Category Archives: High Dynamic Range (HDR)

Night Assault / Ghost Hikers – Stacking Action

Here is an example of star trails and people-made trails. It uses the same old stacking tricks I’ve been espousing in several articles on my BLOG.

Hikers brave the famous cables on Half Dome in Yosemite at night. The moon was about 90% illuminated and this was taken as astronomical twilight began. Hikers with headlamps blazing hiked up the cables in this multiple exposure shot spanning about 18 minutes.

Permits are required every day of the week. Rangers are there checking quite often.

NOTE Photos of the cables from this angle make it look like the ascent is brutally steep. It is STEEP. The slope of Half Dome on the left side is about 45 degrees. The slope on the right is about 65 degrees. The slope the hikers are taking is about 39 degrees with a section in the middle that is almost 45 degrees. I say this because it’s NOT that much steeper than a flight of steps which is normally about 39 degrees. Of course there are no steps here and thousands of hikers have smoothed the granite enough that good footwear is a necessity. The consequence of a slip and fall are quite a lot more serious than a slip on a flight of stairs. To say that you have to “pull yourself up” the cable is not at all true (fear or bad footwear might drive you to try that, though!) But you will want to to keep at least one hand on the cables at all times. DO NOT attempt to walk up in sneakers, flip flops, or dress shoes. Wear hiking boots or climbing shoes. You will probably slip and die if you don’t have good footwear. Several have already done the slip, fall, die thing, so you won’t be doing anything original or creative. So don’t, please!

By the way, coming down is more daunting! I suggest going down backward always keeping your arms fully extended and at least one strong grip on the cable.

End of An Era meets Half Dome [C_033409-11tm]

Improving Your Panoramas

Hi, I am Eric Harness, one of the instructors of Star Circle Academy. I want to first thank Steven for the great intro, also for his inspiration and his mentorship.

Steven asked me to add some important details to his Panorama Pursuit article.  So here I will expand on the information that Steven described by adding important panorama setup considerations, shooting tips and my work flow.

Panorama’s give the viewer context and detail that is not possible with standard photo sizes.  So use this to your advantage to show the viewer interesting elements to heighten the scene.   A scene worthy of shooting is worth the effort to set up the shot properly.  Seek wide open spaces where the relationship between elements gives an emotional connection to the place or thing.  A lot of landscape photographers like to exclude human elements in landscapes. However, including people, cars, and other human sized things helps to pull your viewer into the scene.   Park your car on the rock, leave the door open, have your friends pose looking into the scene.  Just make sure you connect the people in the scene to the rest of the scene. Highlight their interest or the viewer will not be interested at all.

People stop to look at what others are looking at all the time.  Let me give you a great example.  I often visit a large national park and I will often stop to photograph the animals on the side of the road.  I stop and ask my passenger to point out the window. Or for even more effect I have my passenger a poke big lens out the window even when there is nothing there!  People behind us stop and look while I slowly creep away.  This happens all the time – not just in the park but also at the mall, or art gallery, or along the road.  I use this natural human curiosity to look at what others are looking at to my advantage and put these on-lookers in my panorama!

Setting Up the Shot – The Tripod

It may seem like an after thought but once you bump your tripod in the middle of a panorama shoot you will be reminded about the importance of your base.  All of the elements depend on having a solid base so spend careful time to set it up.

  1. Extend the legs in a manner that allows the head to be as level as possible.
  2. Spread the legs so that the weight of the head and camera is over the center of gravity of tripod.

Even if you are not using a pano head the extra effort will help preserve the edges of your image (trust me it looks like your camera is on a roller coaster when it is not done correctly).

This multi-row panorama was not leveled before the intial shooting. The fix at this stage is to crop or fill but in this instance would make the image un-usable.

 

 

 

 

 

 

 

Any wiggle in the base will cause tiny misalignments in your images which can cause blurry stitches or fuzzy images (especially for HDR panoramas).

Managing Subject Distance and Parallax

Parallax errors occur when close and far objects shift in the frame relative to one another. This problem occurs when the camera is not rotated around the optical center of the lens.  The shift between close and far objects in more noticeable than the shift between two objects that are far away. If you keep all elements – especially important subjects – far enough away you will be less likely to encounter parallax error. Like Steven, I am not about to jump into the fray over the terminology wars over “nodal point” or “No Parallax Point” discussion.  However for an example of parallax error have a look at Figure 1 and Figure 2 below. Figure 1 shows proper alignment on the “no parallax point”, while Figure 2 shows how parallax results in an inconsistency.

