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In order to get the premium results the field flattener for
ESPRIT 150 can deliver the distance between the last
lenses to the sensor should be exactly 100mm. This
distance is called the field flattener "back focus".
The rings are designed to provide 100mm 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 a 48mm filter inside the focal extender
A 48mm (2") filter can be mounted inside the DSLR extender tube if
needed. By example using a light pollution reducer filter may allow pictures
of the night sky even in suburban areas.
1.
Inside the focal extender a 48x0.75 mm thread can receive any
48mm (2") filter.
2.
Insert the filter and screw it on the thread. Do not over tight the
filter.
Use a tissue when screwing the filter to avoid fingerprints.
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 border of the T-Ring adapter to the sensor, thus share the same extension rings
to ensure the 100mm 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 last lenses
of the field flattener
to the CCD
sensor
is exactly 100mm.
As it can be difficult to evaluate the position
of the field flattener lenses inside the frame,
the distance can be more conveniently
measured from the lenses mount edge, as
shown in the picture on the left.
From there to the sensor, the correct distance
should be exactly 96mm.
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.
