Bowmoreman
Clear enough skies
Reged: 09/11/06
Posts: 9062
Loc: Bolton, MA
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Quote:
Jay, I think you might have spilled some white out on your CSC.
Yeah, like Jay's the ONLY one... Mine pretty much, ahem, [insert large sound opposite of blowing out] 
Course if mine were BLUE tonight, I'd still be in...
Go SOX!!!!!!!!
Jay: you've got me "curious" to experiment as well; I can try by building an aperture mask, and playing with the variables of magnification and EP...
The Pleiades make a nice comparison target, as does the double/double...
hmmm
Clear skies (to all who aren't watching the Sox!) 
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Dave
MI250 SBS mounted: C11Hyperstar,FSQ106ED,TOA130NFB;Lunt60THaB1200FT/DS50
Visual:DM6, XT10i w/ZambutoMirror,RTP
EP: 31T5, Ethos (21,17,13&8),10XW,5XW,3.5XW; Paracorr T1
MallincamColorHyper+,QSI583WS,QHY8
SBIG STV eFinder
Denk II: (2x24Pan,2x10XW)
Gerbings Heated clothes, Wilder Skies Observatory (BYO#90), Speco9"Monitor
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Bowmoreman
Clear enough skies
Reged: 09/11/06
Posts: 9062
Loc: Bolton, MA
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Quote:
Quote:
I'm not really interested in the technical aspects with magnification and exit pupils, etc., but more about the perceived quality of the view. I appreciate that the stars in the Double Cluster sparkle in my 80mm against their black background, but they're far less satisfying than the pure quantity of stars against a much lighter background in my 12". The detail's there even though the overall contrast is not.
Jay: If you want to know why there are percieved differences in the view so make the view more pleasing, then it is necessary to understand these concepts and how they apply.
As far as "contrast" goes, there are accepted definitions in the astronomy world, we need to stick with those definitions so we are all on the same page.
As far as I can see what you would like is a dark/dim background of the 80mm and the brightness of the 12inch scope when viewing targets like the double-cluster from your backyard. There is no easy solution to this simply because of the technical issues, the brighter view of the big scope shows more stars and shows more light pollution. With a small target, then one simply increases the magnification and the sky is blacker and there are more stars to see. With a big target, one cannot do this and see the entire target in the same field of view.
But here is where some understanding of the technical details can help one get the good views. Widefield eyepieces minimize the exit pupil for a given true field of view. This is one reason they are popular with observers using big, fast telescopes.
Looking up the size of the double cluster in Perseus, it about 0.75 deg. In your 12 inch F/5 Newtonian, the 13mm 100degree AFoV Ethos will provide a 0.85 degree TFoV, nicely framing the double-cluster while keeping the exit pupil to a reasonably dark 2.6mm.
I like to get the good pleasing views. These do not just happen accidentally. They happen partly because I understand something of the basics of brightness, aperture, focal ratio, aberrations etc so I can optimize the view of a given target by choosing not only the right telescope but also the right eyepieces. These understanding are part of what I call "observing skills" that one develops as one progresses.
jon
Jon: you couldn't be MORE right on the double cluster with the Ethos in a f5 (or 4.7) dob...
that was my first target, and the framing, the darkness (Jay's "contrast") and the view were spectacular... I was totally hooked.
This thread is a revelation to me; thanks for starting it, Jay, and thanks to everyone else for the contributions!!!
Now if I could just get some anti-whiteout for my CSC (and have the Sox sweep Colorado) and THEN get some clear skies!
Clear skies
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Dave
MI250 SBS mounted: C11Hyperstar,FSQ106ED,TOA130NFB;Lunt60THaB1200FT/DS50
Visual:DM6, XT10i w/ZambutoMirror,RTP
EP: 31T5, Ethos (21,17,13&8),10XW,5XW,3.5XW; Paracorr T1
MallincamColorHyper+,QSI583WS,QHY8
SBIG STV eFinder
Denk II: (2x24Pan,2x10XW)
Gerbings Heated clothes, Wilder Skies Observatory (BYO#90), Speco9"Monitor
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jayscheuerle
Post Laureate
Reged: 01/16/06
Posts: 4675
Loc: S. Philadelphia, PA
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Quote:
In other words (and sorry to repeat myself): if the views in a large scope seem more washed out, you are possibly not using enough magnification (and it *is* easy to fall into that trap if you're used to another scope - we all have our habits), and if for some reason you can't increase magnification (seeing, framing,...) you can simply use a filter to get rid of the "troublesome" light to match the light gathering of the smaller scope -- and keep a better resolution.
This is something to play with! Between the LP in the city and our poor East Coast U.S. seeing, my magnification falls apart before my background ever gets close to dark. Of course, with streetlights all around me, dark adaptation is out of the question without a darkened hood that connects my head to the focuser. 
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Fight indignorance!
120ED, 12" f/5 Green Goblin, 6" f/5 Eero2, 4.5" f/8 PortaBowl, 8" f/5 Big Red Ed.
