Synta/GSO Finder Bracket for Astro-Physics AP130GTX

If you've ever had a hankering to attach a cheap and cheerful Synta or GSO finder scope (or red dot finder) to your spendy Astro-Physics AP130GTX triplet refractor,  then this 3D printed design is for you.


I had forgotten (or did not want..) to buy the fancy Baader Vario finder and rings from Astro-Physics when I bought my AP130GTX. Since I had a 3D printer and some cheap no-name China red dot finders, I figured I'd design a finder bracket.


There's a bit of a complication because the AP refractor has its finder bracket screws coming out at a 20-degree angle, and the two screw holes are quite far apart. I also did not want to secure the finder bracket with a single screw. This bracket is appropriately curved to fit the AP refractor, and the screw holes are also tilted for proper alignment.





Right-Angle Finder Adapter for Takahashi Polar Scope

This is a Yashica/Contax right angle viewfinder, which can be obtained from ebay for under $20:




I decided to 3D-print an adapter allowing this finder to be attached to a Takahashi polar scope, so when using the polar scope an observer can avoid a stiff neck.  The adapter can be found here.

Here is the Contax right-angle viewfinder attached to the polar scope on a Takahashi Space Boy mount. The adapter has two holes that need to be tapped for M4 for the set screws. 3D printing technology isn't repeatable enough at a sub-0.5mm scale to allow a tight press-fit on both the Contax finder and the Takahashi polar scope, at least when using PLA (succeeding prints may be too loose or too tight, hence the need for the set screws).



Potentially if using ABS or HIPS it might be possible to exploit the material's flexibility for a press-fit on both the Contax finder and the polar scope eyepiece end.

Takahashi EM-1S Ersatz Polar Scope

I bought an old Takahashi EM-1S mount from Yahoo Japan, but it did not come with a polar scope.  Since this mount is 25+ years old, I was not even sure if a polar scope could be bought for it. Also, the Takahashi polar scope is expensive, and since I got the EM-1S fairly cheap (for a Takahashi..) I figured it would not be worth it to buy the current polar scope.


As luck would have it, I had a Celestron 6x30 "Long Eye Relief" finder scope, and I thought it might be possible to adapt this finder scope as a primitive polar scope for the EM-1S. The outer diameter of the eyepiece portion of this finder is about 24mm, and the barrel itself is 32mm in diameter. After three attempts, I came up with this design for an adapter, and 3D-printed it. The finder scope is a bit of a loose fit, so I added two masking tape shims:


There are three 3mm diameter holes in the circumference of the adapter, which must be tapped with an M4 tap and grub screws inserted to hold the finder scope in place.

Here is the ersatz polar scope in position. The adapter is a very tight fit in the Takahashi mount's RA bore. A strap wrench would be needed to remove the adapter. So it is important to place the finder scope into the adapter, and secure it with the grub screws, before inserting the adapter into the mount's RA bore. Some whacking was necessary to get the adapter to seat (although a previous version I made did not require whacking, so it's probably down to non-repeatability at sub-mm level in the 3D printer).


The polar scope manhole cover (cap) still threads on nicely: