The effect of seeing
Started by ronbee, 08/23/2002 06:45PM
Posted 08/23/2002 06:45PM
Opening Post
Posted 08/25/2002 08:49AM
#1
Ron
I enjoyed reading this link. I write whilst outside terrible{V} seeing is evident with a cold Southerly wind.
Certainly one gets the steady airy disc a lot easier with smaller apertures.
I have noticed quite a difference with my 100 and 130 mm refractors.
On one of the few occasions I have put both up on the same night the seeing was near perfect for the 100 mm (I)but clearly a {II} or {III} with the 130 mm. Both scopes star test in excellent seeing as perfectly as I can ascertain.
The airy disc sizes gives clues to the seeing in arc seconds on that night.
Also my smaller 63 mm refractor is almost always a {I} or {II}, unless it is a {V}.
Only on two(out of 40 odd) occasions have I had the 130 mm show perfect airy discs.
Perhaps this helps explain why around 80 -100 mm is an optimum size for a high quality refractor.
An interesting aside I read off a link on this forum (Todd Gross quoting others)that many believe that unobstructed refractors handle seeing better compared to obstructed apertures of the same size.
bset wishes
Kevin B
I enjoyed reading this link. I write whilst outside terrible{V} seeing is evident with a cold Southerly wind.
Certainly one gets the steady airy disc a lot easier with smaller apertures.
I have noticed quite a difference with my 100 and 130 mm refractors.
On one of the few occasions I have put both up on the same night the seeing was near perfect for the 100 mm (I)but clearly a {II} or {III} with the 130 mm. Both scopes star test in excellent seeing as perfectly as I can ascertain.
The airy disc sizes gives clues to the seeing in arc seconds on that night.
Also my smaller 63 mm refractor is almost always a {I} or {II}, unless it is a {V}.
Only on two(out of 40 odd) occasions have I had the 130 mm show perfect airy discs.
Perhaps this helps explain why around 80 -100 mm is an optimum size for a high quality refractor.
An interesting aside I read off a link on this forum (Todd Gross quoting others)that many believe that unobstructed refractors handle seeing better compared to obstructed apertures of the same size.
bset wishes
Kevin B
Funding Member
