Recognizing that no single optical design is best for all applications, OGS can supply
Newtonian, Classical Cassegrain, Wright-Schmidt, Maksutov or Ritchey-Chretien systems
configured to specifically meet your needs. Each instrument type has its own particular
advantages and shortcomings. For lunar and planetary work, the large image scale produced
by long focal length (f/10 and greater) Cassegrain telescopes is ideal; however, their
restricted field of view limits their usefulness for observing extended deep-sky objects.
Shorter focal length f/5 Newtonians and f/6.3 Schmidt-Cassegrains, with their wider
fields, are more suitable for this class of object, but will suffer from inferior off-axis
image quality, spherical aberration, and coma.
Where versatility is the key, OGS recommends the Ritchey-Chretien as it combines compact
size, light weight and excellent on-and off-axis image quality in one design. It is the
optical design chosen for nearly all of the new, state-of-the-art observatory telescopes,
and is the same optical system as that used in the Hubble Space Telescope.
The following graphic shows spot diagrams of 1/2 degree off-axis star images produced by
a 10" f/8.5 Ritchey-Chretien, a 10" f/10 Schmidt-Cassegrain, an f/5 Newtonian
and an f/8 Classical Cassegrain. The superior image quality of the Ritchey-Chretien design
is apparent.
f/8.5 Ritchey-Chretien
f/10 Schmidt-Cassegrain
f/8 Classical Cassegrain
f/5 Newtonian
The Ritchey-Chretien is coma-free, whereas the Schmidt-Cassegrain, Newtonian and
Classical Cassegrain are not. The RC design utilizes hyperbolic primary and secondary
mirrors which correct coma. The OGS Ritchey-Chretien system has a flatter field than
production SC systems because of its lower secondary amplification factor, 2.9x versus 5x.
The resultant lower f-number also provides the RC with a wider field and faster
photographic speed.
Because the Ritchey-Chretien design has only two air-to-glass surfaces (compared to 4
for the SC) and no refracting elements, it has less light loss and a greater spectral
range than the Schmidt-Cassegrain making the RC ideal for use with CCD cameras.
OGS TELESCOPE SPECIFICATIONS
Ritchey-Chretien
| Model |
RC-10 |
RC-12.5 |
RC-14.5 |
RC-16 |
RC-20 |
RC-24 |
RC-32 |
| Clear Aperture |
10.0" |
12.5" |
14.5" |
16.0" |
20.0" |
24.0" |
32.0" |
| f-No. |
f/9 |
f/9 |
f/7.9 |
f/8.4 |
f/8.1 |
f/8 |
f/7.6 |
| Secondary Dia. |
4.00" |
4.50" |
5.50" |
6.00" |
7.25" |
8.50" |
12.25" |
| Back Focus * |
9.75" |
9.25" |
9.00" |
10.00" |
10.5" |
11.5" |
12.5" |
| Tube Dia. |
12" |
15.5" |
18" |
19.5" |
24.5" |
29" |
39" |
| Tube Length |
31 |
40 |
40" |
48" |
54" |
66" |
78" |
| Mat'l ** |
Mg/AL |
Mg |
AL |
AL |
AL |
AL |
AL |
| Weight |
30 lbs. |
40 lbs. |
70 lbs. |
85 lbs. |
150 lbs. |
210 lbs. |
340 lbs. |
| Focuser Tube I.D. |
2.5" |
2.5" |
2.5" |
2.5" |
4.2" |
4.2" |
4.2" |
| Delivery |
Pls.
Inquire |
Pls.
Inquire |
Pls.
Inquire |
Pls.
Inquire |
Pls.
Inquire |
Pls.
Inquire |
Pls.
Inquire |
| OGS*** Mounting |
HP-75 |
OGS-75 |
OGS-75 |
OGS-100 |
OGS-100 |
OGS-140 |
OGS-190 |
Classical-Cassegrain
| Model |
CC-10 |
CC-12.5 |
CC-14.5 |
CC-16 |
CC-20 |
CC-24 |
CC-32 |
| Clear Aperture |
10.0" |
12.5" |
14.5" |
16.0" |
20.0" |
24.0" |
32.0" |
| f-No. |
f/15 |
f/16 |
f/16 |
f/14.25 |
f/16 |
f/16 |
f/10 |
| Secondary Dia. |
3.00" |
3.50" |
4.00" |
4.25" |
5.00" |
6.00" |
8.50" |
| Back Focus * |
9.75" |
9.25" |
9.00" |
10.00" |
10.5" |
11.5" |
12.5" |
| Tube Dia. |
12" |
15.5" |
18" |
19.5" |
24.5" |
29" |
39" |
| Tube Length |
40" |
45" |
54" |
54" |
72" |
84" |
82" |
| Mat'l ** |
Mg/Al |
Mg |
AL |
AL |
AL |
AL |
AL |
| Weight |
34 lbs. |
46 lbs. |
85 lbs. |
95 lbs. |
160 lbs. |
230 lbs. |
350 lbs. |
| Focuser Tube I.D. |
2.5" |
2.5" |
2.5" |
2.5" |
4.2" |
4.2" |
4.2" |
| Delivery |
Pls.
Inquire |
Pls.
Inquire |
Pls.
Inquire |
Pls.
Inquire |
Pls.
Inquire |
Pls.
Inquire |
Pls.
Inquire |
| OGS*** Mounting |
HP-75 |
OGS-75 |
OGS-75 |
OGS-100 |
OGS-100 |
OGS-140 |
OGS-190 |
Electronic secondary focuser is included on all models
* Back Focus as measured from the rear mounting plate of telescope.
** OTAs available as open truss or closed, in Al, Mg, or carbon fiber
*** Minimum suggested mounting requirement.
(All specifications are nominal measurements and subject to change without notice.)
