Celestron RASA 8

Users in team Dwarfstars: Capt Kang (From Sep 2020 ~)

• Specification

1. Optial design: 8'' Rowe-Ackermann Schmidt Astrograph

2. Lens diameter: 200mm

3. Focal length: 400mm

4. Focal ratio: 2.0

5. Weight: 7.7kg (OTA)

• Pros

1. Super fast astrograph. Incredibly fast focal ratio F2 !!!

2. Short exposure time (20-120 seconds) will allay your concern on tracking issues.

• Cons

1. Designed solely for astrophotography. unable to use this telescope for visual purposes.

2. Attaching filter wheel & OAG is out of option with RASA 8. if you use them, they would block most of the light.

3. Extremely short back focus. 29mm from the top surface of the lens group cell. Due to the limited back focus, using DSLR or a camera with a long back focus is out of the question.

4. Collimation is very difficult as there is no center mark on the primary mirror or secondary mirror like other telescopes.

5. If you collect Chromatic data with RASA overnight, you will achieve about 50-60Gb of raw files to process. It means you will also need a high-performance computer for image processing.

6. Accessories for Rasa 8 are very expensive. For example, Baader F2 narrowband filters(USD 600 -USD 1,000), Starizona filter drawer 7 set ( USD 600), Astrozap dew shield for Rasa 8(USD 241).

7. Focusing at F2 is very challenging especially during winter. the critical focus zone is extremely small.

8. Do not expect pinpoint stars with Rasa. As the altitude of the target changes with time, the mirror will be shifted slightly and would have a large influence on its collimation, unlike other slower telescopes.

9. There are limits on your choice of camera because camera will be attached in front of the aperture . The cylindrical shape is advantageous and the diameter of camera must be less than the corrector lens cell.

10. For narrowband imaging, the filter for fast optical will be required due to band shift.

11. there will be significant halos on RASA 8 images with bright stars compared to other telescopes.

Verdict

One-line summary : apochromatic refractor F/8 x 16 = Rasa 8 F/2

I would like to say that this telescope has many downsides and an overwhelming advantage.

If you are a husband with 3 children and barely have enough time to go out to take photos once or twice a month, RASA 8 can be one of the most ideal telescopes for you. This incredibly fast telescope will allow you to take 3-4 object at an acceptable level in a single night.
But if you want to make visual observations and choose an easy way, don't look at this fascinating telescope.