The Nikon D810a. A Formidable Challenger

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1 ASTRONOMY TECHNOLOGY TODAY Your Complete Guide to Astronomical Equipment THE 10MICRON GM 1000 HPS FREEDOM FROM LAPTOP TETHERING OBSERVING THE SUN IN COLOR WITH THE MALLINCAM XTREME OPTIC CRAFT MACHINING The Nikon D810a A Formidable Challenger Volume 9 Issue 4 September-October 2015 $6.00 US

2 The Nikon D810a Image 1 - Nikon s first and formidable entry to astrophotography. A Formidable Challenger By Richard S. Wright, Jr. The Nikon D810a Nikon has officially tossed its hat in the ring with the release of a DSLR specifically targeted for astrophotography. The Nikon D810a (Image 1) is based on the high-end D810, but with a few tweaks to optimize the camera for astrophotography. This is a similar approach Canon took with both the 20Da and the 60Da, however Nikon has gone the extra mile on the D810a. In addition to the modified IR-cut filter that allows more of the deep-red hydrogen-alpha (Ha) light from emission objects, they have removed the anti-aliasing filter on the chip for sharper details and have added some astrophotography-specific features to the firmware, including a new long-exposure manual mode. When I first heard about this camera and saw its price (retails around $3,800.00), I was a bit taken aback. Literature from Nikon claimed the camera is best suited for astrophotography and not normal daylight photographs, and I could not see spending that much money on a DSLR that could only be used for astrophotography. A cooled one-shot color camera could be had for much less, or a modified used Canon Rebel can be found on ebay for only a few hundred dollars and is likely to offer far more than 1/10th of the performance for only 1/10th of the price. Further reading led me to believe the D810a would be great for nightscapes possibly the very best you could do for nightscapes, even but I d be in no hurry to trade in my Canon 5D Mark III for one. These were my first thoughts, never having used one, of course. Opportunity Knocks At Software Bisque, I ve written many of the camera plug-ins for TheSkyX Pro, with my first being for the Canon DSLRs, because I was an avid Canon DSLR user already. A few customers, and one good friend, have been asking for Nikon support, and so I downloaded their SDK (Software Development Kit) and was reading up on what this might entail and how much work it might be. Nikon contacted me a few days later to see if they could help in the process, and a week later I had a loaner D810a from them to experiment with and of course to shoot with! The first thing I did was take some normal pictures with the 50-mm lens they sent me, so I could get familiar with the camera. It s bad enough my three Canons all have the buttons in different places. Now I m on a Nikon, and the controls at first were a bit bewildering Image 2 - Contrary to my expectations, the camera works just fine for normal photography, too. and far different from what I was used to. A brief look at the manual and a little play time outdoors, and I was quite comfortable in no time shooting snapshots, however. Contrary to my expectations, the camera is similar to the Canon 60Da in that, yes, you can actually take regular daylight photographs and they come out quite nice (Image 2). I always shoot raw anyway, so I was ready and willing to have to manually adjust the white balance on each image anyway, but they, on a whole, looked just like I was shooting with one of my unmodified cameras (shot outdoors with the daylight white balance selection) without much additional tweaking. Astronomy TECHNOLOGY TODAY 33

