My astronomy project:
TS130 refractor to Nikon D800 adapter

Content:

1. TS130 to Nikon adapter
2. Adapter prototype
3. Implement of a duo narrow filter
4. Preparing for first light
5. Aberration analyze
6. Shorten the adapter length
7. Adjust tilt and back focus
8. To be continued

Note:
I take no responsibility or liability for what are written here, you use the information on your own risk!

1: TS130 to Nikon adapter

A year ago I replaced my Canon 6D DSLR camera with a Nikon D800 DSLR, both of them are full frame. I get much better image data with the Nikon and now I want to adapt the Nikon camera to my TS130 APO refractor. At the same time I prepare the adapter between the telescope and camera to hold a 2" filter. I have ordered a duo 7nm narrow band filter, the wave lengths it pass through are H-Alpha and OIII. The OIII line is weaker and it is between the green and blue wave length. My refractor is a f/7 and my 300mm Pentax 645 lens is a f/4 and should handle it with ease. They don't recommend to use this filter on faster telescopes than f/3.5. A friend to me use a similar filter on his f/6.3 refractor with good results. It's partly the same adapters that I use as before for both the lens and the telescope.

The old field flattener adapter:

To my refractor telescope I have a 3" field flattener from Altair Astro. The design is old, I think it was made for the old Meade 7" APO refractors and the Pentax 67 camera system, wide field and lot of back focus, 116 mm. I ordered that field flattener together with an adapter (above), from M80x1 to T48 threads and on top of that a thin Canon adapter. To the telescope it connect with a M92x1 thread. Now I have to design something similar to my new needs. I design it in 3D CAD and then 3D-print it.

It's not only an adapter between the camera and telescope. I have implemented an Off-Axis adapter, 2" filter holder and a tilt adjustment.

It will look something like this when finished.

CAD design:

This is the part that connect to the telescope's field flattener, M80x1mm. The three screw holes at right are for the tilt adjustment of the optical system.

My earlier adapter between the Pentax 645 lens and Nikon camera had some light leakage. Now I design the joint between the two parts as a slit where the collar is extended to prevent this light leakage. The field flattener has a back focus of 116 mm, that's why the adapter is so long. I designed it to be 1.4 mm shorter to have some margin when adjusting the tilt and back focus.

It's a corresponding slit on the Off-Axis adapter. I have also changed the bracket for a new compact (10x10x10 mm) prism that I recently have bought. I have not received the duo filter I ordered yet and have to wait until I get it to finish the design. This earlier design can only take an unmounted filter. The built length is calculated to 24.37 mm to fit the Pentax 645 system which has a back focus of 70.87 mm. The Nikon DSLR back focus is 46.5 mm. I reuse this design but add a new extension that fit the telescope's M80x1 mm thread.

It's a bit confusing about the field flattener's back focus. Sometimes it says to be 116 mm and sometimes 106 mm both with telescope at focal length of 900 mm. I think the difference is because in the 106 mm case they measure from the top of threads of the field flattener, and for 116 mm they measure from the base of the threads. But the height of the threads are not 10 mm, it's 8 mm. To my earlier Canon 6D camera which has 44 mm back focus and the original adapter length is 61.3 mm. First I used a 11 mm adapter to the Canon camera, 61.3+11+44 = 116.3 mm. Then I noticed that another place say that the back focus is 106 mm and I changed to a 1.5 mm thin camera adapter. Optical train, 61.3+1.5+44 = 106.8 mm which match the 106 mm better, I think that was a mistake. Anyway it isn't so sensitive with a 1x field flattener with this long back focus. The focal length of my TS130 refractor is 910 mm.

In the case of the Nikon I have 69.5 mm (my own 3D printed adapter) + 46.5 = 116 mm. My adapter can be fine adjusted in length by a couple of mm (69.5 -0.7 to +2.5 mm).

This is the side that connect to the Nikon camera, it will seal against the camera body with a 63x2 mm O-ring between. I have removed the bayonet from the camera to save some space, 2.2 mm. When taking it apart for cleaning of the sensor I have to open it with the three tilt screws or the M80x1 thread, not perfect but make the construction more stable.

Many hours later, on the left one I have added a slit that goes into the middle one to solve the problem with light leakage. Middle is the tilt adjuster which now have the corresponding slit. Right, the adapter to the TS130 telescope with field flattener, M80x1 mm. The middle and right part will be fused together when they are 3D-printed.

I have bought a new PLA filament in matte black, maybe it reduce the reflections a bit. The four small holes to the right are for the lock screws because I haven't solved how to 3D print a M80x1 mm thread yet.

Prism bracket:

The last detail, a bracket to hold the prism in place. I changed the design to use a prism instead of the earlier first surface mirror. I can make the design more compact with that. In my first design with a mirror the lens's bayonet almost collide with the mirror bracket.

Here is the prism bracket in its place, at the rectangular tube is where the light ray travel up to the guide camera. It can be adjusted a couple of mm in and out. The edge of the prism must at least be 13 mm from the optical axis when having a full frame sensor (36x24 mm).