Beer

Didn't like much this Guiness Dublin Porter thing...

Wine

The first sip was good , not bitter.

It was smooth and can be taken again. Like it.

A Tracking Platform/Mount for Astrophotography

This has been taken from: 
1. http://www.garyseronik.com/?q=node/52 
2. http://www.dpreview.com/articles/2705562354/building-using-a-tracking-mount-for-astrophotography/print

This simple, easy-to-build mount provides the perfect introduction to long-exposure astrophotography.

Round stars. That’s the difference between astrophotos captured with a camera that tracks the sky’s motion versus one that doesn’t. Traditionally you’d make a tracked photo by placing your camera piggyback on a telescope with a motorized equatorial mount. But that’s a lot of equipment to deal with if all you want are some nice-looking constellation portraits or a shot of a newly discovered comet — especially if you have to travel to reach your favorite dark-sky destination.

This view of the Eta Carinae Nebula was shot in Costa Rica with a camera riding on the tracker described here.

The mount described here provides one of the easiest ways to track the night sky with your camera. Known generically as a barn-door tracking platform, it’s easy to make and works well for camera-and-lens astrophotography. I built the tracker shown here based on one recently made by Ohio telescope maker Ed Jones and on a platform built by Sky & Telescope’s Dennis di Cicco in the mid-1980s. Ed and Dennis used parts they had lying around, but I used components sourced online and from local hardware stores.

As the parts diagram at the end of this article shows, the tracking platform consists of two triangular pieces of plywood joined along one edge by a pair of hinges that serve as the mount’s polar axis. Your camera attaches to the top piece via a photographic ball head (available at any camera store), while the bottom piece (the base) mates to an ordinary camera tripod.

The tracking action comes from raising the top plate at a precise rate. This is accomplished with a motor, a pair of spur gears, and a curved length of threaded brass rod. The only tools needed for this project are a jigsaw, drill, screw-driver, and soldering iron.

Construction Details

Begin by cutting the two wooden parts from ½-inch-thick plywood. These pieces are almost identical — the hump to accommodate the motor on the base is the main difference. The only critical dimension is the distance between the hole for the threaded rod and the center of the hinge pins. This must be as close to 7.14 inches (18.1 centimeters) as you can make it. In my mount, the hinge pins hang off the end of the base by almost ¼ inch, which is where the 6.9-inch dimension in the plans comes from (6.9 + 0.24 = 7.14). If the hinges you purchase are different, you’ll need to adjust the length of the boards accordingly.

Next, drill the necessary holes in both wooden parts. Note that the distance between the holes for the motor shaft and the drive bolt is 1¼ inches. (If you choose a different motor and gears, this spacing may change.) To allow the two gears to mesh properly, one of the motor-mounting holes is slotted to provide a little room for adjustment.

The other hole that needs special attention is the one on the base board that the curved drive bolt goes through. To avoid binding, you want the bolt to pass through as thin a layer of wood as practical. Use a ½-inch Forstner or spade bit to countersink a hole in the underside of the base board to a depth of about ⅜ inch. Drill the rest of the way through with a standard ¼-inch bit.

After you drill all the holes, give the wood parts a protective coating. I used MinWax paste finishing wax, but any suitable paint or polyurethane will do. Finally, insert the T-nut into the bottom board and attach the hinges.

Bending the Drive Bolt

For the mount to track accurately, it needs a curved drive bolt. But how do you make an accurate bend in a length of threaded rod? Ed Jones described a simple method in which he drew the required curve on a piece of paper taped to a flat surface. Next, he placed the threaded rod onto the paper and gradually bent it until the curve in the rod matched the one drawn on the paper.

For my mount, the radius of the required curve is 7.14 inches. However, you need to subtract half the thickness of the threaded rod from this dimension for the curve to match the inside radius of the bend. A 7-inch-radius curve is close enough for this purpose. Because it’s difficult to evenly bend a short length of threaded rod, start with a piece that is at least 1 foot long. Once you’ve achieved a good curve of the correct radius, use a hacksaw to cut out a 4- or 5-inch-long section — choose the piece that most closely matches the desired curve. A segment of this length will yield around 1½ hours of uninterrupted tracking.

