Category Archives: Camera

Photographing Aurorae with a Night Capable Camera

Photo 1: Jupiter and diffuse, but bright aurora on our first night. f/3.5, 5 sec, ISO 4000, 20mm

This is part 2 of a multi-part series on observing and photographing an Aurora. Please read Aurora: The Bewitching Glow for background information including information about what an aurora is, when, how and where it can be seen, and photographs from Aurorae we observed near Fairbanks, Alaska.

So I Have to Get Lucky?

Before we jump into the details and the 3 keys for getting a good aurora photo, I think it is wise to set expectations about how likely you are to see a truly astounding aurora. Photo 1, above is one of the first captures I got on the first night on site (December 14). It was unexpected because the weather had been completely overcast all day. On December 17, the display was ASTOUNDING. I asked staff at Borealis Basecamp – which caters to aurora goers – as well as locals in Fairbanks, and I poured over the data to determine just how lucky we were to see the jaw dropping display we observed. The short answer is… “luck comes over time”. We used the Book and Hope method described in the first article to observe the aurora, arriving on December 14, 2023 and departing on December 18th – that is 4 nights onsite. But because we didn’t use the Monitor and Go method what we couldn’t have foreknown is how much the sun would cooperate with our aurorae dreams.

Diagram 1: M and X class solar flares in December, 2023.

Take a glance at Diagram 1, above from the SpaceWeatherLive.com archive. Fortuitously the most energetic solar flare (category X) in the preceding SIX YEARS occurred on the first day we arrived (and on New Years eve). The solar wind travels at over a million miles an hour (1.6 million kilometers per hour). But the sun is 92 million miles (147 million kilometers) away, so the effect of the flare on aurora production may occur in as little as 36 hours or as many as 4 days later. Even during a solar maximum events of this magnitude only occur infrequently. December 2023 saw two X class flares in one month – there were zero X class flares in the prior 5 months at all! The Kp Index exceeded 5 a total of 16 times in the 4 month period which means an exceptional once a week event might be a reasonable expectation during this part of the solar cycle.

Eli Fox, the chief photographer at Borealis Basecamp and the man who runs much of the Borealis Basecamp social media [Instagram] [Facebook] told me that exceptional aurora events occur on average about once a month or less.

A solid plan and good luck go hand in hand. But do not let that dissuade you. The displays we saw on two other nights were very pleasing and still produced great pictures.

Can I Get a Good Photo with ANY Camera?

Photographing aurorae is not different from the night photography we cover extensively on this site. If your camera is able to take acceptable Milky Way photos, it’s a good candidate – the aurora is generally much brighter than the brightest portions of the Milky Way.

Photo 2: Looking up. Bright fast moving aurora. Notice The big dipper at the left.
f/2.8, 2 sec, ISO 6400, 18 mm

While these articles are now starting to show their age, the principles still apply:

  1. High performing cameras (or see Which Camera is Better for Night Photography?)
  2. What to Look For in a Night Photography Lens

Surprisingly, some cell phones can do a respectable job and we will cover using cellphones in the next article in the series.

For any night photography the following minimums are recommended:

It also helps to become very familiar with the settings and controls for your camera and tripod – familiar enough that you can operate them in the dark with little or no additional light. That level of familiarity comes with practice… so if you are out of the habit, we strongly suggest practicing in your back yard (or in a dark closet). Practice while wearing the gloves that you intend to use! I discovered that merino wool glove liners were sufficient to keep my dominant hand warm even when the temperature dipped to -20F – but there was no wind and I avoided allowing any snow to remain on my glove liner – preferring to use my gloved hand or jacket sleeve when brushing away snow. Snow on my glove liner would have melted due to my body heat and made me miserable. I carried a pair of outer gloves with me, in fact, I kept a glove on my non-dominant hand at all times while my dominant hand had only the glove liner. The other outer glove remained in my pocked with a chemical hand warmer activated should my hand get cold!

Additional Photo Gear for Dealing with Excessive Cold

I brought quite a lot of gear to prepare for the affects of extreme cold on my person and my camera equipment. The camera equipment I brought included:

1. Five power banks – these were used to power “dew heaters” (aka lens warmers), as well as heated clothing.
2. Four of the powerbanks also were hand-warmers, most have built in lights.
3. Pouches in which I could keep the powerbanks, chemical handwarmers, as well as cables.
4. A large sealable plastic bag that can hold the entire camera and lens.
5. Carabiners to hold the pouches to my tripod.
6. And my standard practice of affixing velcro to key places near the top of my tripod with the mating velcro on the back of my intervalometer(s). This keeps the intervalometer in a usable place and prevents it from falling or catching the wind.

The pouches had operational electric hand warmers or chemical hand warmers to keep the power bank in them warm. I thought about, but did not use external batteries for my camera. Conceptually using external batteries permits using a larger battery (or using plug-in power) as well as keeping the camera batteries warm without warming the camera. The extreme cold is GOOD for your images. Deep sky astrophotographers typically use super-cooled sensors for their work, and your camera benefits from the cold, too, in the form of less noise.

If you use chemical hand warmers (charcoal, salt and iron filings), they need some airflow to keep generating heat – so don’t put them in a bag with no airflow. Indeed, if you want to reuse them, you can put them in as small a possible plastic bag to extend their life.

However I did keep spare batteries in my interior pockets where my body heat would keep them warm should I need to swap batteries. With the power banks, I also brought extra cables, an extension cord, and a 7 station USB charger. Of course all the regular stuff is needed, too… battery chargers for your camera batteries, cables, lens cloths and more. Another item I strongly recommend is gaffers tape which you can use to seal viewfinders, and lock down focus settings. And a large Ziplock bag. I also like to use a lens band (basically a large rubber band) to prevent focus or zoom settings from changing unexpectedly.

What Can Go Wrong?

Several aurora photographers wondered why I brought dew-heaters (lens warmers). These devices wrap around the end of the lens and via a power bank keep the lens warmer than the surrounding air to prevent dew (condensation) or frost from forming on the lens. Those with more experience than me typically did not use such devices because in the extreme cold dew is not typically a problem. BUT I did have complications I didn’t anticipate. In warmer, more humid climates, dew heaters can be the difference between getting a shot of “lens fog” and getting a great night shot.
The lens warmer is attached by cable to a power bank. More than once the pouch containing the power bank got bumped off my tripod yanking down on the lens ring which, unfortunately, altered either the zoom or the focus of the lens. In part for that reason I stopped using the lens warmer. But I did notice that more than once my breath crystalized on the outer lens surface. The take away here: in the extreme cold, keep your breath away from the camera as much as possible! And if you do use a lens warmer, find a secure way to attach it to your tripod so it can not yank on your lens.

From time to time I would use the viewfinder to frame my shot. But on my Sony Alpha 7R III camera, the frost from my breath condensed on the viewfinder resulting in two problems. The moist air from my breath froze on and made the viewfinder cloudy and I couldn’t see through it, and the sensor that turns off the back LCD when your eye is at the sensor got confused and refused to turn the LCD on. Effectively I was unable to use the LCD or the viewfinder to make adjustments. Fortunately this happened as the aurora was quiescing so I put my camera in a SEALABLE plastic bag, and brought it indoors.

Bag Your Camera! And Other Tips…

Why bag your camera? If you take your very cold camera indoors it will almost immediately form frost and condensation in the warmer more humid air – much like your iced drink glass forms condensation. Unfortunately condensation can occur INSIDE the lens and INSIDE the camera (e.g. on the sensor). Whenever I move the camera from a cold environment to a warmer one I bag and seal it and keep it in the bag until it has warmed to room temperature (about 1 to 3 hours). I can take it back out to a cold environment immediately if I wish. Keeping desiccant in the bag is not a bad idea, either! Oh, and you may find it advisable to remove your memory card and battery from the camera before bagging it so that you can examine the contents of the card or charge the battery while you have the bagged camera in a warmer environment.

