What’s the Longest Usable Shutter Speed for Astro-landscape? (Part II)

In Part I of this article I wrote about the subtleties of managing different variables to determine the best exposure for maintaining star points in astro-landscape photographs. We learned that determining the longest usable shutter speed based on sensor size, focal length and cardinal direction was the starting point for all astro-landscape photograph images.

Additionally, considerations for depth of field and image quality needed to be taken into account. When an image contains a nearby foreground element, a smaller aperture is required to increase depth of field. When an image will be printed to a high degree of magnification, the ISO must be kept as low as possible to maintain image quality. Either choosing a small aperture or a low ISO will require a longer shutter speed, increasing the probability of the stars being rendered as trails or lines in the sky. This is something we try to avoid as much as possible, so finding just the right compromise of these three exposure variables is key to successful astro-landscape photographs.

Under the Milky Way. 20 seconds, f/2.8, ISO. 20mm lens.

400 vs. 500

In Part I of this article, the concept of the 500 Rule was briefly mentioned without explanation. In this second part, I will explain what it is and how to use it.

An internet search of the 500 Rule turns up a lot of information, much of it contradictory. I have been unable to find a clear answer as to when, how or by whom it was created. It is a fairly crude tool to help with determining the longest usable shutter speed for star points. Simply stated, if you divide 500 by the focal length of your lens, the result is the maximum number of seconds you can expose without star trails with a full-frame DSLR camera. The 500 Rule does not take print size or camera orientation into account, nor does it accommodate APS-C or smaller sensors.

If you delve into those search results, you’ll find a variety of highly technical alternatives and variations to the 500 Rule. If you are as much into mathematics as photography, check out TL-Photography or Greg Boratyn’s sites. My goal is to keep things simple and convenient.

“The 400 Rule results in shorter shutter speeds, and greater likeliness of sharp stars.”

The 500 Rule often yields unsatisfactory results. This is in part due to modern cameras having higher resolution than those available when the rule was first used, and in part because it doesn’t account for camera orientation or the possibility of large-format prints. Therefore, instead of the 500 Rule, I propose using the 400 Rule (divide 400 by the focal length of your lens to reveal the maximum number of seconds before star trails begin to appear). The 400 Rule results in shorter shutter speeds, and greater likeliness of sharp stars.

For APS-C cameras, the 250 Rule yields approximately equivalent results. Another way to determine shutter speeds for APS-C cameras is to use the 400 Rule and then divide the result by the crop factor, which is 1.5 for Nikon and Sony cameras, and 1.6 for Canon cameras. Since our goal is to keep things simple, I suggest using the 250 Rule, which yields almost identical results.

Below you can see the results of test photos shot with a 24mm lens on a full-frame camera, shot at shutter speeds ranging from 8 seconds (very sharp stars) to 30 seconds (very apparent motion).

8 seconds

10 seconds

15 seconds

20 seconds

30 seconds

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8 seconds

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10 seconds

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15 seconds

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20 seconds

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30 seconds

All of these images were shot with a 24mm lens. Above, see the transition of how much apparent motion is visible at different shutter speeds. Below, click/tap each to view at full size.

Putting This Into Practice

Let’s look at some examples.

For a 20mm lens on a full-frame camera, using the 500 Rule results in a maximum shutter speed of 25 seconds (500 / 20 = 25).

With the same 20mm lens and full-frame camera, the 400 Rule yields a maximum shutter speed of 20 seconds (400 / 20 = 20).

If you use that same 20mm lens on an APS-C camera, you end up with only 10 seconds as your longest usable shutter speed (250 / 20 = 12.5). If you instead use the 400 Rule and then divide by the crop factor, you get 13 seconds for a Nikon APS-C camera, (400 / 20 = 20, 20 / 1.5 = 13) and 12.5 seconds for a Canon APS-C camera (400 / 20 = 20, 20 / 1.6 = 12.5).

If your head is swimming with all of these calculations, remember that the results are constant for each focal length. This means that you can precalculate the longest usable shutter speed for each focal length lens in your bag, and make a cheat sheet to carry with you. This modified rule still does not account for camera orientation, but because you are starting with shorter maximum shutter speeds, it’s more likely that you will end up with star points rather than star trails.

