ESHall
member
Reged: 05/26/09
Posts: 24
Loc: Mufreesboro, TN
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Hello to all. I have a question about my viewing of Pleiades. I was observing with a 9.25 SCT using different eyepieces ranging from 59x to 242x. What I saw was a few dozen of the brighter stars but none of the star field behind them. The field behind the brighter stars was black. I could look at it with my 10x50 Binoculars and even my 8x50 Finderscope and see the brighter stars sitting on a rich star field. What am I doing wrong? I'm still a novice with the SCT and DSO's but still learning. Any advise would be appreciated.
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Ed
CPC9.25 XLT
Jason 60x910mm (1984 vintage)
10x50 Binoculars
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jrbarnett
Eyepiece Hooligan
Reged: 02/28/06
Posts: 4349
Loc: Petaluma, CA
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I don't think you're doing anything wrong. Rather, I think you're being confronted with a sad fact about long focal length instruments - narrow fields of view.
Figure your 10x15 binoculars are taking in over 5 degrees of sky. In contrast, your 9.25" SCT at 59x with a 43 degree AFOV shows less than 3/4 of a degree. The area of sky captured in the 10x50s is about 45 time larger. The 9.25" SCT shows thousands more stars when you sweep it through the same area captured in a single binocular field, except that it cannot do it all at once like the binoculars can.
Binoculars are like you can't see the trees for the forest. The scope is like you can't see the forest for the trees. 
Regards,
Jim
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"I do not know what I may appear to the world; but to myself I seem to have been only like a boy playing on the seashore, and diverting myself in now and then finding a smoother pebble or a prettier shell than ordinary, whilst the great ocean of truth lay all undiscovered before me."
- Sir Issac Newton
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skyward_eyes
Carpal Tunnel
Reged: 12/12/06
Posts: 2105
Loc: Arizona
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Nothing wrong with anything your doing or your scope. The problem is your scope is not for wide field views, with its long focal length it has a narrow field of view. To get around this some of my friends have an Orion Short Tube 80 refractor on top of their C-8s and C-11s for wide field views allowing them to have both worlds, wide field viewing and narrow field with the C-11 or C--8. With the right mounting hardware you can piggy back a short tube 80mm refractor atop your C-9.25
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ensign
member
Reged: 12/16/08
Posts: 41
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I, too, am something of a newbie so you may want to verify this recommendation with others who are more experienced. But, as I understand it, you can get a focal length reducer for a SCT that will reduce its focal ratio to 6.3. I believe that this will also have the effect of significantly widening the true field of view for any given eyepiece.
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- Mike
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Modified 10" Sky-Watcher Dob
William Optics Megrez 110/EZTouch
Nagler Type 4 - 12,17,22
Pentax XW - 10,7
William Optics UWAN 28
Siebert Observatory class 40
Other assorted items too numerous to mention
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Ptarmigan
Carpal Tunnel
Reged: 09/23/04
Posts: 2366
Loc: Arctic
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It's the FOV. A binocular has wider field of view than a telescope. I am glad you got to see the Pleiades. Great object! 
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Ptarmigans=Cute and Cuddly
Meade Starfinder 8
Nikon 10x50
Rebel XT
Edited by Ptarmigan (07/11/09 08:13 PM)
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94bamf
professor emeritus
Reged: 12/15/08
Posts: 722
Loc: Kansas City,Mo
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I don't know how many degrees wide Pleiades is, but I would imagine a focal reducer and a widefield 2 inch eyepiece would really widen the true FOV that your scope could see.
For a pretty reasonable cost, with This and This, you should be able to get around 1.85 degree true FOV assuming no vignetting, which is more than twice as wide as a 1.25 inch 40mm plossl... Of course you will also need a 2 inch diagonal..
Edge correction might not be great with the 42mm GSO superview and the focal reducer, you could always get a better eyepiece, just plan on spending a fair amount for quality long focal length 2 inch eyepiece..
Ken
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Telescopes:
Celestron C6 SCT on CG4 mount
Skywatcher 8 inch F/5 Newt on a GEM
Celestron 8 inch Starhopper Dob
Celestron Oynx 80ED
Celestron C130 Mak
Celestron C102HD
Binoculars:
Nikon 7x35 Action
Nikon 7x50 Action
Zen Ray Summit 10x42
Celestron 10x42 Noble
Orion 10x50 Scenix
Celestron 10x50 Noble
Pentax 12x50 PCF WP II
Celestron 15x70 Skymaster
Oberwerk 20x60
Zhumell 20x80
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AlanK
professor emeritus
Reged: 01/26/07
Posts: 512
Loc: Auckland, New Zealand
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It's about 2 degrees (4 full moon diameters) wide.
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Clear skies!
