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A tight double

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#1 btschumy

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Posted 11 August 2004 - 09:29 AM

Last night as I was experimenting with my new binocular mount, I decided I would see how close a double I could split with my Obie 20x90s. From my yard there is a lot of light pollution and the skies were a bit hazy as well. This didn't give me a lot of choices for stars.

After splitting several in the upper teens (arcsec) I needed something tighter. Looking at a double star list I noticed that omicron Ophiuchi was a 10.3" pair with magnitudes 5.4 and 6.9. That seemed a good challenge. Sure enough, when on axis, I could just barely detect the companion sitting next to the primary. I don't think I could do sub-10" unless the components were very evenly matched.

#2 Guest_**DONOTDELETE**_*

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Posted 11 August 2004 - 11:24 AM

I should test my splitting ability with the BT100. It seems to me that doing this is a good "sky to eye" test of all the optics involved. Everytime I go out with the best intentions of doing this, I always get distracted with viewing other heavy bodies and then the time flies.

#3 EdZ

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Posted 11 August 2004 - 12:07 PM

Bill,
for the 20x90s try gamma Delphinus, the tip of the dolphin. 4.5-5.5/9.6"
I've split that one with 20x80s and 16x70s. I can see the elongation with 15x70s.

NW
You will soon have an opportunity to see Mesartim, y Aries, the perfect double at 4.8-4.8/7.8” with components lined up exactly due 0.00 N/S. You should be able to see it at under 25x.

Some examples that might be good targets for higher powered binoculars say 25x to 40x are:

Struve 1121 in the center of M47, 7.9-7.9/7.4".
I split this one in the BT100 with the 24.5mm eyepieces at 25x.
I've also split it easily with Celestron 25x100s.

Struve 953 in Mon at 7.2-7.7/7.1”, just below the Christmas Tree cluster,
I split this one "easily" in the BT100 at 36x with a pair of 17mm Orion Sirius plossls. I've also split it with Celestron 25x100s.
I've seen it elongated but not split with the 20x80 Standards.

also try for:
zeta 7CrB at 5-6/6.3”
95 Herc 5.0-5.1/6.3"

Splitting doubles like these with binoculars is as much a test of your own acuity as it is the resolution of your optics.

edz

#4 btschumy

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Posted 11 August 2004 - 12:36 PM

Ed,

Thanks for the additional tests. I'll see what I can do in the next few days and report back.

#5 jack savard

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Posted 11 August 2004 - 05:04 PM

if you have to split everything like this may be you nead more X power

when I see a global cluster and I do no see the star I use x4 glass ;the one at 10.00 we use for reading ; over my normal glass

or I use my x5 or x8 gloeller magnifier ;I clip it to my glass and that it more power lest field but able to split

I have 25x100 for starting x 25 is good fot split
may be you try whit x2.5

:tonofbricks:

#6 KennyJ

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Posted 11 August 2004 - 05:12 PM

Jack,

I'm sure our resident "professor" Edz appreciates more than most what INCREASED MAGNIFICATION can reap.

So do I.

BUT --personally , I think it more interesting to attempt to establish what is the LEAST magnification AND / OR least APERTURE through which such tight doubles can be resolved.

Kind regards -- Kenny.

#7 Guest_**DONOTDELETE**_*

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Posted 11 August 2004 - 08:32 PM

Thanks for the suggestions EdZ. I'll give them a look.

#8 btschumy

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Posted 11 August 2004 - 10:57 PM

Well I just got in from trying Gamma Delphini (9.6") and 95 Herculis (6.3"). The one in Delphinus was pretty easy for the 20x90s. I could definitely see black in between. However, try as I might, I was unable to convince myself that I was even seeing elongation in 95 Herculis, much less a split. The fact that it was almost at the zenith didn't make it any easier for me either :lol:. I'll revisit it this weekend when I'm out at the Central Texas Star Party.

#9 EdZ

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Posted 12 August 2004 - 07:12 AM

Good work on y Del.

You should not, and probably will not, see a 6.3" double with a 20x binocular. That would mean your visual acuity could see down to 20x6.3 = 126 arcseconds, rare indeed. That one is for the 25x and higher models.

Your next best hope will be Mesartim, y Aries at 7.8". When Orion comes around again, train you gaze on the Trapezium. You should defintely see three and you may see four. Seeing the four separated means you split the closest components at 8.7". These two should pose a significant challenge for any 20x binocular.

edz


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