cpsTN
Pooh-Bah
Reged: 04/26/07
Posts: 1353
Loc: Murfreesboro, TN -- 36N 86W
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With my 8" dob a couple nights ago, I every so slightly split each double pair in Lyra using 200x. Does it normally take this much power? The stars were only about 50* up, in the West.
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Charles Sands
Observing since 12/29/86
8" f/5.9 dobsonian (Zhumell DSH-8), with 8x50 RACI
70mm f/5 achromatic refractor (Orion GoScope)
15x70 Celestron SkyMaster binos
S&T's POCKET SKY ATLAS
Kodak EasyShare Z915 digital camera
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The heavens declare the glory of God;
and the firmament sheweth His handywork
Psalm 19:1
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Clive Gibbons
Mostly Harmless
Reged: 05/26/05
Posts: 14099
Loc: Oort Cloud
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How good was the seeing?
When the air is turbulent, you might have trouble with the double-double.
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A few telescopes of dubious value.
Understanding wife, two curious cats and one sadly departed.
"Semper ubi sub ubi"
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cpsTN
Pooh-Bah
Reged: 04/26/07
Posts: 1353
Loc: Murfreesboro, TN -- 36N 86W
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I never have understood the ratings system for seeing.
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Charles Sands
Observing since 12/29/86
8" f/5.9 dobsonian (Zhumell DSH-8), with 8x50 RACI
70mm f/5 achromatic refractor (Orion GoScope)
15x70 Celestron SkyMaster binos
S&T's POCKET SKY ATLAS
Kodak EasyShare Z915 digital camera
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The heavens declare the glory of God;
and the firmament sheweth His handywork
Psalm 19:1
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Anonymous
Unregistered
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Hi Charles,
As I live just a few hours west of you, I know what you mean about the bad seeing a couple nights back. Monday night, upper-level winds and low-level turbulence here were so bad I had trouble getting any magnification; so like Clive mentioned, that might be why you had trouble.
That said, normally I can regularly split both pairs of Eps Lyra at 80x with my 102mm. Last night was a good night and actually split them at 60x.
I've also noticed over the years I always have to use more magnification in a dob or cat than in a refractor for double stars. Not that refractors are better, but they have no CO's, no diffraction spikes, nor do they usually have coma to contend with. Happy viewing.
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azure1961p
scholastic sledgehammer
Reged: 01/17/09
Posts: 761
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Generally speaking, split with dark space inbetween and a comfortable view is 140x and up. While Steve mentions 80x with a 102mm aperture and then 60x, bare in mind, at 102mm the image has four times LESS the brightness and so glare is reduced considerably.
With 8" 120x to 140x and up is pretty good. At 70x for example the brilliance and irradiating glare is just so overwhelming, its a no go. Can i tell its double - well yes, but it doesnt approach the clean definition of higher magnification when all that light is now spread out some and the details can come forward unpolluted with glare.
Super-low magnifications are a tough call to make as though it were a litmus test of optical-visual standard. The same things that make larger aperture so dandy on finer resolution also have their own baggage of over-brilliance when the lowest mags are used as a rule of thumb on brilliant tight doubles.
My favs - around 140x to 173x thru my 8" newt.
Pete
PS: Oh by the way, really sounds like your seeing was terrible or your mirror wasnt adjusted to the air temp enough . In decent seeing though with 200x... oh you'll see the split alright. It'll still be a fairly delicate observation as the seeing and the subject itself are so close to the wire, but , its there to be had when all else accomodates.
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Edited by azure1961p (09/02/09 07:01 PM)
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walt r
Post Laureate
Reged: 02/13/07
Posts: 3523
Loc: Doylestown, PA
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I've found that in my larger aperture scopes dimming Eps Lyra with an ND filter can make a huge difference.
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Walt
Obsession 18" f/4.45 #1370 AN/SC
MK67 Deluxe 6" f/12 Mak-Cass, Super Polaris GEM, JMI MicroMax DSC
DIY 60mm f/6 Achromat
Cookbook 245 CCD
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Anonymous
Unregistered
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You are so right with your comments. Low power isn't a judge of optical quality at all; for me I use it as a sample of the night's seeing quality.
