Celestron 91073 Instruction Manual

Specifications

Optical Design Rowe-Ackermann Schmidt Tube Dimensions 24.7” length, 9.3” diameter

Aperture 203 mm Tube Weight 17 lbs

Focal Length 400 mm

Back focus
(from top of lens group housing)

29 mm

Focal Ratio f/2.0

Back focus
(with M42 camera adapter)

25 mm

Central Obstruction 93 mm (46% of aperture diameter) Spot size < 4.6 μm RMS across FOV

Optical Coatings

Enhanced aluminum,
Starbright XLT multi-coatings

Wavelength Range 400 – 800 nm

Optical Window 46 mm Ø, removeable Off-axis Illumination 93% at 11 mm off-axis
Focuser Ultra-Stable Focus System Image Circle 22.0 mm Ø , 3.15°

Cooling Fan 12V DC, MagLev Usable Field

32.0 mm Ø, 4.6°, only minimal performance loss
at edge of FOV

Telescope Instruction Manual

Model: 91073

CELESTRON TWO YEAR LIMITED WARR ANTY

A. Celestron warrants this product to be free from defects in materials and workmanship for two years. Celestron

will repair or replace such product or part thereof which, upon inspection by Celestron, is found to be defective in
materials or workmanship. As a condition to the obligation of Celestron to repair or replace such product, the product
must be returned to Celestron together with proof-of-purchase satisfactory to Celestron.

B. The Proper Return Authorization Number must be obtained from Celestron in advance of return. Call Celestron at

[phone] to receive the number to be displayed on the outside of your shipping container.

All returns must be accompanied by a written statement setting forth the name, address, and daytime telephone
number of the owner, together with a brief description of any claimed defects. Parts or product for which replacement
is made shall become the property of Celestron.

The customer shall be responsible for all costs of transportation and insurance, both to and from the factory of
Celestron, and shall be required to prepay such costs.

Celestron shall use reasonable efforts to repair or replace any product covered by this warranty within thirty
days of receipt. In the event repair or replacement shall require more than thirty days, Celestron shall notify the
customer accordingly. Celestron reserves the right to replace any product which has been discontinued from its
product line with a new product of comparable value and function.

This warranty shall be void and of no force of effect in the event a covered product has been modified in design
or function, or subjected to abuse, misuse, mishandling or unauthorized repair. Further, product malfunction or
deterioration due to normal wear is not covered by this warranty.

CELESTRON DISCLAIMS ANY WARRANTIES, EXPRESS OR IMPLIED, WHETHER OF MERCHANTABILITY OF
FITNESS FOR A PARTICULAR USE, EXCEPT AS EXPRESSLY SET FORTH HEREIN. THE SOLE OBLIGATION OF
CELESTRON UNDER THIS LIMITED WARRANTY SHALL BE TO REPAIR OR REPLACE THE COVERED PRODUCT, IN
ACCORDANCE WITH THE TERMS SET FORTH HEREIN. CELESTRON EXPRESSLY DISCLAIMS ANY LOST PROFITS,
GENERAL, SPECIAL, INDIRECT OR CONSEQUENTIAL DAMAGES WHICH MAY RESULT FROM BREACH OF ANY
WARRANTY, OR ARISING OUT OF THE USE OR INABILITY TO USE ANY CELESTRON PRODUCT. ANY WARRANTIES
WHICH ARE IMPLIED AND WHICH CANNOT BE DISCLAIMED SHALL BE LIMITED IN DURATION TO A TERM OF TWO
YEARS FROM THE DATE OF ORIGINAL RETAIL PURCHASE.

Some states do not allow the exclusion or limitation of incidental or consequential damages or limitation on how long
an implied warranty lasts, so the above limitations and exclusions may not apply to you.

This warranty gives you specific legal rights, and you may also have other rights which vary from state to state.
Celestron reserves the right to modify or discontinue, without prior notice to you, any model or style product.
If warranty problems arise, or if you need assistance in using your product contact:

CELESTRO N, LLC. Customer Service Department
2835 Columbia Street • Torrance, CA 90503 • Tel. [phone]
Monday-Friday 8AM-4PM PST • ©2018 Celestron • All rights reserved • 10-18

NOTE: This warranty is valid to U.S.A. and Canadian customers who have purchased this product from an authorized
Celestron dealer in the U.S.A. or Canada. Warranty outside the U.S.A. and Canada is valid only to customers who
purchased from a Celestron’s International Distributor or Authorized Celestron Dealer in the specific country. Please
contact them for any warranty service.