Figure 1: These two images resulted after rotation around the "No Parallax point". Note how the foreground bars align with the same background objects.

If the lens rotation is NOT made around the “no parallax point”, then foreground and background objects shift as shown in Figure 2.

Figure 2: Two adjacent images with parallax - Note where the middle bars appear in relation to the steps behind them.

Alain Hamblenne has written an excellent article about how to align a panorama head in the horizontal and vertical directions. Note that Mr. Hamblenne refers to the no parallax point as “the entrance pupil“.  Even if you do not have a panorama head, the procedure Mr. Hamblenne describes will help to determine where the best center of rotation is. If you are lucky – as Steven was – you may find that your lens ring mount is almost the perfect place. Rotation around the tripod mount point in the camera is almost certainly not the best point.

Focusing for a Panorama

Focusing is not that hard in my opinion; just know your hyperfocal distance!  Yes, learn it for your lenses at different F-stops. Get out the tape measure and start pixel peeping.  Look up the resources on the web (DOFMaster) and learn to tell the distance by eye and turn off auto focus, then manually focus the lens.  Ok, focus done!  Furthermore, if you are doing this at night no worries you know if by heart if you don’t then turn on the million candle power flashlight (your cheater to activate your autofocus in the dark, then turn  autofocus off).

Getting the Proper Exposure Range

Let me first cover why I do HDR (High Dynamic Range) Panoramas. There are generally two reasons 1) the Sun, 2) your camera sensor.  Most panoramas span a large tonal range because of the directional light from the sun thus one edge might have a different exposure value then the opposite edge.  To make it even more difficult your camera’s sensor is not capable of capturing that level of tonal range in one photo.  Thus we take multiple exposures (bracketing) to capture a wider tonal range to represent what was really there.  Now that we have explained why bracketing for an HDR is important it is critical to determine the proper exposure range. Since the scene may span the tonal range from a dark canyon to a bright sunny area getting the proper exposure range is important.  There is no camera capable of capturing such a wide range of tones in a single photo.  But how do you decide the exposure range of the bracket and where the middle exposure is?  This is the method I recommend: Set the camera to Aperture priority mode and set the metering mode to a single meter point.  Then swivel the camera to some of the brightest and darkest areas in the range of your panorama. Then average the highest and lowest limits to select the middle of the range and then select bracketing that will encompass the approximately the whole range.    Remember to switch back to Manual mode and set the exposure to the middle of the range and select your bracket.  Typically as Steven suggests a two exposure bracket on either side of your middle will give you enough exposure range for most HDR panoramas.  I will typically set my bracket at a full stop and take a range of five exposures for my HDR.

Here is an example of calculating the proper exposure. Assume the darkest area of your panorama meters at 1/30 of a second at f/9. And the brightest area meters at 1/300 of a second.  30+300 = 330 and half of that is 165, so the middle of the exposure is about 1/160th – or whatever is closest. That’s not too wide a range. From 1/160th  plus and minus two stops covers both 1/30 and 1/300th.

Shooting and Overlap

Now your camera is set up for taking the photos but where should you start?  Some people use the degree scales on the tripod head to determine the overlap but I don’t recommend this.  Why?…well by not seeing what is in the photo you can’t determine if there is enough detail for the software you will later use to detect the overlapping elements in the photo.  Areas with large expanses of water or sky have little detail and will be hard to stitch.  The overlap I recommend is 30% to 50% but I have been forced to use 10% in areas of sky between trees.

I have to first decide where to start and end, what direction do I go.  I look at what I want on the edges of my panorama the I pick something further out then that to start and stop at.  If I want to include the top of a peak then  I will make sure to include some buffer in case I need to do some cropping.  Therefore, I will pick a solid landmark like a distinctive tree I call these left and right anchor.  This element usually will run vertical through the frame so I will run into it if I do a multi-row panorama.   I will center this object then I will I always start from the first frame at the left and go right just for consistency.  If I am doing a multi-row panorama I usually place the horizon on the lower third of the image to maximize the amount of sky I can get  but I always start from the bottom left then march to the right till the anchor is well within my frame the I tilt the camera up to capture the next row proceeding right to left till I reach my anchor then move the camera up again and proceed left to right again.

The first photo usually take in a set is a simple shot of my hand to indicate that this is the beginning of a new pano.  I cannot tell you how many times this has come in handy in determining quickly where the shots from one pano end and the next begin.  Also it help me to quickly group the photos so I do go through my photos say “that’s a crappy photo—delete” then only to realize it was the middle of a panorama (I have done that).