I'll agree with both comments here about glare as it really can make it difficult on doubles like Sirius & Antares. But when I had my dobs, it seemed like the spider's diffraction spikes and bloated airy disks are what got in my way more, making me use higher mags. Doesn't mean I don't like looking at doubles and open clusters with dobs, they're still down-right beautiful.
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David Knisely
Postmaster
Reged: 04/19/04
Posts: 8778
Loc: Beatrice, Nebraska
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Quote:
I never have understood the ratings system for seeing.
Generally, seeing is more properly rated in arc seconds. This is the amount of disturbance which a star's diffraction disk might get blurred into. Usually, seeing of an arc second or better is considered pretty good, while 0.5 arc seconds is very fine and somewhat rare. I use some standard closely-separated double stars as well as the appearance of my scope's diffraction pattern to judge the seeing. I generally get between one and three arc second seeing around here (except the other night, when it went down to close to 0.5 arc seconds at times). Then, there is the Antoniadi seeing scale:
Antoniadi Seeing Scale
It is more aperture dependent than absolute, and is a little subjective, but is still better than the unqualified numerical (i.e. one to ten or one to five) seeing scales many people tend to use. 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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cpsTN
Pooh-Bah
Reged: 04/26/07
Posts: 1353
Loc: Murfreesboro, TN -- 36N 86W
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Seeing so many people state that they could split the DD with small apertures, I knew it couldn't be as hard as I was making it.
In my OP, I meant "EVER so slightly", not "EVERY so slightly".
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Charles Sands
Observing since 12/29/86
8" f/5.9 dobsonian (Zhumell DSH-8), with 8x50 RACI
70mm f/5 achromatic refractor (Orion GoScope)
15x70 Celestron SkyMaster binos
S&T's POCKET SKY ATLAS
Kodak EasyShare Z915 digital camera
--------------------
The heavens declare the glory of God;
and the firmament sheweth His handywork
Psalm 19:1
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Clive Gibbons
Mostly Harmless
Reged: 05/26/05
Posts: 14099
Loc: Oort Cloud
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Quote:
I never have understood the ratings system for seeing.
Take a look at this website which shows a good representation of the Pickering system.
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A few telescopes of dubious value.
Understanding wife, two curious cats and one sadly departed.
"Semper ubi sub ubi"
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Ziggy943
Carpal Tunnel
Reged: 08/11/06
Posts: 1833
Loc: Utah
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At 200x both pairs of E-Lyrae should be well split. I normally like to go to about 210, so basically the same. I prefer the higher mags on double stars. Seeing doesn't have to be all that good to split these pairs but having it high is a definite advantage.
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May your skies always be clear,
Ziggy
www.slas.us
4" Mak
#1, 160mm F8 TEC (born 1-18-2007, 27 lbs, 45.5" long), on AP900
6" F17.5 (D&G lens) (first light 6-7-2008)
9" F/14.9 Alvan Clark (1915), on Byers 812
14.25 F/5.5 Newt in a roll off observatory
Others, that have come and gone
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azure1961p
scholastic sledgehammer
Reged: 01/17/09
Posts: 761
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One thing that seems to get not enough mentioning isn't just the size of the seeing like 1" or less and so on, but the speed of the seeing. There are a lot of nights Ive "split" .5 stars through an 8" aperture. But the seeing wasnt phenomenal it was just SLOW enough that i could pick out the details in time. In those cases it was 1-2 or 2-3 o n a 1 to 5 scale with 1 being the best. Even in the faster seeing of the cooler to colder months, like planetary details, success can be had if you can match the speed of the seeing with your eye-brain. Ofcourse, then theres all out failure seeing that no quickness of eye-brain can counter.
Pete
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Don Allen
sage
Reged: 07/07/05
Posts: 416
Loc: Charleston, SC
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I use the zoom to give a good view. The 7mm does not give my 53 year old eyes a good solid dark space split so I am going between 150x and 175x.
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Don
SV 80S S/N 0043
LXD75
35 Pan, 17T4, 7 Nag, 3-6 Nag Zoom
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hfjacinto
Almost got me
Reged: 01/12/09
Posts: 3021
Loc: Union,NJ
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On my 9.25 I need at least 180X to split the double double. At 300X I can see a clear separation and at 500X on a super clear night I can see a wide separation.
Remember this is NJ an its rare that I have great nights of seeing.
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Celestron 9.25 w/FeatherTouch Focuser, ASGT Mount
Meade SN6 w/Moonlite Focuser, LXD75 Mount
Orion EON 80 MM APO Refractor
5,6,9 MM Zhummel Planetary 17 MM Nagler T4
31,36 MM Hyperion 15,19,23 MM Axiom LX
6.7,8.8 MM Meade UWA & 11,13 MM Nagler T6
Planetary, OIII and Narrowband Filters
Thousand Oaks Dew Control w Kendrick Heaters
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Hrundi
Pooh-Bah
Reged: 02/06/08
Posts: 1490
Loc: Estonia
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I've done it at x50 in my 12", but sometimes it's tenuous at x120. I've had nights where I've not managed to do anything with the double double. These nights end up being dominated by galaxies.
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azure1961p
scholastic sledgehammer
Reged: 01/17/09
Posts: 761
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Its funny, or a serious reality check on those nights when you wing by this double and its cut clean and stark and then you know the seeing gods are smiling on you.
Pete
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Erik Bakker
professor emeritus
Reged: 08/10/06
Posts: 688
Loc: Haren, The Netherlands, Europe
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Hi Charles,
Like others said, 80x should do the trick, although easier around 140x and up. Keep in mind that reducing glare is an issue in scopes 7" and up. In my Q7 I prefer 180x -500x for tight doubles, never under 180x. Then again, the DD is easy, not difficult.
CS,
Erik
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Visual astronomer, main instruments:
Fully mounted Questar 7 P-BB
Vixen FL 70S f/8 fluorite
on Gitzo 224 / Manfrotto 501
Sets of Brandon, TeleVue, Celestron and Zeiss eyepieces
Leica 8x32 Trinovid
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dpwoos
sage
Reged: 10/18/06
Posts: 219
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My seeing isn't all that hot, and I can't remember the last time it was so bad that I couldn't get a decent split at less than 150x. Maybe you haven't done a lot of multiple star observing, and so you haven't developed this observing skill and don't know what to expect? I think that the other (likely) possibility that no one has mentioned is that your eyesight is the problem. There are a growing number of folks in my astro club who have trouble splitting the closer doubles/triples. The best way to diagnose this is to observe with others, and compare what they see to what you see.
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Illinois
professor emeritus
Reged: 12/18/06
Posts: 729
Loc: near Chicago, Illinois USA
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I use my Orion 80mmED refractor and I can see Double Double easily on 120 power. Not easy on my 10" Dobsonian until around 200 power! I think that coma in dobsonian that you need little higher power to able to see very close double stars!
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Astronomer since 1975!
Orion 80mm ED refractor and
iOptron CubePro mount
Meade 16" Lightbridge Dobsonian
Orion 10" SkyQuest Classic Dobsonian
Tele Vue Eyepieces
Canon EOS XS 1000D
Orion Planetary 5 mm and
Orion Expanse Wide-Field 6mm eyepiece
4.5" F5 Reflector since 1982!
Orion Narrowband and SkyGlow filters
Member of IDA, let's fight light pollution!
Old Edmund 6"F8...donated to cousins
Super Polaris C8...donated to Byron Observatory in Illinois
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David Knisely
Postmaster
Reged: 04/19/04
Posts: 8778
Loc: Beatrice, Nebraska
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Quote:
I use my Orion 80mmED refractor and I can see Double Double easily on 120 power. Not easy on my 10" Dobsonian until around 200 power! I think that coma in dobsonian that you need little higher power to able to see very close double stars!
No, most of this is due to atmospheric blurring and the brightness of the stars as seen in the larger scope. The larger aperture resolves the "seeing" while the smaller one merely has most of the seeing masked by the scope's lower resolution. On a really good and stable night with my 10 inch properly cooled, I have little trouble telling the double-double has four stars at powers from about 57x on up, although they tend not to be a really clean split until something over 150x. 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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