Baader Planetarium’s new Filter Changer and Camera Tilter (FCCT) has been designed exclusively for use with the Celestron RASA 8 Astrograph and a range of QHY cameras. The unit combines a filter changer with camera tilt adjustment mechanism for covering the largest possible field size that the RASA8 can suppply, enabling sharp image corners and ultimately fast fine corrections to the optical plane without having to remove the camera from the RASA 8″ each time and adjustment is required.
Background: Celestron’s most transportable astrograph, the RASA 8″ – Rowe-Ackermann Schmidt Astrograph, can capture spectacular deep-sky wide-angle images in seconds. This incredibly fast f/2.0 system is the perfect telescope for modern astronomical CMOS color cameras, smaller CCD cameras and mirrorless cameras. What would otherwise require several nights of exposure time can be accomplished with the RASA in a single night – in principle. Until now, the most severe obstacle was to get the stars in each corner of the chip really round and minimised in size – i.e. to correct for any image tilt. To do this, the camera had to be removed in order to gain access to the adjustment screws located in the front of the Schmidt corrector plate on the lens assembly unit. But whenever the camera is put back in place, unavoidably this will result in a small lateral offset of the mechanical image train, which causes another corner of the image to show slightly distorted stars.
Solution: This problem is solved by using the FCCT since the camera is not required to be removed from the telescope anymore.
Only the RASA 8 has the image plane is so close to the Schmidt plate that the original front adjustment screws cannot be reached as soon as a camera is connected. To remedy this shortcoming, the FCCT can accommodate specially designed, 3D-printed thin filter drawers and, in addition, precisely align the chip plane within fractions of a millimeter by means of easily accessible adjustment screws positioned 120° apart at the side of the filter chamber. This makes working with the RASA 8 a pleasure, without having to fight for a perfect image position for a long time.
For the FCCT, we offer three sizes of 3D-printed filter drawers that exclusively accommodate unmounted filters with diameters of 31 mm / 36 mm and 2″ (unmounted diameter = 47.4 mm). Smaller filters than 31mm very often lead to vignetting in the image corners even with small chip sizes and force cropping of the image content. For this reason we do not offer the smallest possible filter size of (unmounted) 1¼” filters for the RASA 8″. The large angle of view of 14 degrees forces to choose filters as large as possible to avoid image deterioration at the corners as well as vignetting and reflections. A filter should at minimum be 20% larger in diameter than the chip diagonal.
The design of the Baader FCCT is of revolutionary importance for the successful use of the RASA 8. The performance of this RASA 8 optics is praised everywhere in the highest tones – only the difficult (better impossible) adjustment of the stars in the chip corners was a nuisance from the beginning. Many users have to work on the move and often did settle for a somewhat blurred image corner in order not to lose precious exposure time.
Digital post-processing of such images then consumes much more time. Already in the test phase of the FCCT very good image results have been achieved by well-known astrophotographers.
For all extremely fast astrographs with focal ratios around f/2, special filters are needed. For these telescopes we offer two families of CMOS optimized f/2 Highspeed and f/2 Ultra Highspeed filters. The filter choice has to be decided by the sky quality. Out of the abundance of light from cities, excellent results are obtained with f/2 Ultra-Highspeed filters. For only moderately brightened night skies, the 6.5nm f/2 Highspeed filters are a good and very affordable choice. With conventional filters, which are designed for the relaxed focal ratio of classical telescopes, a shift of the central wavelength (CWL) occurs when applied to fast astrographs. In extreme cases, the CWL of a nebula region may even be completely outside the half-width of a filter. Therefore, specially manufactured f/2 filters are indispensable for such optics.
Scope of supply: The following items are included with the FCCT (I/II)
- FCCT I or FCCT II with inserted dark slider and two 0.5mm spacer rings for focus finetuning
extra long 2mm hexagon screwdriver as torque wrench (28cm long), as well as short 0.9mm, 1.3mm and 1.5mm hex keys
- Three M2 hexagon socket screws for camera adaption
- Filter-Extractor-Tool for inserting/extracting the filter drawer
- Storage bag for four filter holders (to be purchased separately)
- 1 Pair Cotton Cloves for mounting sensitive accessories (#2905050, € 5,-)