Attach the drive bolt to the mount’s top board with an acorn nut, lock washer, and flat washer on the top side, and a plain nut and washer underneath. At this point you’ll likely find that the bolt doesn’t pass cleanly through the hole in the base. Simply grasp the threaded rod near where it attaches to the top board and gently bend it a little until it goes through the hole without scraping or binding.

The tracking action of the barn-door mount is achieved by lifting the upper board at the correct rate by means of a motor driving a nut on a threaded rod.

A key part of the assembly is the drive nut, which couples the large gear to the threaded rod. I used a blind well nut (shown below) purchased at my local Home Depot (and available form numerous online sources, as a Google search will reveal). A 10-32 nut glued with two-part epoxy to the underside of the gear should work as well.

Prepare the gear by inserting the blind well nut and trimming off the rubber flange. I had to enlarge the hole in the gear slightly with a round file for a good friction fit. If you choose to glue a nut to the underside of the gear instead, make sure that the nut is accurately centered over the hole. The easiest way to do this is to use a spare 10-32 bolt wrapped with a few strips of paper or masking tape so that it fits snugly into the hole. Thread the nut into place and apply the glue, making sure you don’t get any epoxy on the threads. Once the glue has set, carefully unscrew the bolt and remove the paper strips. Thread the assembly onto the drive shaft and en-sure that it turns smoothly.

Next, slip the small gear onto the motor’s drive shaft, and attach the motor to the bottom board with nuts and bolts. Adjust the height of the small gear until it’s even with the main drive gear, then lock the set screw. Pivot the motor until the two gears engage properly, and tighten everything down.

The Drive and Electronics

The motor used in this design turns at 4 revolutions per minute (rpm). It’s a 3-volt DC gearhead motor manufactured by Hankscraft (model 3440-3V). You’ll need a pair of gears to reduce the motor’s speed to 1 rpm. I used a 16-tooth gear attached to the motor and a 64-tooth gear driving the nut on the threaded rod. Most of these parts are available from a wide range of sources. Mine were purchased from Stock Drive Products/Sterling Instruments (SDP/SI). If you decide to use a motor that turns at a different rate, you’ll need different gears to achieve the required 1 rpm. You also have to make sure there’s enough clearance between the motor housing and the drive bolt so the latter doesn’t collide with the former.

One nice feature of the DC motor is that its speed depends on the voltage of the power supply — a precise and constant voltage is all it takes to ensure accurate tracking. The voltage-regulator circuit shown in the diagram below is easy to build and allows you to fine-tune the motor’s speed to precisely 1 rpm. The components aren’t particularly exotic, and you should have no trouble getting them from a local electronic- parts store or online from places like Mouser Electronics or Digi-Key.

My regulator circuit is housed in a plastic project box and uses a standard RCA-type jack to connect to the motor. Note that the positive and negative leads are reversed from those shown on the motor. This is to ensure that the motor runs counterclockwise, which is the correct direction for use in the Northern Hemisphere. (Photographers in the Southern Hemisphere users will want the motor to run clockwise.) If the motor runs the wrong way, the tracking platform is literally worse than useless!

Testing and Using the Tracker

Before attempting your first photograph you have to adjust the motor speed so that the large gear turns at exactly 1 rpm. The easiest way to do this is to mark one of the gear’s teeth with a felt pen and add a small tick mark to the base. Run the motor, and start your stopwatch just as the marked tooth aligns with the tick. After exactly one minutes, stop the motor and see where the marked tooth is relative to the index mark. (For increased accuracy, let the motor run for two to five minutes.) Adjust the multiturn potentiometer and repeat the test until you get the motor running at the correct speed.

To use the tracker, place it atop a camera tripod and sight along the hinge pin to aim the mount at Polaris. As the photos show, I use a red-dot finder for polar alignment, though this is more a matter of convenience than accuracy. You could also use a finderscope or, as Ed Jones does, a laser pointer. In situations where I cannot see Polaris, I use a compass and inclinometer to set up the mount — the compass to adjust the mount in azimuth, the inclinometer to match my location’s latitude.

Once the mount is polar aligned, you should switch on the motor and let the drive run for a minute or so before opening your camera’s shutter. This allows things to settle down and enables the motor to take up any slack in the drive.