Workshop attendees on the salt flats of Death Valley National Park.

The way to make sure you are using the best shutter speed for the situation is to review your images in camera at full magnification, and adjust the time accordingly. Bear in mind that you should check all sky areas in the frame, because the stars closer to north may be sharp while those farther away are not––even in the same image!

You’ll need to consider the various factors—star sharpness, depth of field and focus, and image quality—and make the best exposure decision you can based on prioritizing those factors. It’s a combination of science, art and simply what feels right for the image. Getting to the place where you have a strong sense of when it feels right is simply a matter of practice, so get out there under the stars and photograph.

Lance Keimig is a partner and workshop leader with National Parks at Night. He has been photographing at night for 30 years, and is the author of Night Photography and Light Painting: Finding Your Way in the Dark (Focal Press, 2015). Learn more about his images and workshops at www.thenightskye.com.

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UPCOMING WORKSHOPS FROM NATIONAL PARKS AT NIGHT

The Right Angle: Creating Texture and Shape When Light Painting

The word photography means to draw or paint with light. When I first began studying photography, I was told that along with composition, the study of light would be a lifelong endeavor. Over the years, I’ve found this to be an absolute truth.

The master painters knew light intimately. They were genius at using light to define, shape and illuminate their subjects. This skill came from careful attention to the way light wrapped around their subjects. The way it reflected off them. The awareness of color in the shadows and the recognition of specular highlights.

We can learn from them. We can learn from paying careful attention to light and the way it plays on our subjects.

One factor crucial to painting in your own light is the angle of the beam. This is critical in bringing out texture and creating depth in your images (Figures 1 and 2). Painting your subject from the position of your camera will result in the least flattering light. Painting it from the side will produce the most texture and dimension.

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Figure 1. Painting at the same angle as the camera will produce the least-interesting version of your scene.

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Figure 2. Painting the subject from the side will result in the most texture and dimension.

The two images of the star (Figures 3 and 4) show the difference between a subject painted straight on and one painted from the side. The star in Figure 3 was painted while I stood right at the camera, which was about 8 feet from the subject. Notice how flat the image is; it displays very little depth. The photography term for this is “front-lit.”

The star in Figure 4 was created by standing to the side of the star while painting, very close to the fence, and again about 8 feet away. Everything in the scene begins to show more texture. The star becomes much more three-dimensional.

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Figure 3. Created under city lights using an exposure of 30 seconds, f/8, ISO 200, and lit from the front.

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Figure 4. Same ambient light and exposure, but lit from the side. Notice how the shadows add texture to the image. (Click/tap either image for larger view.)

An abandoned gas station (Figure 5) made another good subject for showing the difference between a front-lit subject and one that is side-lit. The image was created by simply standing right next to the camera while illuminating the scene.

Whereas I created the image in Figure 6 by painting from many different angles. I divided the painting of the walls into two sections. For the left wall, I stood off to the left but close to the wall and then painted inward. I did the same for the right wall. This left the chair and ground very dark. Placing my flashlight about 8 inches from the ground, I painted across the scene to give the litter-covered concrete lots of texture. I painted the chair last by getting about 5 feet from it and painting downward.

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Figure 5. This old gas station in rural Arizona was illuminated using only a flashlight. There were no city lights to influence the overall exposure, but the moonlight was moderate, so I used an exposure of 2 minutes, f/11 to keep the ambient light low. In this image, I light painted from the front ...

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Figure 6.  ... whereas in this frame I light painted from the side in multiple locations. (Click/tap either image for larger view.)

This light-painted old building (Figure 7) was a typical situation of establishing the ambient exposure for the night sky and then light painting the buildings. The ambient exposure was 4 minutes, f/8, ISO 200. This exposure left the building quite dark. Using my 65-lumen flashlight, I began by painting the building from the right for about 1 minute, moving further to the right as I painted. Noting the shadows of the porch posts on the building will give you an idea of my angle while painting.