FCC NOTE: This equipment has been tested and found

to comply with the limits for a Class B digital device, pursuant
to part 15 of the FCC Rules. These limits are designed to
provide reasonable protection against harmful interference in

a residential installation. This equipment generates, uses, and
can radiate radio frequency energy and, if not installed and used in accordance with the instructions,
may cause harmful interference to radio communications. However, there is no guarantee that
interference will not occur in a particular ninstallation. If this equipment does cause harmful interference
to radio or television reception, which can be determined by turning the equipment off and on,
the user is encouraged to try to correct the interference by one or more of the following measures:

• Reorient or relocate the receiving antenna.

• Increase the separation between the equipment and receiver.

• Connect the equipment into an outlet on a circuit different from that to which the receiver is connected.

• Consult the dealer or an experienced radio/TV technician for help.

This product is designed and intended for use by those 14 years of age and older.

3. Point the astrograph at a bright star and focus the camera. Center the star in the camera’s

field of view.

4. Defocus the star by about one turn of the focus knob.

5. Inspect the defocused star diffraction pattern. When collimated, the pattern should look like a

concentric donut. If the pattern is concentric, no adjustment is necessary. If the “donut hole” is
not centered within the pattern, then some adjustment is needed.

OUT-OF-FOCUS STAR I MAGE FOR COLL IMATED TELESC OPE

6. There are three pairs of collimation screws. Each pair works together as a push-pull tilt adjustment.

Using the hex keys, adjust the collimation by loosening and tightening one of the pairs of collimation
screws. Always loosen one of the screws first, then tighten the other one. Adjust one pair of
screws at a time.

7. If the defocused star pattern is thin on one side, adjust the collimation screws so the st ar moves

towards the thin side, then adjust the position of the astrograph to re-center the star. Repeat this
until the defocused star image is concentric.

OUT-OF-FOCUS STAR IMAGES FOR TELESCOPE NEEDING COLLIMATION

2.0

Mounting the Astrograph

The RASA 8 has a CGE dovetail mounting bar. This is compatible with mounts that accept a CG E or
Losmandy-D style dovetail. The astrograph itself weighs 17 lbs., so a mount with a load capacity greater
than that is required to ensure good performance when a camera and any accessories are added.

Choosing a Camera

When choosing a camera to use with the RASA 8, there are several things to keep in mind.

1. Sensor size– The optical design is optimized for use with sensors

that have a diagonal size up

to 22 mm. It will still perform well with up to 32 mm diagonal sensors, but field illumination in
the corners will be reduced.

2. Pixel size– The RASA 8 work s effectively with a wide range of sensor pixel sizes. Unlike many

telescopes, it can work well with smaller pixels (i.e. less than 5 μm2) due to its fast focal ratio
(F/2.0) and short focal length (400 mm).

3. Obstruction– Since it mounts in front of the optics, use a camera

that blocks as little of the

aperture as possible. Best results will be obtained with cameras that have a cylindrical design
and an outer diameter of less than 100 mm. Many astronomical CMOS and “Hyperstar
compatible” CCD cameras are especially well-suited to the RASA 8.

4. Backfocus– For all flat-field astrographs, including the RASA 8, it is important that the

camera’s sensor is positioned at the proper distance from where it mounts to the telescope.
Otherwise, performance at the edge of the sensor, especially larger sensors, may suffer. For
the RASA 8, this location is 29 mm from the top surface of the lens group cell. A camera’s
backfocus, also known as its flange focal distance, is the distance between the camera sensor
and where the camera body mechanically connects to a camera lens or telescope. Therefore,
cameras with sensors deeply recessed within their body having more than 29 mm of backfocus
cannot be used with the RASA 8 as the sensor cannot be placed at the proper location.

DSLR cameras cannot be used with the RASA 8 due to their large obstruction and long backfocus.