Another unanticipated problem was that the extreme cold made the intervalometer cord quite stiff. It behaved more like a coat hanger than a wire. I strongly recommend using either a corded, or cordless intervalometer – you need it as a shutter release. The reason for the shutter release is to keep from adding any shake or wobble to the process of taking a photo – which occurs just by pressing the shutter button. A shutter release locked in “on mode” also allows you to take endless shots unattended which if you wish, you can assemble into a star trail like the photo below.

Photo 6: Applying Comet style star trails (with a satellite) (97) 6-second exposures. (each f/3.5, ISO 4000, 19mm) Total 9 min 42 secs.

Finally, I had difficulty adjusting the settings using the top dial on my camera – I believe also due to frost from my breath. I say “I believe” because it occurs to me that with my lightly gloved hand I may have been trying to rotate the function knob instead of the upper adjustment wheel. REMINDER: Get familiar with your camera before you get into the exciting environment where you may easily forget a step or two while gawking at the sky.

The Three Most Important Aurora Tips

Once you have all your gear, have a solid tripod (which you set up properly and securely) and are ready to begin photographing the amazing aurora… there are three very important things to NOT skimp on doing and double checking.

  1. Confirm (check) focus frequently especially after any bumps or changes in zoom.
  2. Do NOT judge the quality of the exposure by the display on the LCD. The only way to insure a good exposure is to look at the histogram (separate RGB channels is best).
  3. Adjust your exposure as needed to meet the circumstance. Aurora can go from dim to very bright and very bright to dim. They can move hardly at all, and they can dance about in the sky at a dizzying pace. So this means not only should you pay attention to those exposures, but you might want to avoid fixating on one area of the sky.

Tip 1: Checking and Setting Focus

The best way to check focus is to shoot an image and zoom in and check for the sharpness of any stars on the LCD. The best way to get focus right is to pre-focus at infinity when there is sufficient light (e.g. using a streetlight, the moon or a very bright star). While cameras can SOMETIMES successfully self focus most of the time they cannot without bright, motionless light in the distance. One way to get a good focus is to use live view, zoom in and hand adjust focus until a star is as compact as possible. But do not stop there… TURN OFF auto focus! You can set some lenses to “MF” or “Manual Focus”, but another strategy – perhaps easier – is to set your camera to do focus only when you press a separate focus button. Typically a camera is set to focus as you press the shutter – and that’s definitely NOT what you want.
If you’re not sure where to focus, we recommend either focusing on stars or if that seems difficult, you can focus on anything that is more than 50 feet away from you and that will be sufficient for wide-angle lenses.

Then take an exposure and confirm the focus is spot on. I took a whole sequence of exposures with lovely snow flocked trees in the foreground, but I made the mistake of not confirming my focus was spot on! It is also worth noting that the aurora may be diffuse and therefore not have a clear focus point… so don’t judge by the aurora! By the way, we also strongly recommend that you set a fixed White Balance (e.g. cloudy or daylight), disable long exposure noise reduction, and turn on high ISO noise reduction.

Some cameras have a “focus peaking” setting that you can enable. Focus peaking colors those areas of the image that are in focus (red is easier to distinguish in a night shot). This tip comes from Eli Fox, and is something I did not know is present on my Sony!

One last tip, focus MAY change as the lens gets colder or warmer – so do check periodically.

Tip 2: Verify Proper Exposure using the Histogram Feature

Diagram 2: An aurora photo with over exposed elements (see red pointers). The histogram (top right) shows a spike at the right – brightest end – of the range.

My modus operandi when shooting is to hand shoot a few images doing the focus check AND a histogram check before I set the camera up to take continuous exposures. I then periodically stop the exposures to double check the histogram. One additional help here is to turn on over exposure highlighting if your camera supplies it. With that feature on, over exposed areas will generally blink where there are overexposed pixels to let you know what areas are over. Overexposure is very difficult to recover from. The goal is to minimize the overexposures but get the images as “bright” as possible to capture the most information. I then usually shoot a shot with the lens cap on (or my hand covering the lens) so I can tell that I’ve changed settings or adjusted the field of view. Elements at the “bright” end of the spectrum by themselves don’t mean there are over exposures. By the way this is also why we strongly recommend you shoot your photos in RAW – or like we do RAW plus the smallest JPEGs.

