100mm to 150mm Refractor Binoscope (New!)

100mm to 150mm Erect Image Binoculars

Shown below is the completed 100mm F6 Binocular telescope with the light covers on. The light covers are made from corrugated white plastic sheet which are covered with stick on black velvet on the inside. The bottom and side light covers are glued to the aluminum frame to provide rigidity. The upper light cover is removable for access and held on with magnetic tape.

I will now describe in detail how to make the 100mm F6 version of this flexible binocular telescope platform.

Shown above is the basic construction design which can be adapted to accommodate 100mm to 150mm lenses. The focal ratio should be at least F5.5 to avoid vignetting in the combination of the two inch Crayford style focuser and the Adjustable Bino Backs (ABB) . The design principle is to make a very robust frame which does not flex when changing the altitude and azimuth and to keep the IPD adjustment and the final critical merge as part of the ABB capabilities. There is nothing new in this approach which was invented (patent expired) by Tatsuro Matsumoto and has been offered for many years but at a cost which really only makes sense if you are creating a Binocular Telescope with two Takahashi OTAs' (or other very high performance OTAs) where perfection is the goal. Here we are trying to make a very good binoscope for about $1000 if using two 131mm F5.5 achromats (~$250 each when available from Surplus Shed) or about $700 if using two 106mm F6 achromats from Aliexpress. (~$120 each). The ABB units described here permit the use of two OTAs up to 180 mm in diameter thus two 150mm objectives in their mounts would fit.

Photo of one of the Adjustable Bino Backs (ABB) with helical IPD adjustment (52mm to 72mm) and adjustment screws for final critical image merging. Both the left and right ABB units have adjustment screws permitting perfect alignment of each OTA (Optical Tube Assembly) and final merging of the images.

The really critical detail in the construction of the ABB units is the twist angle between the two mirrors which needs to be 70.5 degrees. Any error in this angle will lead to image rotation and the two images will never merge over the full field of view. Fortunately there is a simple means to ensure that this angle is 70.5 with less than 0.1 degrees of error and that is by using an accurate bubble level. You need to find a truly vertical wall and then holding one of the 60mm blocks in the left hand (for the left hand ABB), you push the 2 inch barrel against the vertical wall and by changing the twist angle while rotating the 2 inch barrel on the vertical wall you will find there is only one unique position which makes the bubble exactly in the center. Later you will hold the other 60mm block in the right hand, push the 2 inch barrel against a vertical wall and find the unique twist angle that puts the bubble in the exact center. As I will show later you should use silicone for gluing this twist angle to give you time to make the bubble as close as possible to the center. Once you have the correct twist angle, support the ABB unit so that nothing will move for 15 minutes. Now place the unit on the vertical wall again and recheck that the bubble is still exactly in the center. If a tiny adjustment is necessary there will still be time since the silicone will not be fully hardened.

For the explanation of the construction details I will describing a build using 106mm F6 objectives, however the .stl files for other sizes of objectives will be in the Tinkercad Gallery.

Shown below is the focuser I used. Two required for approximate total cost of $180

Here is the Aliexpress page for the 106mm F6, achromats with green FMC coatings. Two required for approx cost of $250

Two 60mm and two 42mm mirrors are required for the ABB units with a total cost of about $120

Two helical adapters 17-31mm are required at a cost of about $50

Here is the precision compass used for setting the twist angle of the ABB units

This is the black stick on felt I use to cover all the interior surfaces of the binocular telescope. It is amazingly non reflective and I found it beats any of the flat blacks on the market. It is easy to use and creates a robust surface that will never flake off.

Here is a photo of the 100mm F6 Binoscope without light covers. The initial views of the globular cluster M13 were very encouraging! The weight of the Binoscope is only 11lbs and the simple Dob mount is easy to build, easy to operate and very stable. An adjustable height observing chair is required to permit comfortable views from the horizon to zenith. Although the amount of optical path offset provided by the ABB units would allow up to 150mm objectives to be used, in my opinion the sweet spot for keeping the weight and cost down whilst still providing very good optical performance are these 106mm objectives (100mm aperture).

There are quite a lot of parts to print and assembling the ABBs is quite difficult and requires a great deal of care. I hope that a few people out there will take up the challenge and start building this binocular Telescope. I'm here to help. E-mail me at [email protected] if you need any assistance.