Next I moved onto the porch and stood in front of the far-right window. Hiding the front of my flashlight from the lens, I swung the flashlight from right to left for about 30 seconds as I pointed toward the ground in front of the porch. This caused the light and shadow in front of the house. Keeping my flashlight in one position kept the shadows on the ground sharp. If I had physically moved the flashlight from right to left, rather than swung it from a single position, the shadows would have become softer and less defined. Because I was much closer, the ground is lighter than the building. I then repeated this process standing in front of the far-left window.

To complete the effect, a student popped a flash in the window on the right side of the building and then again on the left side of the building. This gave the impression of interior lights being on.

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Figure 7. I love to visit Grafton ghost town during workshops in Zion National Park. On this occasion, I was teaching a night photography workshop with Gabriel Biderman. Our group was focused on shooting the night sky while light painting the various buildings.

In Figure 8, the only moonlight striking the scene is on the ground in front of the truck. The ambient exposure of 2 minutes, f/8, ISO 100 kept the moonlight foreground somewhat dark. Using my 65-lumen flashlight, I started by painting the back wall from the camera’s far left. This distance created a broader beam, which covered most of the wall at once.

Next, I moved close to the truck and somewhat behind it. From this vantage point I painted the grill, fenders and windshield. This gives the truck a heavy side-lit, almost back-lit feel.

At this point I moved around to the right of the camera and painted the truck from that side. I spent less time painting here, so it wasn’t as bright as the other side. Filling in some light from this side helped give the truck dimension and kept it from being pure black in the final image. I created highlights in the scene by moving very close (1 foot) to the headlamps and painting each one for a couple of seconds. To finish the image off, I painted the inside of the cab for a couple of seconds from each window.

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Figure 8. I photographed this old truck at Nelson ghost town in Nevada. Our workshop group was photographing under a full moon, but most of this truck was in the shade of the building.

Paying careful attention to the way light wraps around and reflects off of your subject is a great learning experience. Notice light while you’re looking at magazines, watching TV or walking down the street. Take into account the angle, color and quality of the light. When it comes time to supply your own light, remember these lessons. Experiment with different vantage points and keep your flashlight at a severe angle to your camera.

Never paint from behind the camera!

Note: This article is adapted from an excerpt of Tim’s ebook The Magic Light Painting (Peachpit).

Tim Cooper is a partner and workshop leader with National Parks at Night. Learn more techniques from his book The Magic of Light Painting, available from Peachpit.

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UPCOMING WORKSHOPS FROM NATIONAL PARKS AT NIGHT

Expose to the Left: How to Really Maximize Image Quality at Night

Note: It has come to our attention that some readers are not seeing the photos in this post as intended. Please know you are not alone, that others have reported the same. See the Comments section below for more information.

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We hear everyone in the photography industry talking about image quality, image quality, image quality. We especially hear about this in any circle of people chatting (or writing) about night photography. Conversations (and books, articles and blog posts) are rife with opinions and advice about how to push the limits of our cameras and lenses in order to get the best image quality in low-light situations.

But at what cost? We get so caught up in capturing all this dim light that we don’t notice that we’re making decisions that in every other photography situation are actually detrimental to image quality:

• opening the aperture as wide as it will go
• leaving the shutter open for long periods of time
• jacking up the ISO to numbers far beyond what the photographers of yesteryear would even believe as factual

Ideally, night photographers need to be thinking the other way around: How do we improve our low-light photos in a way that capitalizes on everything we know about shooting in daylight? The answer is straightforward, and it all boils down to shooting with this philosophy, with this technique: Expose To The Left, otherwise known as ETTL.

What is ETTL?

Like its fraternal twin ETTR (Expose To The Right), ETTL is a way to maximize image quality, except while ETTR is used in daylight, ETTL is used at night.

How does it work? It’s simple. With your camera set to Matrix metering, shoot a test exposure that’s probably a couple of stops darker than the meter reading. You can just guess—accuracy doesn’t matter, kind of like with print film. Looking at your histogram, adjust the exposure downward and keep firing test frames until all the data is crammed up against the left side, or the “shady side,” of the graph. We push that histogram over by using a smaller aperture, a faster shutter speed, a lower ISO.

