|
Bill Weir
scholastic sledgehammer
Reged: 06/01/04
Posts: 894
Loc: Metchosin (Victoria), Canada
|
|
Quote:
Quote:
We're talking about surface brightness of extended objects (not stars). You cannot brighten that beyond the naked eye value, regardless of your aperture or magnification.
The point of larger aperture is to gather more light. Otherwise, why covet large aperture?
Not always. For me sometimes aperture is about resolution. In fact with most of the professional astronomers that I know (which is many)resolution is a huge part of the reason they want aperture.
When observing the Moon with a larger scope I can see way more fine detail than with my smaller scopes.
Bill
--------------------
6'' Orion SkyQuest
12.5'' f/5 Custom Truss Dob
William Optics 80mm ZenithStar II ED Doublet
f/5 25" newtonian on a giant GEM, any time I want
Observing sessions grand total for 2007, 171.
So far in 2008, 115
|
Joe Bergeron
Vendor - Space Art
Reged: 11/10/03
Posts: 845
Loc: Upstate NY
|
|
Obviously you can reduce the brightness of an image by reducing the aperture. The reverse is not always true. A 3" scope operating at 30x produces an exit pupil of 2.5mm...an easy fit into your eye. A 9" at 30X gives a 7.5mm pupil...a tight squeeze into your eye, but a brighter image. With a 20" it's 17mm. At this point, unless you're an owl, most of the moon's light will be shining onto your iris, not entering your eye. The image will look no brighter than the 9" scope's image. With a 100" scope equipped with a gigantic eyepiece giving 30x, the exit pupil is now over 3 inches across. I think you can appreciate you'll have a hard time taking advantage of all this light with your little eyeball. You won't gain the full benefit of all that aperture until the magnification is much higher, at least 360X. Even then, the Lunar image will be so big and its light so spread out that its per unit brightness will be the same as in a 3" scope at 11X.
--------------------
Seven telescopes of a diverse nature.
Multiple chums glittering in the sky. New friends await.
My Web Site
English Lessons for Amateur Astronomers
|
Centaur
Pooh-Bah
Reged: 07/12/04
Posts: 1123
Loc: Chicago
|
|
Thanks for the explanations.
--------------------
For astronomical graphics, including
monthly wallpaper calendar, visit:
www.CurtRenz.com/astronomical.html
Curt Renz - "Centaur"
|
panhard
Carpal Tunnel
Reged: 01/20/08
Posts: 2574
Loc: Markham Ont.
|
|
From the general comments here. Did I just waste my money on a polarizing filter for lunar viewing?
--------------------
Orion xt10i
8 & 17mm Hyperion eye pieces
koning 32mm 25mm skywatcher eyepieces
lumicon 0111 & antares variable polarizing filters
12x50 binos
A love for this hobby
"What goes around comes around."
"She who must be obeyed."
Herb c
cloudy nights my # 1 site
43.53°n 79.17°w
|
Winnie
super member
Reged: 04/28/07
Posts: 117
Loc: Las Vegas
|
|
NO!!! Although Lunar viewing will not permanently damage your eyes, polarizers make full Moon viewing with low power ep's much more tolerable. If you use high power on the full Moon, you will dim the view and likely not need a polarizer at all. Well, depending on your aperature, of course.
--------------------
CPC925 GPS
Feather Touch Microfocuser
C130 Mak
Celestron Plossl Kit
15mm Pan
9T6 Nagler
Canon 10x30 IS
|
Tim2723
The Moon Guy
Reged: 02/19/04
Posts: 5121
Loc: Northern New Jersey
|
|
No indeed. You certainly haven't wasted your money. While you may find that you don't use it every time you view the Moon, or that you don't adjust it constantly, it still remains one of the most useful accessories for the lunar observer. Its primary advantage is that it's adjustable. A 12% filter might be too little for you, yet a 25% be too much. Let's say you need a 17.5% filter only for the low power of your particular set up. You would adjust the polarizer accordingly and leave it there, but you now have your ideal Moon filter. Further, you can adjust it to meet the requirements of any scope you use.
Some observers get the best use from adjusting the filter for every individual veiw, others never use filters at all. But all that is utterly irrelevant, since it is your eye, and only your eye, which must be satisfied.
--------------------
The crwth will set you free!
|
panhard
Carpal Tunnel
Reged: 01/20/08
Posts: 2574
Loc: Markham Ont.
|
|
Quote:
No indeed. You certainly haven't wasted your money. While you may find that you don't use it every time you view the Moon, or that you don't adjust it constantly, it still remains one of the most useful accessories for the lunar observer. Its primary advantage is that it's adjustable. A 12% filter might be too little for you, yet a 25% be too much. Let's say you need a 17.5% filter only for the low power of your particular set up. You would adjust the polarizer accordingly and leave it there, but you now have your ideal Moon filter. Further, you can adjust it to meet the requirements of any scope you use.
Some observers get the best use from adjusting the filter for every individual veiw, others never use filters at all. But all that is utterly irrelevant, since it is your eye, and only your eye, which must be satisfied.
I am glad to hear that. 
--------------------
Orion xt10i
8 & 17mm Hyperion eye pieces
koning 32mm 25mm skywatcher eyepieces
lumicon 0111 & antares variable polarizing filters
12x50 binos
A love for this hobby
"What goes around comes around."
"She who must be obeyed."
Herb c
cloudy nights my # 1 site
43.53°n 79.17°w
|
|
1 registered and 2 anonymous users are browsing this forum.
Moderator: desertstars
Print Thread
|
Forum Permissions
You cannot start new topics
You cannot reply to topics
HTML is disabled
UBBCode is enabled
|
Thread views: 966
|
|
|
|
|
|
|
Previous
Index
Next
Threaded
[Re: 
Edit
Reply
Quote