The PortaBowl-a $100 4.5" f/8 ball-scope YOU can build!
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Stelios
Pooh-Bah
Reged: 10/04/03
Posts: 1484
Loc: West Hills, CA
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I'm highly suspicious of the aberrator program simulations. This based on some other images published from time to time here on CN, which conflict with my observing experience. Too many things can screw up such theoretical results, including quality of the optic, collimation and seeing.
My advice would be to anyone here trying to form a conclusion from rhetoric, no matter how well reasoned: SEE FOR YOURSELF.
Go to a star party. Look through a quality say 5" APO at planets, and then through a few 10" or 12" DOBs of the commercial variety. Then make up your mind which of *THOSE* images you'd like to see. Because that's what you will be seeing, not what someone deduces you *should* be seeing.
No, larger aperture does not mean less contrast. This theoretical answer has nothing to do with whether you'll enjoy the views better. Perhaps if you raise the volume to the absolute maximum on your stereo, you'll be able to hear some extra detail. So what. Go back and lower it to where you actually like the music.
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APM/TMB 115/805 APO
9.25S - GT
Naglers: 17T4, 13T6, 3-6 zoom
UWANs: 28mm, 7mm
Pentax 10XW, 10mm Radian
Misc EP: 50mm Parks, 42mm GSO, 2x TV Barlow
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Jon Isaacs
Postmaster
Reged: 06/16/04
Posts: 32442
Loc: San Diego, California
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Hi:
A few thoughts:
- Sky darkness for any given eyepiece is not a function of aperture but rather of focal ratio. This is because the exit pupil depends on focal ratio. For any given magnification, it is a function of the aperture/light gathering.
- A good way to see the importance of the exit pupil and magnification is with a Zoom eyepiece. Last Night I was using a 22mm-7.3mm Zoom. This is a factor of 3 in magnification and a factor of 9 in brightness, it is dramatic to watch the image darken as one zooms in.
- Jay is finding that there are trade-offs, the small telescope gives a dark sky but understandably does not show as many stars. This is expected, there is no one perfect telescope for all objects, there is not even one perfect telescope for any one obect. This is one reason why often more experienced observers will have 2, 3, 4 or more telescopes.
- Last night I was figuring that I had probably enjoyed viewing the Double Cluster in Perseus more than a thousand different nights and I was trying to think back as to my most favorite view. I have had lots of great views but I think probably the best have been 30+ year old 6 inch F/8 Newtonian using either a 32mm Plossl or a 24mm TV Widefied. It has enough aperture to see many faint stars, at F/8 it has a well corrected coma free field of view and it works nicely with simple eyepieces.
But I have had many, many wonderful views of the double cluster, whether from my back yard or the dark skies, with a 60mm refractor or a 16 inch Newtonian, each is different in it's own way, like looking at a painting from different angles, in different lighting, from far back or up close.
Just some stuff to think about...
Jon
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jayscheuerle
Post Laureate
Reged: 01/16/06
Posts: 4675
Loc: S. Philadelphia, PA
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And this hobby provides nothing if not stuff to think about.
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Fight indignorance!
120ED, 12" f/5 Green Goblin, 6" f/5 Eero2, 4.5" f/8 PortaBowl, 8" f/5 Big Red Ed.
The PortaBowl-a $100 4.5" f/8 ball-scope YOU can build!
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FirstSight
Postmaster
Reged: 12/26/05
Posts: 7676
Loc: Raleigh, NC
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Quote:
And this hobby provides nothing if not stuff to think about.
And lots of time to think about all that stuff on cloudy, rainy nights. That there's lots of stuff to think about is a really great thing because there's lots and lots of cloudy, rainy nights to provide enough time for all that thinkin' there is to do..
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Chris M., aka "First Sight"
Orion XT12i Dob with Moonlite CR-2 focuser
TeleVue NP-101 refractor
WO Megrez 90 refractor
UniStar Light mount
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jayscheuerle
Post Laureate
Reged: 01/16/06
Posts: 4675
Loc: S. Philadelphia, PA
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Quit poking fun at my CSC... 
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Fight indignorance!
120ED, 12" f/5 Green Goblin, 6" f/5 Eero2, 4.5" f/8 PortaBowl, 8" f/5 Big Red Ed.
The PortaBowl-a $100 4.5" f/8 ball-scope YOU can build!
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rickertk
sage
Reged: 06/14/07
Posts: 244
Loc: Outer Philadelphia suburbs
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Jay, just out of curiosity, how much observing do you do in the evening vs. the early morning? Looking at Saturn in the early mornings, it often seems like the views are much steadier than of say Jupiter in the evenings (and this is when Saturn was still pretty low in the sky). CSC generally seems to agree with that. I'm not sure how much of that will translate into your more urban setting, but it might be worth trying sometime as we get into winter.
Keith
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Oberwerk 11x56
Orion 8XTi
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