How do I take the photos so I don’t miss a photo in the bracket and keep my photos aligned?  I use continuous release mode and remote release to lock the shutter to shoot all the images in the bracket before I look in the view finder to align the next set in the panorama.  This allows me to pay attention to the things around me like people moving into the shot or time the shots to avoid the wind instead of counting shots.

Automated HDR and Stitching – PTgui

As Steven suggested use your favorite HDR program and stitching engine to combine the images.  I recommend using PTgui because of the enormous amount of control and power.  But there are other stitching engines out there: Autopano, Microsoft ICEPhotoshop, HUGin and the list goes on.  I use PTgui because I can HDR and stitch all at once. PTgui can run in batch modes to automatically identify which images belong in a single pano and start the stitching.  In the newest version of PTgui you can zoom in on the preview panorama, mask out the “unwanted tourist” and preview your stitch lines.  The software also allows you to output the images in the set as a photoshop “.pdb” file in layers or the entire blend and stitched panorama.  Thus you can fix certain elements of the photo like shaking branches or moving people. All of the dedicated stitching engines PTgui, Autopano, and Hugin allow you to take full control and stitch low contrast photos by adding control points to the elements that match in your overlapping areas telling the software these areas are the same.  Control points help the software to match corresponding points despite any distortion caused by the lens.  Manual alignment is not possible in Photoshop CS5 or Microsoft ICE.  PTgui control points are a huge advantage in aligning stubborn images with little detail.  Find some details that overlap and are easily recognizable in the two photos zoom in and click on the pixels that represent the same object in each photo. I like to use distinctive branches, tips of trees or jagged mountain tops; something that has a sharp edge and will be easy to match the pixels in the other photo.  Once a few manual control points are added the software takes over and starts aligning the matching points automatically.  With a sufficient number of control points the software can use the information to warp and stitch the images into the final panorama.

 

Manual Processing HDR then Stitching

If you don’t have an engine that can handle both HDR mapping and stitching at the same time no worries you just have a few more steps.

First do HDR blending using the images of your main subject, meaning the people or the thing you are using to draw your viewer into the photo. Save the HDR settings for the main subject and process the rest of the bracketed images using the saved settings.  Doing HDR blending first and then stitching is much less error prone than stitching first and then blending.

Once the blending is to your liking drag the blended images into the stitching engine and let the software do the rest of the work.

What About Stitching Night Images?

If night images are what you want to stitch, please stay tuned as the next article will cover panoramas in your night photography.

Resources

Finally let me point you to fantastic resource for more on panoramic imaging.  Panoguide – a forum for panoramic imaging.  Panoguide is a in-depth discussion of the hows and whys of panoramic photography. They have an expansive “How to section”.

Thanks for reading, as always comments and questions are encouraged.  If you have found this interesting please forward to your friends and follow us on Facebook. If you are interested in this topic (panoramas), night photography, shot planning, or super cool post processing techniques come and join us for a workshop.

Alignment (Part 2 of 2)

If you are finding these articles useful, please spread the word. Share us, Tweet Us, Digg us. Like us on Facebook. And if you would like one on one instruction please consider a Star Circle Academy Workshop. Now back to your regularly scheduled program.

In a previous column: Alignment Part 1 of 2, I touched upon the many elements that complicate capturing the moon near an object on the horizon. Here they are again for consideration:

  • The amount of moon illumination changes daily.
  • The moon’s rising and setting location must be accurately calculated – and it changes daily.
  • Exposures to capture moon detail require the right amount of foreground illumination.
  • The site chosen must have an unobstructed view of the sky in the desired direction.
  • To get a “big moon” it is necessary to get far enough away from the foreground.  If too close, depth of field problems may arise.
  • A well supported telephoto lens is required.
  • Capturing a shot of the moon near the horizon means the atmosphere must be relatively clear of clouds, dust and haze and when very low in the horizon there is more atmospheric distortion.

Figuring out how to tackle the moon location is computationally challenging. Fortunately with the internet there are many free resources to aid in this endeavor. And more fortunately, there is one tool which is almost ideal for the task: The Photographer’s Ephemeris.

We will address the problems step by step.

  1. Obtain the appropriate camera gear.
  2. Identify a suitable target.
  3. Calculate how far away we want to be from the target.
  4. Identify possible vantage points to shoot that target.
  5. Verify (visually, if possible), that the target is viewable from the vantage point and that there is sky behind our target.
  6. Verify that the moon will pass near our target and at an opportune time of day.
  7. Determine how high in the sky the moon should be.
  8. Fine tune the location to be sure the geometry is correct.
  9. Pray for good weather!

