Celestron Rowe-Ackermann 36 f/2.2 Schmidt Astrograph V2

Overview

The Celestron Rowe-Ackermann Schmidt Astrograph (RASA 36 cm) delivers a coma-free, astigmatism-free flat field over a large image circle (60 mm) and an extended spectral range (400-900 nm). This astrograph is designed exclusively for use with a camera.

Component Identification

The following components are part of the RASA 36 cm:

• 1. Lens Group: The primary optical assembly.
• 2. Schmidt Corrector Lens: The corrector plate at the front of the optical tube.
• 3. Lens Group Housing: The main body housing the optics.
• 4. Dovetail Saddle: A CGE-style dovetail saddle for mounting.
• 5. Dovetail Accessory Rail: An additional rail for mounting accessories.
• 6. Focuser Knob: Used to adjust the focus by moving the primary mirror.
• 7. Cooling Fan: Located in the rear cell to aid in cooling the optics.
• 8. 12 VDC Socket for Cooling Fan: Connection point for the cooling fan's power.
• 9. M48 Camera Adapter: The included adapter for connecting cameras.
• 10. Locking Ring with Teflon Washer: Secures the camera adapter to the telescope.
• 11. Battery Pack with 8 AA: Provides power for the cooling fan (batteries not included).

Mounting the Astrograph

The RASA 36 cm features a CGE dovetail saddle, compatible with mounts accepting CGE or Losmandy-D dovetails. Weighing 34 kg, a mount with a higher load capacity is recommended for optimal performance, especially when a camera and accessories are attached. Due to its size and weight, two people are required to move and mount the RASA 36 cm. Handles on the rear cell can assist with lifting. For custom mounting, the rear cell has two sets of M8x1.25 mounting holes, reinforced with threaded inserts.

Installing the Camera

The included M48 camera adapter allows for the attachment of a DSLR camera. A 48mm 'wide T-ring' specific to your DSLR camera brand is required. For astronomy cameras with sensors smaller than 'full-frame' (43mm diagonal), the M48 adapter may also be suitable. In such cases, optional adapters like an M48-to-M42 adapter and M48 extension tubes might be necessary to achieve the correct back focus, which is 55mm with the M48 adapter. For cameras with larger sensors, a specialized camera adapter is recommended for optimal illumination. Consult the 'Camera Adapter Requirements' diagram on the Celestron website for guidance.

Note: The steep light cone of the f/2.2 optics means the camera body itself can cause vignetting. Even with the astrograph's large illuminated field, cameras with large sensors may experience vignetting if the sensor is recessed deeply into the camera body, which is common with full-frame DSLR sensors.

Steps to attach your camera:

1. Place the knurled locking ring over the camera adapter and screw it loosely onto the lens group housing. The Teflon washer should be positioned between the locking ring and the camera adapter.
2. Screw the camera body onto the camera adapter.
3. Carefully hold the camera so that the camera adapter sits flat against the lens group housing.
4. Screw the locking ring completely onto the lens group housing. Tighten the ring until the camera adapter is secure against the housing. Do not overtighten.

Camera Alignment: Once the camera is installed, its orientation can be adjusted by slightly loosening the locking ring. Loosen the ring no more than 1/8 turn, rotate the camera to the desired position, and then retighten the ring. Ensure you do not overtighten.

Cooling and Fan Operation

The RASA 36 cm performs best when its optics have reached thermal equilibrium with the ambient air. The cooling-down period depends on the temperature difference between the astrograph's storage location and the environment. It is advisable to store the astrograph in a cool place and set it up outdoors for about an hour before imaging sessions. The rear cell of the RASA 36 cm is equipped with a cooling system featuring a fan that helps the optics reach ambient temperature. The fan draws air through grilles located on the outer edge of the rear cell, which also prevent dust from entering the astrograph. The cooling fan is powered by the included battery pack, which requires 8 AA batteries (not included). Insert batteries as indicated in the battery holder. Connect the battery pack to the socket next to the fan to turn it on. When the optics have cooled and you are ready to image, remove the battery pack to turn off the fan.

Focusing

The focuser moves the primary mirror within the rear cell. The RASA 36 cm V2 utilizes the Ultra-Stable Focussing System (USFS), designed to minimize main mirror shift during focusing and long exposures. To focus, turn the focuser knob until the image in the camera appears sharp. If the knob stops turning, it has reached its limit; turn it in the opposite direction until the image is sharp. Turning the focuser knob too quickly can lead to missing focus without seeing an image. To avoid this, try focusing on a bright star first, ensuring it is visible in the image even when slightly out of focus. An optional focuser motor is highly recommended and is fully compatible with the RASA 36 cm V2. More information is available on the Celestron website.

