Tag Archives: battery

Astrophotography – The Polarie

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.

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

As a sky tracking device

Power On – all Night Long!

Got DSLR, Need Power?

Figure 1: Luggable (9,000 mAh, 10 pounds) Big.

I have built two different rigs for powering my Canon 40D, 50D and 5D Mark II cameras. Each of the beefy battery solutions here can run continuously for up to a dozen hours – and longer. When I say a dozen hours I mean a dozen hours of continuous shooting. One rig I call my luggable weighs about 10 pounds and uses a 12 volt, 9,000 mAh sealed lead acid battery in a box that can be used to jump start a car – it has jumper cables on it.  The total capacity of the battery is 108 watt-hours. My second lightweight solution is 7.4 volt, 8,000 mAh (56 watt-hour) combo that is much more portable because it weighs less than two pounds. I explain what “mAh” and “watt-hour” mean in the glossary below. To power a Canon DSLR a battery eliminator is required. Battery eliminators can be purchased from Canon ($$) or after market companies ($) or the can be fabricated (¢) by anyone who knows which end of a soldering iron is safest to hold. See below under “Battery Eliminator” for options.

*If you have a Nikon, e.g. model D200 you may find a somewhat simpler solution – or more complicated depending on your point of view. The D200, for example, can be paired with  the EH-6 AC adapter which mates with a DC power connector on the camera. The EH-6 apparently supplies 13.5 Volts to the connector. One D200 owner found that he could attach a 12V battery directly to the DC-in connector and power his camera. And attaching a 7.4V battery seemed to work just fine! Unfortunately the on-camera connector is not a standard size and it seems nearly impossible to get one without plunking down cash.

Figure 2: Lightweight, Small, Powerful (8,000 mAh, 1.3 pounds)

So why did I bother to build these things? I typically like to hike into the wilderness, set up my rig for star trail work and go to sleep. The shutter will be open nearly continuously for 4, 6 or even 8 hours at a time. While my descriptions are specific to the Canon, a similar approach works for other cameras and camera vendors. Indeed, the Nikon D40 battery, the EN-EL9, is a 7.4V battery, too.

Six hours of run time is more than can be achieved with a single high capacity battery and  also beyond the capacity of a battery grip that holds two high capacity batteries. Since I hike with my solution it must be portable.

The luggable rig pictured above in Figure 1 is obviously not ideal for hiking. The “Start It” unit weighs almost 10 pounds. On the other hand, I can keep the jump start kit in my car and perhaps avoid a dead car battery. The “Start It” will fully charge if I connect it to the car accessory power plug for 2-3 hours which is convenient when driving to remote locations.

The lightweight rig at about half the capacity is highly portable. Indeed, two BP-970 camcorder batteries totaling about 3 pounds exceeds the power of the luggable solution. Nontheless I use both solutions.

Let me walk through each solution.

Luggable Jump Start or Car Battery Based Solution

The Jump Start battery solution is good for more than just powering the camera. The heft of the battery makes it a pretty good ballast for stabilizing my tripod. The 12 Volt starter battery is also better suited for use with a dew heater to keep the camera lens from fogging, it can be used with other 12V appliances – anything that plugs into a standard car power socket (aka a cigarette lighter).  Sealed lead acid batteries can supply more power in very cold weather (freezing and below) than lithium technology. Oh, and you can use it to jump start your car if needed! The down side, of course, is it’s heavy. Not something you want to hike with for miles and miles (though I have). Also any power solution for based on a jump start battery can also work if plugged directly into a car! Here’s what you need:

  1. Portable power source one of
    • 12V Car battery or jump start device.
    • Your car (that power/cigarette lighter socket can come in handy)!
  2. DC-DC converter because a 12 volt battery is too strong to power a camera which wants to be fed 8.2 volts or less.
  3. Dummy Battery or Battery Eliminator options are:
    • Buy a battery eliminator: eg. the Canon DR-400 $30.
    • Cannibalize an old/non-working battery or hack up a new, cheap one.
    • Build a battery dummy out of wood, plastic, or similar non-conducting substance.
  4. Cabling and strapping to carry and secure the rig (I use a bungee cord to attach it to my tripod)

The device I bought, the Jump Start, is a small 12V auto battery with a handle, jumper clamps and a power port (cigarette lighter) socket.

The luggable solution also requires a DC to DC converter. The converter will accept anywhere from 12 to 18 volts and has a dial to select the output voltage with choices of 3/5/7.5/8/9 or 12 Volts. The $19 device lists itself as a 3000mA (3.0 amp) unit.  The converter has an inline fuse to “blow” if too much electricity runs through it – this is a good thing as it will help protect the camera and the battery. The device I purchased from Fry’s Electronic is labeled “3000 mA Rhino Intelligent Adapter” but I haven’t been able to match that with anything on the internet or find anything similar.  The closest match I found is a 1 Amp unit, or this unit.  Many people like me have a big assortment of “cigarette lighter” chargers, and one of them may be able to do the job. Inspect the unit carefully to determine its output voltage and capacity which are often labeled right on the unit. For example the label might read: Input 12VDC, Output: 7.5VDC 500ma which means its output is the right voltage, but at only 500 milliamps it may be too puny to keep the camera fed.

Figure 3: A 3amp 12V selectable converter which includes 7.5 V.

I discovered that an old Nokia cell phone charger, the Nokia LCH-8 converts 12 to 24V from your car battery to 7.5 volts DC at 650 ma. In theory this might be enough except that I’ve read reports on the internet that measured peak usage for the Canon is 1.4 amps (1400mA). Clearly the Nokia can’t sustain that much current, but if it is for a short period there is an electrical trick to allow this – add a big capacitor. I haven’t tried using the Nokia charger.

Other Luggable Soltions

There are other options, too. For example Harold Davis purchased the Vagabond II Portable Power System ($299). This is also a beefy (really beefy) battery which features 12 volt output and a built in inverter for powering a 120 Volt outlet. The battery sports 240 watt-hours. That is huge. The most serious detraction is the weight and bulk. It is a self contained system that weights 18.6 pounds. If the 120 volt output is used, it also means that an A/C adapter for the camera must be used. The Vagabond’s built-in inverter must be paired with an A/C adapter for AC-DC conversion. Converting power from 12 volts DC to 120 Volts AC and then back to a DC voltage will cause as much as 35% of the electrical energy to be wasted – but given the huge size of the battery and the additional versatility the loss of power may not matter.  A smaller, lighter cousin is also available the Vagabond Mini.  At $240 and 3.5 pounds total weight it is more portable. The unit still has a substantial 130 Watt-hour rating.

Lightweight Camcorder Battery Solution

The camcorder or Remote Control (RC) battery is a lighter and more portable solution that uses off-the shelf parts – but assembly is still required. Lithium technology does not supply as much power in very cold climates as a lead-acid car battery solution. Camcorder batteries are large compared to the 3oz battery for my cameras and camcorder batteries are relatively hefty at almost 1 pound. But, with that weight you get 5 to 7 times as much power! Taking two of these with you on a back pack trip is feasible. Not something you can say about a 10 pound solution! In fact, 8 pounds of Lithium Ion (camcorder  batteries) will last longer than 40 pounds of sealed lead-acid batteries.

At the core of the lightweight solution is a camcorder battery and a charger suitable for that battery. I blatantly ignored the “do not disassemble” label on my charger. The unit I purchased has two  phillips screws located beneath a large sticker on the back. After disassembly I discovered that there was plenty of room inside the case for an additional power jack (6). I wired a power jack into the unit by finding where the spring loaded battery contacts went, carefully cutting the wires and attaching them to the power connector, then attaching wires from the power connector to the place the battery contact wires originally went. The power jack that I  added has a “Normally Closed” switch which completes a circuit when there is no plug in the jack. It was probably not necessary to take the precaution, but safety when 120 volts are involved is a good thing.

Figure 4: The components

I purchased these:

  • A: a replacement BP-970 Camcorder battery. Several capacities are available. I chose two 8,000 mAh batteries at $31 each from Amazon. I also purchased a charger for this battery.
  • B: a camcorder battery charger for the above battery.
    This @ $10, or this @$15 seems just fine. I have also purchased another charger: the Lenmar which is a tinkerers dream because it comes with easily modifiable plates to accommodate different batteries.
  • (1) 20 or 22 gauge stranded wire. I suggest red and black, but black wasn’t available so I used white. About $6
  • (2) M size inline power jack. $4 #274-1577
  • (3) M size power connector plug (two needed) $1.50 each  #274-1569
  • (4) electrical tape for strain relief $2
  • (5) 3/32″ heat shrink tubing $3
  • (6) M size chassis mount power jack.$3.50  #274-1582

I made these

  • B: charger with additional “battery out” power jack (6).
  • C: power cable using stranded 20 or 22 gage wire (1) with 3/32″ heat shrink tubing (5) at the ends and in the middle for strain relief and a (2)
    power jack. I also used a velcro cable tie for neatness (Home Depot?)
  • D: BP-511 battery eliminator – I gutted an old BP-511A battery unsoldering the circuit board with a low wattage iron. I then soldered a  length of red wire to the “+” lead and length of white wire to the “-” lead. I tied a loose knot on the inside (strain relief) and passed the ends through the battery case by making a hole with my soldering iron. I used the barrel of a recently turned off soldering iron to shrink the tubing until it was tight and made sure that where the wire entered and exited the battery it did so through the heat-shrink tubing. I the glued the
    battery case back together with hot melt glue along the corners on the inside.
  • E: Power connector (used M size power connector (2))
  • F: “Cheater” power cable – basically a length of double wires with a part number (3) soldered at each end.
    *** You may be wondering why I didn’t just put a plug  (3) at the end of the battery eliminator – it’s because a DC-DC converter will normally provide a PLUG not a socket. I can also make a longer or shorter cheater cord if need be.

The two screws that hold this unit together are underneath the big sticker on the back. I poked holes through the sticker using a phillips screw driver.

If you are uncomfortable with messing with the guts of the charger, you can modify a plate from the Lenmar charger instead. The Lenmar comes with interchangeable plates to accommodate different batteries. or you can get a cheap travel charger. I find it convenient that my charger and “battery connector” are the same unit. And the charger is quite light.

Not shown, but also required:

  1. low wattage soldering iron.
  2. Small gauge wire stripper.
  3. Diagonal cutter or needle nose pliers with cutter,
  4. small parts holder (chip clips will work).
  5. A drill (and drill bit of the appropriate size for the chassis mount jack (6)).
  6. You may also need a phillips, hex or regular screwdriver to disassemble the battery charger.I originally purchased a sub-mini audio connector and tried to use that as the power connector but the connection was not crisp or reliable.
  7. And finally you may also need contact cement and/or a hot glue gun to reassemble the battery eliminator and possibly the charger as well.
  8. Patience.

The Battery Eliminator

Unless your camera or battery grip has a power connector any “big battery”solution will require a battery eliminator (parts C, D and E) or a DC input plug (hooray to Nikon for getting this part right, boo for the lack of availability of those connectors!). You can buy a battery eliminator – see more below – for many cameras but I found it easy to make a battery eliminator for my BP-511 battery out of a junk battery. For Canon cameras the battery eliminator plugs in where the battery goes and wires exit through a rubber gasket and are then connected to an external power source. While making a BP-511 eliminator was easy, I also tried to make an LP-E6 battery eliminator from a new (but cheap) LP-E6. I gutted the battery and soldered wires. The outcome was less than stellar as the contacts in the LP-E6 are small and very close together.

Those who fear the soldering iron can purchase an ACK-E2 or a cheaper knock off. Had I found the $20 knock off I would not have bothered hacking up a battery.  The ACK-E2 includes a battery eliminator and an AC power adapter to power the camera from a 110 volt outlet – I almost never am near wall power, but I can use the battery eliminator.   For my other camera, the 5D Mk II Canon sells the ACK-E6AC. Cost is  about $140. Like the ACK-E2 the ACK-E6AC includes a battery eliminator and an AC wall unit. However I found an equivalent unit for $39. No need to struggle with disassembling and soldering a battery eliminator!

My two cautions about these knock off units are:

  1. I doubt the AC components are UL listed. The knock offs certainly feel cheap.
  2. The connector between the AC unit and the dummy battery is not standard. Different manufacturers use different connectors. The connector on my ACK-E6AC knock off matched the Radio Shack M size power plug I had already been using. Oh happy day!

NOTE: Some camera models, like the Canon 5D Mk II have batteries with “chips” in them to help the camera know the current battery state. Your camera may – or may not – require this chip. Without the chip the camera nags you whether it is “ok” to use a battery that it can not talk to.  Just say yes.

Figure 5: The homemade BP-511 battery eliminator installed in a Canon 40D camera.