The camera gear element of the puzzle is easy: get the longest telephoto lens available. 2,400 mm will work great with a 35 mm (full frame) camera. I do not have anything that big (or expensive), so I use a 70-200 mm lens with a 1.4x extender on a 1.6 crop factor camera.  That effectively gets me 200 \times 1.4 \times 1.6 = 448 mm focal length. The “short” focal length of 448 millimeters means I can not fill my frame with the moon – it would take 32 moons laid out in a grid. Getting more foreground in the shot creates more opportunity for an arresting image however. Besides, those really big lenses are not only expensive, but unwieldy. In fact, they call them telescopes! Working with a crop camera in this scenario is a benefit.

No telephoto? Well then I probably would not bother – at least I would not bother trying to capture moon DETAIL.

Picking a Target

The moon is obviously one of our targets, but we want something interesting in the foreground to pair the moon with. Ideally we want a target that clearly stands above the surroundings and preferably one that allows us to get the proper distance away to maximize the “big moon phenomenon”. How far away?  Here is an easy formula: multiply the height of the object by 114.6.  If the object is 100 feet tall, the proper distance is 1,114.6 feet away.  If the object is 20 meters tall, the distance is 2,292 meters.  If 6 inches, then a distance of 687.6 inches is about right.

For the curious, the number 114.6 corresponds to 1 \div {\tan{(0.5)}}, where 0.5 is the number of degrees of the angular size of the moon from anywhere on earth. If shooting from somewhere else in space more advanced trigonometry may be needed.

It might be tempting to start with something short and nearby, like a golf ball. But getting a good depth of field is going to be difficult.

Let’s get started on the target, shall we? Fire up The Photographer’s Ephemeris (TPE) and follow along with me.  Switch to Ephemeris Mode (it is the first selection in the upper left). In the search bar (lower left), enter “Pioneer Park, San Francisco, CA“.

Now would be a good time to make the TPE window as large as possible, and select the “Satellite” mode in the map.

Figure 1: Pioneer Park Coordinates and Elevation according to TPE

Right above the upper right corner of the map you should notice two things: an elevation (here shown as +190 ft), and the GPS coordinates (37.8…blahblahblah).  If you prefer metric (or it shows metric and your prefer feet, you can change that using “Configure”).

Looking at the zoomed in map, put the cursor over the map near the bottom and click and drag upward. The map should move and soon you should see a conical shape casting a long shadow. Hooray. You found the Coit Tower. Double click in the center of the structure and it should look about like this.

Figure 2: Coit Tower in Pioneer Square, San Francisco, CA

Here I cheated and moved the elevation (+266 ft) and the GPS coordinates on to the image from above the map from the bar above.  I also zoomed out a bit so you can see the parking lot that you first landed on.

Did you notice that the elevation moved up from 190 to 266 feet?  You gained 76 feet in just a few parking spaces! It is steep there, but that number is NOT a measurement of the height of the tower, my friend. That is the elevation of the BASE of the tower. Don’t believe me… click a few spots near, but not on the tower or the building.  Click things farther away if you like, I’ll wait.  As you can see from the image at left taken from the parking lot, there is clearly not a gain of 76 feet between the two places.  The elevation information comes from a variety of sources, mostly the United States Geological Services (USGS) data.

What you hopefully learned is not to COMPLETELY trust the elevation shown. The elevation does not include buildings or trees and is not that precise, but it will probably be good enough.

In a while you will need to know the height of the tower above the base. Guess where you can find that? Yep, Google. Did you find it yet? It’s 210 feet (65.4 meters) tall.

So doing the math: ideally we’d like to be 210 x 114.6 feet away (24,066 feet or 4.5 miles) to have the moon’s apparent size be as big as the tower. Unfortunately going to the east, our choices are mostly in the San Francisco Bay, farther away on the Oakland Shore (near the Bay Bridge), or closer. Treasure Island looks like a good spot. It’s 2.11 miles and there is a lot of flat, publicly accessible shoreline to move along to align the moon behind the Coit Tower.  And besides even though the Coit Tower sits up on a high hill, only about the top half of the tower is above the sky line. So 2.11 miles might work out very nicely.

Since we have chosen a site to the east of the Coit Tower when can the moon appear behind it?  Near moon SET of course.