3 Image 3 - The D810a is a big boy with a full-frame sensor. Image 4 - Vignetting on the Esprit 150 was small and not objectionable. Just the Specs, Ma am This is a big hefty full-frame camera (Image 3), and it s not playing around. Raw files are around 45 megabytes, or so, and are 7360 x 4912 pixels (36 megapixels). This is a full-frame 25.9 mm-x-24 mm sensor with quite small 4.88-micron pixels. All the raw files are not the same size, as there is some lossless compression going on, so the size varies slightly with content. FITS files, on the other hand well, we ll get to that a little later. Canon has led the world of DSLR astrophotography for years, so I think it s appropriate and fair to draw some comparisons, but I m not intending for this article to be a shoot out, so bear that in mind. For starters, this is a full-frame chip, larger than the APS-C sized chips used in most Rebels. Nikon s D810a is more on a par with the Canon 5D, 6D, etc. This is at least one good reason this camera costs more than a budget Rebel. Large chips are nice, especially when you re doing wide-field or nightscapes, but they can also be more prone to vignetting if you don t use the right lens, or on telescopes with a fast focal ratio. The D810a uses the Nikon F-Mount, and the chip is 2.5 mm further back into the camera than the Canon cameras. One of the implications of this is that you cannot use a Canon lens (with an adapter) on a Nikon camera; they cannot come to focus (you can, however, do the opposite). Another is that, if you have a focal reducer or flattener, you ll need a different spacer distance for a Nikon than you do on a Canon. 2.5 mm does not sound like much, but it s a huge distance when it comes to getting good focus, or a correctly flattened field. I d expect vignetting to be worse than a Canon, but only slightly so. To test this on one of my nights out with the Esprit 150, I shot some flats (I d have done this anyway, of course). The vignetting (Image 4) is slightly worse than it is on a Canon 5D Mark III, but not really objectionably so. Image 4 is stretched considerably to make it stand out better in the magazine, but the fall off is not severe, and good flat calibration works very well. The vignetting on my f/3 Veloce with the Canon, on the other hand, is borderline objectionable, and I wish I could have tried it with this camera (the clock was ticking), but I imagine it would be quite bad. A fast camera lens would probably be a better choice on this camera than a fast astrograph, if you want good data all the way to the edge of the field. At f/7 and at f/5 on a highquality refractor, I was quite happy with the results, which I ll present a little later. The side of the camera has jacks for a microphone and earphone, an HDMI output, and a USB port for downloading images or controlling the camera via software (Image 5). The USB port (middle one shown) is a USB 3.0 Micro-B type port. Since my loaner was really an engineering sample, not a full retail package, I had to scrounge to find one of these cables. The D810a also sports a special Manual mode for astrophotography that Nikon labels M* (Long-Exposure Mode). In this mode, you can set exposures from 4 to 900 seconds 34 Astronomy TECHNOLOGY TODAY

4 Image 5 - USB 3.0 Micro-B and HDMI ports. Image 6 - The new Long-Exposure Manual mode shoots up to 15 minutes. (Image 6). This is ideal for starscapes or astrophotography where a computer is not available to control longer exposures (most cameras manual modes only allow up to 30 seconds before you have to use an intervalometer in Bulb mode). There are a couple of drawbacks to this mode, however. Of note are that you cannot control the camera with a computer and software while in this mode (just use normal Manual), movie mode is not available, either, nor auto-bracketing or HDR shooting. Exposure smoothing does not work in Time Lapse Photography mode either, but these seem reasonable compromises given the uses of this mode. The fact that this camera has a Time Lapse mode is also a big plus, no intervalometer is required unless, of course, you really have a good reason to shoot over 15 minutes. Do not mistake the lack of movie mode for a lack of live view. You can use live-view mode and zoom in on a star using the back LCD screen for focusing. In fact, the zoom level on the Nikon goes up to 23x, considerably more than the 10x I can get on my Canon cameras; this is very nice for getting tight focus on a star. In this mode, along with an exposure countdown, you have a sort of mirror lock (regular mirror lock is also available), and this is ideal for shooting on a sky tracker. After pressing the shutter button, a few seconds will go by while the vibrations of your hand die down, and then the camera will cease live view and begin exposing for the preprogrammed time. As you ll see later, I got very good results in this way. I thought the ISO ranges were very reasonable, as well, for a camera dedicated to serious astrophotography. At a certain point, cranking up the ISO is just like turning up the volume on a static filled radio signal, so the available modes do not go up too ridiculously. The available range is ISO 200 to 12,800, with an extra 0.3 to 1.0 EV below, and 0.3 to 2.0 EV above. I also liked the virtual-horizon overlay that can be shown on the live-view display (Image 7). It s very easy to lose the horizon in the dark when you re framing up a nighttime photo and end up with a crooked shot, and I thought this was a feature I d make use of often. Unlike my Canon, the D810a horizon is not just a 2D line that rotates, but a 3D outline of a plane that shows you not only your tilt left and right, but also forward and backwards. Finally, on the hardware front, there is a viewfinder shutter (Image 8). When the mirror is up for long exposures, stray light from behind the camera can enter the viewfinder and find its way down into the camera body, potentially adding glare or gradients to your image. A simple switch to the upper left of the viewfinder flips the shutter open and closed. In The Field This is all well and good, but how does the camera do at actual you know astrophotography? Pretty well, it turns out. We ve had precious few nights suitable for astrophotography in southeast U.S. this summer, so I made the best of any night Mother Nature would throw Astronomy TECHNOLOGY TODAY 35

