The largest scope I have looked through is a 10" dob, how big of a jump would a 13.1" dob be? What does that translate into, about a 75% increase in light gathering power? On paper that sounds like a lot. Compared with a 10" dob, is a 13.1" a totally different experience?
10" and 13.1" dob, how big of a difference?
Started by explore, 12/27/2002 01:49AM
Posted 12/27/2002 01:49AM
Opening Post
Posted 12/27/2002 02:45AM
#1
Yes!
A 13" scope which has a well made mirror can present a sizeable increase in brightness to objects because of the greater area. Since you mentioned a 13.1 you're probably looking at an f4.5 Coulter or similar scope.
This brings into consideration the other effect, which is a change in f-ratio which also increases the apparent field while decreasing the effective magnification of a given eyepiece. Most 10" scopes have a bit more f-ratio and thus have a narrower field of view than their larger brethren.
This gives the viewer a 'port-hole' effect whereby the experience under the skies goes from watching a picture on a wall to watching scenery roll by while in a stateroom on an ocean liner. This effect is awesome and enjoyable!
A 13" scope which has a well made mirror can present a sizeable increase in brightness to objects because of the greater area. Since you mentioned a 13.1 you're probably looking at an f4.5 Coulter or similar scope.
This brings into consideration the other effect, which is a change in f-ratio which also increases the apparent field while decreasing the effective magnification of a given eyepiece. Most 10" scopes have a bit more f-ratio and thus have a narrower field of view than their larger brethren.
This gives the viewer a 'port-hole' effect whereby the experience under the skies goes from watching a picture on a wall to watching scenery roll by while in a stateroom on an ocean liner. This effect is awesome and enjoyable!
Posted 12/27/2002 03:51AM
#2
the jump from 10" to 13" is pretty similar proportionally to the jump from 3" to 4" or from 6" to 8".
In my experience this is enough of a jump to make a significant difference in amount of detail that you see in side-by-side comparisons, but not a big enough jump to make for a "totally different experience" as you put it, from what you experienced before.
You're looking at a 72% increase in light grasp but keep in mind that difference in brightness has to get up to about 40% or so just to get to be really noticeable to most people.
When stepping up in aperture it seems to me that increases of around 50% diameter make the 'worthwhile' step-up threshold. Different people may have different personal thresholds of course.
In my experience this is enough of a jump to make a significant difference in amount of detail that you see in side-by-side comparisons, but not a big enough jump to make for a "totally different experience" as you put it, from what you experienced before.
You're looking at a 72% increase in light grasp but keep in mind that difference in brightness has to get up to about 40% or so just to get to be really noticeable to most people.
When stepping up in aperture it seems to me that increases of around 50% diameter make the 'worthwhile' step-up threshold. Different people may have different personal thresholds of course.
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