A perfect example is a photo I made in Gates of the Arctic National Park, of the wingless bats that live in Inverted Canyon. I was shooting under a new moon. My first-guess exposure was 20 seconds, f/2.8, ISO 6400, which resulted in a rather “traditional” histogram, as seen in Figure 1.

Figure 1. Initial, best-guess test exposure.

But I didn’t want traditional—I wanted ETTL and all the advantages that come with it. So I closed down the aperture to f/5.6 and dropped the ISO to 1600. That gave me a better ETTL histogram (Figure 2), but still not good enough.

Figure 2. The histogram of the same scene, stopped down quite a bit.

So I cut another two stops of light by dropping my ISO again, to 800, and increasing the shutter speed to 10 seconds. The resulting histogram (Figure 3) was certainly close—close enough to be effective, in fact. But it resulted in what I call a “Thick Shady” histogram, wherein you can see that all the image data is pushed to the left, but you can still make out a slope of data curving up on that left side. By increasing my shutter speed to 2 seconds, I was able to narrow that to a slim line of histogram data (Figure 4)—or what’s known as “Slim Shady.”

Figure 3. My third exposure—not a bad one for ETTL, but we can get it even better. …

Figure 4. Histogram of my final “Slim Shady” exposure. Perfect ETTL.

What did I gain by doing this? Consider my initial, traditional-histogram exposure of 20 seconds, f/2.8, ISO 6400:

• That 20 seconds introduced long-exposure noise.
• That f/2.8 gave me paper-thin depth of field.
• That ISO gave me high ISO noise.

All of which are bad for image quality.

However, my ETTL exposure was 2 seconds, f/5.6, ISO 800, which fixed every one of the dire consequences of that first exposure. You can see how sharp the final image is in Figure 5; no long-exposure noise, adequate depth of field, no high ISO noise. Moreover, f/5.6 is the sharpest aperture for the Nikon lens I was using, which further improved the final image. Click/tap to see the photo at full size. Not a blurry pixel in sight. Not a spot of noise. The image quality is perfect.

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Figure 5. Wingless bats in Inverted Canyon, Gates of the Arctic National Park. 2 seconds, f/5.6, ISO 800. (Click/tap for larger view.)

Ancillary Advantages of ETTL

In addition to image quality, ETTL has other advantages.

As crazy as it sounds, you can “freeze” action even in the dark. Because you’re not worried about all the tedious challenges of maintaining highlights, midtones and shadow details, you can manipulate your shutter speed to almost anything you want. For example, while doing a night shoot at Upward Falls in North Cascades National Park, I didn’t want motion blur in the water. But because I was using ETTL, I was able to shoot at 1/60, f/4.5, ISO 2000. Subsequently, I got great image quality while freezing the action of the falls (Figure 6) despite the low light.

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Figure 6. Upward Falls, North Cascades National Park. 1/60, f/4.5, ISO 2000. (Click/tap for larger view.)

Another side benefit of ETTL is that you can hand-hold your camera when making night images. Even under the new moon! Because you can shoot at those higher shutter speeds, you don’t really need to carry a tripod into the field with you. However, all five of us at National Parks at Night are Manfrotto Ambassadors, so we avidly recommend that you carry one anyway.

Drawbacks of ETTL

As great as ETTL is for improving image quality in night photography, there are some obstacles to work around.

For one, this exposure technique gets trickier when you’re light painting. It’s especially troubleshome when you’re using a sunbeam-like flashlight such as the Coast HP7R, because it completely ruins your hard-achieved left-biased exposure. How? By adding light. But don’t fret—there’s an easy solution.

Figure 7. Coast HP7R flashlight with snoot by Light Painting Brushes, modified for ETTL light painting.

If you’re using ETTL to determine exposure for a scene you need to light-paint, then get a snoot that fits onto the end of your flashlight, such as the Universal Connector made by Light Painting Brushes. Cover the far opening of your flashlight with a thick and subsequently expensive layering of gaffer’s tape (Figure 7, above). With this modified snoot on your flashlight, you won’t impair your ETTL exposure. This is exactly what I did to light-paint a night wildlife scene in Voyageurs National Park (Figure 8).