If you want your diagram to look exactly like mine, change the calendar to June 15, 2011. And change the Ephemeris mode to “Detail” (use the D key, or click the box down near the calendar).

When you switch to Detail mode, a hollow little gray marker will appear. Usually to the right of the red marker near the right edge of the map. Don’t lose it – you’ll need it in a minute.

Calculate the Moon Location Near Moon Set

You may have noticed all those colored lines extending from the Coit Tower in Figure 2. Here is what they mean: the light yellow line is the direction of sunrise, the orange line is the direction of sunset. The light blue line is the direction of moon rise and the dark blue is the direction of moon set.  All by itself that won’t help much. To see the moon setting in the west behind the Coit Tower, you obviously must stand to the EAST. But where?

Zoom out your map until you can see the Coit Tower on the left, and Treasure Island on the right. Make sure you are in Detail Ephemeris mode (you’ll know when you see a graph like this:

Figure 3: Sun/Moon graph and time slider.

Your map will look something like this:

Figure 4: SF Bay Map with Coit (lower left) and Treasure Island (upper right)

I have stripped off all the stuff around it to focus your attention. You’re focused, right?

Now would be a good time to play with the time slider. Click and drag it. Whoa! Did you see the lines moving? The skinny ones, that is.  There is a lot going on here, but the one thing you’re not yet seeing is where you need to stand to see the moon behind the Coit.

Stephen Trainor, the author of TPE put a cool feature in this tool. He did so because I asked politely and I support him with donations – I urge you to do so too. Buy his iPhone/iPad version of the tool (or Android if that’s available) or make a donation if you’re using the desktop (free) version of the Ephemeris. It’s the right thing to do!

Move your time slider to 5:13 as in Figure 3.  Now hold down the shift key. Did you see the thin blue line jump out? That blue line traces roughly where the shadow of the moon would appear. It can’t be completely accurate, however since the exact location would have to take into account topography, trees and man-made structures. We helped ourselves around that worry by choosing a flat shoreline where not much can get in our way.

Now would be a good time to find that hollow gray marker. Lost it? Click “D” then “D” again. It will appear near the right side of your map connected by a dim gray line to the red marker.

Hold down the shift key again, and drag and drop the gray marker on the Treasure Island shore DIRECTLY over the dark thin blue line.  Zoom in if you have to and get the marker EXACTLY on the line. And try not to stand behind a building or a palm tree.

You probably didn’t notice, but three things appeared at the bottom of your Ephemeris Graph in the box labeled Geodetics.  Those are: Apparent Altitude (which here will be negative), Change in Elevation (also negative), and Distance and Bearing.  Each time you move the gray or red marker it will recalculate the distance, altitudes and angle between gray and red.

One last little coup for now… notice next to the word Geodetics it has a little red and gray dot with an arrow over the top? Yeah, click that. The gray and red locations magically flip. Now all of your altitude and elevations will be positive. The calculations are FROM red TO gray. Since red is at sea level now, and gray up 266 feet on the top of Pioneer Hill the angle above the horizon toward the hill is  positive: specifically the base of the Coit tower is 1.1 degrees above the horizon. So can we conclude that the moon must be 1.1 degrees high in the sky?

NOPE. Sorry, we can’t. So close and yet SO far!

Q: What is wrong? Did you figure it out?
A: TPE has no idea how tall the Coit Tower is! (Stephen tells me one day he’s going to add the ability to specify the height at the red or the gray marker), but for now, YOU have to make that adjustment yourself. I’m afraid it’s going to involve some math. Trigonometry, actually.

What is the CORRECT Angle?

If you can answer this question, you’ll get the solution. “If an object at 2.12 miles away is 210 feet taller than the current 1.1 degree elevation, how many more degrees will that be?”

\tan^{-1}(Height / Distance) = altitude\ in\ degrees

Or in this case  InverseTangent( 210ft / 11311ft ) = 1.06 degrees.

So the CORRECT altitude is 1.06 + 1.1 or 2.16 degrees.

Hint Use the built in calculator in MS Windows in Scientific mode (Alt+2). Set the units to degrees. To get to the inverse tangent function (also called tan-1) use the “i” (inverse) key.

