Category Archives: Lens

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. is one site I like. 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.

Tip: Star Bursts

An artifact sometimes called a star burst or star filter and sometimes incorrectly identified as lens flare consists of spikes of light that radiate from bright light source(s) as in Photo 1, below. These sometimes pleasing spikes are not that difficult to achieve without using tools, or filters, or image manipulation.  Here we explain how to get these potential eye-pleasers, and also how to avoid them.

Driven to Diffraction [5_020199]

Photo 1: Diffraction Spikes in a Night Scene. Taken with a 7-blade aperture at f/14

First, let’s call these spikes what they are. The lines radiating from a bright light source – e.g. the streetlamps in Photo 1 – are diffraction spikes. When light encounters an edge it warps around the edge just as a wave in the ocean can flow around a boat. Where are these edges in my camera? Should I fear for my safety? The sharp edges are inside your lens! The mechanism, sometimes called an iris,  that controls your aperture is made from a set of 5 to 15 blades that open and close to change the size of the opening in the lens. This opening controls how much light is allowed to pass through your lens onto to your sensor or film.  Usually photographers refer to this opening as their f/stop.


f-stops or f-numbers refer to the size of the opening in the iris as a proportion of the lens diameter and focal length. It is not all that important to know – or even understand what this means, but if you want to dig in deeply, I suggest Matthew Cole’s “A Tedious Explanation of the f/stop“.

If you, like me, are wondering how reflection, refraction and diffraction are related – here is a succinct definition from PhysicsClassroom:

Reflection involves a change in direction of waves when they bounce off a barrier; refraction of waves involves a change in the direction of waves as they pass from one medium to another; and diffraction involves a change in direction of waves as they pass through an opening or around a barrier in their path.

So in short, refraction is what your lens is designed to do: pull in light and focus it using multiple lenses. Internal reflection causes flare and is mostly undesirable. Diffraction is also an unintended consequence of lens design – unless you want that star burst. When “stopped down” (larger f/stop numbers) diffraction produces noticeable spikes. To make spikes more prominent increase the f/stop to f/11 or higher. How much depends on the construction of the lens.

The number of spikes created is unique to each lens and depends on the number and shape of the blades in the lens. Spikes always appear in pairs. An even number of blades produces an equal number of spikes. In Photo 2 below you can count 8 spikes. Many lenses have six blades and thus produce six spikes. Lenses with an odd number of blades produce twice as many spikes as blades – so Photo 1 may have been taken with a lens having 14 blades (unlikely), or a lens with 7 blades which is correct for the the Canon 16-35mm 2.8 L II lens.

Of course you can also buy star filters, if you wish. But stopping down is sufficient. There is one more simple way to produce diffraction spikes: place tiny dark threads (or hairs) over your lens.  Two threads at right angles will produce 4 spikes.

Note that when you “stop down” (use large f/numbers) the dirt and dust on your sensor will become more apparent as small dark dots or lines. It is also true that the stronger the diffraction the less sharp your image will be overall.

GEO ism [5_030572]  + TRIVIA Contest!

Photo 2: Diffraction spikes from a lighthouse. Notice how many spikes?

What if you do not want those spikes? Answer: keep the aperture as open (wide) as possible. Photo 3,  shot at f/5.6, shows almost no diffraction spikes.  Do not be confused by the radiating beams from the top of the lighthouse. Those beams are from the Fresnel lens in the Pigeon Point Lighthouse which throws out focused light in 24 directions simultaneously.  Notice in Photo 3 that the moon has some vague spikes but the bright lights in the windows and doors show almost no sign of diffraction spikes unlike Photo 2.




Photo 3: This f/5.6 photo reveals no noticeable spikes from the windows and the moon has barely noticeable spikes. The spikes from the lighthouse are from the 24-beam Fresnel lens - not diffraction.

The Contest Results

Here was the two-part question we asked in the Trivia Contest.

  1. What caused the starburst effect seen (in photo 2)?
  2. Without resorting to photo editing is it possible to get a different number of spikes? If so, how?

More than seven contestants provided answers to the trivia challenge. We scored each answer as follows: Full credit was awarded if both questions were answered completely. a score of 50% was achieved by clearly identifying stopping down and diffraction as the cause of the starburst effect.  An additional 50% was awarded if the answer mentioned changing lenses having a different blade configuration as the means for changing the number of spikes.   Partial answers got partial credit, so for example one answer to “How do you get a different number of spikes” was “stop down further” – that scored zero points – stopping down further may make the spikes more pronounced but does not change the number of spikes. The answer “The number of spikes is based on the number of blades in the lens” we scored at full credit even though it doesn’t mention swapping lenses as we felt that switching lenses was implied.  Final scores ranged from 40% to 90% correct.  For the purpose of this trivia contest any score over 65% was deemed correct.

Those answers scoring 66% or higher in the order they answered were:

Congratulations to Brian who is signed up for the November Star Circle Workshop in Lone Pine, CA. If Jack or Deborah attend they will receive a $25 rebate – and that is in addition to the current early sign up discount.

Discount registration expires on April 30, 2011Sign up soon to save yourself $100.

