11 replies to this topic

[corduroy]

Hello, I built a barn door tracker last week based on this design.

It's sitting on a Fancier FT-717AH pan/tilt fluid head and has a Smith Victor BH5 ball head.

I have not had the opportunity to hook up the motor to it yet but have taken some manually tracked 30s shots that look decent. It's a pita to rotate that gear at a constant rate with cold hands & fingers!







I do have a question regarding how the main gear sits. This gear has a blind well nut pressed into the center and the gear sits on the bottom platform. Is this OK? Most of the barn door tracker pictures I have seen have this main gear sitting up off the bottom platform a few mm. I am not sure how they accomplish that. The friction between the gear and wood is low but I am wondering if that could impact the tracking.

I also have to figure out the polar alignment scope. I have it positioned on the end of the top platform but it is not pointing at the same place the hinge pin is. For my trial I just aligned the platform hinge pin with polaris by eye.

[Ultron]

Nice job!

I would put a nylon washer in between the wood and the gear. That might help.

I never put a polar scope on mine.
Do you have a pic of the motor you are using?

[evan9162]

I aligned the polar scope on my barn door tracker by doing the following:

-Point my camera so it's approximately aligned with the axis of rotation
-Center Polaris in my camera's frame by moving the alt/az of the tripod
-Start with the tracker in the fully closed position. Open it up completely (just lifting it by hand) while observing how Polaris moves within the camera's framing. Use live view on your camera for this.
-Adjust your tripod angle (alt/az) until Polaris doesn't move when you open/close the tracker
-Re-center Polaris in your camera frame using the ballhead on your tracker
-Zoom in with live view, and repeat the opening/closing/alignment steps. Once you are at 10x live view, and Polaris doesn't move when you open/close the tracker, then your hinge is pointed exactly at polaris
-Adjust the aim of your Polar scope so it's center crosshairs/dot/etc point at Polaris

Your polar scope is now aligned (parallel) with the axis of rotation of your tracker.

[corduroy]

Nice job!

I would put a nylon washer in between the wood and the gear. That might help.

I never put a polar scope on mine.
Do you have a pic of the motor you are using?

Thanks, the motor is from SDP-SI. Part # A 3Z16-0040A about $30.

Motor is connected via rca cable to control box.


Inside the control box. The blue item is a potentiometer that I will set to get the large gear to spin at 1 RPM:

[corduroy]

I aligned the polar scope on my barn door tracker by doing the following:

-Point my camera so it's approximately aligned with the axis of rotation
-Center Polaris in my camera's frame by moving the alt/az of the tripod
-Start with the tracker in the fully closed position. Open it up completely (just lifting it by hand) while observing how Polaris moves within the camera's framing. Use live view on your camera for this.
-Adjust your tripod angle (alt/az) until Polaris doesn't move when you open/close the tracker
-Re-center Polaris in your camera frame using the ballhead on your tracker
-Zoom in with live view, and repeat the opening/closing/alignment steps. Once you are at 10x live view, and Polaris doesn't move when you open/close the tracker, then your hinge is pointed exactly at polaris
-Adjust the aim of your Polar scope so it's center crosshairs/dot/etc point at Polaris

Your polar scope is now aligned (parallel) with the axis of rotation of your tracker.

"Point my camera so it's approximately aligned with the axis of rotation"

Do you mean like this?

[bunyon]

I've put a small notch next to the hinge so that I can lay a laser pointer against the hinge. The notch keeps it snug and in line. I then point the laser where the pole should be. Seems to work.

On these motorized trackers, how do you rewind? Can the motor be reversed? (Mine is still a manual operation - fine for when I'm travelling and the image is all I'm doing but it would be nice to take it with me observing and let it run while I observe.

[corduroy]

I disengage the motor drive from the large gear, lift the top platform up and spin the large gear up toward the top platform by hand.

[Dwight J]

I read in S&T years ago an article about barn door trackers and how to manually track without a motor. iIRC, using a 50mm lens on a 35mm camera, you use a second hand on a watch and turn the slow motion in RA once every 15 seconds rather than continuous. This rate will vary depending on the camera lens used and the size/curve of you RA bolt. This may be worth a try and would be slightly less of a pita.

[evan9162]

On these motorized trackers, how do you rewind? Can the motor be reversed? (Mine is still a manual operation - fine for when I'm travelling and the image is all I'm doing but it would be nice to take it with me observing and let it run while I observe.

All I do is open the tracker a bit (which naturally lifts the lead screw gear away from the motor gear), then spin the leadscrew gear back up the threaded rod by hand. On my tracker, the gear is attached to a machined aluminium threaded hub, so there is some mass to it. That means I can flick the gear to keep it spinning, and it rewinds back up the threaded rod in only a few seconds. I don't even bother turning the motor off.

Once rewound, I drop the door of the tracker back down, and it re-meshes with the motor gear automatically.

My tracker was using a gearhead DC motor, driven by an adjustable voltage regulator. I'm in the process of converting it over to a stepper motor. I could probably easily add a rewind button that both reverses the controller, and boosts the stepping rate to 20-30x that of normal tracking. However, that's a lot of work to save 15 seconds of fiddling every 30 minutes.

[bunyon]

Thanks for the tips.

On my tracker, I turn a quarter turn every 15 seconds which is plenty accurate at 18mm. At 85mm I turn continuously and slowly. It's painful and tedious but I only use it when I'm traveling somewhere I can't take a mount or other scope and am just shooting some casual shots. Works pretty well.

[evan9162]

I'm shooting for doing 1 minute or more at 250mm. Just the vibrations from touching the tracker will ruin the shot at that FL, never mind the errors from tracking by hand. I can already do 30 seconds with a pretty high keep rate. I'm hoping the more consistent motor speed from a stepper will allow me to extend my exposure time.

[evan9162]

I aligned the polar scope on my barn door tracker by doing the following:

-Point my camera so it's approximately aligned with the axis of rotation
-Center Polaris in my camera's frame by moving the alt/az of the tripod
-Start with the tracker in the fully closed position. Open it up completely (just lifting it by hand) while observing how Polaris moves within the camera's framing. Use live view on your camera for this.
-Adjust your tripod angle (alt/az) until Polaris doesn't move when you open/close the tracker
-Re-center Polaris in your camera frame using the ballhead on your tracker
-Zoom in with live view, and repeat the opening/closing/alignment steps. Once you are at 10x live view, and Polaris doesn't move when you open/close the tracker, then your hinge is pointed exactly at polaris
-Adjust the aim of your Polar scope so it's center crosshairs/dot/etc point at Polaris

Your polar scope is now aligned (parallel) with the axis of rotation of your tracker.

"Point my camera so it's approximately aligned with the axis of rotation"

Do you mean like this?

You don't have to flop your camera over like that, just make a good effort to get the camera pointed parallel to the hinge axis.