NOTE: If you do not want to do the trigonometry, there is another way to find the angle: use your camera.  Go to the desired site, take a picture with your telephoto lens aimed level with the horizon and with the top of the object visible. Determine the angular field of view of your lens/camera combination. Then measure the height of the target on the image and use the ratio of the height of the target to the field of view.  That sounds complicated, but it’s actually pretty easy. Using a 200mm lens, my angular field of view is 4.3 degrees. My photo shows that the tower spans 1000 of 1800 possible pixels. So the tower is 4.3^{\circ} \times (1000 / 1800) = 2.388^{\circ}

Now that we know the moon altitude must be 2.16 degrees we do not have to start over. Let us make sure the red maker is back on the tower and adjust our slider until the moon height is 2.16 degrees, then follow the line of the direction of the moon set to get our new location.

Of course if we move significantly higher, lower, nearer or farther away we must recheck the angle calculations.  In a hilly or mountainous location it is extremely non-trivial to get all the heights and angles just right. Using the “Terrain” mode of the map may help, but changes of a few dozen feet may make a big difference in the alignment.

Just remember the following things:

  1. The satellite maps may be out of date. A tree, building, crater, fence or obstacle might be in the location you want – or directly in front of it.
  2. There is no substitute for prechecking the line-of-sight BEFORE the event (see 1 above)
  3. Terrain maps are not visible when zoomed in.
  4. Elevations of the terrain are ROUGH.
  5. Moving 10 feet to the left or right may make or break the shot.
  6. I am NOT available to solve your trigonometry problems! Ok, I am but there will be a fee!

But wait, there’s more!

Getting the Ideal Exposure

To get the ideal scenario for moon details AND foreground light, it helps that the sun is on the opposite side of the sky and sometime during Civil twilight. In Figure 3, above, notice how the time we arrived at (5:13 AM) has the moon 2 minutes before Civil twilight.

Wondering what Civil twilight is? It is the legal equivalent to either dusk or dawn. Dusk when the sun has set, dawn when the sun has not yet risen. Signs that say park hours are “Dawn to Dusk” mean something quite precise. But those times change daily. For more click on the word “Civil” in the Ephemeris and it will tell you! Or take a look here.

The ideal exposure for detail in a full moon is about 1/100 of a second at ISO 100 and f/9. But atmospheric conditions, and the moon’s altitude may significantly affect the settings to use.  The best choice of aperture is to stop down enough for a sharp shot that keeps the foreground through to infinity (the moon’s focal distance) in focus.  If your foreground is at or beyond your hyperfocal distance (as it most probably will be), you’re good to go.

The problem, of course, is that your foreground is probably not going to fare well unless it is also well lit – so bracketing your exposures is always a great idea. The darker the twilight, the wider the bracketing needs to be.

Verifying The Sight Lines

After all the calculations and planning, a group of Bay Area Night Photographers ran out at the crack of before dawn to capture the “Full Moon Set behind Coit Tower“. One of the bleary-eyed ambitious photographers was Phil McGrew. Phil get’s extra kudos for going the morning before the planned event (that’s two thermoses worth of coffee) and here is what he got:

Photo 5: Coit Tower? And the Moon by Phil McGrew

The moon is in the right spot, but, whoops, there is something else in the shot, too! A big square building blocking the view behind the tower.  A more thorough scouring of the map in Figure 4 might have revealed the problem (see Figure 5).  Behind the Coit, and set up on a hill are a series of apartment buildings.  From almost anywhere else on Treasure Island, or Fort Baker in Marin, the Coit tower sits all by itself on the skyline.

Figure 5: Oops! (Click to see it larger)

What are the takeaways here:

  • There is no substitute for direct observation from the planned location. Any number of things can be a problem from light posts, billboards, trees and shrubs to, well hulking square buildings in the line of sight.
  • Extra scrutiny of the sight lines in TPE *might* save one from a needless trip to get a direct observation.
  • Knowing the local topography helps as does picking a structure or formation that clearly stands above the surrounding area.

Phil also discovered that the lack of brightness on his foreground meant he had to choose between exposing for moon detail, or exposing for the foreground. In Photo 5 he nailed a great foreground exposure and might be able to tease some moon detail out of the RAW file.  Or he could resort to…

One Last Trick – HDR

First I am a hater of images that have been composed by dropping a well exposed (oversized) moon into a separately taken landscape. There are technical challenges to embrace here so why not embrace them! Besides my desire as a scientist and engineer is to maintain reality through honest acquisition.

I am not, opposed, however, to using technology to overcome the limits of technology. Namely a camera can not readily capture the range of exposure – brightest to darkest – that the human eye can so a trick called “High Dynamic Range” photography (also called tone compression, tone mapping or image fusion) is sometime a necessity.