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Figure 8. In Voyageurs National Park I got an opportunity to photograph these greater horned marmots. Unfortunately the moon was new, and it was winter in northern latitudes, so I needed to light-paint my subject—obviously quite cautiously. The need for light painting introduced a further obstacle to achieving a good ETTL exposure, which I circumvented by using the snoot method described above. (Click/tap for larger view.)

Another option is to apply a thick layer of black paint over the front of the flashlight lens. Just be sure to use removable paint, so you can peel it off, lest you have to head back down the trail in the dark. 

Along the same lines, a strobe is even more detrimental to ETTL, because even though that light burst comes and goes in a flash, it’s really bright. For this situation, I suggest foraging your closet for the case your strobe came in when you bought it. Then put the strobe in that case before firing it. Even better, see if you can buy an extra case and put the flash in both. Extras are pretty easy to find on eBay. (Well, maybe not now that I’m sharing this tip.)

Lastly, pixel-peepers will notice that the ETTL approach diminishes highlights a bit. But don’t worry about it. Just like Meghan Trainor sings in her catchy pop song—“It’s all about that bass, about that bass, no treble”—it’s similar for night photography. It’s all about the shadows, about the shadows, no highlights. After all, night photography is all about photographing within the biggest shadow in the whole world. Seize the shadow.

A Final Note on ETTL

Some photographers accomplish the ETTL effect solely in post-production. In other words, they photograph the scene with a “traditional” exposure. Then they import the photo to Lightroom, pull the Exposure slider all the way to the left, and then reduce the Shadows setting a tad. But the effect just isn’t the same. Get it right in-camera.

I suspect that the ETTL technique will be new to many people reading this, but I promise two things: 1) It will result in better image quality in your night photos. 2) It’s easy to learn, and fun!

If you decide to experiment with ETTL, please do come back and share your results in the Comments section.

Note: It has come to our attention that some readers are not seeing the photos in this post as intended. Please know you are not alone, that others have reported the same. See the Comments section below for more information.

Chris Nicholson is the author of Photographing National Parks (Sidelight Books, 2015). Learn more about national parks as photography destinations, subscribe to Chris' free e-newsletter, and more at www.PhotographingNationalParks.com.

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UPCOMING WORKSHOPS FROM NATIONAL PARKS AT NIGHT

How I Got the Shot: Walkway to the Stars at Dry Tortugas National Park

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Star stack over the moat wall at Florida's Dry Tortugas National Park. © 2016 Gabriel Biderman.

The Location

Last year, an amazing time-lapse video brought awareness to one of the most remote national parks in our country, Dry Tortugas. Three days after I watched that stunning piece, I was invited to come down and create my interpretation of the largest masonry structure in the Americas, under the night skies, all while doing prep work for our workshop in Dry Tortugas this coming July.

Dry Tortugas takes some effort to get to: Go as far south as you can in the continental U.S., then turn right and go 70 miles out into the sea. The fastest boat gets you there in just over two hours. As I walked around the deck of the boat, all I could see was an endless horizon in every direction. It was like looking at an infinite blank canvas, which can be thrilling and definitely a little daunting. Eventually a small red dot on the horizon turned into a larger box, then a brick rectangle, until … it finally became Fort Jefferson looming ominous above us.

I had a good eight hours to scout the fortress, which encompasses the whole island. I was immediately drawn to the walkway, which creates a moat around most of this engineering marvel. The fort’s overall shape is hexagonal. I was paying attention to a few things as I made my way around the six-angled pathway. First, I noticed that at each turn, and at a low enough angle, the road seemed to meet the horizon.

This emphasized an infinite passage to the sky.

OK, I like that.

The next thing that came immediately to my mind: Does one of these paths point directly north? If we can blend that straight line to meet an epic circular star trail, I think we have a winner!

Lighting and Conditions

In an ideal world I would have planned this shoot around a new to half moon. It was summer and Milky Way season, plus the fort offers so many light painting opportunities. But the only time we could coordinate my visit was around a full moon, so I had to embrace the idea of lots of light. Fortunately the sky was clear except for some clouds that hovered over the far horizon.