Installing a Camera

If using a camera that mounts with M42 threads, the supplied M42 camera adapter can be used.
This will likely require utilizing optional M42 extension rings to place the camera sensor at the
proper location. When using the M42 camera adapter, the required backfocus distance is 25 mm.
So, for example, if the backfocus of a camera is 17 mm, then 8 mm of M42 extension ring(s)
between the camera and M42 camera adapter will be needed. For best results with larger sensors,
get the backfocus within 1 mm of the required distance.

The supplied C-thread camera adapter can be used to attach any camera which mounts with
a standard C-thread. If the camera’s sensor spacing meets the C-thread standard (i.e. 17.5 mm
backfocus), no additional adapters are required.

For use with Canon or Sony mirrorless cameras, Celestron offers optional RASA 8 camera adapters.
These have a bayonet mount, and position the camera sensor at the proper location.

Other cameras will require a custom camera adapter. Also, cameras with relatively large sensors
may benefit from a custom camera adapter to best illuminate the sensor. Refer to the “Camera
Adapter Requirements” drawing at Celestron.com (located on the RASA 8 webpage under the
“Support and Downloads” tab) to determine the custom camera adapter design.

To attach your camera:

1. Place the knurled retaining ring over the camera adapter.

2. Thread the retaining ring clockwise onto the lens group cell at the front of the RASA 8.

Make sure the camera adapter seats flatly on the lens cell and tighten the retaining
ring until the camera adapter is snug against the cell. Do not over-tighten the ring.

3. Thread the camera body onto the camera adapter. Camera orientation can be adjusted later.

Alternatively, the camera adapter, with retaining ring attached as in step 1, can be first connected to the
camera. Then, while holding the camera, thread the retaining ring onto the lens group cell.

CAUTION: Over-tightening the retaining ring can cause the lens group cell to rotate
relative to the Schmidt corrector, which may affect optical alignment. Keep the camera
adapter snug against the lens cell, but do not over-tighten the ring.

Adjusting Camera Orientation

Once the camera is installed, you can adjust its orientation by slightly loosening the retaining ring.
Loosen the ring no more than 1/8th turn, rotate the camera as desired, and retighten the ring.
Remember not to over-tighten the ring.

Cooling Down and Fan Operation

Optical performance of the RASA 8 will be best when it has reached thermal equilibrium with the
outside air. The greater the temperature difference between the astrograph and the outdoors, the
longer it will take to cool down. It is a good idea to store the astrograph in a cool area and keep it
outside for an hour or so before imaging.

The RASA 8 rear cell is equipped with an air cooling system utilizing a fan to facilitate cooling the
optics to the ambient temperature. The fan pulls air through the mesh vents located on the perimeter
of the rear cell. The mesh prevents dust from entering the astrograph. The supplied battery pack
powers the fan. It requires 8x AA batteries (not included). Install the batteries as indicated in the
plastic mold of the battery holder. Plug the battery pack into the jack near the fan to turn it on. When
ready to image, unplug the battery pack to turn the fan off.

Alternatively, the fan can be powered with a 12V DC power source supplying at least 100mA.
Connect to the fan jack with a 5.5 mm/2.1 mm tip positive DC power plug.

Focusing

The focuser moves the primary mirror forward and backward within the rear cell. The RASA
8 utilizes a redesigned focus system, called the Ultra-Stable Focus System, which minimizes
unwanted lateral movement of the primary mirror when focusing or slewing the astrograph.

To focus, turn the focus knob until the image appears sharp in your camera. If the knob will no
longer turn, the focuser has reached the end of its mechanical travel. In this case, rotate the knob in
the opposite direction until focus is achieved. A single turn of the focusing knob does not move the
primary mirror much; it takes about 30 turns to go through the entire range of focus. If focusing
on a dim object and the focus knob is turned too quickly, it is possible to go right through focus
without seeing the image. To avoid this problem, try first focusing on a bright star so the image is
visible even when out of focus.

Celestron offers a focus motor which is compatible with the RASA 8. A focus motor can be a great
convenience when astroimaging, as the focusing can be done from the same computer

that is

controlling the camera.

Attaching Accessories

The RASA 8 includes a CGE dovetail accessory bar which is also compatible with accessories
which work on Losmandy-D plates. The dovetail accessory bar can be used to mount an
optional guidescope.

A Celestron finderscope can be attached using the pairs of threaded holes in the rear cell of the
astrograph. These holes have Phillips-head screws in them when not in use.

Removing the Optical Window

If using a filter somewhere in the light path, or if the camera has an optical window, it is
recommended to remove the optical window in the lens group cell. This maintains the best
optical performance of the astrograph.

To remove the optical window:

1. Remove the camera and camera adapter.

2. Carefully grasp the knurled edge of the optical window cell within the lens group cell, and begin

rotating it counter-clockwise. If the edge of the window cell cannot be grasped initially because
it is too recessed, use the slots in the window cell to begin rotating it.

3. Unthread the window cell completely, and carefully remove it from the lens group cell.

4. Store the optical window in a place where it will not get scratched or dirty.

Celestron offers a light pollution filter for the RASA 8 which conveniently mounts in place of the
optical window. This improves image contrast in skies which have significant light pollution.

Dew Prevention

The Schmidt corrector is especially susceptible to condensation because the glass is directly exposed
to the night sky. If the temperature of the astrograph drops below the dew point, dew may form on the
corrector within minutes. The easiest way to prevent dew is to add an optional 8” dew shield, which
shrouds the corrector and slows radiant cooling. If conditions are more severe, a dew heater can be
added to apply slight heat to the corrector to keep it dry all night.

Do not store the astrograph if covered in dew. Allow it to dry first without the dust cover on. Storing optics
when wet can promote mold growth on the optical surfaces.

Cleaning of the Optics

Dust, debris, and fingerprints on the optics will generally have little effect on imaging with the RASA 8.
However, if the external surfaces of the Schmidt corrector or the lens group become excessively dirty,
they should be cleaned. Dust can be removed with a blower bulb or an optical cleaning brush. Then, use
optical cleaning solution and lens cleaning tissue to remove any remaining debris or stains. Apply the
solution to the tissue and then apply the tissue to the lens. Use low pressure strokes, do not rub in circles.
When cleaning the corrector, strokes should go from the center to the outer edge. Use a new tissue for
each stroke so as not to spread any oils or debris.

To minimize the need for cleaning, keep the dust cover on the astrograph when it is not in use.
Cleaning the internal optical surfaces should only be done by the Celestron Repair Department. If your

RASA 8 needs internal cleaning, please call Celestron for a return authorization number and price quote.

Collimation

The RASA 8 optics are factory aligned, and should not normally need collimation adjustments. However,
adjustments can be made to the tilt of the lens group, if needed, to collimate the entire optical system.
The primary mirror and corrector are permanently aligned at the factory, and cannot be adjusted.

The astrograph must be collimated with a camera installed. Using a camera

that does not obstruct the

light path (i.e. the aperture of the Schmidt corrector) or that has a cylindrical body is recommended;
this makes it easier to see concentricity of the defocused star diffraction pattern.

Equipment needed:

3 mm Hex key
2 mm Hex key
Mount and camera set up, ready to image

1. Install the camera on the astrograph.

2. Slightly loosen the retaining ring and rotate the camera adapter so the three slotted

openings in the adapter allow access to the collimation screws. Retighten the retaining ring.

Overview

1 Schmidt Corrector 7 Focus Knob

2 Lens Group 8 Dust Cover

3 Lens Group Cell 9 Battery Pack (Batteries not Included)

4 Dovetail Mounting Bar 10 C-Thread Camera Adapter

5 Cooling Fan 11 M42 Camera Adapter

6 12V DC Jack for Cooling Fan 12 Retaining Ring

The Rowe-Ackermann Schmidt Astrograph 8 (RASA 8) is an incredibly fast (F/2.0) 8” aperture optical system that delivers a flat field without optical aberrations. It is capable of
capturing stunning deep-sky astronomical images without the difficulties presented by slower and longer focal length telescopes. The astrograph can only be used with a camera.

