Hi guys,
I would like to get opinions on the maximum usable aperture for Singapore seeing condition, strictly for planetary viewing. Me thinking of getting an instrument with just enough aperture that maximize the local seeing condition (i.e. use different instrument for mersing trips). What do u guys think? 5" unobstructed? 8" obstructed? 12"? 14" (gotta be kidding, right?)?
Again, this is strictly for planetary viewing, for DSO aperture always rules.
What is the maximum usable aperture for Singapore?
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Canopus Lim
- Posts: 1144
- Joined: Fri Jun 03, 2005 12:46 pm
- Location: Macpherson
Arief I think you need to ask those who have the 15" to comment if that is the maximum aperture for planetary.
12.5" is definitely good for Singapore skies. For Jupiter 320x is a good magnification for Very Good nights. 400+ magnification is for Excellent nights (seldom happens). For Saturn, excellent night 500+, average nights 320x.
The seeing varies, there are times that 220x is the max for Jupiter... I rate that as lousy seeing. Usually the average seeing is about 260x for Jupiter. Note that I rate this magnification based on how steady the image is at that magnification. I do not like to over magnify and I prefer images that are steady, even if it is lower magnification.
A 12.5" at 320x gives 1mm exit pupil which is good brightness for picking out low contrast details and high contrast details at the same time. Use other scopes at 320x, and it will be dim; it becomes harder to see low contrast details due to the eye not having enough light to see such low contrast. If you were to use a 8", that would give 0.6mm exit pupil and low contrast details can get lost in the process. A larger scope gives you the opportunity to go at higher magnification and retain the low contrast details. Low contrast details can be faint belts on Jupiter, festoons that are about the same colour as the background etc, shades/ colour difference in the belts etc.
However, the most important thing is, get out to observe more. One can see more details on a smaller scope that is brought out more often than a white elephant large scope. Therefore size also counts..
12.5" is definitely good for Singapore skies. For Jupiter 320x is a good magnification for Very Good nights. 400+ magnification is for Excellent nights (seldom happens). For Saturn, excellent night 500+, average nights 320x.
The seeing varies, there are times that 220x is the max for Jupiter... I rate that as lousy seeing. Usually the average seeing is about 260x for Jupiter. Note that I rate this magnification based on how steady the image is at that magnification. I do not like to over magnify and I prefer images that are steady, even if it is lower magnification.
A 12.5" at 320x gives 1mm exit pupil which is good brightness for picking out low contrast details and high contrast details at the same time. Use other scopes at 320x, and it will be dim; it becomes harder to see low contrast details due to the eye not having enough light to see such low contrast. If you were to use a 8", that would give 0.6mm exit pupil and low contrast details can get lost in the process. A larger scope gives you the opportunity to go at higher magnification and retain the low contrast details. Low contrast details can be faint belts on Jupiter, festoons that are about the same colour as the background etc, shades/ colour difference in the belts etc.
However, the most important thing is, get out to observe more. One can see more details on a smaller scope that is brought out more often than a white elephant large scope. Therefore size also counts..
AstroDuck
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Canopus Lim
- Posts: 1144
- Joined: Fri Jun 03, 2005 12:46 pm
- Location: Macpherson