Let's get started: first cut 8 pieces of the aluminum angle 300mm long for 600mm focal length 106mm objectives, or 430mm long for the 700mm focal length, F5.5, 127mm objectives where eyepiece holders are not used. Do not counter sink the holes since it will make it difficult to create a tight fit with the 3D printed end plates.

Scuff up the aluminum with sandpaper and glue two of the pieces together with devcon two part plastic epoxy (it works well on the aluminum although I'm sure other 2 part epoxies would work as well) Do this again with two more pieces. You should now have both the top and bottom joined aluminum pieces.

Now go ahead and print the Objective Holders, the focuser holders and the side bearings. The .stl files can be found in the Tinkercad Gallery:

100mm Part#10 Focuser Plate
100mm Part#11 Objective Mount
100mm Part#12 Side Bearing
100mm Part#13 Objective Locking Ring
100mm Part#14 Dew Shield

Now go ahead and start assembling the aluminum pieces and the end plates together using 3/4 inch 8-32 flat head bolts and 8-32 nuts which are installed in the end plate slots Initially I did counter sink the holes but I recommend not to do this and rather use flat head 3/4 inch 8-32 bolts since it will enable you to fit the aluminum angle tightly into the corners of the 3D printed end plates. Some filing and adjusting the drilled hole in the aluminum may be necessary to achieve as tight a fit as possible.

Make sure the frame is as square as possible. Tighten the screws so nothing moves, although later everything will be glued and the bottom and side light covers will be glued on to ensure a very strong frame. Attach the focusers and now we will check the alignment of the front and back end plates. You will need to print an objective cover with a central 4mm hole and a laser collimator with a 2 inch adapter (see photos below).

100mm Part#15 Objective Cover

Print objective cover to aid in collimation, attach 1.25 to 2 inch adapter to the laser collimator:

Adjust the focuser location until the laser beam disappears through the central hole in the objective mask. Do the same with the left hand focuser. Adjustment of the focuser bolts only moves the laser beam in the vertical tilt direction. If some slight horizontal adjustment of the laser beam is required a small re-alignment of the frame squareness may be necessary. When the laser beam is perfectly disappearing through the central 4mm hole on both optical paths tighten all the bolts on the frame and focusers.

Next Install the air spaced objectives into the objective holders. This has to be done carefully because the spacer is very thin and very fragile. I recommend taping the two pieces of each objective together with very thin Kapton tape to keep everything together and aligned while you slide each objective into their respective holder. Next push in both objective locking rings to hold the objectives in place. Later the objective locking rings will be glued in place.

Next you will need to print all the parts for the left and right ABBs. Shown below are the 3D printed parts to make one ABB. The parts from left to right are the following. Print Parts# 1 through 6 twice and then one Part#7 and one Part#8.
ABB Part#1 Two inch focuser barrel
ABB Part#2 60mm Mirror Block
ABB Part#3 60mm Mirror Holder
ABB Part#4 IPD Helical Adapter
ABB Part#5 42mm Mirror Block
ABB Part#6 42mm MIrror Holder
ABB Part#7 Left Eyepiece Holder
ABB Part#8 Right Eyepiece Holder

The .stl files are available by searching in the Tinkercad Gallery. If you are using F5.5 objectives you will need to print different 42mm Mirror blocks which permit 25mm Plossl Eyepieces, without the 1.25 inch barrels, to be glued directly into the mirror blocks. This reduces the total optical path length through the ABB units and reduces any vignetting that would occur with fast F5.5 objectives. If you are using the 127mm F5.5 objectives, 25mm Plossls will provide a fixed 28X magnification with generous eye relief, and glorious, comfortable views of the night sky.

The 42mm Mirror Block part for F5.5 objectives is:
ABB Part#5a 42mm Mirror Block
Search for it in the Tinkercad Gallery.

Building the 60mm Mirror Block:
First lets install the 4-40 brass inserts into the 60mm Mirror Block. The inserts need to be as straight as possible and to aid this I filed down one of the inserts to act as a guide (see photo below) Screw a 4-40 insert on to a 1 inch 4-40 bolt along with the guide before you install it into one of the holes.

Insert the 4-40 bolt with the guide and 4-40 heat insert into one of the holes in the 60mm Mirror Block:

Apply a hot soldering iron to the head of the 4-40 bolt until the heat insert slowly slides into the 60mm Mirror Block:

Repeat with the second 4-40 insert:

View of both 4-40 inserts installed where the top of the inserts are just below the surface of the block:

.Next we are going to glue the 60mm mirror into the 60mm mirror holder. Add a small blob of silicone into the bottom of the 60mm mirror holder:

Position the mirror on the silicone so that it is pushed against the end away from the adjustment screws holes, but do not press the mirror all the way down on to the silicone. The mirror should be slightly above the level of the holder at this point.