Retaining

Ring

Camera
Adapter

Mounting Holes

For Finderscope

Optical

Window Cell

Collimation
Screws

10

11

12

8 9

2

1

3

4

6 7

5

Caractéristiques techniques

Type d'optiques Rowe-Ackermann Schmidt Dimensions du tube Longueur 24,7”, Diamètre 9,3”

Ouverture 203 mm Poids du tube 17 lbs

Longueur de focale 400 mm

Mise au point arrière
(depuis le haut du boîtier du
groupe de lentilles)

29 mm

Ratio de focale f/2.0

Mise au point arrière
(avec adaptateur de caméra M42)

25 mm

Obstruction centrale 93 mm (46 % du diamètre d'ouverture) Dimension du point < 4,6 μm RMS sur le CDV (Champ de vision)

Traitements optiques

Aluminium amélioré,
multi traitements Starbright XLT

Plage de longueur d'onde 400 – 800 nm

Fenêtre optique 46 mm Ø, amovible Illumination hors-axe 93 % à 11 mm hors-axe
Système de mise au point Système de mise au point ultra stable Cercle d'image 22,0 mm Ø , 3,15 °

Ventilateur de refroidissement CD 12 V, MagLev Champ d'utilisation

32,0 mm Ø, 4,6°, avec per te de performances minimes

au bord du CDV

Mode d'emploi du télescope

Modèle : 91073

GARANTI E LIMITÉE DE DEUX ANS CE LESTRON

A. Celestron garanti ce produit comme libre de défauts de matériaux et de fabrication pour une période de deux

ans. Celestron réparera ou remplacera ce produit ou une partie de celui-ci lorsqu'il a été déterminé, lors d'une
inspection par Celestron, que le produit est défectueux en raison d'un défaut de matériaux ou de fabrication.
Comme condition à l'obligation de Celestron de réparer ou remplacer un tel produit, le produit doit être retourné
à Celestron avec la preuve d'achat satisfaisante pour Celestron.

B. Le Numéro d'autorisation de retour correct doit être obtenu auprès de Celestron avant de renvoyer le

télescope. Appelez Celestron au [phone] pour recevoir le numéro à indiquer sur la surface de votre
carton de livraison.

Tous les retours doivent être accompagnés d'un message écrit comportant le nom, l'adresse et le numéro de
téléphone joignable en journée du propriétaire, ainsi qu'une brève description des défaillances déclarées. Les
pièces ou le produit ayant été l'objet d'un remplacement deviendront la propriété de Celestron.

Le client est responsable de tous les coûts de transport et d'assurance, vers et depuis l'usine Celestron, et doivent
donc prépayer ces frais.

Celestron s'engage à faire des efforts raisonnables pour réparer ou remplacer toute produit couverte par cette
garantie, dans les trente jours suivant leur réception. Si une réparation ou un remplacement s'avère durer plus
que 30 jours, Celestron en informera le client le cas échéant. Celestron se réserve le droit de remplacer tout
produit qui a été retiré de sa gamme de produits disponibles avec un nouveau produit ayant une valeur et des
fonctions équivalentes.

Cette garantie sera annulée et sans obligation si l'apparence ou les fonctions du produit ont été modifiées, ou s'il a
subit des abus, une mauvaise utilisation, manipulation ou réparation non autorisée. De plus, les défaillances du produit
ou les détériorations dues à l'usure normale ne sont pas couvertes par la garantie.

CELESTRON REJETTE TOUTE GARANTIE, EXPRESSE OU NON, DE MARCHANDABILITÉ DE FONCTIONNALITÉS
POUR UNE UTILISATION PARTICULIÈRE, SAUF SI MENTION EXPRESSE DANS CE DOCUMENT. LA SEULE
OBLIGATION D E CELESTRON SOU S CETTE GARANTIE LIM ITÉE EST DE RÉPARATION OU DE R EMPLACEMENT
DU PRODUIT COUVERT, DANS LE RESPECT DES TERMES ÉTABLIS DANS CE DOCUMENT.
CELESTRON REJETTE EXPRESSÉMENT LES PERTES DE PROFITS, DOMMAGES GÉNÉRAUX, SPÉCIAUX,
INDIRE CTS OU CONSÉCUTIFS Q UI POURR AIENT RÉSULTER DE L’INFRACTI ON DES TERME S DE LA
GARANTIE OU DÉC OULANT DE L'UTILISATIO N OU DE L'INCAPACITÉ D'UTILIS ER UN PRODUIT CELESTR ON.
TOUTE GARANTIE I MPLICITE Q UI EST ET QUI NE P EUT ÊTRE DÉCLINÉE SERA L IMITÉE À UNE D URÉE DE DEUX
ANS À PARTIR DE LA DATE D'ACHAT IN ITIALE.