18 inch f4.5 Obsession #1637
12 inch f5.4 reflector
Just another frozen astronomer
Kumeu Observatory
Auckland NZ
7,276 deep sky objects incl 4,670 ngcs
Who dares - observes!
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David Knisely
Postmaster
Reged: 04/19/04
Posts: 8290
Loc: Beatrice, Nebraska
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Quote:
I don't know how many degrees wide Pleiades is, but I would imagine a focal reducer and a widefield 2 inch eyepiece would really widen the true FOV that your scope could see.
For a pretty reasonable cost, with This and This, you should be able to get around 1.85 degree true FOV assuming no vignetting, which is more than twice as wide as a 1.25 inch 40mm plossl... Of course you will also need a 2 inch diagonal..
Edge correction might not be great with the 42mm GSO superview and the focal reducer, you could always get a better eyepiece, just plan on spending a fair amount for quality long focal length 2 inch eyepiece..
Ken
With the Celestron 0.63 focal reducer/corrector and my 40mm Mk-70 Konig (46mm field stop), I can get very close to two degrees of true field of view in my NexStar 9.25, but the outer portions of the field are quite strongly vignetted. The vignetting became noticable at about 0.75 degrees away from the center of the field, which is a field of view diameter of about 1.5 degrees. That is barely enough to get most of the Pleaides in the picture, but I still greatly prefer the view of the cluster in my 80mm f/5 refractor (3.9 degree true field) or my 100mm f/6 refractor (4.39 degree true field of view). Clear skies to you.
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David W. Knisely
Hyde Memorial Observatory
http://www.hydeobservatory.info
Prairie Astronomy Club
http://www.prairieastronomyclub.org
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ESHall
member
Reged: 05/26/09
Posts: 24
Loc: Mufreesboro, TN
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Thanks for all of the good advice. Is it only because Pleiades is so large that the FOV is a problem? Will other DSO's also be a problem with the 9.25 SCT? Also when I was viewing Pleiades why did I not see what appeared to be thousands of stars behind the few dozen brighter ones? I moved the scope around because I thought I didn't have Pleiades in my EP but never did see any stars behind the brighter ones. Is that normal? Does the narrow field of view also affect the depth perception? Thank for all your help.
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Ed
CPC9.25 XLT
Jason 60x910mm (1984 vintage)
10x50 Binoculars
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JakeSaloranta
sage
Reged: 09/18/08
Posts: 238
Loc: Sisu, Sauna, Sibelius...
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Quote:
Is it only because Pleiades is so large that the FOV is a problem?
Yes. Best views of Pleiades come with things that provide a large field of view. Such as a pair of binoculars. M45 looks amazing with 15x70 binoculars but looses a lot of its beauty when viewed with an 8" dobson @ 38x
Quote:
Will other DSO's also be a problem with the 9.25 SCT?
Deep sky objects that are scattered such as huge open clusters will always require very large field of view or are best just viewed with small binoculars. So if you use big magnification on objects that you shouldn't - you better be ready to pay the price for it 
Quote:
Also when I was viewing Pleiades why did I not see what appeared to be thousands of stars behind the few dozen brighter ones?
M45 has roughly 100 (actual) members so it is not THAT rich.
Quote:
I moved the scope around because I thought I didn't have Pleiades in my EP but never did see any stars behind the brighter ones. Is that normal?
Seeing fainter stars behind a glare of a brilliant star is always problematic so I'd say it is normal.
Quote:
Does the narrow field of view also affect the depth perception?
The more magnification you have on telescope the fainter stars you should see.
/Jake
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Magellan
professor emeritus
Reged: 01/26/06
Posts: 696
Loc: Dartmouth, NS Canada
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the only thing interesting to me about M45 is trying to detect the nebula. I have detected the nebula around Merope. I think the designation is NGC 1435.
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Jeff D
Skywatcher 12" Collapsible Dobsonian
Coulter Odyssey 2 8" Dobsonian
Celestron Nexstar 102SLT
Antares EQ-5 Mount
Celestron Skymaster 15x70
Messier Certificate Count: 110/110
RASC's Finest NGC: 1/110
St. Croix Observatory RASC-Halifax
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arpruss
scholastic sledgehammer
Reged: 05/23/08
Posts: 858
Loc: Waco, TX
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One option for such large and bright objects is to have a nice, big finder attached to the scope. Saturday night, I was showing M7 to a couple at our local public star night. It obviously didn't fit in the one degree field which was all I had available on my 13" (I eventually need one of those 42mm EPs), but it showed up nicely in the 13x68 finder I had just made (with a $12 lens from MASILMW, and a 27mm Kellner that I wasn't using anymore), so I had one person look through the main scope at a zoomed-in view, while the other looked through the finder at a view of the cluster as a whole.
Talking of the nebula around M45, is the glow of it localized around the brighter stars, or is it spread out evenly between them? I did once see glow around the brighter stars with my 8", but suspect it of being an artifact.
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Coulter Odyssey 13.1" split-tube
Coulter Odyssey 8"
Home-made 7.8" F/4 dobsonian travel scope
Home-made 68mm F/5.3 achro (typically used as finder on 13.1")
Skymaster 15x70
BPTs4 8x30
32mm Plossl, 30mm Rini, 27mm Kellner, 13mm Hyperion, 6mm TMB/BO Planetary, Owl 2X Barlow
Palm TX with AstroInfo and RescoViewer
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David Knisely
Postmaster
Reged: 04/19/04
Posts: 8290
Loc: Beatrice, Nebraska
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Quote:
One option for such large and bright objects is to have a nice, big finder attached to the scope. Saturday night, I was showing M7 to a couple at our local public star night. It obviously didn't fit in the one degree field which was all I had available on my 13" (I eventually need one of those 42mm EPs), but it showed up nicely in the 13x68 finder I had just made (with a $12 lens from MASILMW, and a 27mm Kellner that I wasn't using anymore), so I had one person look through the main scope at a zoomed-in view, while the other looked through the finder at a view of the cluster as a whole.
Talking of the nebula around M45, is the glow of it localized around the brighter stars, or is it spread out evenly between them? I did once see glow around the brighter stars with my 8", but suspect it of being an artifact.
The brightest portion of the nebulosity around the Pleiades is the so-called "Merope Nebula". It extends around and for about 20 arc minutes to the south of the star. I have seen it in my 100mm f/6 refractor as a very dim broad fan of light. The other nebulosity is somewhat fainter and more difficult, appearing as just a diffuse glow around some of the stars. There is a bit of a glow around Maia which has a dim extension to the north towards Asterope, but it is not as easy to see as the Merope nebula. Clear skies to you.
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David W. Knisely
Hyde Memorial Observatory
http://www.hydeobservatory.info
Prairie Astronomy Club
http://www.prairieastronomyclub.org
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Magellan
professor emeritus
Reged: 01/26/06
Posts: 696
Loc: Dartmouth, NS Canada
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David,
Would a UHC or OIII filter help with the nebulosity?
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Jeff D
Skywatcher 12" Collapsible Dobsonian
Coulter Odyssey 2 8" Dobsonian
Celestron Nexstar 102SLT
Antares EQ-5 Mount
Celestron Skymaster 15x70
Messier Certificate Count: 110/110
RASC's Finest NGC: 1/110
St. Croix Observatory RASC-Halifax
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David Knisely
Postmaster
Reged: 04/19/04
Posts: 8290
Loc: Beatrice, Nebraska
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Quote:
David,
Would a UHC or OIII filter help with the nebulosity?
Although I have seen the Merope nebula with the Lumicon UHC using a 10 inch Newtonian, it is better shown in a broad-band filter like the Lumicon Deep-sky. The UHC is just a little on the narrow side for most reflection nebulosity, as the light from the nebula covers a wide part of the visual spectrum rather than just a few emission lines (the OIII would be even worse than the UHC). Clear skies to you.
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David W. Knisely
Hyde Memorial Observatory
http://www.hydeobservatory.info
Prairie Astronomy Club
http://www.prairieastronomyclub.org
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TimD
scholastic sledgehammer
Reged: 02/16/05
Posts: 908
Loc: CA USA
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I like the Pleadies best in my 25x100 bino's. Definetely a FOV issue with any scope of long F Length and narrow FOV
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Takahashi TSC 225
WO Megrez 102
Meade ETX 90, ETX 125
Meade LX90
Classic Orange tube C14, C90, C5+
Etc,Etc,Etc!!
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Hrundi
Pooh-Bah
Reged: 02/06/08
Posts: 1249
Loc: Estonia
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Pleiades is strictly a finderscope object for me.
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Tony Flanders
Post Laureate
Reged: 05/18/06
Posts: 3469
Loc: Cambridge, MA, USA
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Quote:
Thanks for all of the good advice. Is it only because Pleiades is so large that the FOV is a problem? Will other DSO's also be a problem with the 9.25 SCT?
A few other DSOs are too big to fit in your scope's FOV, but not all that many. And some of the ones that are too big -- notably the Veil and the Andromeda Galaxy -- are very, very fine when viewed piecemeal in multiple fields of view. In fact, I prefer them that way.
Having said that, a small, richest-field scope or a good pair of binoculars would be a wonderful complement to your SCT. Not surprisingly, the objects that are too big to view with your scope happen to include some of the very finest in the sky. The Pleiades being a prime example.
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Tony Flanders
First and foremost observing love: naked eye.
Second, binoculars.
Last but not least, telescopes.
And I sometimes dabble with cameras.
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