Celestron 94175 User manual

Celestron International • 2835 Columbia Street • Torrance, CA 90503 USA • Phone: [phone] • Fax: [phone]
©2011 Celestron • All rights reserved. #94175-INST (0511)
The Celestron Reducer/Corrector Lens for SCT Telescopes
(#94175)
INTRODUCTION
Imagine having two telescopes in one — a long focal
length instrument for lunar and planetary work and a
short focal length scope for deep sky observing and
astrophotography. With the Celestron
Reducer/Corrector Lens that’s exactly what you get.
Designed specifically for Celestron Schmidt-
Cassegrains, this unique lens reduces the focal length
and f/ ratio of your telescope by 37 percent turning
your long focal length telescope into a fast, short focal
length instrument. An f/10 instrument now works at
f/6.3 while an f/11 instrument works at f/7. For visual
use this means you get lower power with the same
eyepiece and a wider field of view. Photographically
you also get a wider field and much shorter exposures.
The #94175 Reducer/Corrector Lens is not compatible
with Celestron EdgeHD optical systems.
In addition to reducing the focal length and f/ratio the
Celestron Reducer/Corrector Lens also reduces field
curvature significantly so you get a flatter, well
corrected field.
The advantages of the Reducer/Corrector Lens are not
limited to celestial photography alone. For terrestrial
photography you’ll find the faster f/ratio allows you
to use slower film or shoot in lower light level
situations and still properly expose your subject. And,
this fully multi-coated lens provides maximum light
transmission with near full-field illumination.
INSTALLATION
The Reducer/Corrector Lens is easy to install:
1. Remove all the accessories from the rear cell of your
SCT telescope. If you have a C11 or C14, remove all
the accessories, but leave the reducer plate attached to
the rear cell of the telescope.
2. Thread the Reducer/Corrector Lens onto the rear cell
of the telescope (or the reducer plate of the C11 and
C14) by rotating clockwise until tight.
3. Thread the desired accessory (i.e., T-Adapter, 1-1/4"
Visual Back, Star Diagonal, or Off-Axis Guider Body)
onto the Reducer/Corrector Lens.
The Reducer/Corrector Lens is now installed and
ready for use.
USING YOUR REDUCER/CORRECTOR LENS
There is no change in the basic operation of your
telescope with the Reducer/Corrector Lens installed.
However, because of the shorter focal length the
magnification and actual field are different for any
given eyepiece. Remember this when figuring
magnification and actual field.
Focus your telescope as usual (i.e., turning the focus
knob until the image is sharp). The sharpest possible
focus for a given eyepiece is about 3 to 4
counterclockwise turns of the focus knob from the best
focus point without the Reducer/Corrector lens
installed.
Although the Reducer/Corrector Lens diminishes the
small amount of field curvature common to all
Schmidt Cassegrain telescopes, it does not completely
eliminate it. For low power visual use, the sharpest
possible images across the majority of the field is
obtained by first focusing on the stars at the center of
the field. Make sure you come into sharp focus by
turning the focus knob counterclockwise. Once sharp,
turn the focus knob approximately 1/12th of a turn
counterclockwise.
For optimum photographic focus, obtain the sharpest
possible focus in the center of DSLR view finder. Make
sure you come into sharp focus by turning the focus
knob counterclockwise. Once the image at the center is
sharp, rotate the focus knob 1/24th of a turn
counterclockwise.
Because the field of view is very close to flat, you can
leave the Reducer/Corrector Lens in place at all times.
High power views will provide flatter fields all the
way to the edge, both visually and photographically. If
you plan on high power eyepiece projection
photography, you may consider removing the lens.
NOTE: Due to the short focal length of the telescope

Celestron International • 2835 Columbia Street • Torrance, CA 90503 USA • Phone: [phone] • Fax: [phone]
©2011 Celestron • All rights reserved. #94175-INST (0511)
with the Reducer/Corrector Lens attached, you
should NOT use an eyepiece longer than 35mm focal
length.
CARE AND MAINTENANCE
One added side feature of the Reducer/Corrector Lens
is that it acts as a dust seal for the telescope,
preventing various contaminates from entering the
optical system. If you leave the Reducer/Corrector
Lens on the telescope, be sure to replace the plastic
lens cover on the lens when not in use. This will
minimize dust build-up on the lens itself. If the lens is
removed from the telescope, both plastic covers
should be replaced.
When handling the Reducer/Corrector, be careful not
to touch the lens itself. Failure to do so may result in
smudging the lens.
Special care should be taken when cleaning any
optical instrument so as not to damage the optics. If,
over time, you do experience dust build-up, use a can
of pressurized air to remove it. This is done by
removing the caps from both sides of the diagonal and
spraying the stream of air for approximately 2 to 4
seconds on each side of the lens.
Further cleaning, if necessary, can be done with
cleaning solution and white tissue. You can use
commercially-made camera lens cleaner, or mix your
own. A good cleaning solution is isopropyl alcohol
mixed with distilled water. The solution should be
60% isopropyl alcohol and 40% distilled water.
Apply the cleaner to the tissue and apply to the lens.
Remove residue cleaning solution with a clean tissue.