Multiple Exposure Mode with Nikon D810

A couple of months ago I was researching neutral density filters for long exposure landscape photography when I came across a forum post describing an alternative. I learned that Nikon’s DSLRs will add a number of exposures together (the maximum depends on the body) into a NEF RAW file with what they call “Multiple Exposure” mode. The summation of the set of images into a single file has an effect similar to a long exposure. In some cases it has an even bigger effect because you can control the delay between each exposure, something useful when blurring moving clouds, for example. The advantage of doing this in camera is that the output is a RAW file, making it much more editable (or so I’d expected).

I first tried out the mode in Elora, Ontario in the gorge where the Irvine Creek meets the Grand River. I brought water sandals so that I could stand in the river and my tripod with ball head for quick and easy framing. I mainly used the AF-S 18-35mm f/3.5-4.5g on the D810. I added a circular polarizer to cut down on glare, remove reflections from the water and slow down the shutter speed by a couple of stops.

I shot at in aperture priority, f/11 to f/16 at ISO Low 1 (ISO 31). Shutter speeds varied from 0.5 to 1.6 seconds. After framing and taking a test image I  set the camera to sum 10 shots with auto gain on. With auto gain the camera takes 10 shots, each at 1/10th of the total exposure (I assume shutter speed) and then adds them together to match the total exposure as if it had been one shot. In fact, the EXIF data reports the conditions as if it had been one photo. I was pretty happy with the way the photos looked! The water was blurred but the non-moving scenery was nice and sharp. After downloading the images to my computer and trying some edits in Lightroom my happiness faded.

The first thing I noticed was the that blacks were heavily clipped and stayed totally black with adjustments. Later I found that sections of water were posterized. The D810 is a camera with fantastic dynamic range and this was something I’d never seen before. Here is an example:

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Above is the NEF using just Lightroom’s default import settings. Below is the image after some normal edits.

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Here are a couple of crops, showing clipping at the top left and posterization on the bottom left.

I had a hunch. I checked the image settings and confirmed that I was shooting in 12 bits. The D810 is capable of generating 14 bit files but I don’t use them because I’ve honestly never needed to. However, in multiple exposure mode each of the images that make up the final image is shot underexposed.

In 12 bits images there are 4096 DN (digital numbers, or signal levels). Let’s say a very dark object uses 10 DN in a 12 bit image. Now, when shooting in multiple exposure mode with 10 images, that 10 DN object is only going to be 1 DN in each of the images because the exposure is 1/10th of normal. 1 DN is well into the noise floor and could even show up as 0 DN (i.e. clipped). When adding the 10 images together, all those noise-limited pixels remain clipped or at least heavily affected by noise. 14 bit images have 16384 DN worth of information. The same dark object that was 10 DN in 12 bit mode would be 40 DN in 14 bit mode. At 1/10th of the exposure you’d have 4 DN of signal, which is much less likely to clip.

Likewise, smoothly varying features like water and sky lose a lot of data when underexposed and can become posterized.

To test my theory I took a series of shots, all underexposed by about 3 stops. They all started off like this:

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I then brightened each image to a normal exposure. First I’ll show the two images that were not multiple exposure (left is 12 bit and right is 14 bit):

Apart from slight exposure difference, they’re pretty much the same. Now, the 10 shot multiple exposure images (again, 12 bits on the left and 14 bits on the right):

The 12 bit image is horrible! The 14 bit image is pretty good. Looking closely it’s still not perfect compared to the single 14 bit image but still passable. I haven’t found any discussion of this condition online which is why I’m writing this post.

With my newfound knowledge, I returned to Elora a few weeks later and this time shot entirely in 14 bit mode. I think the outcome was much better!

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Thanks for reading!

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A Foggy Saturday

We’ve had a week of fog and unseasonably warm weather here in Southern Ontario. This Saturday I took advantage of the moody atmosphere to grab a few photos. The first two are from a walk at RIM Park with the D750 and AF-S 70-200mm f/2.8 VR (a lens I’ll talk about soon).

The night shots are from the X100s.  Lately I’ve been playing with the X100s in full manual mode (AF, shutter and aperture). It’s slowed down my shooting but I’ve enjoyed having full control and better consistency from shot to shot. My method is to first set exposure for the scene using the LCD in the view finder and then switch to the optical view. To focus, turning the focus ring on the lens activates the virtual split prism, where the centre of the image is magnified and superimposed with a split image generated from the AF phase-detection sensors. Focus is achieved when the split image is aligned.

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Photos of the Month – June 2016

Well, I haven’t posted in forever. To get myself back on the path to regularly blogging I’m going to try doing a few ‘Photos of the Month’ posts to recap the best images from the month. Most of these were taken with my pretty new Nikon D750 (I’m sure I’ll be writing about it soon) and the rest were with the X100s.

Enjoy!

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Trip to Arizona Part II – The Grand Canyon

Well, I crossed off another item on the bucket list in April with my visit to the Grand Canyon. I woke up at 5AM at the hotel in Flagstaff and hit the road before the sun rose so that I’d get to the canyon in the early morning light. I probably don’t need to say a lot about the place. It was epic and vast. I was there early enough that I was totally alone in some spots, without a person in site. That all changed a few hours later when it was teeming.

I walked down the Kaibob trail about 1200 feet and experienced a 15-20 degree (Celsius) temperature change compared to the top. The hike down was easy. The hike up was strenuous and parching.

I stayed past dark and parked myself at Lipan Point for the sunset and night sky shots. Unfortunately I ran the batteries out in the D700 but the X100s was up to the task! The night sky shot here is a panorama of X100s shots. Here are my 22 favourites spanning 7AM to 10PM.  D700 and X100s, AF-S 18-35mm f/3.5-4.5G and Sigma 35mm f/1.4, 85mm f/1.8G.

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7 shot panorama with X100s

7 shot panorama with X100s

Studio Cat Portraits

Last weekend I tried using my new background kit (stands + white seamless) to shoot some portraits of our cats, Gracie and Professor Noam Chomsky. For the key light I used an Alien Bee B800 with gridded beauty dish from camera right, somewhat close to the posing stool. A Paul C Buff Brollie Box on a 2nd B800 was the fill light, set back from camera left. Both lights were set to equal output power, so distance controlled the intensity on the cats. The background light was a 3rd B800 with barn doors to control the spill.

“Posing” the cats was an exercise in patience. While Gracie eventually chilled out on the stool and let me get a long series of shots, Chomsky had no interest. The lamb skin helped but I still only had 10 seconds after setting him down before he’d run away to the bedroom.

I shot withe the D700 + AF-S 85mm f/1.8 G on a tripod and cable release, allowing me to shoot from the floor between the camera and cats.

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Simplifying Travel with a 35mm Lens – Part 2: Vancouver, BC

When getting ready for a work trip to Vancouver last week I must have re-packed my camera bag at least 5 times before settling on the Sigma 35mm f/1.4. Vancouver is a city with big views and as much as I wanted to simplify the travel kit I knew that there would be many occasion where a wide field of view would be needed. In the end I stuck with the 35 for its simplicity and beautiful optics and thankfully I had no regrets.

In the woods I shot at f/1.4 and ISO 1600. For epic landscapes I shot panoramas at tiny apertures. Again the focal length was perfect for capturing scenes just as I saw them.

All below are D700 + Sigma 35mm f/1.4. Some here are of my co-worker, Connor, trying to capture the perfect selfie. Others are of Clevelend Dam, English Bay and downtown Vancouver, Lynn Canyon, TRIUMF, and Granville Island.

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