Certains états n'autorisent pas l'exclusion ou la limitation des dommages indirects ou consécutifs ou la limitation
de la durée d'une garantie implicite. Il est donc possible que les limitations et exclusions ci-dessus ne s'appliquent
pas à vous.

Cette garantie vous donne des droits légaux spécifiques, et vous pouvez également avoir d'autres droits qui varient
d'un état ou d'une province à l'autre.

Celestron se réserve le droit de modifier ou de cesser la production de tout modèle ou style de produit, et cela
sans préavis.

Si des problèmes liés à la garantie surviennent, ou si vous avez besoin d'assistance pour utiliser votre produit,
contactez :

CELESTRO N, LLC. Service à la clientèle
2835 Columbia Street • Torrance, CA 90503 • Tel. [phone]
Monday-Friday 8AM-4PM PST • ©2018 Celestron • Tous droits réservés • 10-18
NOTE : Cette garantie est valable pour les clients américains et canadiens qui ont acheté ce produit auprès d'un

revendeur agréé Celestron aux États-Unis ou au Canada La garantie en dehors des É.-U. et du Canada n'est valable
que pour les clients ayant acheté le produit d'un distributeur international de Celestron ou d'un distributeur agréé
dans le pays en question. Veuillez communiquer avec eux pour toute réparation sous garantie.

Remarque relative à la FCC : Cet équipement a été

testé et déclaré conforme aux limites d'un appareil numérique de

classe B, conformément à la partie 15 des règles de la FCC. Ces

limites sont conçues pour fournir une protection

raisonnable contre les interférences nuisibles dans une installation

résidentielle. Cet équipement génère, utilise et peut émettre de l'énergie

radiofréquence et, s'il n'est pas installé et utilisé conformément

aux instructions, peut causer des interférences nuisibles aux
communications radio. Cependant, il n'y a aucune garantie que des interférences ne se produiront pas dans une
installation particulière. Si cet équipement cause des interférences nuisibles à la réception radio ou télévision, ce
qui peut être déterminé en éteignant et en rallumant l'équipement, l'utilisateur est encouragé à essayer de corriger
l'interférence par une ou plusieurs des mesures suivantes :

• Réorienter ou déplacer l'antenne de réception

• Augmenter la distance entre l'équipement et le récepteur

• Connectez l'équipement à une prise ou à un circuit différent de celui du récepteur.

• Consulter le revendeur ou un technicien radio / T V expérimenté pour obtenir de l'aide

Ce produit est conçu et prévu pour être utilisé par des personnes âgées de 14 ans et plus.

3. Pointez l'astrographe vers une étoile brillante, et mettez la caméra au point. Centrez l'étoile dans le champ

de vision de la caméra.

4. Dépassez le point de mise au point de l'étoile d'environ un tour de molette de mise au point.

5. Inspectez le motif de diffraction de l'étoile hors mise au point. Une fois la collimation effectuée, le motif

doit ressembler à un doughnut concentrique. Si le motif est concentrique, alors aucun ajustement n'est
requis. Si le « Trou du doughnut » n'est pas centré dans le motif, alors des ajustements sont requis.

IMAGE HO RS MISE AU P OINT D'UNE ÉTOI LE POUR U N TÉLESCOPE E N COLLIMATIO N

6. Il y a trois paires de vis de collimation. Chaque paire est utilisé de concert pour un effet de pousser-tirer

pour ajuster l'angle. À l'aide de la clef Allen, ajustez la collimation en desserant et en serrant l'une des
paires des vis de collimation. Desserrez toujours l'une des vis en premier avant de serrez l'autre. Ajustez
une paire de vis à la fois.

7. Si le motif de l'étoile hors mise au point est plus mince d'un côté, ajustez les vis de collimation de manière

à ce que l'étoile se déplace vers le côté plus fin, puis ajustez la position de l'astrographe de manière à
recentrer l'étoile. Répétez ces étapes jusqu'à ce que l'image de l'étoile soit concentrique.

IMAGES D'ÉTO ILES NON M ISES AU POI NT DANS UN TÉLES COPE NÉCESS ITANT UNE COLL IMATION

2.0