Category Archives: Astrophotography

Theory vs Reality in Photography

Several topics in this BLOG have provoked impassioned debate. We really appreciate that. Steven is a Software Engineer by training. Eric is a Molecular Biologist, and Harold is a jack of all trades. In addition to being an author and professional photographer, Harold’s background includes being an Attorney at Law and a Software Engineer. We do “geek” like nobody’s business!

I, Steven am raising the geek card just to let you know that we do care about precision – but we care MORE about great photography and applying real-world principles to real-world problems.

Streaking Or Not?

The biggest debate has been about what factors lead to streaking (trailing) in Night Photography shots of the stars. Shots of the night sky may produce noticeable streaks if the exposure length exceeds certain bounds with specific camera factors (focal length, sensor size and sensor geometry). But there are a huge set of assumptions behind the visibility of those streaks that are often overlooked. One assumption is that the finished image sizes are proportional to the size of the sensor used to create them – when does that happen in real life? Another assumption is that the viewing distance is proportionally related to the finished image size. These sound like they are reasonable, but in the real world, a print from a crop camera and a full-frame camera are extremely likely to  be made in the same finished sized and viewed from whatever distance the viewer chooses!

In the desire to get the math exactly right, many people trip over one or more of those assumptions. Our article about why the 600 Rule is a misguided way to determine the proper exposure length has had many proponents and opponents espousing the “inerrancy of the mathematics” and all the missing factors we may not have included. I love math, but: my assertion is that Reality beats theory when producing an image.  And that’s why the conclusion of the article is that the proper exposure length is an aesthetic decision more than a mathematical one.  The mathematics guide, but do not govern what the best choice(s) may be.

All Photography Involves Tradeoffs

I really enjoyed my Physics classes, especially mechanics. But I also remember all those exercises that included clauses like “neglecting friction”… In the real world friction with the the air and from tire contact on the ground is why a car on a flat road comes to a stop even though no brakes are applied.  Air friction (drag) is why it takes eight times as much power for a plane to fly twice as fast.

The reality of physic is why a lens, or sensor is always a tradeoff of something for something else. Perfect optics or a perfect sensor behavior is not possible at any cost. In the same way, a photographic exposure is always a tradeoff of one thing for another. If you need a faster exposure with a given amount of light you can: increase the exposure time, increase the sensitivity, or admit more light by opening the aperture. Of course you can also change more than one thing at a time. Indeed you MUST change more than one thing. Any change to one of the three factors requires a corresponding change to one or more of the other factors.

What Exposure Settings Should I Use?

If you ask me this question, I apologize in advance for rolling my eyes (it has been known to happen). I can give you a STARTING point, but remember that a starting point involves tradeoffs and conditions that can not be entirely foreseen. How warm is it? How much moisture, dust or particulates are in the air? How much turbulence in the atmosphere? How much artificial (or natural light)? What are the predominate colors of the light (white balance)? How efficient is your sensor? How sharp are your optics? How far away is your foreground from your background? What is that largest aperture available? How sharp is your lens at that aperture and at that zoom? What is important to you in the scene you’re trying to capture? And what are you trying to accomplish?

My best advice: try an exposure and see what you get. When all there was was film, precision was a lot more important than it is now in the digital world where you can immediately see the result with a histogram and a myriad of other data to help you decide what to try next.

In fact, here is your assignment.  Go out when it is dark and shoot a photo of the moon.  How dark is entirely up to you. Your photo MUST show the same kind of detail that you can see with your eye – the craters and the gradations from light to dark areas.  Use a telephoto lens – notice I am not telling you how telephoto, that’s also your choice. If the moon is “blown out” – and it probably will be, decrease the exposure. Keep taking photos until you get as much detail as you can.  You will almost certainly need to use manual mode to set your exposures.

What settings did you come up with?  In our “Catching the Moon” webinars we provide starting settings and also advice about how those settings may need to be changed.

For an extra challenge… see if you can get the moon AND stars in the same shot. What settings did that require?**

4 Moons 4 U [B_049969] Composite

**In retrospect, it was evil of me to suggest this. In only the most extraordinary circumstances is it possible with current technology to get a featured moon AND stars.  The example above required 3 separate exposures.


Hunting Comets and other faint objects in not-dark skies

AirGlow Comet [5_070386]

It turns out the much hyped PanSTARRS C/2011L4 Comet is not living up to the hype. Unfortunately failure to meet the over exhuberant expectations  is common since predicting brightness and visibility of an object like a comet is a difficult science. In fact, it’s part science, part black art and part good guessing – mostly the latter.

The photo above was taken on March 12 when the moon and PanSTARRS nestled closely together. The close quarters made finding the comet much easier despite the bands of clouds passing by.  The strategy for finding the comet in that case was simple: use a telephoto lens, put the moon at the right edge of the photo and take different exposures periodically and at different settings (e.g. +2, 0, and -2 stops). Then hunt for smudges.

The IDEAL telephoto lens would be one that was a few angular degrees wider than the difference between the moon’s position and the comet’s position. How to determine the position of each is discussed in the last section below. Figuring out the angular view of your lens is easy using online tools like this one from Tawbaware, makers of Image Stacker (like that program!). If you know the field of view at your minimum and maximum zoom, you can use that information to your advantage.

Finding the Comet with a Nearby Moon

The point at the moon strategy made finding the comet easy because:

  1. There is no way you’d be able to see the comet if you were not able to find the much brighter moon nearby.
  2. On that one night, the comet and the moon were within 4 degrees of one another.  That’s quite close.

I know some people tried to find the comet using wide angle lenses. That strategy might work, but the comet is such a tiny thing and it’s visibility is so tenuous based on the atmosphere, light pollution, and sky brightness that you may only realize – as many did – that you captured the comet after carefully inspecting your photos at home.

Contrails and Comet Tails [B_050938]

The truth is you are unlikely to see PanSTARRS by eye or in your camera’s view finder unless your conditions are nearly ideal.  Hopefully ISON which is coming in December will be brighter and better.

Finding the Comet when the Moon is Farther Away

The following night, both the comet and the moon had moved relative to the sky. On March 13, the moon was 12.5 degrees above the comet and about 4 degrees farther west (again, how I knew this is coming in just a minute).  So one simple strategy for finding the comet would be to zoom your telephoto lens so that it has a field of view of about 14 to 15 degrees in the long direction which for me, is 80 millimeters focal length on a 1.6 crop factor camera.

On a tripod with the camera in portrait orientation adjust the view so that the the moon is in the upper left of the frame. Shoot bracketed shots. Check the lower right corner of each one for the tell-tale comet smudge.  Keep readjusting the view so the moon remains in the upper left for each shot. Zoom out a little bit too, in case your geometry is a little off. Eventually as it gets dark enough or the sky clear enough you should find it.

In fact the way I found the comet last night without using my camera but by using my telescope. The program Clinometer (on my iPhone) measures angles. I sighted the moon with my 8″ Dobsonian telescope and measured the angle along the telescope barrel using the inclinometer program. I then lowered the altitude (elevation angle) of the telescope by 12 degrees to match the altitude of the comet. Then I slowly rotated the telescope northward until I found the comet.  It wasn’t easy from my urban location, but it wasn’t impossible either.  By the time I was able to find the comet it was only about 6 degrees high in the sky – that’s way too low if you have trees, hills, and houses nearby to deal with.  In theory, this strategy would work with a telephoto lens or with binoculars, however, binoculars need to be steady and where I spied from last night had streetlights in the distance and the flare and glare from those streetlights made finding the faint comet nigh impossible.

What if there is no Moon to Find the Comet With?

Unfortunately starting on March 14th, the moon will be quite far from the comet, so the opposite strategy is required:  Use a landmark in a known direction as the starting point and look “upward” from the horizon.  In other words, zoom your telephoto lens so that the field of view covers the angle from the horizon to the comets altitude (angle) above the horizon.  Don’t forget that as the earth spins this angle changes every minute! Orient you camera in landscape mode and point it as close as you can to the correct direction (azimuth). Look along the top of the frame to see if you’ve captured the comet.