In the morning of June 15th, moonset behind Coit Tower was the target as describe earlier. That evening, moon rise behind the Transamerica Building was the goal.

You can click the diagram to the left to see where we were. As kismet would have it, the very parking space that I had calculated at the correct spot was open and I pulled in!

The haze was heavy, contrast was low. But in the end, the moon peeked (and peaked) right on schedule and right where it was supposed to go. It is always satisfying when things work out like that. More satisfying if the weather is great.

Rising Moon Collage

Photo 6: Moon rising over San Francisco (through the haze)

The fifth shot in the panel above is like all of the others in that it is a three-shot bracketed exposure combined using Photomatix Pro. The three shots were:

Figure 7: Bracketed Exposures

A wider bracketing range may have helped, the haze was quite thick. Using Photomatix Pro, playing with the knobs a bit I got this result:

Yellow Moon [5_032356-8tm]

Photo 7: High Dynamic Range Composite of 3 Images

I can only imagine what having a clear day to shoot in might have accomplished.

Best of luck on your alignments!

Comments, questions, praise, quibbles over the math – we’ll listen. Find us on Facebook.  Or attend one of our workshops. Want to keep it cheap, hook up with me, Steven in the Bay Area Night Photography group.

 

Alignment (Part 1 of 2)

Sometimes alignment is everything. As an amateur astronomer at heart I am fascinated by the course of celestial bodies through the heavens and how they coincide with terrestrial features (is that strange?). Buildings, lighthouses, arches, and yes, observatories all beg to be photographed as they are kissed by the moon, the sun, or the Milky Way.

One example is shown in Photo 1, below. The moon is rising behind the Lick Observatory. The observatory is perched on the top of Mount Hamilton overlooking San Jose, California.  The photo was taken from the shore of Halls Valley Lake in Joseph D. Grant Park County Park. But it was not serendipitous – it was purposeful.  Days and weeks worth of planning were required.

Moon Lick [5_009717]

Photo 1: The full moon rises over Lick Observatory, Mount Hamilton, San Jose, California

An alignment of man-made artifacts and the moon occurred on the night of a total lunar eclipse.  It also was not completely accidental – but I can not claim I knew I would capture it:

Airplane Transits the Partially Eclipsed Moon

Photo 2: An airplane transits the partially eclipsed moon.

But sometimes the moon just happens to be in the right spot, as in this photograph by May Wong which captured the moon in an interesting alignment while hiking up a trail in Mission Peak Preserve.

Photo 3: (May Wong) The moon teed up on Mt. Allison's Tower

Many fascinating views of the sun and moon can be found in books by Harold Davis one particularly interesting example is “100 Views of the Golden Gate Bridge“.

Planning Moonshots

Ignoring happy accidents for a moment, getting the moon to align with some terrestrial object involves quite a bit of calculation. While there are some great tools to aid the lunar photographer (The Photographer’s Ephemeris, for example), it helps to understand why the moon is a difficult object to catch.  Starting with the first problem:

The Moon is BRIGHT

Jewel [C_029690]

Photo 4: Long exposure for details during a total eclipse - notice the few stars.

Indeed the moon is a very bright object as most people discover when they try to capture any of the details of the moon. Typically the full moon requires settings of f/9, ISO 100, and 1/100 of a second to preserve detail; but at night, those  settings result in everything else being a deep black, therefore to get moon details and foreground details there must be some illumination.  The best time is before sunrise or after sunset and more specifically the very best time is on the cusp between nautical twilight and civil twilight.  I will explain what those are in Part 2.  Of course the moon also makes planning harder by the changing daily illumination. In 29.53 days the moon completes one full cycle from new where the moon is in line with the sun and not illuminated; to full – opposite the sun in the sky and fully illuminated; and back to new. Surprisingly, however, the exposure needed to capture moon detail does not change very much until the moon becomes a slender sliver. When in the sliver phase longer exposures can capture moon detail in the darker (unlit) portions of the moon though this effort comes at the cost of blowing out detail from the lit edge.  In the extreme case, as when eclipsed (Photo 4) longer exposures are needed.

This brings us to the second problem:

The Moon’s Path through the Sky Changes Daily

As if the changing illumination were not enough the moon’s path through the sky  dramatically changes from day to day. At my latitude (39 degrees north) the moon rises about 42 minutes later each day.  The compass direction (azimuth) at which the moon rises and sets also changes significantly from day to day.   Capturing the moon near the horizon during twilight ALWAYS means attempting a shot of either a slender crescent moon or a full moon.  In most months at most 2 days near the full moon provide full moon capture opportunities. What about the other phases? During the first quarter, the moon is highest in the sky near sunset. During its last quarter the moon is highest in the sky at sunrise. So in short, at first and last quarter you have to shoot nearly straight up to get the moon.

