IMPORTANT
: It is essential that corrector optics (field flattener or reducer/flattener) be
placed at a precise distance from the ccd sensor in your camera. The CCD sensor in
your camera is where the image is made. If the sensor is not the correct distance from
the flattener, the stars around the edge of the field will be distorted. The first thing you
need to know is the “backfocus” of the camera you will be using. The backfocus of the
camera is the distance from the attachment thread on the camera to its ccd chip. In most
DSLR cameras with the necessary t-ring added, this distance is 55mm.
Your field flattener or reducer/flattener also has a
backfocus specification. Its backfocus is the dis-
tance from its rear of the flattener or reducer/flat-
tener to where the field is precisely flat. It is
important that the backfocus of your camera matches the backfocuser of
the flattener or reducer/flattener.
On ccd cameras this distance varies widely so you may need to add
spacer rings and/or extension tubes. Also, it may be necessary to adjust-
pacing by a millimeter or two to obtain optimal results.
15
With Single Lens Reflex Cameras (DSLR’s) remove the
lens and replace it with a t-ring that has the same size
thread as the flattener. The backfocus must include the
thickness of the t-ring that is attached to the camera in
place of the camera’s lens. When you add a t-ring to your
Canon or Nikon DSLR, this distance from the thread on
the t-ring to the ccd chip in the camera is about 55mm.
Our flatteners may be ordered with a “55 mm backfocus.”
Use one of these if you are shooting with a DSLR.
Attaching your DSLR camera to the telescope is easy.
Focuser Flattener or T-ring
Reducer/Flattener DSLR
With other ccd cameras, the backfocus distances vary.
Check with the maker of the camera to determine the
backfocus of your camera. If the distance is less than
55 mm you will need to add extension tubes and/or
spacer rings to make up the difference. For example, if
your camera has a 35 mm backfocus you will need 20
mm of extension tubes to get the flattener 55 mm from
the ccd chip in the camera.
Stellarvue produces a variety of spacer rings and
extension tubes. Visit our astro-photography accessory
page on the web at:
http://www.stellarvue.com/astro-photography/
Focuser Flattener or Extensions
Reducer/Flattener CCD Camera
STEP 3: Unthread the
2” adapter from the
focuser drawtube
STEP 4: Thread the
flattener to the drawtube &
camera to flattener.
STEP 1: Remove the
camera lens
STEP 2: Install an
oversized (48 mm) t-ring