Although a curved-bolt barn-door camera platform is a simple piece of equipment and easy to build, it can produce excellent results, as this phto of Orion shows.

After shooting for a while, you’ll notice that the drive gear needs to be reset. This is easy to do. Switch off the motor, lift the top board so that the two gears disengage, and spin the drive gear counterclockwise until it is back near the top of the curved bolt. Gently lower the top board back into position (taking care to ensure the gears mesh), and resume shooting.

I’ve found this tracker to be the ideal photographic plat-form for travel. So far, it’s accompanied me on numerous trips. including visits to Costa Rica and to the Mt. Kobau Star Party. Since it’s so lightweight and takes up so little room in my suitcase, there’s really no reason not to bring it along.

Note: This is an updated and expanded version of an article I wrote for the June 2007 issue ofSky & Telescope magazine.

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Building & Using a Tracking Mount for Astrophotography

RustierOne | Photo Techniques | Published Sep 5, 2012

August 26, 2012 

Introduction

Astrophotography may involve exposures of several minutes or more. Since the sky appears to move due to Earth's rotation, such exposures often require some way to track the sky's movement during that exposure. This article describes building and using a simple, relatively inexpensive "Barn-door" tracking mount based on an article by Gary Seronik in the June 2007 issue of Sky and Telescope magazine, page 80. Since reprints of that article may  be hard to obtain, you can view the plans online at

http://www.garyseronik.com/?q=node/52

I will not attempt to duplicate those plans here in my article. But I will add my comments and photos of my implementation of the plan. Be sure to consult the plans for construction details and important points not covered here.

The Barn-door mount gets its name from the two plates of plywood with a hinge connecting them, like a barn-door. We see it pictured above installed on an old Celestron equatorial wedge, which has adjustments for altitude and azimuth. The mount can also be placed on a heavy-duty photo tripod. A gear head on the tripod with altitude & azimuth adjustments can make polar alignment much easier.

The view above shows the tracking mount and equatorial wedge on a very solid Celestron Tripod.

Building the Mount

For the most part I followed Gary Seronik's plans carefully. Since I intended to install the mount on an equatorial wedge, I modified the size and shape of the bottom plate to match the circular outline of the wedge as shown below. Also since my supply of scrap plywood did not include any 1/2-inch plywood as called for in the plans, I used some nice 3/4-inch plywood. This change could make the mount a bit heavy for installation on a photo tripod. So in that case it might be best to stick with the plan's use of 1/2-inch plywood.

One of the keys to this type of mount is the hinge between the two plywood halves of the mount. The upper plate with camera moves relative to the lower one via that hinge. In the Northern Hemisphere the hinge pinmust be pointed at the North Celestial Pole (near the North Star) for the mount to track accurately. Of course for those located in the Southern Hemisphere, the pin must be directed to the South Celestial Pole.

 Gary's plan uses what looks like a pair of door hinges. I chose to use a single piano hinge, which allows the hinge to be the full width of the upper plate. I also relocated the ball-head camera mount from the center of the upper plate to the top edge, as shown in the above photo. This was necessary to avoid the problem of my articulating camera monitor not being accessible when the camera was pointed up.

Some Tips For Construction

The 10-32 threaded brass rod, which drives the upper mount plate and camera, is curved to a 7-inch radius. It is driven upward by a nut epoxied to the bottom of the large gear, which is turned at 1 RPM. Below the bottom plate is a 4 RPM, 3 VDC gear motor, which drives the rod through a 1:4 spur gear set (16-tooth and 64-tooth). Motor speed is adjusted with a variable DC supply (visible above) powered by a 9-volt battery.

I prefered not to install a stop nut on the drive rod below the bottom plate, as called for in the plans. Thus if the drive is inadvertantly left running, it will not stall at the end of the rod, possibly damaging the gears or the motor.

Further Tips For Construction

Another key feature of this mount is that the distance between the center of the hinge pin and the points where the curved drive rod penetrates the two plates must be exactly 7.14 inches. This is necessary so that when the nut (attached to the large gear) is turned at 1 revolution per minute on the 10-32 drive rod, it will rotate the upper plate and camera at exactly the correct rate to match the sky's rotation.

The image above shows the drive rod penetrating the upper & lower mount plates at a 7.14-inch distance from hinge pin.

The photographer can sight along the hinge pin to align it with the celestial pole. On my setup I installed a green laser to be parallel to the pin. The laser beam is then pointed at the celestial pole via adjustments on the equatorial wedge or photo tripod to ensure that the hinge pin is polar-aligned. The image above shows the camera pointed south of the celestial equator.

Aligning the Green Laser With the Hinge Pin

The green laser is installed in an adjustable mount, much like a telescope's finder scope. The method to align the laser beam to be parallel to the hinge pin is as follows:

• Lift the upper mount plate, disengaging the two gears.
• If necessary, spin the large gear so that it is snug against the upper plate.
• Turn on the laser, noting the spot where the beam hits a distant target.
• Rotate the plate through about 90 degrees.
• If the laser beam is not parallel to the pin, the laser spot will move on the target.
• Adjust the laser in its mount (via the 6 nylon adjustment screws) until the laser spot no longer moves on the target when the plate is rotated. When that is achieved, the laser beam is parallel to the pin.

When the camera is pointed north of the celestial equator as shown below, the laser and its mount can be  removed to avoid interference with the camera and its monitor.

This image shows the green laser and its mount removed from the top plate to give clearance for the camera.

The Green Laser and Its Mount

It is important to use a green laser rather than the more common red laser. This is so because the human eye ismuch more  sensitive to green  light  than red. A red laser would simply not be visible in the sky during polar alignment. 

Shown here is the green laser in its mount made from white, 3/4-inch PVC pipe. Threaded into each end of the mount are 3 nylon screws for adjusting the aim of the laser. The middle screw on top activates the laser push-button switch.

Finishing the Mount

After assembling the mechanical parts of the mount, the project can be completed by making the variable DC  power supply for the motor. I purchased most of the parts for this at my local electronics store. The 10-turn potentiometer for adjusting motor speed was purchased on-line. With a little planning, I was able to fit all of the electronics into a rather small plastic project box, which also houses the 9-volt battery. The box's metal cover serves as a heat sink for the adjustable voltage regulator integrated circuit. When the power supply is not in use, it can be disconnected from the motor by use of a set of quick disconnects on the wire leads.

My experience shows that with simple tools (jig-saw, drill press, screwdriver, hacksaw, soldering iron, etc.) it is possible for someone with limited skills to construct a workable tracking mount.

When describing this mount, I have used the term “inexpensive”, which  is of course relative. I estimate that my mount has cost around $185 (US).  If one is needed, a heavy-duty photographic tripod can easily add more than $100 to the total. Take note of the following link to “Mounts for Astrophotography” by Jerry Lodriguss:

 http://www.astropix.com/HTML/I_ASTROP/MOUNTS.HTM

In that reference Jerry states “… good, inexpensive German-equatorial starter mounts for astrophotography are difficult to find for less than about $750 - $1,000.” So in light of that observation, the roughly $200 cost of the Barn-door mount is very reasonable. And the results can be quite good.

For those so disposed, a Barn-door type mount can be purchased at

http://www.astrotrac.com

for $580 ( plus tax and shipping, subject to the current exchange rate for Euros). There are other commercially available tracking mounts such as inexpensive equatorial mounts for telescopes.

Using the Tracking Mount

Before using the mount, it is important that its drive rate be set so that the large gear (with its attached nut) rotates once per minute. This can be easily accomplished by putting a small permanent mark on one tooth of the large gear as well as a small index mark on the bottom plate next to the gear. One simply adjusts the supply voltage until it takes a minute for the gear to make one revolution. Additional accuracy can be achieved by timing for a longer period, say 5 minutes. Be aware that the power supply output voltage (and tracking rate) can vary as battery voltage drops as well as with temperature changes. So it might be best to check the drive rate before each photo session.

Also note that after about a cumulative hour of tracking, it is necessary to reset the mount  as follows:

• Lift the upper plate, disengaging the gears.
• Spin the large gear and its nut until it snugs up against the upper plate.
• Lower the plate and re-engage the gears. This will enable another hour or so for tracking. 

