Prime Focus - What's That All About? Making the Adapters.

Prime Focus - This is the next thing on my list of things to try,

In layman's terms, this is attaching the camera directly to the telescope, with no lenses on the camera or eyepiece on the telescope. You rely on the bare camera sensor being placed directly onto the prime focal plane of the telescope for its bare configuration and mirror design.

You can read more about the focal planes on this page:

Ok, so how am I going to connect the camera to the telescope as I don't have any suitable adapters?

Well, that's where the beauty of the 3D printer comes in again!

Here are the range of adapters I printed for the task;

Using the models from the earlier FTZ Adapter ( I had made, I was only interested in the Z-Mount flange.

Connecting to the telescope was either via the 2" or 1.25" However, I didn't know where the focal plane of the telescope was and after much searching I found that the camera sensor is 16mm behind the lens flange face.

Here is the bare camera, you can see the exposed sensor shining red. Unlike a traditional DSLR, the Z Series are mirrorless with no other mechanics.

The 2" adapter attached to the camera;

Below, is the 2" adapter connected to the camera and fully inserted to the scopes 2" mount on the focus adjuster;

2" Adapter

The 2" mount on the telescope was pretty un-restricted in depth (other than eventually hitting the secondary mirror assembly, so I made an adapter with a 75mm nose, that would give me an adjustment range of around 100-150mm (allowing for the focus head extension to be taken on and off as well as the movement of the focus head). The adapter had a distance of 20mm from the flange face to the start of the nose, but could have made that smaller if I found I could achieve focus. I did this to provide a more appealing/stronger profile to the piece.

Here is the Tinkercad model for the 2";

1.5" Adapters

I made 3 different 1.5" adapters. The reason I did this was I also had 3 Barlow Lenses. These lenses had 2x, 3x and 5x magnification. You can read more about Barlow Lenses at

The recess on each of the lenses was also slightly different, so wanted to be able to fully insert the adapters into the Barlows, to allow more flexibility with focal length adjustment, so I made them with the respective nose lengths of 30mm (2x), 40mm (3x) and 50mm (5x).

30mm Nose

40mm Nose

50mm Nose

In the next post we will take a look at what output was achieved using prime focus.

Please subscribe to my YouTube Channel - Dave's Astrophotography. And please leave comments, suggestions and questions on the video comments.

I also have a Facebook page 'Dave's Astrophotography', so you can visit and follow at:

Clear Skies!