Tip 3: Do Not Fixate

This tip has two parts. Do not forget to recheck at LEAST your exposure histograms periodically, and do not fail to look around in the sky. While you might have the perfect foreground, the aurora behind you or above you may be the most spectacular thing you will ever see. If you do not get a photo, it may as well have never happened! And while we are on this subject, do you notice how GREEN the snow appears in the right side of the photo below (as well as earlier photos)? They are reflecting the predominate color (557.7 nano meters wavelength) coming from the aurora. This is one of the possible problems with obtaining natural looking aurora photos.

Photo 5: The recorded color (right) gives an eerie green, but the left is hand desaturated in post processing.

As noted in Aurora: The Bewitching Glow (part one of this series), there are other colors as well. This can have the affect of making the landscape look “eerie”. Eerie landscapse can be combatted in two ways. One way is to be thankful for and take advantage of light pollution (or some moonlight), and the other is to post process the photo to desaturate the areas that look unnatural e.g. as is done above in photo 5. All the other rules of good photo composition apply as well. If the photo would look pleasing without an aurora, then it will be even better if there is an aurora. But if the scene is chaotic or not well framed, it will take an incredibly amazing aurora to save it. I think the main take away here is: experiment with different compositions, directions and settings.

One last point. The aurora can move very slowly or surprisingly rapidly. If you take a long exposure for a fast moving aurora it will “smear”. But a dim, slow moving aurora may require a longer exposure or a higher ISO or both. Consider the examples below. At the left is an approximation of one ten second, ISO-6400 exposure (f/2.8, 18 mm) created by combining 5 2-second exposures and the second is a single 2 second exposure. The “eye” of the aurora is overexposed and much of the swirly detail is lost. However even if the ISO had been dialed down or the aperture stopped down to prevent overexposure, the capture over the longer time interval would lose some of the fine detail – in much the way that a moving flashlight or a moving camera would create a smear. But do notice that more stars are visible in the longer exposure because 10 seconds is sufficiently short for an 18mm shot that the stars themselves are not smeared (much). To understand this a bit better, the best resource we know of is
described in our article: 600 Rule?

In fact, if you’d like to get an idea how fast an aurora CAN move in real time, here is a video sequence – not a timelapse – from Eli Fox

VIDEO: Real Time aurora used by permission from Eli Fox.

Well, that’s it for how to use a “night capable camera” to take aurora photos. But stay tuned, we have at least two more articles on the subject coming soon including:

How to Take Aurora Photos with a Cell Phone

All about Borealis Basecamp

As always, feel free to ask questions using the comments below. Thanks for the gift of your time reading this… and if you’ve found value in it, please do share the link with those you know who would appreciate it.

Canon vs Nikon

CanonVsNikonSteven Christenson is a long time Canon user who recently also added a Nikon D600 to his stable of camera bodies. The thought behind adding a Nikon was to get a higher performing body than his Canon 5D Mark II *and* subject himself to Nikonology so that he can be more effective at teaching workshops. Workshop participants tote many brands of cameras, the dominant brands being Canon and Nikon. As an additional side benefit Steven can now tease himself about owning a lesser camera.  🙂

Steven does NOT believe that a Nikon is automatically a lesser camera nor that a Macintosh is a computer substitute – these are things he says just to spark friendly conversation.

Previously Steven – a Canonite, and Eric Harness – a Nikonian have swapped cameras for a spell to encourage cross-education. It seemed time to bite the sensor – so to speak – and not rely on using Eric’s equipment. Steven is using the Nikon D600 with (and without) a Rokinon 24mm f/1.4 manual focus lens for night photography and astrophotography. Steven took both the Nikon D600 and the Canon 5D Mark II on a 3-week tour of Europe which provided plenty of time to form conclusions about the operational differences between the cameras. As a result of his experiences learning and using the Nikon he presents his top issues and keeps score to decide which brand is better from an ease of use point of view.

fEE – An Aggravating Error

Right out of the bag, literally, things went poorly for the new Nikon.  With the new lens mounted backward* on the Nikon body all of Steven’s attempts to take pictures were met with fEE. You may be thinking, yeah, but didn’t you just say he mounted it backward?  Well, no, Since childhood he’s learned that “righty-tighty, and lefty-loosey” define how one tightens and loosens things. But the Nikon is reversed. To attach the lens you rotate it LEFT, not right.  Ok, so if the problem wasn’t the backward rotation of the lens to mount it, what was it? It turns out, that the Rokinon 24mm f/1.4 lens *is* able to have the camera control the aperture BUT you *must* set the lens to f/22 or the fEE error results. It’s not optional. This seems ludicrous. When he puts a manual focus / manually controlled aperture lens on a Canon it all works just fine, that is, in the Canon metering works just fine.  Why Nikon insists on messing with the aperture on a manual lens is troublesome. This behavior sabotages one trick that time-lapse photographers use to prevent the camera from random fluctuations of the iris (and coincidentally needless mechanical wear). Left to the camera slight changes in the aperture result in visible flicker. Timelapsers, therefore, use the “depth of field” preview button and then slightly twist the lens to disconnect the electrical contacts thus preventing the camera from monkeying with the aperture. Since the Nikon control of the lens is mechanical, not electrical, it’s not clear if there is a clean way to keep the Nikon from messing with the manual aperture control on the lens. We are adding a point to Canon’s score for more sensible behavior.

Score : Canon 1, Nikon 0

Can’t Focus

OutOfFocusThere was another problem, too. After mounting the Rokinon on the Nikon, it was impossible to focus at infinity.  Checking the diopter controls, the security of the lens mount, etc. resulted in no joy. Since both lens and camera were a gift, Steven worried that he’d have to tell his wife that something was broken. Indeed, something is “broken” but exactly what is not clear BECAUSE when he turned ON the Nikon, it suddenly became possible to manually focus the lens at infinity.  Remember this is a MANUAL focus lens! Steven regularly sets up his Canon and pre-focuses with the camera turned off. His initial thought was that the Nikon hadn’t pulled the aperture open… but the view didn’t become brighter when the camera was turned on so something else odd is going on. What? Don’t know, and it’s an intermittent issue. Canon gets another point for not having this bizarre behavior.

Score: Canon 2, Nikon 0

Viewfinder = Confusion

The next headbanger came when Steven tried to actually shoot with the camera.  The viewfinder was filled with all the content intended but the shot was far different from the view in the viewfinder. How different? Well there was about 30% more in the view than appeared in the shot.  Unfortunately this unexpected twist meant that Steven’s first night shots of the sky over Santorini were unstitchable due to insufficient overlap. Do you know what the problem is?

Steven couldn’t figure this one out, though weeks later he pleaded with Eric for help and Eric resolved the problem!  Here is a clue: the image size was also much smaller than expected: 3936×2624 pixels rather than 6016×4016.  Apparently the camera either came preset to or was somehow accidentally put into “DX” mode where only the center of the sensor is used. This behavior is readily noticeable when using Live View. In a warped way, I guess this is what allows Nikon users to mount any lens to any Nikon body – cropped or not – and get a result.  Canon’s approach is to not permit mounting of a crop factor lens on a full frame body.  The Nikon center crop mode results in smaller files. If that also achieved faster frame rates a full point advantage would be awarded to Nikon, but that doesn’t seem to be the case. Nikon scores 0.5 points for versatility (though we are sorely tempted to subtract points for unexpected behavior).

Score: Canon 2, Nikon 0.5, Steven -1, Eric +1

Chameleon Lenses

ChameleonSteven intentionally got the Nikon G-Mount Rokinon 24mm f/1.4 for it’s speed and because it’s a form factor that he didn’t already have. But a nice little side benefit came with it. Because of the lens mounting schemes used, it is possible via a cheap little adapter to use pretty much ANY Nikon lens on a Canon body (but NOT vice versa). Nikon gets a full point for this benefit.

Score: Canon 2, Nikon 1.5, Steven -1, Eric 1

Finding Your Way Around

ConfusedObviously the menu systems are different on a Nikon and Canon. Mostly its a matter of taste. Both Canon and Nikon camera models regularly and needlessly re-arrange the names and locations for settings.  There is no clear winner here. Likewise the locations of buttons and the features on those buttons move around as bodies change – sometimes maddeningly so.  Steven doesn’t have enough experience with Nikon to form an opinion about this, but every one of his 3 Canon bodies has buttons “needlessly moved”.  For example the top-deck light button moved from the innermost to the outermost button. Why? Canon must have been bored. Steven does find it annoying that the top deck light on the Nikon D600 is built into the on-off switch… and the light doesn’t stay on long!  In fact, locating the Nikon on-off switch just above the settings wheel has resulted in several unintentional turn-offs of his Nikon.  Accidental power off is happening less over time though.

One example of a difference in philosophy between the Nikon and the Canon is in the ISO setting. On Canons you press the ISO button (top deck), then spin the wheel. You can change the ISO one-handed.  On the Nikon, you must hold a button (lower left) on the back and spin the control with the other hand – two-handed control. I prefer one-handed control it’s easier in the dark. On the other hand, you must wade through several menu settings to format a card in the Canon. A double, double-button press (plus a selection) allows you to format one of the two cards in the Nikon. It’s a little SCARY that I can accidentally format one or both cards by accidentally holding the wrong buttons on the camera.

An example of a Nikon gaff is in image delete. Press delete then press delete again and poof, image shredded.  If Steven fumbles (and he’s known to do that) it means an image can go up in smoke by accident. The Canon method is to press delete then require a scroll and a third operation for confirmation.  It’s a little more tedious, but safer.  It is clear, however that the Nikon has more buttons and more controls available with less total fumbling. So we award Nikon another 0.5 points. And now the score is tied (except that Eric is leading Steven significantly).

Score: Canon 2, Nikon 2, Steven -1, Eric 1

Light Leakage

Light leak through the viewfinder.  ISO 4000, 30 seconds

Nikon D600 Light leak through the viewfinder. ISO 4000, 30 seconds

In astrophotography and landscape astrophotography it is very useful to collect dark frames. A dark frame is a normal shot but with the lens cap on and the goal is to capture an image with stuck pixels or black level offset to fix other images taken with the same settings and at the same temperature.  Much can be learned about this in our BLOG.  Anyway, while shooting dark frames indoors with a capped lens, Steven was very distraught to discover that significant amounts of light can leak in through the eyepiece of the Nikon D600 and render the dark frame (or any high ISO night shot for that matter) unusable. Above is an actual shot. While it is true that light entering the viewfinder of a Canon 5D Mark II (and other cameras) can fool the metering system, Steven has never observed light leakage of the severity that the Nikon D600 displays.  Both Canon and Nikon offer eyepiece covers to solve this problem., but in truth, the cap doesn’t seem necessary on a Canon except when metering. Canon wins another point here.

Final Score

BoxingGloveCanon 3, Nikon 2, Steven -1, Eric 1

At a final score of 3 to 2 in favor of Canon does this contest feel like it has been rigged? Have you used both types of cameras? What is YOUR favorite feature or biggest pet peeve? Leave a comment!

Extraordinary Vision

Last month, one of Steven’s images was featured in the great (and free) Extraordinary Vision magazine issue 9 which is published online via iTunes.  

I_305-0347This month in Extraordinary Vision issue #10 you’ll find 17 pages of instructions on finding and photographing the Milky Way. If the article seems familiar, it is! The Extraordinary Vision article is an updated and combined version of our three-post series on the Milky Way:

If you haven’t checked out the magazine, please do – not just because of the Milky Way content, but because Angelo Ioanides does a fantastic job curating and writing great content. And it’s FREE – just like the content on our BLOG.

First page of the article.

I_305-0346

 

 

 

 

 

 


Click the image below to find the Extraordinary Vision Magazine:

Extraordinay Vision Magazine published on iTunes

 

 

 

 

What you Need to Know About Histograms

Original Publish Date: 11-September-2013
Last Revision: 11-April-2016

If you ask us what is the most potent tool a night photographer can wield, we’ll tell you: the histogram.  Unfortunately nearly all of the histogram information available seems to spend too much effort talking about what a histogram should look like and not enough time explaining what a histogram is… or that there are many different histograms and not all are equally useful. For example there are: luminosity histograms constructed from thumbnails created by the camera, there are color histograms created from the same thumbnails, and then there are luminosity and color histograms based on the actual sensor data – but those are rare. And of course there are still more histograms.

In the Beginning [41_03766]

In my early days I took what I thought was a fabulous photo of the fog creeping up against Mount Allison. It looked SO good on my LCD that I knew I was going to be in love with it. When I got home I realized that it was far from ideal. It was woefully underexposed and very noisy. That’s because I didn’t think to look at the histogram. At the time noise handling was not great and it wasn’t until recently that I was able to tease a half-decent image out of the data.

Deconstructing A Histogram

The best way to understand a histogram is to experiment. But before we launch into some experimentation, let me take a stab at explaining what a histogram is.

A histogram is a graph that shows the distribution of brightness (luminosity) over the range from the darkest possible to the brightest possible pixel.

Each vertical column reveals the number of pixels in the image that have that brightness level.  Usually the left edge is the darkest possible pixel – black – and the right edge is the brightest possible pixel – but there are some variations in histograms which we’ll cover in a moment.  Here is a degenerate, but perfectly valid histogram.

LuminosityHistogram_degenerate

A histogram showing only three brightness levels – nothing brighter than mid range.

In the graph above, we see that there are some (we don’t know how many) of the darkest possible luminosity.  A lot of pixels that are relatively dark – corresponding to the tallest line, and a few pixels in the “midrange” of possible brightness values at the next stubby little line. The image from which the histogram was made is this one:

BoringImage

A degenerate image composed of several primary colors.

Looking at the image, it is pretty obvious that the little bump on the far left of the histogram is the black frame around the border. The tall line in the histogram is the brown, and the little bump near the middle is the orange color.  What may be puzzling is that the orange looks pretty bright and you would not expect it to fall only about half way across the range from darkest to lightest values. In fact there IS clipping in the red channel – but we don’t see that in our luminosity histogram above! We’ll see why in a moment.

post-it-note-thIf one of the columns reaches the top of the graph it does NOT mean a “blow out” has happened. Likewise if a column appears at the right or left edge of the graph it does not mean that data has been lost or “blown out” – it does indicate that there MIGHT be a problem.

ColorHisto.bmp

At right is another histogram for the same data, 4 of them, actually. This was created using Photoshop’s “All Channels” view.

Rather than luminosity, the top histogram is in mode RGB showing each of the colors in this simple image against the maximum for that color.

The Red Histogram shows a complete range of reds from the darkest possible in the black border to the lightest possible. And here is where we first get a clue that quite a bit of the red is in the extreme right hand side of the histogram.  Most of the red is contained in the brown color.

The Green histogram shows the darkest possible green (i.e. black) and some green in the left 1/5th of the possible values, while the blue histogram shows only black and very dark blues.

Admittedly the image is not illustrative of a typical photograph of any kind. It does show clearly how the histogram corresponds to the values in the image.

HistogramLayersII.bmp

The image was created from additive layers using blend mode Linear Dodge ADD. Each layer has been constructed in different colors using the color value shown.  It is easy to calculate the majority of RGB triplets as: R=128, G=64, and B=32+16 (48).  The maximum values for an 8-bit image would be 255,255,255 – the value of the “whitest possible white” in this color space.