Trivia Contest: Starbursts

Hello dear readers.  I would like to engage you in a little trivia challenge.  If I get good responses I’ll continue with yet more challenges – and prizes!  Share this with your buds (after you’ve taken a crack at it), and yes, there is a prize. Read on…

Trivia Question

This is a multi-part question. Answer both parts in a sentence or two to get in the game.  Good luck.

  1. In Photo 1 below, what caused the starburst effect seen near the top of the lighthouse and the porch light in the lower right?
    NOTE: The starbursts were not added or modified by photo editing.
  2. Without resorting to photo editing is it possible to get a different number of spikes? If so, how?

Photo 1: What caused these starbursts at Pigeon Point Lighthouse, Pescadero, California?

Contest Rules

The winner will receive $50 in cash – provided the following rules are met:

The prize will go to the first entrant who has correctly answered the trivia challenge and also attends the November, 2011 Star Circle Academy workshopIt is not necessary to sign up for or attend a workshop to enter the contest. The order in which the correct and valid entries are received (as determined from the timestamps on the comments) shall determine eligibility for the prize.

The staff of Star Circle Academy shall at its sole discretion determine which of the entrants have correctly answered the trivia challenge. If no entries are received or no correct answers are submitted no prize will be awarded.

How to Enter

To become a contestant, you must provide your answer in the form of a comment here 0r by using the “leave a comment” link at the bottom of this article. Only one entry per contestant is allowed. You must include your complete, correct name with your entry and a valid email address.  Your email address will not be shown or used in any way except to contact you regarding this contest.

The staff and immediate family of Star Circle Academy are not eligible to win though they may enter the contest.

Entries will be kept secret until the contest ends on April 15, 2011 at 11:00 PM Pacific Daylight Time.  Thereafter the first 10 entries judged to be correct will be revealed, along with the answers to the trivia challenge.

Good luck!

Stacker’s Checklist

Created November 2, 2010
Last Updated April 19, 2019

Note: Items in RED are suggestions that apply in particular to star trail captures and may be changed based on circumstances at the scene and goals.

Site Selection

  • Sunrise, Sunset, Moonrise, Moonset and moon phase all known.
  • Safe area, travel paths known


  • Camera, tripod, release plate, camera batteries, memory card, lens, intervalometer + batteries, lens hood, rain protection, headlamp, flashlight/torch, and items for light painting.

On Site

  • Tripod set up – no leaning (center column should be vertical) – leg locks tightened.
  • Camera aimed, leveled.
  • Camera locked onto tripod. Head tightened.
  • Tripod weighted/secure and everything is wobble free. Keep the tripod low and out of the wind for best stability. Do not extend the center column.
  • Neck strap removed or secured to prevent wind throw. Intervalometer and any other cord, or wiring also secure. Velcro on the intervalometer and the tripod leg is a handy trick.
  • Save GPS coordinates and/or mark site with glow stick / other?

Camera Settings

  • Manual Mode, Bulb exposure
  • ISO 200  (varies but from 100 to 800, and up to 6400 if capturing meteors or the Milky Way)
  • Single Exposure
  • LCD brightness down
  • Image review time off
  • Record in RAW
  • White Balance = daylight (Auto not recommended)
  • Aperture f/4 (f/1.4 to f/7.1)
  • Auto focus OFF
  • Image stabilizer (vibration reduction) OFF
  • Long Exposure Noise Reduction OFF
  • Mirror Lockup OFF
  • Auto Exposure Bracketing OFF
  • Focus Assist OFF (this often fires an infra-red beam/red beam and will annoy other photographers). On many cameras this feature is on the flash unit/speedlite. On Nikons, this resource may help.

Timer Setup & Test

  • No delay, length of exposure = 1:59 minutes (adjust based on conditions. A 2 minute total interval is a good starting point), interval = 1 second, Num exposures >= 120
  • Timer cabled to camera
  • Test sequence (lens cap on) – Verify that second shot starts before canceling.

Focus & Final Framing

  • Check image composition, field of view.
  • Set camera to Aperture priority mode (not needed if it is already dark)
  • Take several bracketed shots in daylight or twilight: if it is already dark take a high ISO “range finding” shot. E.g. 2000 ISO for 30 seconds.
  • Pixel peep and adjust focus until sharp.

Battery and Card Shuffle

  • Remove memory card and insert second card. Format new card in camera.
  • Take second set of bracketed shots.
  • Return camera to Manual/Bulb mode.
  • Turn off camera and remove battery.
  • Reinsert battery (or insert fresh battery).
  • Verify that all settings are correct (See Camera Settings, above)

Final Steps

  • Check for wobble. Start by lightly jostling the camera, tripod, center column and even walking around in the area to make sure no movement occurs.
  • Set DELAY on interval timer appropriately (at least 5 seconds).  Goal is to start and/or end in twilight.
  • Secure cables for timer, external batteries (and neck strap). Do not block battery or memory card access.
  • Switch to aperture priority mode (so that your manual settings do not change), take a single image and re-verify focus. If already dark, take a high-ISO range finding shot for this task.
  • Switch back to Manual/Bulb.
  • Verify all camera settings as described in Camera Settings
  • Start Timer and verify that the timer is running.
  • If practical wait for first two shots to complete.
  • NOTE: You can leave the lens cap on for the first few exposure to collect DARK frames.

My thanks to Mike W. for comments and improvements to this checklist.

Additional References