IMPORTANT
: It is essential that these corrector optics (field flattener or reducer/flat-
tener) 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 dis-
tance from the flattener, the stars around the edge of the field will be distorted. So the
first thing you need to know is the “backfocus” of the camera you will be using. The back-
focus 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. It’s 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 backfocus 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. It may be necessary to adjust the
spacing by no more than half a millimeter to obtain optimal results.
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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 or reducer/flattener. The backfocus must include 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 dis-
tance 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 using the SFF3 is
easy.
SFF3 Flattener T-ring
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/
Sff3 Flattener Extensions CCD Camera
STEP 3: Unthread the 1 1/4” and
2” adapters from the focuser but
leave the rotator in place.
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
