Quote:
Originally Posted by marki
The refractors have an advantage on planets with their higher contrast but lose out with their wide fields and in any case there are only 3 planets worth looking at in my book.
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Its important to understand that a 50% obstructed instrument reproduces high contrast objects just as well as an unobstructed one. For example high contrast objects like lunar craters, double stars, planetary Moons etc will still look the same in a large obstructed instrument. Its the loss of the ability to reproduce lower contrast detail that is the problem..a lot of planetary detail is in the low contrast area.
The obstruction causes light to be thrown from the Airy Disc into the surrounding rings in the diffraction pattern. In the presence of inclement seeing this can cause star images to appear a little more bloated than they might otherwise . Pure spherical aberration in an unobstructed system will have exactly the same effect. This can sometimes be confused with loss of contrast although it is really loss of sharpness which indirectly effects the ability to reproduce low contrast features.
Mark