Finding objects in the sky can be one of the most frustrating aspects for amateur astronomers, especially ones starting out on this hobby. This task is becoming ever more difficult as light pollution increases where only second magnitude stars can be seen from many people's backyards. The binoculars shown here are very comfortable to use because of the 90 degree eyepieces, weigh less than 800 grams (28 oz) and enable 7th magnitude stars to be seen over a 6.5 degree field of view. They can be mounted on a photo tripod with a small video head.. It is easy to merge the images while viewing and they provide ~7X magnification with inexpensive 25mm plossls.
This set up enables a smart phone running a suitable planetarium app to be used as an accurate means to quickly and efficiently find celestial objects in the sky. Many people assume that the smart phone planetarium apps are not accurate because they are not using the right app for the task or they are not mounting the smart phone in the most convenient way, There are so many planetarium apps out there it is important to chose one that has certain features. Three features that I think are important are:
1) The app should display a true photo of the sky showing down to at least 7th magnitude stars
2) The app should have a quick and simple means of applying a compass correction to calibrate the compass (azimuth) on a nearby bright star within 30 degrees of the object you are searching for.
3) The app should be able to display approximately a 6.5 degree field of view which will match the view in the 7X50 binoscope shown here.
One free app that does this is Sky Guide. This app has an easy to apply compass correction by holding your finger on the screen for 2 seconds and then sliding your finger to bring a bright calibration star into the horizontal center of the screen matching the view in the 7X binoculars. To bring the calibration star in to the vertical center of the screen the smart phone mount should be adjustable in the vertical plane over +/- a few degrees (see photo).
The important features of the mount is that it must hold the iphone securely and as high as possible to permit viewing when pointed at the zenith. After calibrating the star image on the smart phone you enter the desired object into the app and follow the guide arrow on the screen. When you are near the object you look back and forth from the screen to the 7X binocular finder until you see the same star field in both. You have effectively positioned the binocular finder on the searched for object using visual plate solving using your eyes and brain. I use a small door on the iphone mount to mask out a circular 6.5 degree field of view on the iphone screen so the image on the iphone will exactly match what you see in the 7X binocular eyepieces. Shown below are all the 3D parts you will need to print A few modifications have been made to the original prototype parts shown in the actual photo of the full assembly at the top of the page.
This set up enables a smart phone running a suitable planetarium app to be used as an accurate means to quickly and efficiently find celestial objects in the sky. Many people assume that the smart phone planetarium apps are not accurate because they are not using the right app for the task or they are not mounting the smart phone in the most convenient way, There are so many planetarium apps out there it is important to chose one that has certain features. Three features that I think are important are:
1) The app should display a true photo of the sky showing down to at least 7th magnitude stars
2) The app should have a quick and simple means of applying a compass correction to calibrate the compass (azimuth) on a nearby bright star within 30 degrees of the object you are searching for.
3) The app should be able to display approximately a 6.5 degree field of view which will match the view in the 7X50 binoscope shown here.
One free app that does this is Sky Guide. This app has an easy to apply compass correction by holding your finger on the screen for 2 seconds and then sliding your finger to bring a bright calibration star into the horizontal center of the screen matching the view in the 7X binoculars. To bring the calibration star in to the vertical center of the screen the smart phone mount should be adjustable in the vertical plane over +/- a few degrees (see photo).
The important features of the mount is that it must hold the iphone securely and as high as possible to permit viewing when pointed at the zenith. After calibrating the star image on the smart phone you enter the desired object into the app and follow the guide arrow on the screen. When you are near the object you look back and forth from the screen to the 7X binocular finder until you see the same star field in both. You have effectively positioned the binocular finder on the searched for object using visual plate solving using your eyes and brain. I use a small door on the iphone mount to mask out a circular 6.5 degree field of view on the iphone screen so the image on the iphone will exactly match what you see in the 7X binocular eyepieces. Shown below are all the 3D parts you will need to print A few modifications have been made to the original prototype parts shown in the actual photo of the full assembly at the top of the page.
The base shown below should be the first part to print (Part#1)
Here is the .stl file. You will need to download it and run it through your slicing program (I use Cura) to create the gcode for your specific printer. Or contact me at , astronomybinoculars@petertinkerer.com and I may be able to print it for you. . I print with only 10% fill at standard quality (0.2mm layers) to make it as light as possible and on a Creality CR-10 it takes about 8 hours to print.
| 50mm_part1.stl |
Next, 3D print the movable objective holder (Part#2)
Here is the .stl file:
| 50mm_part2.stl |
Next print the fixed objective holder
The next task is to install 3 pieces of hardware into the fixed objective block. Here is a photo of the hardware. It consists of 2, 6-32 brass inserts and 1 cut off (7mm total length) 1/4-20 hex bolt. When you cut off the hex bolt make sure you file the top of the head flat to remove any raised lettering.
Install the brass inserts into the fixed block as shown below. To ensure that they do not rotate put a small dab of Devcon plastic welder epoxy on the sides. To install the brass inserts use the hardware that will later be used to lock the fixed objective holder block in place. This hardware consists of two 1.25 inch 6-32 bolts, two wing nuts and two washers, see photo. below. Before using this hardware tighten and glue the wing nuts on the 1.25 inch 6-32 bolts so that they are firmly in place and will not slip. Tighten the wing nuts and pull the brass inserts into the holes in the fixed objective holder. Also shown in the photo below is the vertical merge adjustment screw. This is a 1 inch 8-32 bolt which has its end sharpened to a point. A knurled brass piece is screwed on to make it easier to grip with thumb and finger.
Use one of the 1.25 inch 6-32 bolts to pull in the 6-32 brass inserts into the fixed block
Next install, with a small dab of plastic welder epoxy, the cut off hex bolt into the bottom of the fixed block. Make sure that the head of the bolt is recessed below the bottom of the fixed block by about 0.5mm, see photo below. If necessary shorten the 1/4-20 hex bolt.
Next install the hardware in the sliding objective block. The hardware consists of one 1/4-20 T nut. The T nut has cut off edges and is about 9mm long (~3/8 inch), Install the T nut with a dab of Devcon plastic welder, see photos below:
When you install the T nut use a guiding 1/4-20 rod so that the T nut is held in accurately in place while the plastic welder glue sets up.
Next, print the IPD adjustment wheel:
Here is the .stl file for the IPD adjustment wheel:
| 50mm_ipd_adjustment_wheel.stl |
The hardware for the IPD adjustment wheel consists of a 3 1/2 inch 1/4-20 carriage bolt
Next screw in the 1 inch long 4-40 bolt into the IPD adjustment wheel to create the thread. Make sure the bolt goes in until you feel the head bottom out. Do not over tighten or you will strip the threads.
Next remove the 4-40 bolt and prepare to mount the IPD brass rod and wheel into the frame.
Insert the IPD wheel into the frame which should be a snug, sliding fit with as little play as possible but not so tight that it does not turn easily. With the larger opening in the IPD wheel facing up, insert the threaded rod until you can see light coming through the hole, see photo above. Now screw in the 4-40 bolt into the IPD wheel until it bottoms out and the IPD brass rod is held in place, see photo below:
Next, the 8-32 T nut is glued in place in the bottom of the frame. This T nut will hold the 8-32 bolt for the vertical merge of the images.
8-32 T nut glued in place with a dab of the Devcon plastic welder, see photo below:
Next attach a 70mm long 15mm wide, strip of felt. I use a small piece of self stick black flock paper.
Next push the sliding block into the frame guides until the IPD threaded rod touches the T nut in the sliding block. Now start rotating the IPD wheel to pull the sliding block along the guides. The felt or flocking strip takes up any free play of the sliding block but still enables it to be moved along the guides by turning the IPD wheel.
Next install the fixed block using the 6-32 bolts. Do not over tighten the wingnuts.
Next screw in the two objective barrels and glue in the two 45 degree Amici prisms making sure they are correctly orientated. If you prefer to check everything is working before you glue them, wrap the Amici prism barrels with a thin wrap of tape and push them into the objective holders with some force. They should only rotate with some effort so they stay put when not forced to rotate. You can mark their position and glue them in later when you are sure everything works correctly.
As you can see from the photo above the handle for moving the unit in altitude and azimuth has also been added. The 1/4-20 threaded rod length can be from about 8 inches to 12 inches and preferably made of brass. The grab handle is glued on the ened of the rod. Here is the .stl file for the handle end.
| alt-azm_handle__3_.stl |
Now mount the unit on the tripod ball head: