Meade ACF 0.68x User manual

Introducon:
The Meade 0.68x focal reducer is designed for use with Me-
ade’s Advanced Coma-Free (ACF) telescopes, of any aperture,
using the 2”-24 (2” diameter, 24 threads per inch) rear cell
thread. This rear cell thread is standard on all Meade ACF tele-
scopes. The 0.68x focal reducer consists of 4 lenses in 2 groups
with all air-to-glass surfaces fully mul-coated with broadband
an-reecon (BBAR) coangs for maximum light transmis-
sion and image contrast. It provides good correcon across
a 28mm image circle making it ideal for APS-C sized sensors.
Meade’s ACF focal reducer reduces the eecve focal length
of the main telescopes opcal system by a factor of about
one third. When used with Meade’s f/10 ACF, the resulng
eecve f/rao becomes around f/6.8. When aached to
Meade’s f/8 ACF, the resulng eecve f/rao will be around
5.5, resulng in a substanally “faster” opcal system that
cuts exposure mes in half while increasing the eld of view.
The reducers opcal design provides full illuminaon of a 22mm
diagonal image sensor and nearly full illuminaon out to 28mm,
with just slight vigneng that is corrected with at eld calibra-
on. It boasts a generous 105mm of back-focus distance to the
image plane, measured from the reducer’s ange, or 100mm
on-axis from the last lens, allowing loads of space for imaging
train accessories such as a lter wheel and/or an o axis-guider.
Installaon:
To install the focal reducer onto your Meade ACF tele-
scope, rst remove the threaded protecve dust cap from
the reducer. Then thread the reducer directly onto the
back cell of the telescope using the 2”-24 TPI threads.
The included T-adapter, with a length of 50mm and an M42x0.75
thread, is well-suited for various applicaons to achieve the
nominal 105mm back focus required by the reducer. It’s suit-
able for use with DSLR cameras equipped with a t-ring, as
well as many cameras with a 55mm depth-to-sensor distance.
For dedicated astronomy cameras, addional adapters (us-
er-supplied) may be needed to reach the reducers nomi-
nal back focus distance. See Fig. 5. Various adapters of dif-
ferent length and aaching thread sizes are available from
third-party suppliers. These addional adapters typically con-
nect to the M42x0.75 t-thread connecon at the end of the
included T-adapter and then to your camera or lter wheel.
To determine the length of the addional adapter (if need-
ed), locate the depth-to-sensor distance for your camera.
This is oen called the camera backfocus. This is the dis-
tance from the cameras mounng point to the image sensor
and is usually found in the camera instrucons or webpage.
Next, measure the distance the other equipment in your
imaging train requires. This includes lter wheels, o-ax-
is guiders, electronic focusers, connecng adapters, and
anything else between the focal reducer and camera sen-
sor. Add up the camera’s backfocus distance and oth-
er image equipment distances. This is the total work-
ing distance (X) required by your imaging equipment.
Note: If using the Meade Zero-image Shi microfocuser, the
minimum needed backfocus for this device is 60mm with
the focuser draw tube fully retracted. When using this fo-
cuser, removal of the included 50mm T-adapter is necessary.
Since the focal reducers nominal back focus is 105mm when
measured from its mounng ange, subtract the distance in
mm your imaging equipment requires (X) from 105mm to
get the adapter length (Y) needed to reach nominal focus.
Meade ACF 0.68x Focal Reducer
with 50mm T-thread Adapter
Looking at or near the Sun will cause irreversible damage to your eye. Do not point this telescope at or near
the Sun without a proper solar filter attached.
Fig. 1: ACF 0.68x Focal Reducer Fig. 2: 50mm T-thread Adapter
Fig. 3: Focal Reducer Lens System
Fig. 4: Typical DSLR Conguration

If the calculated distance (Y) is 50mm, only the includ-
ed 50mm T-adapter is needed to reach nominal focus.
If the calculated distance (Y) is less than 50mm, you need
to remove the included 50mm T-adapter and replace
it with a shorter adapter with the length you calculat-
ed to reach the 105mm back focus distance. This short-
er adapter will need to have the 2”-24 female thread on
one side to aach to the focal reducer. The other side of
this adapter will thread onto your imaging equipment.
If the calculated distance (Y) is more than 50mm, addional
T-adapters will be needed to reach the nominal 105mm back
focus distance. To determine the adapter length needed, sub-
tract the calculated distance (Y) from 50mm (since the included
T-adapter is 50mm) to determine the needed adapter length.
Proper Care and Maintenance:
Avoid cleaning the focal reducer opcs as a lile dust on the
surface causes virtually no degradaon of image quality and
should not be considered reason to clean the lens. DO NOT
disassemble the focal reducer to clean the interior lens sur-
faces. When absolutely necessary, dust should be removed
with gentle strokes of a camel hair brush or blown o with an
ear syringe (available from telescope shops or the local phar-
macy). DO NOT use a commercial photographic lens cleaner.
Organic materials (e.g., ngerprints) on the opcs may be
removed with a soluon of 3 parts dislled water to 1-part
isopropyl alcohol. One drop of biodegradable dishwashing
soap per pint of soluon may also be added. Use so, white
facial ssues and make short, gentle strokes. Change ssues
oen. Store the focal reducer in a dry, dust-free environment.
Looking at or near the Sun will cause irreversible damage to your eye. Do not point this telescope at or near
the Sun without a proper solar filter attached.
89 Hangar Way, Watsonville, CA. 9507689 Hangar Way, Watsonville, CA. 95076
[phone] www.meade.com(800) 626-3233 www.meade.com
REV 01 12/23
Specicaons:
Focal Reducon:.........................................................~ 0.68x
Unvigneed Field of View:..........................................22mm
Corrected Field of View:..............................................28mm
Opcal Coangs:........................................fully mul-coated
Back Focus Distance:
Flange Distance:............................................ 105mm
On-axis Distance:..........................................100mm
Reducer Threads:
Telescope Side:..................................2”-24 (female)
Camera Side:.........................................2”-24 (male)
50mm Adapter Threads:
Telescope Side:..................................2”-24 (female)
Camera Side:..................................M42x0.75 (male)
Dimensions(Reducer + Adapter):......2.3” diameter x 2.95” L
Weight(Reducer + Adapter):.........................................8.5 oz
Meade Instruments Warranty:
The Meade Instruments Statement of Limited Warranty is
published at: www.meade.com/supports/warranty/
A printed copy of the Meade Statement of Limited Warranty will
be made available by Meade upon written request. See below
for Meade contact information.
Warranty Claim
Meade Instruments
89 Hangar Way
Watsonville, CA 95076 U.S.A • [phone]
[email protected] • SUBJECT: Warranty Claim
(Y) (X)
Fig. 5: Back Focus Distance to Camera