Gear

Because I had only one night to scout, I brought a bunch of gear, including two rigs so that I could stay as productive as possible on a short summer night. The gear I used for this shoot was:

• Nikon D750
• Nikon 14-24mm f/2.8 lens
• Gitzo 2545T-82QD Series 2 Traveler tripod and ball head
• Tether Tools Case Relay
• Vello Shutterboss II wired remote
• Vello Three-Axis Hot-Shoe Bubble Level

Test Shots

I always take two to 10 high ISO test shots to confirm focus, composition and exposure. Even though it was bright out with the full moon, our eyes adjust and see better than our viewfinder or LCD screen.

The first test shot (Figure 1) of 6 seconds, f/5.6, ISO 6400 was taken at a focal length of 24mm. The histogram showed that it was an average exposure with very little dark shadows and bright highlights.

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Figure 1

The composition wasn’t doing it for me. My main subject was the path, and it was not being given its due with that framing. I moved the rig to the middle of the walkway and went a little wider—from 24mm to 20mm for the second shot (Figure 2).

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Figure 2

Still needed some finesse. So I closed all the legs to the tripod and shot lower and wider, going from 20mm to 14mm. I was also observant of keeping the camera very level—I didn’t want to distort or have converging lines in the fort by pointing at an oblique angle. I also wanted to include lots of stars and sky. Figure 3 is one of my few shots where the horizon is practically in the middle, but the strong foreground of the path plays nicely against the open sky.

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Figure 3

I was almost there. Before I commit to an hour-plus exposure, it is very important to patrol those composition borders and make sure everything is there for a reason. I felt the entry point of the walkway was a little off. I wanted it to be coming in from both of the lower corners, so that path would fill the bottom of the frame and then fade off to infinity (Figure 4).

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Figure 4

Using the Six-Stop Rule, I lowered my ISO from 6400 to 100 and then added the six stops to my shutter speed—which turned 6 seconds into 6 minutes. However, the air temperature was about 75 F, too hot to rip a 6-minute exposure without inducing long-exposure noise. I felt safer using an ISO of 200 and a shutter speed of 3 minutes.

But something was nagging me: That histogram was too average.

I was about to create a dramatic 1- to 2-hour stack of exposures, and I didn’t want it to be average-looking. So I shaved about one-third of a stop off the shutter speed, and set a final exposure of 2 minutes, f/5.6, ISO 250.

I set the camera to Bulb, turned off my LENR and set my Vello Shutterboss to 2 minutes, with a 1-second interval between shots, and an infinite number of frames. I set the timer on my phone and then went to the top of the fort to continue photographing with my other rig for a couple of hours.

Putting it Together in Lightroom and Photoshop

I ended up with 60 2-minute exposures that I was going to stack to create a 2-hour star trail. The exposure was similar across the 60 images, so in Lightroom I worked on one image, making simple Lens Profile corrections and slight adjustments to the Exposure (-45), Clarity and Vibrance settings, and then synced those adjustments to the other 59 images.

Then I selected all 60 frames and went to Photo–Edit In–Open as Layers in Photoshop (Figure 5).

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Figure 5

Depending on how big your file sizes are and how juiced your computer is, this can open in 1 to 2 minutes or 1 to 2 hours. (I recently stacked 600 shots and it took my poor MacBook Air close to 4 hours. Guess who is upgrading their travel computer!)

When my Dry Tortugas image opened in Photoshop, I selected all the layers and changed the blend mode to Lighten. And voila, all the stars connected to create a nice long star trail.

However, the caveat with this post-processing technique is that the Lighten blend mode also stacks any other highlights in the scene—such as, in this case, the white clouds. Photoshop blended all the clouds into one, which was a bit too much for my liking. (Figure 6).

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Figure 6

I turned different layers on and off to find the clouds that I didn’t want in the scene. I unfortunately identified that the first 45 images had clouds cutting right through the middle of the star trail. My two options were to go in and touch up 45 layers, or cut them out completely and go with a shorter star trail. I choose the latter strategy, keeping the last 15 layers and settling for a 30-minute trail with fewer clouds. The remaining first layer had two small clouds that I wanted to remove, so I added a layer mask and used a black brush to paint them out (Figure 7).