SpyGlass’s view shows the direction the camera is facing (Azimuth) and the elevation angle (Altitude)

But what direction should you point your lens or telescope? Use a compass application or actual compass. BEWARE however as the compass applications have lots of gotchas and are only accurate to about 5-10 degrees.  And if you aren’t sure how to use a real compass your local magnetic declination might bite you. Better would be a GPS with a built-in calibrate-able compass.  And perhaps even better still would be to use an application like TPE (which I discuss in my Catching the Moon Webinars) to calculate the correct azimuth from the location you plan to stand.  An application that might help a lot is “SpyGlass
however don’t forget that I found the directional accuracy of my iPhone and iPad to be pretty poor.  Being off by 5 degrees may mean looking in the wrong place.

How Do I Know the Altitude and Azimuth for the Comet?


Unfortunately, that’s a tough one.  I use the free program Stellarium. I then added the comet to the “Solar System Data Base” (search around on the web and you’ll find instructions). I selected my viewing location, dialed in the time, did a search for good ‘ol C/2011 L4 and let it tell me the azimuth and altitude.


Above I’ve dialed up the time and clicked the moon. The highlighted line shows me the azimuth (direction) and altitude (angle above the horizon) for the moon which at that time are 264 degrees or just a little south of west, and 30.5 degrees high.  Clicking on the comet shows 272 degrees – a tiny bit north of west and 9.5 degrees.  So now we know that the comet will be 8 degrees north and 21 degrees south of the moon – and that won’t change significantly for the rest of the night.

Since we also know the direction for the comet is about due west at this time, we can apply the telephoto-lens horizon trick I described earlier.

Another way you can find the azimuth and altitude is by checking my animation HERE – note that the animation is correct for San Francisco  (and most places nearby).  There is also a table of the azimuth and elevation in the text of the Flickr post.


By the way, one way to find the right spot on the horizon is to use the sunset location as a guide.


Review: CamRanger

I am always looking for the best solutions for automating my night photography. In fact, I recently reviewed a litany of products. At the time I didn’t know about the CamRanger product – my friend Rob C. told me about it.

I am now the owner of a CamRanger. Here are my first impressions:


iPhone Application

  1. I ordered from the CamRanger website, selected two day delivery. The box came all the way across the US. From Virginia to California and it arrived in two days. Woohoo! Great store and interaction.  It’s also available through Amazon, but doesn’t qualify for Prime. I figure if I’m going to pay for shipping I’ll order it directly from the company and hope they keep a bit more of the cash.  By the way I paid with PayPal. Sweet. 
  2. The packaging is reminiscent of the iPhone. Everything is nicely tucked into a little box. I was worried briefly because I also ordered two extra batteries. Thankfully they were tucked into the same box.
  3. Included were: Quick start instructions, a charger (wall wart), charger cable, USB to mini USB to connect to the camera, Ethernet cable (for upgrading the firmware), the batteries, a cigarette sized-packet with the CamRanger unit, and a carry pouch with a velcro closure and a carbiner clip.

The CamRanger is an incarnation of the TP-Link portable wireless router. It even says so on the batteries and under the case. Really clever approach! Kudos to them. Of course the firmware has been customized, and they are using the USB connector to drive the camera.  With that arrangement they can do a WHOLE lot more than you can do with a lowly intervalometer.

Essential is the CamRanger application for iPad and iPhone. They are planning to roll out other applications, including one for the PC. Since the device is a portable router, theoretically they could even provide some simple browser driven connectivity.  I loaded the app long before I received the box. You can’t get to square one without the device, however – it won’t show you any of its glorious features until it can talk to a camera. Makes some sense since what you can do depends on the camera it connects to.  I found some blemishes with the application which I’ll enumerate in just a moment.

What Can the CamRanger Do?

Before I criticize, let me first explain what you CAN do with this clever device. And this is just scratching the surface.

  • Focus stacking – let CamRanger control incremental focus for maximum depth of field with your macro (or other) shots.
  • Remotely adjust focus (camera auto-focus must be turned on for this).
  • True HDR using exposure time, ISO or f/stop increments. Up to 7 exposures are allowed.  Intervalometers with this feature can only work in low light since they can only crudely control the camera shutter.
  • Monitor “live view” and captured images. Even delete them when they suck. I am slathering at how this will improve my Astrophotography. Have you ever tried to adjust focus of a telescope pointed nearly straight up – it’s a neck breaker.

