Here is a very versatile adapter from Blue Fireball that can be used for prime focus and fixed or variable eyepiece projection photography with your telescope.
Separate the two parts and the smaller lower barrel by itself is a standard 1.25" Prime Focus T-adapter. Insert the 1.25" barrel into your diagonal or telescope, attach your D/SLR camera to the male T-thread (via a T-ring that is specific to your camera; not included), and you are ready to take photos as prime focus with your telescope or spotting scope. In this set-up, the optical chain will be:
Telescope/Diagonal > Prime Focus T-adapter> T-ring > D/SLR camera
But that is not all. The magnification in the image you shoot depends on the distance between the top of the inserted eyepiece and the camera. This combination eyepiece camera adapter has a sliding barrel design that allows variable projection distances for eyepiece projection photography. This eliminates the need to change eyepieces when different magnification or additional projection enlargement is desired. All you need to do is to slide the outermost barrel away from or towards the telescope and the projection magnification increases or decreases. This additional projection range is particularly useful in high-resolution Lunar / Planetary photography. Of course, you can still change your 1.25" eyepieces to gain an even larger range of magnifications.
You will be able to use many, but not all, 1.25" eyepieces with this adapter. The adapter barrel can accept 1.25" eyepieces up to 38.5mm (1.52") in maximum outside diameter. The length of the upper barrel of the eyepiece (above the eyepiece shoulder, excluding the lower 1.25" barrel) cannot exceed 72mm (2.83") in the shortest setting position of the adapter or 106mm (4.18") in the longest setting position of the adapter. Please check your eyepiece dimensions before ordering to ensure that it will fit inside the adapter.
The prime focus adapter end is threaded to accept standard 1.25" filters so you can use your favorite photography filters as well. The adapter is precision machined from aluminum and black anodized, and weighs 7.1oz. The total length of the adapter can vary between 118.6mm (4.67") and 152mm (6") depending on the eyepiece used and the projection desired.
The lowermost single silver screw visible in the photos is used to secure the 1.25" eyepiece inserted into the adapter. The two other silver screws are used to lock the sliding barrel in place over the inner barrel.