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Figure 7

Once I finished editing in Photoshop, I flattened the layers to keep the file size from exploding, and then did final cropping, sharpening and touch-up in Lightroom (Figure 8).

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Figure 8: Here is the difference between the fully stacked image (right) and one edited down to remove the intrusive clouds.

I do love the blue and green colors in the scene, but to heighten the drama and stay true to how old this building is, I converted the photo to black and white in Silver Efex Pro 2.

Which do you prefer—the color or B&W? Feel free to add your thoughts in the comments section below.

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Be one of the few people to experience Dry Tortugas and Fort Jefferson at night during our upcoming workshop in July. See our Dry Tortugas National Park page for more information.

Gabriel Biderman is a Brooklyn-based fine art and travel photographer, and author of Night Photography: From Snapshots to Great Shots (Peachpit, 2014). During the daytime hours you'll often find Gabe at one of many photo events around the world working for B&H Photo’s road marketing team. See his portfolio and workshop lineup at www.ruinism.com.

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UPCOMING WORKSHOPS FROM NATIONAL PARKS AT NIGHT

Keep the Noise Down (Part II): Examining Your High ISO Test Photographs

In Part I of this article, we learned:

• What is high ISO noise?

• How to prepare for a high ISO test

• How to shoot a high ISO test

Now we're going to learn how to spot disadvantageous noise in our high ISO night photography images. And then I'll show you how to use these boundaries to your advantage.

Pixel-Peeping: Looking at your High ISO Images

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Figure 1. 1 second, ISO 51,200, ambient temperature 50 F.

I'll start by using the images referenced in our last post. Figure 1 above is an image that clearly demonstrates a lot of high ISO noise. You can see it clearly as a pattern of dots in the highlight and shadow areas. Boom. Easy to spot, right?

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Figure 2. 8 seconds, ISO 6,400, ambient temperature 50 F.

At ISO 6,400 (Figure 2), it's much smoother, and the noise is not as apparent. But it's still there.

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Figure 3. 8 minutes, ISO 100, ambient temperature 50 F.

And at ISO 100 (Figure 3), the noise is gone. No surprise here. That's where the highest possible quality is with my camera. Native ISO.

What did I Choose for this Scene?

I am a big fan of dilating time. So I like the ISO 100 shot the best. And that is an aesthetic choice. I'm not concerned about the length of the shutter speed, because there are no stars, so I don't have to choose between star points or trails. And at 8 minutes, the clouds are not totally smeared, yet show enough motion to depict a sense of time passage that I am attracted to. And no noise.

If I had to choose one of the shorter exposure times (because, for example, there were stars in the frame, or the clouds were blurring too much), then I would choose the ISO 800 photo. At ISO 1600, I start to see the noise affect the clouds in a way I don't like. It appears as blotchy areas.

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Figure 4. Left: ISO 800 with acceptable noise. Right: ISO 1,600 with unacceptable noise. (Click/tap for larger view.)

Tip:

Use the Compare View ( looks like "X | Y") in Lightroom to zoom in on two photos at the same time and same position in both photos at once.

Juxtaposition for the Win

I made a PSD from my test set by selecting all the frames in Lightroom, right-clicking and choosing "Open as Layers in Photoshop."

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Figure 5. You may be familiar with this action from Star Stacking!

Then, so I can show you, I used layer masks to reveal a vertical slice of each layer. This way we can see the changes between each of the exposures side by side (see Figure 6 below). (Power tip: I divided the width by the number of images and added rulers to create evenly spaced slices.)

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Figure 6. Finished PSD with layer masks.

So let's look at the highlight transitions:

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Figure 7. Highlights crop from left to right: ISO 51,200, 25,600, 12,800, 6400, 3200, 1600, 800, 400, 200 and 100. (Click/tap for larger view.)

