The Borg 7004 set is an F4 focal reducer kit
for Borg Series 80 scopes (50, 76/77, and 100/101
achromat and ED objectives). Unlike many reducers on
the market, which typically degrade the objective's performance,
the ED F4 reducer is designed to optimize performance
at F4 for modern fine-pixel electronic sensors,
while simultaneously performing the focal length
reduction and field flattening functions.
The set includes
the 4-element (1 ED element) reducer optical
assembly, short tube with drawtube, and spacers
for optimized setups with different imagers.
The optical arrangement is shown above and
the system diagram is shown below.
For optimized imaging performance, the correct
spacer (provided in the 7004 set)
should be used
for the imager being utilized as detailed in
the configurations listed below:
- Borg 76/77 objective with digital SLRs:
- Borg 100/101 objective with digital SLRs:
- Borg 76/77 objective with ST7/8/10 & CFW8:
- Borg 100/101 objective with ST7/8/10 & CFW8:
- Borg 76/77 objective with larger than 28mm
diagonal sensor:
- 3.7mm spacer (parts configured depends on camera)
- Borg 100/101 objective with larger than 28mm
diagonal sensor:
- Spacer none. (parts configured depend on camera)
Note: the ideal reducer position should be such
that the distance of the surface of rear lens
to focal plane is:
- 76/77: 43mm, 100/101: 41mm for sensors
smaller than 28mm (diagonal distance).
- 76/77: 36.4mm, 100/101: 44.7mm for
sensors larger than 28mm.
Instructions for Use
Basic Installation
- Attach the objective assembly to the
129mm tube provided in the 7004 kit.
- Insert the 7004 kit drawtube into the
existing drawtube holder
[7749]
- Connect the drawtube holder to the main
tube (129mm tube).
- Attach the helical focuser
[7835
or
7837]
to the drawtube.
- Attach the rotater ring
[7351]
to the rear of the reducer optical
assembly, including a spacer ring as
required by the imager setup as detailed
above. The rotater ring provides the
correct thread interfaces as well as the
flexibility to rotate the imaging camera
for the desired image composition.
- Connect the reducer assembly from the
previous step to the rear of the focuser
to complete the assembly procedure.
Installing a Filter
The Borg ED F4 reducer supports using a 48mm
filter in the optical path. To install the
filter, unscrew the connection point of the
optical assembly at the point indicated in the
diagram at right. Next install the filter
using the threads indicated and reattach the
two sections of the optical assembly.
Adjusting Focus
To adjust focus, with the helical focuser at
its middle position, set the rough focus using
the drawtube. Once the drawtube is locked in
place, adjust the helical focuser for fine
focus.
Sample Photos
(taken with modified Canon Digital EOS astrocamera)