NOTE: First quarter refers not to the amount of the moon that is lit – it is half lit – but to the phase. Similarly at last quarter the moon is also half lit.

Determining the rise and set times of the moon is not hard. Many sites feature the sun and moon rise times.  www.sunrisesunset.com is one site I like. sunrisesunset.com can generate a calendar for a whole month. With a little experience it is often enough to know what phase the moon is in. For me a calendar that does not feature moon phases is useless!

Once I choose which direction I will be shooting, I then know whether I must shoot near sunrise or sunset. Pigeon Point Lighthouse – my nemesis – is on the west coast. To capture the moon behind it the full moon must be setting – which means the sun is rising.  (It also means a 3:00 AM wake up to allow me time to drive to the coast!) Conversely when  attempting to capture the moon over the San Francisco Bay Bridge, the best viewing locations face east – meaning an evening (sunset) shot is best. One advantage to attempting the full moon is that the sun’s glow illuminates the face of the foreground whereas when shooting a crescent the sun and moon are on the same side of the sky so the foreground is in silhouette.

Now we face problem three:

The Moon is Tiny

In this wide angle shot, it is difficult to even see the moon! It’s there in the upper left, but with the 10mm lens the entire moon occupies about 467 pixels out of the 15,154,290 (15M) total pixels. That’s a paltry 0.03 percent of all the pixels in the image. Of course the moon is not tiny, it is very large but it is so far away that its angular size is 1/2 of a degree or about the width of your pinky finger at arms length.

When the Lights Go Down in the City [5_018683]

Photo 5: 20mm Focal length = tiny Moon... did you spot it?

Often my goal is to include a moon in a way that shows it large and well featured relative to the foreground. There is no practical way to get closer to the moon, so the way to make the moon larger in the frame is to use a telephoto lens (as in photo 1 and 2).

Putting the moon near some foreground element allows me to exploit the large moon phenomenon as shown in Photo 1. But it is not enough to use a telephoto lens – I must also be far enough away from the object in question so that the apparent (angular) size of the moon is nearly equal to the angular size of the foreground object. The proper distance can be measured with the pinky fingernail at arms length, or calculated with some trigonometry. In Part 2 I’ll supply a simple formula that works well. Meanwhile Figure 1 illustrates the challenges involved in positioning and “sizing” the moon relative to a foreground object.

Figure 1: Relative sizes of the moon based on distance from the foreground object. See notes.

NOTE: To keep the lighthouse the same size as shown in images A, B, and C above the focal length must be increased. Alternatively, using one fixed focal length pictures B and C can be cropped from a larger photo.

And there is another complication, too, depth of field. The longer the focal length the harder it is to keep the foreground and the background in focus. And one last complication:

Near The Horizon, Atmospheric Conditions have a Significant (Negative) Effect

Looking straight up there are about 50 kilometers of atmosphere to diminish the quality of a photo. Looking toward the horizon, that number is effectively 38 times as much! The sky must be clear of clouds and haze through the entire distance. And a more sinister thing occurs, too. The atmosphere bends the light. When objects like the sun or moon approach the horizon the atmospheric distortion can become quite noticeable as a vertically flattened object. And finally, due to refraction when the sun or moon appears to be setting, it in fact has already fallen below the horizon and remains visible only because of  refraction.  The take away here is that trying to capture a detailed moon at the horizon is not as effective as capturing the moon at least a few degrees above the horizon.

In Summary

To capture the moon near a terrestrial feature:

  • The moon’s current illumination must be managed.
  • The moon’s rising (or setting location) must be accurately calculated.
  • Exposures to capture moon detail require the right amount of foreground illumination (near twilight)
  • The location chosen must have an unobstructed view of the sky toward the desired direction.
  • To get a “big moon” it is necessary to get far enough away from the foreground to get the relative moon size as desired. If too close, depth of field problems arise.
  • A well supported telephoto lens is required.
  • Capturing a shot of the moon near the horizon means the atmosphere must be relatively clear of clouds, dust and haze.
  • Too low in the sky means there will be significant distortion from the atmosphere.

So there it is: all the complications that must be overcome in order to capture the moon. I just have not written HOW to overcome all those obstacles, that information is coming in the next installment.