    Delete Images from Camera

  • Intervalometer functions: timelapse, and bulb exposures.
  • Complete control of settings (how complete depends on your camera). Nearly all of the settings can be changed remotely including ISO, f/stop, exposure time, metering mode, image size and type… and more.  I even moved the connection from my Canon 5D Mark II to my cohort’s Nikon D800 and had immediate control of his camera and its unique settings.
  • Some features do require manually changing the camera mode knob. For example to get bulb exposures you must be in Manual mode on a Canon 50D or in Bulb Mode on the 5D Mark II.  These peculiarities vary by camera.
  • CamRanger can do everything the EyeFi can do for sending images. EyeFi isn’t supported on CompactFlash media cameras so CamRanger is a great replacement!
  • IMG_0137Focus by touching the iPad screen.
  • Provides a Live View Histogram.
Touch the iPad to select focus point!

Landscape Mode






Portrait Mode


View images from the camera memory card

What Could Use Some Improvement

I’ve ordered my complaints according to how much they affect the way I do most of my work which is night and astrophotography.  Some of these are nitpicking, I know.

  1. There is no sub-second interval for long exposures. I’d love for them to add a “star trail mode” and select the shortest possible interval between shots based on the camera type and behavior. The company says this is a limitation in what they are able to do through the USB connection to the camera.
  2. There appears to be no way to know if a timelapse is running nor can you stop a timelapse in progress.  The CamRanger can continue to run a timelapse sequence without an app driving it.  That’s a plus. But not being able to tell if it is running or to abort a sequence in progress is annoying. CamRanger tells me they are planning to address this in an upcoming release. Yeah!
  3. The pouch for the CamRanger could be improved to:
    • Hold all the items that come in the kit. The pouch can only hold the CamRanger device, USB cable and perhaps an extra battery – not the additional cables or plug-in charger.
    • Add velcro straps so I can wrap them around my tripod leg and secure the pouch to my tripod,
    • Provide a closeable window so I can see at a glance the unit status (i.e.those LEDs which are too bright, see below).
  4. The timelapse settings use spin dials to select the number of exposures and exposure times. The keypad would be more efficient.  It would also be great if the App automatically calculated your elapsed running time based on the number of exposures and a configurable frame rate (like TriggerTrap does). CamRanger is adding the calculation.
  5. The LEDs on the device are pretty doggone bright for night work. Would be great if they were dimmable. Of course that can be achieved by putting the device in the pouch or by putting some semi-opaque tape over the LEDs.
  6. IMG_1564To interact with the CamRanger, you have to switch your iDevice to the WiFi network generated by the CamRanger. Unfortunately that means you can not use your iDevice browser to surf the internet. If there were some fast-switch way to do it, I’d like that. Or better yet, I’d like to integrate the CamRanger into an existing network.
  7. The CamRanger itself comes with a serial number sticker. I’m SURE it will come off or get lost, but you need that serial number to connect to the device. The same serial number can be found on a sticker under the battery cover, though.
  8. The Access Key to join the CamRanger network is all in upper case.  All lower would be easier to type.
  9. My buddy Rob noted that he felt like he was going go have to break the battery cover off. Mine seems to come off quite easily if you hold it correctly.
  10. The CamRanger battery is a custom lithium-ion form factor. You can charge the battery in-device, but there is no additional charger provided.
  11. Sometimes when switching functions, for example when switching to Timer it told me “must turn off live view” which seems a bit strange since it knows how to do it!
  12. I ended up with both my iPad and my iPhone attempting to connect to CamRanger. It caused a problem that was not obviously solvable (Communication Error) until I realized both of my devices were trying to get CamRanger’s attention.

As I noted, some features depend on the way your camera interacts with the USB connection. I didn’t figure out, for example, how to cause my camera to meter the scene for me so that I could manually adjust my exposure – i.e. what I’d normally do with a half-press of my shutter button.

I haven’t tested the range or battery life as yet. Claimed battery life of the CamRanger is 6 hours. There is, however, no on screen indication of the CamRanger’s current battery condition.

Now That I’ve Used it More…

The problems with not being able to see if or stop a timelapse are more than irritating.  The only way to stop a timelapse in progress is to turn off the CamRanger device and turn it back on. It takes about a minute to come back up and meanwhile since the WiFi from CamRanger goes away, my iPad or iPhone will by default switch back to another known network (my home in this case).  That means I have to remember to also switch WiFi networks or I get “unable to communicate”.  I also noticed that for bizarre reasons which are not quite clear I could start a timelapse, but the camera did nothing.  However I *could* use the Capture button.