You might expect that the graph would reflect the 16-bitness of a 16 bit image. The maximum values for each color then would be 65,536, not 255 – but that’s not the way Adobe shows it.  A 65 thousand pixel-wide histogram would be beyond unwieldy.

Did you just have an “aha” moment?

One reason why the histogram is not completely trustworthy is that it is a composite of many luminosity values being lumped into one.  How so? Imagine possible values from 0 to 65,000 shown on a graph with only 255 different columns. A lot of “lumping things together” is present! It is possible to have lots of data in the darkest column and in the lightest column and still not have any blow outs or blacks.  Imagine it this way, suppose there were 100 possible luminosity values, but the graph showed just 20 columns.  The leftmost column would include values ranging from 0 to 4, the rightmost (brightest) would hold values from 95 to 99. So, in theory, you could have no zeroes and no maximums, but your graph would still show you data at each extreme.  This is where the histogram in Adobe Camera Raw is much more useful and accurate. Or to be more accurate, it’s not the ACR histogram that shows that much additional data, but it does indicate when items are being “clipped” – that is, reach the maximum or minimum.  But we’ll get to that in a minute.

In case you haven’t had another AHA moment, we want to explain why the histogram you see on your camera LCD should be regarded with suspicion.  That on-camera histogram is created from the thumbnail JPEG which is also shown on your LCD.  To go from raw data to a JPEG involves lots of operations including scaling 14 bits of information down to 8 bits, taking megapixels of resolution down to kilo-pixels and applying default curves and color assumptions. With that much data manipulation going on, your histogram reflects what your image MIGHT look like as a tiny JPEG and therefore may not accurately reflect what you’ve captured.

Get A Better Histogram: Use Lightroom or Adobe Camera Raw

Below is a much more useful histogram as found in Lightroom or Adobe Camera Raw. Your camera is not going to give you this level of detail- though you might have a highlight and/or shadows clipping indicator which we recommend you use.  ACR and Lightroom both offer shadow and highlight clipping indicators. Clipping indicators are enabled using the triangles in the upper left and right of the histogram or with the “J” key which toggles both indicators either on or off.  If you turn ON the clipping indicates by default blue dots replace clipped shadows and red dots reflect clipped (aka blown out) highlights.

First the wide view.

OverAndUnder_wide

Wide View: Shadow clipping (left arrow in histogram) turned on. BLUE indicates where the values have fallen to zero.

And here zoomed in:

OverAndUnder_zoomed

Zoomed in: We see both clipping in the shadows and highlight clipping (circled -though there are many more).

Notice how in the 1/4 view, we see much more shadow clipping! If we zoom in to 100% it will be even more obvious. As we adjust the exposure, shadows, contrast, highlights, blacks and whites the histogram and the clipping indications are reflected in real time.

Lightroom is also giving you a hint which colors are being clipped.  The blue triangle at the upper right tells you that the blue channel is causing the highlight clipping.  When multiple colors are being clipped, the triangle will include all the colors added together. Here the white triangle for the shadow clipping tells us ALL colors are zero – that is clipped in the shadows.  For this image moving the exposure to the right reveals that the green channel is the most clipped. 

Take Aways

  1. Don’t believe everything you see on the back of your camera display – especially not the image!
  2. Don’t only pay attention to the luminosity graph – it may hide highlight clipping in one or more colors. This is especially true, for example, if you take photos of red roses. You can cause the red channel to clip but the luminosity graph will look fine.
  3. Take a look at the color histogram if your camera has one.
  4. Just because you are taking photos at night doesn’t mean you can’t blow out the stars. Doing so means you’ll lose some color data, but it’s better to blow out a few stars than to have black for your foreground.
  5. Not every histogram (in fact most) won’t be “bell curves” – especially not at night.
  6. Oh, and please shoot in RAW. You keep a lot more of what you shoot that way!

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Clouds, Milky Way and Eerie Formations in Alabama Hills, CA

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