5 Image 7 - The Virtual Horizon overlay is useful in the dark. Image 8 - A viewfinder shutter to keep stray light out of the camera. me. My first opportunity came the night of the Perseid meteor shower. I rented a fast f/ mm Nikon lens from Borrow Lenses ( and took the camera and my Sky-Watcher Star Adventurer sky tracker down to my dark-sky site in South Florida. I took a variety of one- and two-minute tracked shots, and I was quite pleased. The lens was not one of the higher-end models, so there is significant distortion on the edges of the image, plus a little chromatic aberration don t judge the camera by that. The stars (in the middle anyway) are crisp and sharp, and the Ha regions of the emission nebula along the Milky Way stand out wonderfully. Image 9 is a single twominute exposure using the M* mode, at ISO 800 (f/2). I ve superimposed the imaging setup to show what a great combo this is for wide-field shooting. Dodging clouds that evening, I also shot the heart of the constellation Cygnus (Image 10). Many of the Ha-rich emission regions, such as the North American Nebula, Gamma Cygnus, etc., are clearly visible among the dust lanes in this photo. I think this is a pretty good shot considering there was some haze, plus passing clouds, and I had a pretty cheap lens to shoot through. With an appropriate lens, the big chip in this camera is ideal for deep constellation shots. Image 9 - Two minutes on the Milky Way brought out plenty of detail. On A Scope On two different occasions, I had an opportunity to try the camera out on an actual telescope. Kevin Lagore at Sky-Watcher USA loaned me a Nikon adapter for my two Esprit APO refractors, so I had a chance to try the camera on both the Esprit 80 (400-mm f/5) and the Esprit 150 (1000-mm f/7). I used O Telescope s Backyard Nikon to control the camera in both cases, and used the new plugin I wrote that integrates Backyard EOS/Nikon with 36 Astronomy TECHNOLOGY TODAY

6 Image 10 - The heart of Cygnus captured by Nikon. Image 11 - The D810a on a refractor. TheSkyX Pro. For the first test on the Esprit 80, I shot the Andromeda Galaxy at home. I used a Chroma Light Pollution filter, since I live not nearly far enough away from Orlando to get good dark skies from my backyard. Mother Nature, capricious as she is, did not allow me to go as deep as I had hoped, but the camera performed very well. Image 12 is composed of only 45 minutes of exposure time at ISO 800 (5-minute subs). The background noise was much lower than I might have expected from a camera with such small pixels. Something very important to note is the stars in the outcropping of Image 12. I recall an associate once showing me his Andromeda shot with a Nikon camera. He was quite proud of his single exposure and it was very sharp and clear zoomed out. Zooming in, however, there were little black rings around all the stars, the tell-tale sign of in-camera sharpening gone amok on a star field. All DSLR manufacturers (even Canon) do some monkeying with the very-raw off-thesensor data. The less the better for us astrophotographers. It seems Nikon has turned it down a notch with the D810a enough so that we can let techniques specifically aimed at astrophotography work their magic without all the in-camera tweaking aimed at making great wedding photos getting in the way. A month later, another precious clear night was forecast, and I knew it might be my last opportunity to turn the camera loose under good dark skies before I had to return it. I had two projects that night, one of which was an RGB narrowband combo that would not be fair to show as the majority of the data came from narrowband data on an adjacent scope. But when that object had set and the Moon was down, I got an hour and five minutes on the Heart Nebula at ISO 800 with the Esprit 150 at f/7 (Image 13). Again, not as deep as I would have liked before the dew fairies put my night to an end, but I think this is actually quite good for only an hour s worth of data on a DSLR. Mind you, too, the nighttime temperatures in Florida for September are still in the 70s. There was remarkably low noise considering it was warm outside and the camera had been running al- Astronomy TECHNOLOGY TODAY 37

7 Image 12 - Andromeda (45 minutes of exposure time at ISO 800, 5-minute subs). Note the lack of raccoon eyes around the stars. ready for hours before I even started on this target. The Ha regions came out quite nicely, and with more time, I would have been on my way to a showcase image. This does bring me to one potentially serious critique of the Nikon cameras for astrophotography. There is no reporting of the sensor temperature in the exif data. You will need to estimate or take darks at nearly the same time or ambient temperature to match them as best you can. Some image-stacking programs are quite clever about scaling darks appropriately, but I prefer to have my darks at the same temperature with no scaling. With a generous dither, having darks that may not exactly match is somewhat mitigated as well. Despite this, I can t say I am unhappy with any of the images I ve acquired with this camera. Image 13 - The Heart Nebula; a little more than an hour at f/7 and ISO 800. Another approach is to use the in-camera dark subtraction feature that Nikons, like Canon DSLRs, have. This effectively doubles the time it takes for an exposure, however. In both of these cases presented here, this would have left me with far too little data to salvage an image. Instead, I shot the darks when the clouds came, or one dew heater had failed. Finally, if you re of the school of astropho- INTRODUCING THE NEW 1100GTO GERMAN EQUATORIAL MOUNT Image Past the Meridian (up to the full 6 hours) Through-the-Mount Cabling Portability (R.A. & DEC. Axes Separate) 0 to 78 Latitude Range Built-in Precision-Adjust Rotating Pier Base Keypad and/or Computer Control Pre-programmed with PEMPro ASCOM Compatible with Fully Supported Driver Operate with 12V Battery Ideal for 8 Refractors, Cassegrains, Ritchey-Chrétiens and CDKs 38 Astronomy TECHNOLOGY TODAY