Canon cameras have a little rubber gasket that allows a cable to exit the battery compartment. If you build your own eliminator make sure your cable exits your battery eliminator where it will be able to be routed out of the battery compartment. If you do it wrong, you’ll have a battery eliminator that does not work because most cameras do not supply power to the camera electronics unless the battery door cover is fully closed. This is also true for most battery grip attachments.

Voltage, Amperes and Stuff: Background Data for the Electronically Challenged

The typical Canon BP 511 battery supplies 7.4 volts** to the camera and boasts a 1390 milliamp-hour rating. 1390 maH means that if the camera draws 1.39 amps it could run for an hour. That kind of power is possible with lithium batteries – the most power for the least weight of any currently available options. It’s also possible with SLA (Sealed Lead Acid) and a variety of similar battery chemistries. The battery you have in your car is a suitable choice, it’s just quite a bit heavier than most people are willing to carry. Smaller lighter versions of that same battery are available for things like lawn tractors and, “Jump Starters”.

**First you need to know a little secret.
A “12 volt” battery is really around 13.8 volts when fully charged. Likewise the Canon 7.4V battery is about 8.2V when fully charged. During use the voltage will drop to the point where it will no longer be able to service the camera. At that point it is wise to stop using the battery… going further, especially with a lead acid type battery, may permanently damage the battery.

Using a 12 volt car battery with a camera that expects 7.4 volts is, well, a possible cause for problems. The camera probably CAN sip from the 12 volt supply, but it would be kindler and gentler to chop that voltage down using a “voltage regulator”. In particular a “DC to DC” regulator is best here. A DC to DC converter (sometimes called a “buck”) drops the voltage down to a manageable level.

Confused about Volts, Amps, MilliAmps?

Voltage = “pressure”. Imagine a ball. It’s useless unless filled – to the proper pressure with air. Fill it too much and it will pop, too little and it won’t bounce. The
electrical equivalent of “air pressure” is “voltage”. Just as car tires require more air pressure to work than soccer balls do, so do some circuits require more voltage than others.

Amps (or milliamps) = “flow rate”. It will take a lot less time for a tire to go flat if there is a huge hole where lots of air can escape than it will for a pin-prick sized hole. The “rate of escape of air” is the electrical analog of current which is measured in  amps. A milliamp is a thousandth of an amp.

Resistance. In our analog, the “size of the hole” is a good example of the electrical term resistance. And it’s not a surprise since the volume of air that can escape in a second will depend on the pressure and the size of the hole the air can pass through.

Capacitance. A capacitor is a device that can hold a charge. In the air pressure world, a tire is a capacitor. You can fill a tire with air, then use the pressure in the tire a little at a time – or all at once – to inflate something else like a balloon.

mAh – an abbreviation for milliamp-hour.

Milliamp-Hour is one milliamp of current for one hour.  Milliamp-hours or amp-hours describe how much energy a battery can supply and for how long – under normal conditions, that is.

Watt-Hour is another format for specifying the capacity of a battery. To convert from Watt-Hours to Milliamp-hours divide the Watt-hours by the working voltage and then multiply by 1,000.  Thus a 34.2 watt-hour (wH) 7.2 Volt battery has a 4,750 mAh capacity. To convert from amp-hours to watt-hours multiply the amp-hours by the working voltage. If starting with milliamp-hours first  divide by 1,000. A 7.4 volt battery with 7,000 mAh rating is equal to 7,000 / 1000 * 7.4 which is 51.8 Watt-hours

Here is another important tidbit… just because a charger for a camera battery is available does not mean the charger can be used in place of the battery. There are two reasons for this.  The first reason is that chargers MUST supply more than the normal maximum battery voltage. Using an air-pressure analogy: to fill a tire, the pump must exert greater air pressure than the current pressure in the tire. Likewise to charge a battery, a greater voltage must be applied than the final voltage the battery will attain. The second reason is that the charger does not have to supply much current, a trickle is all it needs to slowly charge the battery – just as a bicycle pump can inflate a truck tire. The camera, however, sometimes takes “gulps” of current – more than the charger may be able to supply.

Knowing that a 7.4V battery is really about 8.2V helps makes it clear that ANY voltage in the range of about 7 to 8.5 volts will make a (Canon) camera happy IF it can also supply enough amps.


Timescapes.org has a lot of great discussions.