If care has been taken in constructing the mount according to the dimensions in Gary Seronik's plan, with careful polar alignment, and careful adjustment of the motor speed, this mount can easily provide tracking for some nice astrophotos. I have found that ISO 800 or 1600 with a 2 minute exposure gives nice results. Some of these results are on the next page.

Some Astrophotos Made Utilizing The Tracking Mount

All the photos on this page were obtained using this mount with a Sony NEX-5N camera.  The lens used is an old 1971 Mamiya-Sekor 55mm f/1.4 stopped down to f/3.5. These images are composed of single JPEG shots with no stacking, flat frames or dark frame noise reduction (except where noted). Post processing was mostly just histogram stretching. So there is lots of room for improvement in these areas. The panoramas were assembled using Microsoft's ICE (Image Composite Editor, a free download).

The first three photos shown here were taken at a site in the Blue Mountains of northeast Oregon at  just over 3000 feet elevation. Exposures were around 2 minutes at ISO 1600. There was some light pollution from cars and trucks on a nearby highway as well as from a town (about 17,500 population) just over 10 miles distant and about 2000 feet below. Also the air was dimmed by a lot of smoke from forest fires. Still the results are quite nice.

The view here is in Sagittarius, showing a region in the direction of the center of our Milky Way galaxy.

This image shows a nice star field between the star Vega in the constellation Lyra on the right to Gamma Cygni on the left.

This panorama of multiple images covers a span of the Milky Way from Cygnus on the left to Sagittarius on the right. The change in color from left to right is due mostly to smoke pollution, which is thickest low in the sky to the right. Click to expand image.

 The following panorama consists of parts of 13 photos taken from an elevation of just over 1200 feet in the Coast Range of southern Oregon. Some clouds and  light pollution  affected  the images. Exposures were 2-1/2 minutes at ISO 1600. Long exposure noise reduction (dark frame subtraction) was activated on the camera. This resulted in considerably less noise as compared to the first panorama above.

This view of the Milky Way extends from the Double Cluster in Perseus on the left through Cassiopaeia and Cepheus to Cygnus on the right. Click to expand image.

 Here's wishing you success in astrophotography with this mount.

Its easy to build and fun to use - give it a try!

Some Further Observations and Conclusions

After using the mount for a few months, I have made some changes in its construction and use.

As noted on page 2, I had moved the location of the ball-head from the center of the top plate to its top edge. The purpose was to avoid problems with my camera’s articulating monitor not being accessible when the camera was pointed up. What I discovered after using the mount for a while is that this move just changed the pointing directing where I encountered the interference. The best solution was to mount the ball head on a short wooden post centrally located on the top plate as shown in the image below. This prevents interference with the monitor for most directions the camera is pointed.

The only down side to this solution is that the camera and ball head are located further from the hinge pin, requiring a bit more effort on the part of the motor to lift the weight. But in this position, I seldom have to remove the laser and its mount for clearance.

On page 8 I noted: “Power supply output voltage (and tracking rate) can vary as battery voltage drops as well as with temperature changes”. With that in mind, I had recommended checking the drive rate before each imaging session. I discovered that this was time-consuming and subject to error as the drive rate continued to change during the course of the evening as battery voltage and temperature dropped.

I believe that the best solution to this variation in drive rate is to determine by experiment what voltage supplied to the motor results in the correct tracking rate. If the mount is made carefully according to plan dimensions, the correct rate for the drive nut is 1 rpm. Once the correct voltage is determined, one merely monitors the voltage during the course of an imaging session, making corrections as necessary. To that end I made a set of multimeter leads that can be connected to the power supply via an extra output cord and quick disconnects. This is shown in the following image.

Ball head mounted on wooden stalk; power supply voltage monitored by digital multimeter

One important note on polar alignment: The north celestial pole is not exactly on the North Star (Polaris) – it is located at a point about a degree from Polaris. For best results align on that point rather than on Polaris. For short focal length lenses, Polaris may be close enough. For longer focal lengths, find the pole’s exact location from a good star chart and align there.

Tracking mount with laser for polar alignment and Multimeter for checking supply voltage

Overall the mount has been a joy to use. It is quick to set up and polar align. And the results are satisfying. Here’s a nice image taken with a Samyang 8mm fisheye lens at f/2.8, 2-1/2 minute exposure.