C9.25 vs 150mm 1800mm truss

[tenorotti]

Hi Folks,

How does this scope perform against the celestron classic 9.25? Will it be better on planets and DSOs?

Thanks,

[Mike]

Wow! What a loaded question. The larger aperture of 9.25 inches has greater light gathering ability and so DSOs often appear brighter and may show more detail. However, refractors have much greater contrast, darker sky, mainly due to no central obstruction and less loss of light. Stars are more pinpoint and stand out against the darker background. Long focal length refractors perform very well on planets showing great detail. Smaller apertures are less affected by atmospheric turbulence. Doublet refractors cool down in less than an hour. The large mirror can take hours and if the air temperature is dropping, it may never catch up. The image degradation of an object in larger SCTs whose mirrors have not reached ambient can be great. Keeping dew off the corrector of a large SCT can be a battle. I have seen this many times: A field of telescopes, a number of viewers who gravitate to the refractors and comment to you that they like the view through your refractor better than any of the scopes they've looked through... even though there are much larger mirrored scopes there.

Mike

[tenorotti]

Thanks for responding. I'm in the middle of aperture go big or go home and your 1800mm truss refractor with 6" of glass is tempting . My C9.25 is pretty good but yes indeed cooldown and dew are constant battles. All the best.