The RASA-8 has 25mm back focus from the camera adaptor ring, so if the distance from the camera’s front aperture to the sensor is greater than this, as is the case with a DSLR, focus isn’t possible. Various adaptors are available for different camera threads, but some cameras require spacers to get them into the correct focus position. However, Canon and Sony mirrorless models (APS-C or full-fame) should be fine. Also, DSLRs aren’t compatible because focus cannot be achieved. No finder is included which, considering the price of the instrument, seems mean. There are negatives that need mentioning. In the world of astrophotography f/2 is fast, indicating the RASA-8 can deliver seriously deep sky images in a short time.Īs an example, an f/2 system delivers images of the same exposure depth as an f/10 system in just a twenty-fifth of the time. The RASA-8 has an effective focal length of 400mm and an aperture of 203mm, hence its focal-ratio is f/2. It can be determined by dividing the scope’s effective focal length by its aperture using the same units. In astronomy, the speed of a telescope is also known as its focal ratio. This is a comparative value used to indicate how quickly an exposure of certain depth can be achieved. The RASA also has an impressive optical speed.
#Celestron rasa 8 full#
The result is an aberration free, colour-corrected image, which delivers full illumination and pin-sharp stars over a 22mm image circle with only minimal performance loss over a 32mm-image circle. The RASA’s flat focal plane sits in front of the corrector.
Rare earth elements are used in lens manufacture because of their low dispersion properties, which helps minimise colour fringing.
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