Carefully turn the mirror holder over and lay it flat on a protected surface and push down very gently so that the mirror surface will be at exactly the same level as the plastic holder. The hinge part must be off the side of the flat surface.

After waiting 24 hours turn the mirror holder over and check that the mirror top is level with the plastic and in the correct location against the end away from the adjustment screws.

Prepare the 4-40 threaded rods which will become the adjustment rods for the ABBs, Start with two 1.25 inch 4-40 bolts, four 4-40 nuts and two brass 4-40 thumb nuts, see photo below:

Cut the heads off the 4-40 bolts, preferably with a cut off wheel on a Dremel tool. Make sure the threads are clean and not damaged by running the thumb screws up and down the entire length of the threaded rods and check that there is no binding.

Next thread two 4-40 nuts into the middle of each threaded rod and lock them together tightly:

Install the threaded rods into the 60mm mirror holder as shown. Do not overtighten the brass thumb nuts. They should just snug up to the plastic. The threaded rod should still move around in the hole in the plastic.

Apply some devcon two part epoxy to the head of the brass thumb nuts and the 4-40 threaded rods which protrude from the top of the knurled thumb nut to glue the two parts together. After the glue sets up the thumb nuts should rotate easily but not jiggle up and down in the vertical direction

The 60mm Mirror Holder and the 60mm Mirror Block are now ready to be joined. You have to be careful here.

Use Plastic Bonder super glue for the following steps.

Screw the threaded rods loosely into the 4-40 inserts in the 60mm mirror block. The hinge part of the 60mm mirror holder should be visible and accessible to permit a line of super glue to be placed along the hinge.

Hold the hinge part away from the 60mm Mirror block so you can have access for gluing the hinge. Run a line of super glue on the hinge extension. Now tighten the thumb nuts until there is approximately a 1mm gap between the mirror holder and the mirror block.

Now push the hinge part on to the mirror block. Be careful that it is straight since once you apply some pressure it will glue immediately. There should now be approximately a 1 mm parallel gap between the mirror holder and the mirror block. By turning the thumb nuts the gap should be able to be closed to 0mm or opened to about 2mm at the thumb nut end. By applying different amounts of tightness to the thumb nuts you can create a very small amount of cross tilt. This will be discussed in more detail in the alignment section.

Next we are going to glue on the 2 inch focuser barrel. Apply some super glue to the 2 inch focuser barrel and carefully glue it to the hinge end of the 60mm Mirror Block away from the adjustment thumb nuts. Make sure you are gluing it to the correct end. If you make a mistake you will have to start over again with the whole assembly. Make sure the 2 inch focuser barrel is centered perfectly before apply pressure, A centering 0.5mm centering ring can be printed to help here if you want.

The 60mm Mirror Block is now complete

Building the 42mm Mirror Block with the IPD adjusment Helical for F6 or greater Objectives

Here are the parts you need to do this:

ABB Part#4 IPD Helical Adapter
ABB Part#5 42mm Mirror Block
ABB Part#6 42mm MIrror Holder
ABB Part#7 Left Eyepiece Holder or ABB Part#8 Right Eyepiece Holder
A 17mm ro 31mm helical IPD adjuster and a 42mm mirror

Place a small blob of silicone in the 42mm holder:

Push the 42mm mirror gently into the 42mm mirror holder. The reflective surface of mirror should be slightly proud of the holder. Now place the assembly on to the flat surface of the 42mm mirror block as shown below. If you are using eyepiece holders (F6 Objectives or greater) then the 42mm mirror block is symmetrical and it does not matter which way round the 42mm mirror holder is arrached to the 42mm mirror block. If you printed Part#5a because you will be gluing the 25mm PLossl eyepiece directly into the 42mm block you will need to glue in the eyepiece first and file down any part of the eyepiece thread that extends beyond the bottom flat surface of the 42mm mirror block. This will be explained later in the "Building of the 42mm Mirror Block for F5.5 Objectives".

Now attach the 42mm mirror holder to the 42mm mirror block. This can be done with black silicone or a 3D filament welder (3D Doodler).

To be continued.........let me know if you are building these ABBs.... with an e-mail to [email protected]