But that’s not the end of the pain, unfortunately.

  • The Bulb and timelapse settings are not saved. All settings reset to 0 when a timelapse completes.  If you want to re-run the same program – as I do when I take darkframes after my astrophotography sequences – you have to reprogram everything. That’s tedious.
  • Apparently the interface is not smart enough to know how to do HDRs that exceed the camera settings 30″ exposure time.  On my 50D, for example, an HDR sequence that should shoot at 15, 30 and 60 seconds will not be accepted. However that sequence can easily be achieved by using bulb mode for the last shot and that does not require changing the dial on the camera – so the app could figure it out.  I even tried doing this in “Bulb” mode, but it still didn’t seem to work.
  • The biggest pain in the butt is that the “Autofocus” behavior is not preserved.  What this means is I leave the AF button on on the lens, carefully fine tune the focus, turn it to MF (manual focus mode) on CamRanger and take my shots. If, however I am forced to cycle the CamRanger power it reverts to AF mode by default so the first shot will try to autofocus in the dark – which prevents the camera from shooting.  I’d like to set the default behavior to NOT AF even though I have set AF on the lens.
  • It also appears the timelapse is not aware of the drive mode for the camera.  I often set my camera to the 2-second (or 10 second) delay for two reasons: 1. it lights the self timer on the camera so I know when a frame is about to fire, and 2. In delay mode, an Autoexposure bracket (AEB) will automatically complete from a single press of the shutter. The timelapse settings could know that the minimum delay will be the length of the camera self timer delay (plus perhaps a second).  But it doesn’t use that information.

The good news is that the biggest pain points can be fixed in the app. I suspect some of the more advanced things would require the app to know more about the camera – and are thus less likely to be supported.

The other good news is, it really does save me from breaking my neck trying to get my eye down to the view finder or to view the LCD – when objects are high overhead I’ve had to lay down on the ground to see the LCD – blecch. And it’s great fun to watch the images roll in as the timelapse runs – even from indoors while my poor equipment is out shivering in the cold.

Astrophotography – The Polarie

Published: November 1, 2012
Last Revised: December 16, 2018

We have a once-in-a-while webinar on beginning Astrophotography. The purpose of the webinar is to get people acquainted with the tools and techniques required to delve into this interesting genre of night photography.  As we teach in that webinar the single most important piece of equipment you can buy is an Equatorial Mount.  An Equatorial mount is an apparatus that counteracts the rotation of the earth so that your camera can peer at the same place in the sky for long enough to capture an image without streaks. There are many equatorial mounts that range in price from almost nothing (and not even worth nothing) to more expensive than logic would dictate.  For more background please see our survey of Astrophotography Gear.

One of the newer pieces of equipment in the arsenal is a less-than three pound piece of gear called a Polarie.  Here is what it looks like with a ball head attached to its face.

Polarie – Close Up

What Polarie Can Do

As noted earlier, the primary purpose of Polarie is to counteract the effect of the earth’s rotation so that objects in the night sky can be exposed longer without getting streaking. Below are examples of 42 second exposures using an effective focal length of 215 mm. The image at the left is with the Polarie turned on in normal mode, the middle image is the same length exposure but in 1/2 speed mode, and the right is what you get if you use no tracking at all.

Polarie Test - Telephoto

Tracking is less critical when shooting with wider angle lenses. I ran a test with a 200mm telephoto lens because it is a more difficult scenario. For example when shooting the Milky Way, an effective focal length of 10 to 50mm makes more sense.

A Critical Look At Polarie

I purchased only the Polarie unit (about $400 USD) not any of the accessories. The unit is deceptively heavy at almost 3 pounds but at that weight it is still – and by far – the lightest equatorial mount you can find. The only other device in its weight class at present is the Astrotrac with a starting price about twice as much. The Astrotrac does come with a better tripod mount, however at a total cost of around $1300 USD.  I paired up the Polarie with my Canon 50D and the 70-200 f/4 lens.  The addition of a Giottos ball head brings the total weight of the equipment attached to Polarie to about 6 pounds.

The Positives

  • Inexpensive
  • Good instruction manual
  • Mostly easy to set up and to use
  • Suitable for a beginner
  • Good power for the price.
  • Can be powered with mini USB (or two AA batteries). Claimed life is 4 hours on AA batteries but mine lasted at least 6 hours using rechargeable batteries.
  • Compact and MUCH lighter than almost everything else.
  • Can be used in Northern or Southern latitudes.
  • Tracks at star, solar or lunar rates (and yes, they are all different) as well as a 1/2 speed rate which should be good for Landscape Astrophotography.

The Negatives

  • The back plate can be unscrewed to peer through the axis of the motor and also houses a built-in magnetic compass but the plate is almost flush to the Polarie body and it is quite hard to grip.
  • The inclinometer (angle measurement device on the side) seems like a good idea except that the markings are so small and coarse that to my eyes it is illegible.  The lighted inclinometer *might* help if the North Star is obscured by trees or such.
  • The front plate has a 1/4″ retractable bolt and attaches awkwardly to the motor plate with two thumbscrews that are hard to reach once a head is on the motor plate. I would have preferred that Polarie supply a 1/4 to 3/8″ adapter since most good heads attach via 3/8″ bolts.
  • The battery compartment door is a nail buster to open.
  • Since Polarie will certainly be used with a DSLR camera, Vixen really missed an opportunity to add a remote release cord – I see no jack for one.
  • Not sure what the point of the flash shoe is. I do see the Vixen has another (much larger) inclinometer that can be attached there, but you may be able to do better using an application on your smart phone.
  • The optional polar alignment scope is expensive, and bulky. It’s also complicated to operate because you must remove the ball head and camera from the device. BUT the weight of the camera and ball head is likely to create enough “sag” that the careful measurements will be wasted.  We like the SkyTracker much better in this regard.

There is a sight hole to line up Polaris – the North star. I used only that method to align Polarie and got fair results. To get really long exposures one of two methods will need to be undertaken to increase the alignment accuracy: either invest in a Polarie polar alignment scope at almost double the cost or do drift alignment. Drift alignment is not simple and probably would frustrate the aspiring astrophotographer. The Polarie can be purchased with an optional ratcheting tripod base which might be a good idea, however the stated load capacity of the bundled tripod seems too low to use with a heavy camera.


Remember that you will need at least two heads and you’ll want them both to be ball heads for optimum configurability. The head on the tripod should be sturdy – see below for why.  Below I refer to tripod head – the apparatus that joins the tripod to the Polarie, and to the Polarie head – which is the hardware used to attach a camera to the Polarie.

Problem Areas

In addition to the negatives listed above, there are several other sources of problems including every point where one element attaches to another. For example: the Polarie base if not attached securely to the tripod head can rotate.  If using quick release plates the attachment point creates another source of rotation. If the camera is not securely attached to the Polarie head rotation can occur there, too. All the pieces together may severely tax a cheap tripod head making it difficult to hold up or adjust the load.  In my configuration I found I had to allow some slouching – meaning I had to adjust the camera so it was pointing slightly above my target and then tighten the head so that it would settle to the right place.

What Can You Do With A Polarie?

Maybe we should have put this section first! Some of these things can only be done with a Polarie are highlighted in RED.

  • Point the Polarie straight up and use it as an automatic panning motor for a time-lapse.
  • Align Polarie and take a series of shots of the night sky – the sky will stay in the same place in every shot – and any minor movement can be compensated for using Astrophotography procedures.
  • Outfit your lens with a solar filter and track the sun (e.g. for photographing eclipses or solar activity)
  • Track the moon e.g. to catch the space station flying across its face, the slow creep of the terminator, or just to get a time-lapse as the moon sets or rises.
  • Double your exposure on a landscape astrophotography shot by using 1/2 speed mode.

For more hints tips and examples on how to use Polarie, stay tuned to this channel!

My first test of the Polarie was to track the radiant point of the Orionid Meteor shower. My attempt was mostly a bust due to clouds, however note how stable the time-lapse is – and remember this spans almost 14 minutes of real-time.

Brilliant Meteor Leaves a Trail

Here are two more ways I’ve used the Polarie – as a horizontal panning device
Star Flight and Moonset

As a sky tracking device
Soaring 1920x1080