albert1
Carpal Tunnel
Reged: 01/01/07
Posts: 2249
Loc: Southern New Jersey
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I'm sure to most of you this is a silly question but I'm somewhat new to this and have yet to find an easily understandable answer to the real difference between and f6.3 and an f10 scope.
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Frank331
sage
Reged: 01/06/07
Posts: 423
Loc: Miami, Florida
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well mainly the feilds of view and for imaging the faster the f# the shorter the exposure has to be. see with the F10 scope its almost like looking through a a small tube but with a a faster scope it a more expansive feild of view.
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Ask No Questions, I Tell No Lies
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Frankie: 14 Year old Astro-geek
I tried being reasonable, I didn't like it.
-Clint Eastwood
Meade 114EQ-ASTR "Leo Minor"
 Tricked Out Tippmann 98 Custom " The Enforcer"
Jr. NRA Member
Miami, Florida
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albert1
Carpal Tunnel
Reged: 01/01/07
Posts: 2249
Loc: Southern New Jersey
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Thanks for that. Let me pick your brain alittle more. I'm not interested in taking photos, I just want to view. Let's say I'm looking at the moon with both f #s, what would the difference be?
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Albert
RV6's
Celestron Ultima 2000
Royal Astro's
Lafayette's
1950's 8" f/9 Edmund/Parks Newt
6" 1950's Edmund WF Newt
Tasco 8V
Coulter Odyssey 10
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NeoDinian
Experienced Postmaster
Reged: 10/05/05
Posts: 14043
Loc: Rockford Illinois
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Without knowing the focal lengths of the scope, lets just assume that with the 6.3 you would frame the whole moon with a given EP.. That same EP with the f/10 would only show you about 75% of the moon, and you'd have to pan around to take in the whole thing...
The other way around, if you fill the EP with the f/10, that same EP in a 6.3 would make the moon that much smaller (by a factor of .63 actually), and only fill aprox 63 percent of the EP view. 
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Neo... (Jeff)
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10" LX200-GPS/SMT UHTC "Draco"
 Rockford, Il.
NeoDinian's Eye on the Sky!
Coming soon:
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albert1
Carpal Tunnel
Reged: 01/01/07
Posts: 2249
Loc: Southern New Jersey
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So why would I want an 8" f6.3 over and f10
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Albert
RV6's
Celestron Ultima 2000
Royal Astro's
Lafayette's
1950's 8" f/9 Edmund/Parks Newt
6" 1950's Edmund WF Newt
Tasco 8V
Coulter Odyssey 10
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Frank331
sage
Reged: 01/06/07
Posts: 423
Loc: Miami, Florida
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well when veiwing large nebula and galaxies it benefits you that you can see the whole thing unless you actually awant to look at it in bits and peices
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Ask No Questions, I Tell No Lies
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Frankie: 14 Year old Astro-geek
I tried being reasonable, I didn't like it.
-Clint Eastwood
Meade 114EQ-ASTR "Leo Minor"
Tricked Out Tippmann 98 Custom " The Enforcer"
Jr. NRA Member
Miami, Florida
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Rick Denison
sage
Reged: 04/04/05
Posts: 209
Loc: Central Mexico
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Albert,
One noticeable difference is that with a given eyepiece, the f/10 will give greater magnification than the f/6.3 (assuming identical apertures). To calculate magnification, you divide the focal length of the objective by the focal length of the eyepiece. Let's say you have a 100-millimeter, f/10 telescope (100 x 10 = 1000mm focal length). Using a 10mm eyepiece, your magnification would be 100x. Same aperture but f/6.3, the objective's focal length is 630 mm, so the 10mm eyepiece would give you only 63x.
The tradeoff is that, all else being equal, the shorter focal length will yield a wider field of view.
So, to use your example of viewing the moon, the f/10 would give you a close view, while the f/6.3 would show a wider area on the sky. This is why many people who mostly observe the Moon and planets prefer long-focus, high-magnification telescopes, such as my 127-mm Maksutov with its f/12.1 rating (actually it's even a little longer than that). On the other hand, deep-sky enthusiasts go for short-focal-length, wide-field instruments, like my (currently disassembled) 10-inch f/5.4 reflector.
Hope this helps.
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Rick Denison
León, Mexico (21° 9' N, 101° 41' W)
Unitron 60mm refractor
Orion StarMax 127mm Mak-Cass
Optics from Coulter 10.1-in. Newtonian (awaiting reconstruction)
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NeoDinian
Experienced Postmaster
Reged: 10/05/05
Posts: 14043
Loc: Rockford Illinois
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It also depends on what you want to do with the scope...
If you want wide-field views, get the 6.3 scope.. You and add a focal reducer to make it even WIDER if wanted... Take that same scope and use a Barlow and you'll basicly make it an f/12.6...
If you want DEEP field views, get the f/10.. You can barlow that and get f/20 (or more)... And for the occasional wider view, you can make it an f/6.3 with a reducer...
However, if Imaging is in your thoughts (other than planetary), then you want the FASTER system (f/6.3). HIGH focal ratios are better for planetary work...