8 tography that uses FITS files instead of camera raw files, there is a significant space cost to this. FITS files without the Bayer processing (blackand-white raw data) are 72 megabytes each. If you re using PixInsight, a color FITS saved as 32-bit floating-point data (the default) is a whopping 436 megabytes! As you can well imagine, a computer without a lot of RAM is going to be slow processing these huge files off of disk. Anti-Aliasing? My final imaging test was on the Moon. I haven t said much about the removal of the anti-aliasing filter yet, and this is something that is touted in the marketing literature. This improves sharpness, but can add some moiré patterns to some daytime photography scenes (many professional photographers already seek this feature in stock DSLRs anyway). I think it can improve short wide-field nightscape images considerably, but it does not have as much value for deep-sky long-exposure images through an astrograph. At those pixel scales, the seeing is your enemy, and with the small pixels in this camera, your scale is often going to be quite over-sampled to begin with. I could be wrong about this, but at the time of this writing, I don t have any good data to say otherwise. On my last night out, the clouds were rolling in, and the Moon was in a clear patch of sky. I realized that the Moon would also make a good target to see just how sharp I could go with this camera, as it is a short quick shot that often freezes the seeing effects. The D810a was already on the Esprit 150, which I already know (see my review in the last issue) to be an exceptionally sharp instrument. I slewed to the Moon and began to fine focus with Backyard Nikon. I d take an image and slowly adjust the focus, and then retake the image to compare to the last. It just kept getting sharper and sharper. I was quite satisfied already but realized I had not seen any fall off, so I, again, kept moving the focuser. I was amazed that each image defied my expectations that, by now, I must surely be past best focus. Image 14 shows the end result of a 1/640 second exposure at ISO 200. Although clouds were coming in, the seeing was very stable as well, and this is, to me, an exceptional image. Conclusions For the serious photographer, this camera is certainly on a par with the high-end fullframe Canons. The price differential is substantial from say a Canon 60Da (if you can still find one), but comparing this to a 60Da or a modified Rebel is not really fair. As a stock DSLR, this camera is more on a par with the Canon 5D Mark III, and costs about the same, really, but with some very nice enhancements for astrophotography. If you want a high-end full-frame DSLR that is also well suited for astrophotography without the need for aftermarket modification, this camera is a very good value. Is it twice as good as a 60Da or a modified Rebel for twice the cost? Probably not, but experienced imagers know we often pay a premium for those increasingly smaller steps forward in quality and performance. If you are not budget constrained, this is likely a better choice; at least as far as this astrophotography evaluation is concerned. If nothing else, the larger sensor is a great incentive alone to upgrade. My Nikon shooting friends (you know who you are!) will be pleased to hear that I do like this camera. I d love to keep it. Would I trade it for my top Canon model? Ah, that question is more complex than the trivial comparison of a few features on a check list. I have a considerable investment in Canon lenses, accessories, and experience/practice. Moreover, I ve not evaluated this against my Canon for my other love, which is wildlife and landscape photography. So no, just as you wouldn t trade a spouse for a prettier face that comes along (well, I hope you wouldn t), there s more to a camera Image 14 - The sharpest full-disk lunar image I ve ever taken. choice than meets the eye, and it will take more than a couple of months of astrophotography to convince me to switch (I also have a rich inventory of very fine astrophotos taken with Canon DSLRs, mind you). Would I recommend this camera for astrophotography, though? Absolutely! For me, an invested Canon shooter, the really interesting question is: What s next? The 60Da was not discontinued because of lack of interest in the astronomical community, it was discontinued because the 60D was replaced by a newer model, and that production line was used to make the 60Da. Canon has been supporting astrophotography for quite a while, and I have faith that they will make this an even more interesting game in the coming months and years. Ditto Nikon. Competition works, and Nikon s new D810a is a formidable challenger. Astronomy TECHNOLOGY TODAY 39