This article summarizes back focal distances of various variants of
Gx Mark II cameras. Back focal distances stated here are so-called
optical, not mechanical dimensions. This means the distance includes
prolonging of the back focal distance by plan-parallel glass in the
optical path. However, the thickness of used filters is not included,
because various filter providers use different thickness and cameras
can be used without filters at all.
Design of adjustable adapters
Adjustable telescope/lens adapters are attached
slightly differently depending if the adapter is attached
directly to the camera head (e.g. when camera is equipped with
internal filter wheel) or to the External filter wheel
case.
Mark II adapters are not mounted directly on the camera
head. Instead a tilting adapter base, holding the circular
spring, is always used.
If the External filter wheel is used, the adapted base is
not necessary, as the Mark II External filter wheel front plate
is already designed to hold the spring and it also contains
threads to fix respective adapters.
Adjustable adapters are mounted either on adapter base,
attached to camera head, (left) or directly to External filter
wheel adapter interface (right)
The necessity to use the adapter base on the camera
head eliminates the need of inserting of spacers between camera
head and adapter itself if the particular BFD has to be
maintained. Adapter bases are manufactured in two variants,
differing in thickness, to compensate BFD among camera with
external filter wheel, internal filter wheel and camera without
filter wheel at all.
Thin adapter base is
4.5 mm thick. It
compensates the difference in BFD between camera with External
filter (33.5 mm)
and camera with Internal filter wheel (29 mm).
Thick adapter base measures 17 mm, which is the thickness of External filter
wheel housing. If the thick adapter base is attached to camera
without filter wheel (with 16.5 mm BFD), it provides mounting interface for
adjustable adapters in the same 33.5 mm BFD like camera with External filter
wheel.
Hint: All documentation state Gx Mark II camera BFD
33.5 mm, measured to
adjustable adapter mounting interface. This dimension can be
achieved regardless if internal or external filter wheel or no
filter wheel is used. However, if the camera without filter wheel
is combined with the thin adapter base, resulting BFD is only
21 mm. This combination cannot
be used if particular adapter requires some back focal distance
(for instance OAG or Canon EOS and Nikon bayonets
etc.).
G2 Mark II cameras
G2 cameras use only S (small) adjustable adapters.
Back Focus Distance between sensor and adjustable adapter
mounting interface:
Back Focus Distance between sensor and thin adjustable adapter
mounting interface on the camera without filter wheel:
G2 camera without filter wheel |
|
Camera with M42 × 0.75 (T-thread) or
M48 × 0.75 threaded adapters
with 55 mm BFDBFD
Camera with M42 × 0.75 or
M48 × 0.75 threaded
short adapters
Camera with Canon EOS bayonet adapter (EOS adapter is
available in both S and L adapter sizes, EOS adapter is available
in both S and L adapter sizes, S size
adapter is required for G2)
Camera with Nikon bayonet adapter
Camera with Off-Axis Guider Adapter with M42 × 0.75 (T-thread) or
M48 × 0.75 thread
G3 Mark II cameras
G3 cameras can use both S (small) and L
(large) adjustable adapters. The size (diameter) of the adjustable
adapter interface depends on the adapter used. For instance Nikon
bayonet, M42 × 0.75
(T-thread) or M48 × 0.75 threaded
adapters are available in S variant only, G3-OAG or
M68 × 1 threaded adapter require
L variant of adapter base.
Adjustable adapters are mounted on adapter base when
camera with internal filter wheel or camera without any filter
wheel is used or directly on the external filter wheel front
surface. This means both S and L adapter bases
can be mounted on any G3 camera, but external filter wheels are
made for one particular adapter size only:
Back Focus Distance between sensor and adjustable adapter
mounting interface:
Back Focus Distance between sensor and thin adjustable adapter
mounting interface on the camera without filter wheel:
G3 camera without filter wheel |
|
Camera with M42 × 0.75 (T-thread) or
M48 × 0.75 threaded adapters
with 55 mm BFD (requires
S adapter base or S External filter wheel)
Camera with M42 × 0.75 or
M48 × 0.75 threaded
short adapters (requires S adapter base or
S External filter wheel)
Camera with M68 × 1 threaded adapters
(requires L adapter base or M or L
External filter wheel)
Camera with Canon EOS bayonet adapter (EOS adapter is
available in both S and L adapter sizes,
S External filter wheel needs S variant,
M and L External filter wheels need L
variant)
Camera with Nikon bayonet adapter (requires S
adapter base or S External filter wheel)
Camera with Off-Axis Guider Adapter with M68 × 1 thread (requires
L adapter base or M or L External
filter wheel)
G4 Mark II cameras
G4 cameras use only L (large) adjustable adapters.
Back Focus Distance between sensor and adjustable adapter
mounting interface:
G4 camera with External filter wheel |
G4 camera without filter wheel |
|
|
Back Focus Distance between sensor and thin adjustable adapter
mounting interface on the camera without filter wheel:
G4 camera without filter wheel |
|
Camera with M68 × 1 threaded adapters
G4 camera with External filter wheel |
G4 camera without filter wheel |
|
|
Camera with Canon EOS bayonet adapter (EOS adapter is
available in both S and L adapter sizes,
L size EOS adapter is required for G4)
G4 camera with External filter wheel |
G4 camera without filter wheel |
|
|
Camera with Off-Axis Guider Adapter with M68 × 1 thread (requires
L adapter base or M or L External
filter wheel)
G4 camera with External filter wheel |
G4 camera without filter wheel |
|
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