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Neo... (Jeff)
-=-=-=-=-=-=-
10" LX200-GPS/SMT UHTC "Draco"
Rockford, Il.
NeoDinian's Eye on the Sky!
Coming soon:
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albert1
Carpal Tunnel
Reged: 01/01/07
Posts: 2249
Loc: Southern New Jersey
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I'm looking at an 8" meade 2080 LX5 F6.3 with UHTC. Used and a good price. Can you comment on this scope? Your knoweledge is appreciated. And because I'd like to view the planets, can't I just use a barlow to achieve the desired effect? Thank you.
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jrcrilly
Refractor wienie no more
Reged: 04/30/03
Posts: 30716
Loc: NE Ohio
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Quote:
I'm looking at an 8" meade 2080 LX5 F6.3 with UHTC.
There's an alarm bell; UHTC wasn't introduced until quite a few years after the demise of the LX-5 series. It's much more likely to have either MCOG coatings (which would be OK) or MCSOG coatings (just walk away; you don't want 'em). It's just possible that the very latest ones had EMC coatings (which are very good).
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John C
Battle Cry of Reno
http://www.wadsworthobservatory.com
My Cloudy Nights gallery
AT12RC
AT65EDQ
QSI683WSG-8
Roper Scientific Quantix 6303E "project" camera
mystery EQ mount on the way
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NeoDinian
Experienced Postmaster
Reged: 10/05/05
Posts: 14043
Loc: Rockford Illinois
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To add to what John just said, I would add that if the price is VERY good, and the scope is in good shape (look at the coatings!), then GO FOR IT.. A deal is still a deal. And yes, you can Barlow...
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Neo... (Jeff)
-=-=-=-=-=-=-
10" LX200-GPS/SMT UHTC "Draco"
Rockford, Il.
NeoDinian's Eye on the Sky!
Coming soon:
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BillC
on a new path
Reged: 06/04/04
Posts: 4391
Loc: Lake Stevens, WA, USA
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Butting in where I probably shouldn't . . . again. However, in all this talk, I have seen NOTHING about the size of the secondary obstruction. And that should be one of your primary concerns.
Yes, you can add a Barlow and increase your effective focal length. However, that does NOTHING to decrease the size of the secondary obstruction, which in the 6.3 might be as much as 40%. That creates a hefty loss of contrast on the moon and planets.
Just a thought.
Cheers,
Bill
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William J. Cook, Chief Opticalman, USNR-Ret.
Ophthalmic Tech, Naval Station, Everett, WA
Optical Mechanic, Puget Sound Naval Shipyard
Founder, Amateur Telescope Making Journal
21-year Mgr., Optics Dept., Captain's Nautical Supplies
Optics Mechanic, Ft. Lewis, WA.
Contributing Editor for Numerous Magazines
It's better to be a "has been" than a "never was." But only barely; the pay is about the same!
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firestar
Born to be Mild
Reged: 10/18/06
Posts: 3942
Loc: Cleveland Ohio USA
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You only need to worry about the focal ratio for astrophotography.
A faster scope will be able to gather light quicker,resulting in less tracking error and crisper photos.
Focal length is important,because it determines the useful magnification,for dso"s and planetary detail.
A longer scope will enable more magnification and larger images.
There is no doubt that high magnifications yield beautiful views of the Moon, planets and fine detail in some deep sky objects. However, many objects in the sky are too large to fit into the field of view of a high power eyepiece.
This is where a shorter focal length ota has the advantage.
It can gather wide views of sky albeit with lesser magnification.
You really just need to decide which is more important,planetary detail or wide views.
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Eastlake Ohio
Lots of cheap Asian glass  
Antares 12" Dob,Antares 8" Dob
Meade 8" SCT, Celestron C8 SCT
Zhumell 152 mm F8,Antares 127 mm f9.4
Orion short tube 90 F5.6,Celestron 80 ED F7.5
Imaging Source DMK 21AU04 ccd camera
Stellarvue bv3's with 32,26,23,21,9 mm pairs
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Patrick
Postmaster
Reged: 05/16/03
Posts: 10382
Loc: Franklin, Ohio
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Hi Albert,
Quote:
I'm looking at an 8" meade 2080 LX5 F6.3 with UHTC. Used and a good price. Can you comment on this scope?
You might want to check out Uncle Rod's Used SCT Guide. Lots of good info on used SCT's. Page 11 has info on the 2080 scope you looking at.
Here's another used SCT guide that mentions the 2080 in detail.
I can't address the pros and cons of an f/6.3 system versus an f/10 version other than to say that there are a lot more f/10's out there for what I'm guessing is a good reason..I'm just not sure what it is. Maybe others can comment?
Patrick
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CPC1100;AT66ED;Denk S1;
EdgeHD C8; C6 SCT
6"f/4.8MN ES Comet Hunter
10"f/6 Newt
Vixen GP2;CGEM Mount
Canon 60D;Lodestar Guider
The Lord sits enthroned above the circle of the earth...He stretched out the heavens like a canopy.
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