At 06:25 8/13/01, OC wrote:
Hmm makes my 180 f2... very interesting...
Absolute aperture:
-> 90mm
... wow.
Amount of light multiplication factor / ratio:
-> 6.36 x
another wow...
Equivalent exposure:
-> 6.36x ~7 = 44.5 seconds
Better than the 50/1.2 even. Nice exercise in calculation actually. I've
seen a photograph of Orion's belt with a 180/2.8 and even that was
impressive in that a small black area corresponding to the Horsehead
nebula was distinctly visible as was the Orion nebula. I'll have to try
the 180/2 out.
Even more promising seems the fact that the 180/2 has absolute chromatic
aberration correction (it has no infrared mark even), so that star images
should be even more pointlike and not affected by a red ring effect.
Thanks for the inspiration John.
Even the 180/2.8 is in the same class as the 50/1.4 wide open. Using a 7
second exposure with it gathers the equivalent light from stars as using 23
seconds with the 50/1.4 standard.
The 350/2.8 would be about the same as your 180/2 (in light
gathering). The 250/2 has the most. If I could only afford these three
lenses! Actually, for the cost of any of the three, one could buy an 8"
catedioptric telescope with all the accessories for astrophotography and
probably have some money left over, especially with the 250mm and 350mm.
-- John
-- John
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