I believe the efficiency, transmission vs. reflection, plays a part as well.
One day I’m going to read an estimate of the “light gathering power” increase
from being in a dark site. It’s the starlight we want to gather, after all, not
just the light.
On Jul 20, 2016, at 4:47 PM, William Finch <psychogilgamesh@xxxxxxxxx> wrote:
Well, a 5.5" APO also messes up the math some.
You've got to figure out the square inches of the center obstruction and then
remove it from the square inches of your primary in order to truly compare a
refractor to a reflector.
Plus your collimation of the reflector would need to be dead on to compare
visually.
On Wed, Jul 20, 2016 at 2:21 PM, Mark <markj57@xxxxxxxxx
<mailto:markj57@xxxxxxxxx>> wrote:
Maybe this is a nit, but William got it right when he used the term 'light
gathering capacity'. 'Power' is vague and doesn't take into account optical
design or quality. I get far better views of almost everything with my 5.5"
APO refractor than I did with my 11" SC.
Sent from my iPad
On Jul 20, 2016, at 2:16 PM, Leah S <lphxaz@xxxxxxxxx
<mailto:lphxaz@xxxxxxxxx>> wrote:
of course this works for smaller sizes too
an 8" scope is 4x as powerful as a 4", and almost twice as powerful as a 6".
similarly, 6" is more than twice as powerful as a 4". these are relevant
numbers when someone is asking: should I get a go-to 4" or a non-electronic
6" or 8"?
4" scope = 12.5 sq in
6" scope = 28 sq in
8" scope = 50 sq in
and if you just need to quickly compare two scopes - don't bother to
multiply by pi (it just cancels out). and you don't have to change from
diameter to radius. just compare the square of the diameter of the two
scopes. e.g.
for 4", square of diameter is 16
for 6", square of diameter is 36
for 8", square of diameter is 64
as you can see, the same proportions hold:
an 8" scope is 4x as powerful as a 4", and almost twice as powerful as a 6".
similarly, 6" is more than twice as powerful as a 4".
On 7/20/2016 12:19 PM, roger anzini (Redacted sender twinklescope for DMARC)
wrote:
William,
I knew there was a reason for lugging this big, heavy 16" thing
around, all over the place.
Thank You for giving me the answer in tasty slices.
Best clear skies,
Roger
On Wednesday, July 20, 2016 11:12 AM, Leah S <lphxaz@xxxxxxxxx>
<mailto:lphxaz@xxxxxxxxx> wrote:
after watching this video, I'm hungry... lucky there's a kosher pizza
place nearby. :)
now did you say something about size of telescopes? tell me again while
I'm eating the pizza. :D
On 7/20/2016 9:54 AM, William Finch wrote:
Thought this might be useful for explaining why an 8 inch scope is
twice the light gathering of a 6 inch. Breaks it down in easy English.
https://youtu.be/YAawHbPiQfo ;<https://youtu.be/YAawHbPiQfo>
