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Originally Posted by ving
geoff, with a exit pupil of 7 would the central obstruction come into play (if even if viewed during the day)?
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Hi David,
That depends on several things.
In the daytime the answer would be "yes" in most cases because the observer has a dilated pupil significantly smaller than the 7mm exit pupil. In the evening in most cases the answer would be "no" because the observers pupil will dilate to a much larger size due to the low light levels. However, if you observed an extremely bright target like the full moon you would invariably see the secondary holder because your dilated pupil would shrink due to the exceptionally bright target. That shouldn't be such an issue as most people wouldn't use this scope/eyepiece combination to observe the full moon.
For viewing of dim targets you woudn't see the secondary holder but if your pupil dillation is not close to 7mm and the skies dark, the background sky when looking through the eyepiece takes on a somewhat "milky" appearance and images appear washed out and the selected targets, particularly extended diffuse targets like galaxies and nebula, lack contrast. FWIW this doesnt worry some people and they prefer to use such a combination to gain the additional TFOV. However its not something I like at all and prefer a smaller TFOV with better contrast and an ink black background sky.
CS-John B