As I demonstrated with the X/Y view of ISO 800 and 1,600 in Figure 4, I found a breaking point for quality in the highlights. I do like seeing the whole spectrum of exposures in this crop too (Figure 7). I learned a lot from it.

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Figure 8. Midtones crop from left to right: ISO 51,200, 25,600, 12,800, 6400, 3200, 1600, 800, 400, 200 and 100. (Click/tap for larger view.)

In the midtones (Figure 8), you'll notice it's harder to see the noise because the sandy desert floor of Valley of Fire State Park in Nevada has similar natural patterns. If the composition had no sky in the frame, I could choose a shorter exposure. ISO 12,800 looks great in the midtones. 

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Figure 9. Left: ISO 12,800 with acceptable noise. Right: ISO 25,600 with unacceptable noise. (Click/tap for larger view.)

If you have an interesting sky that requires a short exposure and a foreground that begs for light painting or a longer exposure for car trails, moving water, etc., you can layer the two images together in post. Just shoot them separately and (duh ...) don't move the tripod a single millimeter between frames. It's a common use of imaging technology these days. Purists reject it, but if this is how you make your art, use it to your benefit.

Want to see my original PSD? Download it here. (Careful, it's 2.5 GB!)

When Does High ISO Noise Work?

You'll find that you can tolerate high ISO noise in your night photography when there are patterns that complement the noise pattern. Times when it works are:

• Milky Way star points

• scenes without gradients of color

• black and white post-processing

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Figure 10. Devil's Tower, Wyoming. 30 seconds, f/2.8, ISO 400. Ambient temperature approximately 65 F. (Click/tap for larger view.)

In Figure 10, the desert floor has that quality of patterns that complement the noise pattern. It was a warm night in Wyoming, and even at ISO 400 and 30 seconds, there was high ISO noise. But the sky glow and star points mask it pretty well. The noise comes from the ambient summer heat. It's also worth mentioning that it was very dry with lots of dust in the air.

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Figure 11. 100 percent view of above photo. Screenshot from Lightroom.

The month doesn't always have to be the determining factor—it could also be the temperature. The image below (Figure 12) was also shot in August, but at Crater Lake National Park in Oregon at a much higher altitude, and lower temperature (closer to 40 F). Comparing ISO 400 at 65 degrees and ISO 6,400 at 43 degrees, you'll see a dramatic difference: much less noise.

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Figure 12. Crater Lake National Park, Oregon. 30 seconds, f/2.8, ISO 6400. Ambient temperature approximately 43 F. (Click/tap for larger view.)

And below (Figure 13) is a 100 percent crop to see the magic.

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Figure 13. 100 percent view of photo in Figure 12. Screenshot from Lightroom.

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Figure 14. Left: ISO 400 at 65 F. Right: ISO 6,400 at 43 F. Both at 100 percent crop in Lightroom. (Click/tap for larger view.)

In Figure 14 the areas of solid color between the star points are much cleaner in the example on the right. Thus (to me) it is more pleasing. For pixel-peeping! Which leads me to my final point:

How are you Finishing your Work?

Intent is everything. If you intend to finish your work by printing it, you should evaluate your tests that same way. Print them at the size you intend to show (or sell!) them. Stand at the appropriate distance for viewing and ask, "Does this look right?"

Remember that getting 3 inches away from a print isn't normal consumption of the product. Normal viewing distance is usually twice the diagonal measure of the print.

If you are going to display your images only on Facebook, Instagram or another social outlet, then your quality standards can frankly be much less. But consider the future of your craft: If you want to sell your work for others to enjoy or invest in someday, why not practice the pursuit of the best quality in the present?

If the answer is a solid, "nope," then don't sweat it. You made an image that makes you happy. Enjoy, and move on to making more images.

Homework

If you're up to it, export one or two images where you pushed the high ISO limit and share them in the comments section. Tell us what you do and don't like about it. And tell us what you learned—namely, where does your camera start to fail? At what temperature? Let's see you stretching your camera to the limits.

See more about Matt's photography, art, workshops and writing at MattHillArt.com. Follow Matt on Twitter Instagram Facebook.

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UPCOMING WORKSHOPS FROM NATIONAL PARKS AT NIGHT