Attaching Accessories

The RASA 36 cm is equipped with a CGE dovetail accessory rail, compatible with most accessories designed for Losmandy-D plates. This rail can be used to mount an optional finderscope. A Celestron finderscope can be attached using the two screw holes in the rear cell of the astrograph. These holes are fitted with Phillips screws when not in use.

Removing the Glass Window

If you plan to use filters in the light path or if your camera has a glass window, it is recommended to remove the glass window from the front lens cell to maintain optimal optical performance. The glass window has M110 x 0.75 threads on its outer housing. To remove the glass window: 1. With the camera adapter removed, carefully grip the knurled cell of the glass window. 2. Carefully unscrew and remove the glass window.

Dew Prevention

The Schmidt corrector lens is particularly susceptible to dew formation, as it is exposed to the night sky. Dew can form within minutes if the astrograph's temperature drops below the dew point. The simplest way to prevent dew is by using an optional 14-inch dew shield to shield and insulate the corrector lens. For more severe conditions, a dew heater can be added to gently warm the corrector lens, keeping it dry throughout the night. Celestron offers a range of dew prevention products compatible with the RASA 36 cm. Visit celestron.com for details. Do not store the astrograph if it is covered in dew; allow it to dry first without replacing the dust cover, as storing wet optics can promote mold growth on glass surfaces.

Cleaning the Optics

Dust, dirt, and fingerprints on the optics typically have minimal impact on imaging with the RASA 36 cm. However, if the outer surfaces of the Schmidt corrector lens and the lens group become excessively dirty, they should be cleaned. Dust can be removed with a blower or a camel hair brush. For remaining residue or smudges, use a glass cleaning solution and a lens tissue. Apply the solution to the tissue, then place the tissue onto the lens. Clean the corrector lens with light pressure, working from the center outwards. Use a new tissue for each step to avoid transferring oils or debris. Do not rub in a circular motion. A suitable cleaning solution can be made by mixing 3 parts 99% isopropyl alcohol with 2 parts distilled water. Soft, white paper towels can be used instead of lens tissues, provided they contain no additional lotions or fragrances. After use, replace the dust cap to minimize future cleaning needs. Cleaning of internal glass surfaces should only be performed by Celestron repair services. If your RASA 36 cm requires internal cleaning, contact Celestron for a return authorization number and pricing.

Collimation

The optics of the RASA 36 cm are factory aligned, and collimation adjustments are typically not necessary. However, the tilt of the lens group may need adjustment to collimate the entire optical system. The primary mirror and corrector lens are factory-fixed and cannot be adjusted. The astrograph must have a camera installed for collimation. It is advisable to use a camera that does not obstruct the light path (i.e., the aperture of the Schmidt corrector lens) to more easily observe the concentricity of defocused stars.

Required Tools:

• 2mm Hex Wrench
• 3mm Hex Wrench
• Mount and camera setup, ready for imaging

Collimation Steps:

1. Attach the camera to the astrograph.
2. Slightly loosen the locking ring and rotate the camera adapter to allow access to the collimation screws. Retighten the locking ring.
3. Point the astrograph at a bright star and focus the camera. Center the star in the camera's field of view. Polaris is recommended if possible, as it moves very little over time.
4. Defocus the star by approximately 1 turn of the focuser knob.
5. Examine the defocused star patterns. In a collimated state, the pattern should appear as a concentric donut. If the 'donut hole' is not centered, adjustment is required.
6. There are three pairs of collimation screws. Each pair functions as a push-pull tilt adjustment. Adjust collimation by loosening one screw and tightening the other within a pair. Always loosen one screw first, then tighten the other. Adjust one pair of screws at a time.
7. If the star pattern is thinner on one side, adjust the collimation screws to move the star towards the thinner side, then re-center the star by adjusting the astrograph's position. Repeat this process until the defocused star pattern is concentric.

Technical Specifications

Regulatory Information:

CE, FC markings are present.

FCC Statement: 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 installation. 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.

Distributor and Service for Germany and Austria: Baader Planetarium GmbH - Zur Sternwarte - 82291 Mammendorf Tel.: 08145/80890 - service@celestron-deutschland.de

This product is intended for use by persons 14 years of age or older.

Warranty: 2 Year Warranty. Details at celestron.com/support/warranties

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Celestron Headquarters: 2835 Columbia Street, Torrance, CA 90503 USA.