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In order to get the premium results the field flattener for
ESPRIT 80 can deliver the distance between the last
lenses to the sensor should be exactly 61mm. This
distance is called the field flattener "back focus".
The rings are designed to provide 61mm of back focus
with any DSLR camera. Modifications to this layout, i.e.
by adding a radial guider, will lead to blurry stars images
in the field edges.
Installing the field flattener and a CCD (Charge-Coupled Device) camera
Installing an astronomical CCD camera and its accessories (filter wheel, radial guider…) behind the
field flattener is not as straightforward as installing a DSLR camera. All DSLR cameras have the exact
same distance from the front side of the T-Ring adapter to the sensor, thus share the same extension
rings to ensure the 61mm back focus distance.
CCD cameras differ from one model to another, even in the same brand name, by the threads used and
the body-to-sensor distance. Accessories also have different possible threads and depths, thus the
combination of a CCD camera and its accessories can have any total length and any coupling thread.
A custom coupling ring is needed in order to assemble the CCD camera and its accessories (called the
"optical train") to the telescope's field flattener. The custom ring should be machined
*
to have:
1)
A female M62x1 thread, to screw and secure the ring to the field flattener exit.
2)
A thread compatible with the first component of the optical train.
3)
A length to ensure that the distance from the back of the field flattener to the CCD sensor is
exactly 61mm.
Note
: Inside the box the 6mm ring spacer is
assembled with the field flattener body. When
assembled, the two parts may look as if there were
only one piece. When taking pictures with a CCD
camera it can be useful to remove the 6mm spacer
ring to gain 6mm additional back focus distance
The 61mm distance is measured from the edge
marking the start of the male thread on the field
flattener, to the CCD sensor (See picture on the
left).
Most CCD cameras have also the distance from
their body thread to CCD sensor noted in the
manual, thus evaluating the length of the custom
ring you need can be precisely evaluated.
*
Refer to your local dealer about custom ring supply.
