible to render with a single image what the view through the scope was like. I used the HDR composite of my high resolution setup to generate those images. The processing only consisted in a slight curve adjustment, without any structure enhancement. It is thus very representative of the actual contrasts of the coronal features as they actually appeared visually through the scope.

Visual appearance of the 2017 Eclipse through a 65mm scope. In order to render the visual appearance of the eclipse, download the images (1, 2, 3), open them in full screen on your computer, adjust your monitor brightness at max value and place yourself in a dark environment.