The D810 does well with long exposures. Unfortunately I’m not very experienced shooting very long exposures, but I have tinkered with it. I find there to be a better alternative, call it a pseudo long-exposure, that can be made using a series of shorter 30sec exposures. This method also greatly reduces random noise, and I tend to use this method more than I would take a very long exposure.

Image averaging is nothing new, however, recently forum chatter has increased considerably regarding this topic. It’s a very effective way of reducing noise in images by average-blending two or more images together, usually as layers in Photoshop. Well, I’ve got one better... you can do this and much more, using RAW files, with a neat app call PixelFixer. Also, you probably didn’t know that many Nikon DSLRs can do image averaging in-camera by using the “Auto-Gain” setting in the Multiple Exposure menu. It’s super simple to make butter smooth and noise free images using only the in-camera Multiple Exposure mode. The image below was achieved using Multiple Exposure mode with Auto-gain; Eight 30sec exposures in succession without LeNR, creating a pseudo 4 minute exposure that is noise free.

Unfortunately, the Multiple-Exposure mode is limited to a maximum of 10 exposures. I generally use this setting when I’ve got the camera on a tripod shooting a still life subject or a landscape, something that might require some or heavy shadow pushing in post. When shooting landscapes, which may have moving objects, I generally try keep my exposures long, and shoot the maximum amount of frames possible with multiple-exposure. This usually prevents any artefacts caused by moving trees, waves, etc. If I can’t get an exposure of 1sec or longer, I will avoid the multiple-exposure mode, and shoot off 20-100 frames in quick succession, and then on the computer run them through PixelFixer’s Median or Average blend mode. Remember, PixelFixer works on RAW files, including saving it’s output to RAW. Average blend mode is usually better for landscapes with moving clouds and tree branches. Median works wonders at removing cars and people from a scene, granted they were moving when you were shooting and you took many frames. To read more about image averaging and PixelFixer, please see my blog posts, The Average Blend Mode and Pixel Fixer now with D810 and D750 Support.

The Multiple Exposure technique to average out noise, is a very very useful tool. I have used it for many years to greatly reduce image noise, smoothing tonal and colour gradations, and allow for aggressive shadow pushing when necessary. The image below shows the before and after edit of an in-camera, 8 image Multiple Exposure, with Auto Gain on. There is no visible noise in the image. The edit in LR started with the selection of a flat tone curve, with various highlight and shadow adjustments, followed by some localised adjustments in Photoshop using luminosity masks. Read more about the latter, HERE. Click the image to see a larger version of the edited image.

Coming back to long exposures, I’ve successfully made exposures ranging from 2-5 minutes without
LeNR, and have had only a handful of odd pixels to deal with each time. Even then, manual dark frame subtraction can be done using the same PixelFixer program mentioned above. On the right is a 3 minute exposure with LeNR turned off. The only post processing that was applied was a +1.5 exposure adjustment in LR6, with chroma NR set to 10. Click the image to see it much larger. By comparison, the D700 would show a similar amount of odd pixels in a simple 30sec exposure.

Much like the reasoning behind image stacking for star-trails, I would tend to assemble one long exposure from several shorter ones, that are then average blended in post...or even in camera. In may cases, it mitigates the necessity of using strong ND filters that sometimes have uneven colour casts, but it’ll also avoid the occurrence of hot pixels and thermal noise experienced with very long exposures.

My interest in astro photography and star trails has peaked since the arrival of the D810. It feels easier to do star trails with the D810 than with my D700. Not only does the D810 allow for unlimited shooting in Ch shooting mode (100 image limit on the D700), but the interval timer image limit has been raised as well. Image quality of high ISO long exposures is also considerably better than the D700, especially when it comes to fixed pattern noise (I’ll get to this in a moment). Software such as PixelFixer again proves itself incredibly useful for astro photography, because of it’s ability to remove hot pixels, do dark frame subtractions and apply various blending modes to your RAW files. If you are interested in how I created this and other star trails, read my recent blog post, Attempts at better Star Trails Part II and Better Star Trails in Praxis.

Fixed pattern noise is probably the biggest gripe I have with the D700. While it’s not as prominent as on Canon 5D (I,II and III) cameras, it can come out of the woodwork when applying the average blend noise reduction technique mentioned above. Most noise is random, while fixed pattern noise is, well, fixed. Random noise helps to mask fixed pattern noise, but eliminating this random noise makes fixed pattern noise more obvious.

My median blended D700 images, that have had a little aggressive exposure or shadow push adjustments done, sometimes show this feint pattern. I find it especially noticeable in large evenly toned parts of an image, such as the sky.  So far, I haven’t been able to provoke any fixed pattern noise from the D810, especially with average blended images. Below is an actual pixels crop of how the fixed pattern noise in D700 files can look like... bearing in mind that the D3 and D3s cameras also show this. Even some of Nikon’s official D3s sample jpegs showed this.

I achieved the result below by shooting 50 dark frames (ISO200) and median blending those RAW files using PixelFixer. Then, I applied a +5 exposure compensation in LR, followed by an auto-levels and desaturate adjustment in Photoshop. The more pronounced line around the middle is probably a sensor bifurcation, not uncommon in 35mm and digital medium format sensors.



Image Quality: Part II