Visualize This! (Part Two of Three)

In Part One I said I had to previsualize the affects from five different elements in this scene of the International Space Station streaking over a waterfall during the full moon, and the cumulative effect from all of them. In this installment, let’s look at those elements in detail. In Part Three, we’ll look at how I processed the image in Photoshop. The five elements are:

International Space Station over waterfall

The International Space Station flies over a waterfall during the full moon

The path of the ISS with respect to the overall scene.
The position and exposure for the moon.
Exposure for the water.
Exposure for the stars.
Effect from the mist generated by the waterfall.

The first four are standard fare for visualizing a scene like this. The last one, the waterfall spray, not so much. It’s an issue here only because the waterfall is so large that it generates a lot of spray, which would have a pronounced effect  on how the moon looked when it was that low on the horizon. Let’s look at all five elements in detail.

First, the reason for shooting this scene was to capture the ISS in a landscape setting. I checked the visibility of the satellite on the Heavens Above website. This site is an incredibly useful resource for night photographers and you’ll be hearing me talk about it regularly. The ISS chart generated by the site tells you the magnitude (brightness), precise path, and exact time (to the second) for any location in the world. Of course, the ISS isn’t always visible everywhere, so you have to keep checking to see when it will be visible at your photo location. Also, you have to pay careful attention to the trajectory so you’ll know if the light streak generated by the station will work for your scene. For the magnitude, it’s best to have -2.5 or greater when you’re photographing the ISS. (The lower the value of magnitude, the brighter the object  appears.)

The ISS chart indicated that it would take nearly two and a half minutes for the station to cross the sky above the falls. With an exposure setting of f/4 and ISO 400, there is no way to capture the station in a single exposure without horribly overexposing the rest of the scene and making the moon appear as a wide white streak. Although I knew I’d be isolating the ISS streak and stacking it as a separate layer in the final image, I also knew that if the background sky was too bright it would make it very hard to select the light streak in Photoshop and cut it out of the sky. So as with nearly every image I shoot of the ISS, I shot this one in multiple frames. In this case, it took 18 individual 8-second exposures. With the shutter set to 8 seconds and the drive on continuous high, I locked down the cable release as soon as the ISS appeared and released it once the station had gone out of view. Image 2 shows one of the exposures. (No post processing performed.)

Image 2

Image 2

I already knew the compass position for the view from the top of the waterfall, so when the Heavens Above charts indicated that a bright view of the ISS coincided with the full moon, I had to go out and get the shot. However, after checking  the rise time and azimuth of the moon, I realized that when the ISS passed, the moon would be still mostly hidden behind the trees. I had already planned to shoot separate frames for the moon and waterfall, so this just told me that I’d have to wait a few minutes longer for the moon to rise above the trees. When that happened, I shot image 3 at f/4, ISO 400, 15 seconds. (No post processing performed.) Yes, the moon is totally blown out and yes, I wanted it that way. A “properly” exposed moon in a scene like this would look much more unnatural.

Properly exposing for the water was a critical concern. As with the moon, I knew I’d be shooting a separate exposure for the water and stacking it with the rest of the frames. I also knew that by waiting until the moon rose a little above the trees, the moonlight would illuminate the water. I do a lot of light painting on waterfalls with flashlights and colored gels, but whenever the full moon is out, that’s always the first choice for the lighting. After shooting Image 3, I took Image 4 for the water at f/4, ISO 400, 30 seconds. (No post processing performed.)

Image 3

Image 3

The 18 shots for the ISS and the two shots for the moon and water occurred over a period of about 30 minutes. During this time, the stars moved across the sky (relative to Earth) a fair amount. However, I wanted the stars to show as pinpoints of light, not streaks. I also wanted the sky to be properly exposed. To achieve this, I used the frame for the moon (Image 3) as the exposure for the sky and masked out the sky from all the other frames. More detail about this in Part Three.

The final piece of the puzzle is the waterfall spray. I knew beforehand that this waterfall produces a tremendous amount of spray in high water and that this might affect how the moon looked. I envisioned an ethereal moody effect, with the moon partially obscured behind the spray. As it turned out, the water level in the river was pretty low, so there wasn’t as much spray as hoped for, but it still helped to soften the moon and give it somewhat the effect I was after.

Image 3

Image 4

Okay, I’m fully aware that some of you are probably thinking that I’m making all this up, that I just muddled through the process as best as possible and then figured out what to say about it afterward. You know, the way some photographers write their artist statements: Create the photograph without much thought, and then come up with something artsy to say when they show it. I assure you, though, this is not the case. Remember what I said about previsualization in Part One. You have to do that to make images like this. Everything talked about in this post was rolling around in my head long before I hit the trail for the waterfall.

In Part Three I’ll walk you through the Post Processing techniques used for this image. Until then, previsualize something!  

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