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jrbarnett
Eyepiece Hooligan
*****

Reged: 02/28/06

Loc: Petaluma, CA
Re: My tale of Trapezium F - finally new [Re: mikey cee]
      #5721335 - 03/08/13 10:34 PM

That's odd. I'd figure the spot size would be just as small in a 10" or 12" Dob, and I've never had any trouble with E or F in such scopes. In fact, I find it pretty easy in any scope down to 4" so long as it has decent optics and seeing cooperates.

Regards,

Jim


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jrbarnett
Eyepiece Hooligan
*****

Reged: 02/28/06

Loc: Petaluma, CA
Re: My tale of Trapezium F - finally new [Re: bhuloka]
      #5721365 - 03/08/13 11:09 PM

"So aperture does play a big role here."

Not really. None of these are particularly tight splits, so resolution is irrelevant. The issue with targets like Sirius B and Trapezium E and F is suppression of glare and stray light control. Quality and effectiveness of baffling, not aperture, are key with these targets. A high quality small scope (3" to 4") will have little problem with any of these targets. Heck, a good 80mm handles Sirius B at a mere 70x. Trapezium E and F are easy in a quality 4-incher at just over 100x. Often a larger scopes, and also an obstructed scope, have considerably more difficulty with these targets due to reduced contrast, increased scatter and excessive brightness and glare. Seeing is important too, and larger scopes suffer worse under poorer seeing - another indication that aperture may be the OPPOSITE of what is required on these targets on some nights.

Perhaps the Hubble just has considerably better contrast than the 8" SCT? 8" SCT have monster COs and even with (impossibly) perfect optics, can't achieve diffraction limited system performance. I'll bet that 16-incher has a much smaller CO than the C8, and accordingly a higher potential system Strehl and less scatter.

Regards,

Jim


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azure1961p
Postmaster
*****

Reged: 01/17/09

Loc: USA
Re: My tale of Trapezium F - finally new [Re: nirvanix]
      #5721418 - 03/09/13 12:03 AM

Quote:

Good idea Pete. Right now I have a little 50mm fan at the back of my 10" dob and I don't run it during observing because of vibration. The 120mm fan will move much more air and do it with less vibration.




Lol well if the 50mm is shaking your system the 125mm will too. I don't know why I've been so lucky with the lack of vibration . The tube is 6' long so that's a dampening effect I guess. Try lower voltage to bring the shakes down. I will say I don't run any fan at its rated voltage - its too much power to say nothing of the noise. Try different rubber bands .

Good luck Nirv.

Pete


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buddyjesus
Carpal Tunnel
*****

Reged: 07/07/10

Loc: Davison, Michigan
Re: My tale of Trapezium F - finally new [Re: azure1961p]
      #5721550 - 03/09/13 03:04 AM

Today spent some time in my darkened basement with an artificial star so I could rotate my crown to find the point of least astigmatism in my achromat.

Tonight was above average seeing for Michigan. I used a 9mm K eyepiece in my 4" scope. E was usually there and definitely confirmed with less than one minute of observation. CF sure looked elongated, but after ten minutes of staring I was without definitive separation let alone confirmation.

I know this is brought up every year but it is bothering me more this year than in the past. Who gave the stars the wrong lettering? Isn't the brightest one supposed to be the A? ugh. Always some exception to the rule.


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Bonco
Post Laureate
*****

Reged: 04/17/06

Loc: Florida
Re: My tale of Trapezium F - finally new [Re: fred1871]
      #5722541 - 03/09/13 04:03 PM

Fred from Australia is spot on. Good explanation.
Thanks, Bill


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Bonco
Post Laureate
*****

Reged: 04/17/06

Loc: Florida
Re: My tale of Trapezium F - finally new [Re: buddyjesus]
      #5722549 - 03/09/13 04:09 PM

Quote:

Today spent some time in my darkened basement with an artificial star so I could rotate my crown to find the point of least astigmatism in my achromat.

Tonight was above average seeing for Michigan. I used a 9mm K eyepiece in my 4" scope. E was usually there and definitely confirmed with less than one minute of observation. CF sure looked elongated, but after ten minutes of staring I was without definitive separation let alone confirmation.

I know this is brought up every year but it is bothering me more this year than in the past. Who gave the stars the wrong lettering? Isn't the brightest one supposed to be the A? ugh. Always some exception to the rule.




I'm not sure CF would ever look elongated. Because of the magnitude difference you must have sufficient magnification to create black space between the stars. Best wishes, Bill


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buddyjesus
Carpal Tunnel
*****

Reged: 07/07/10

Loc: Davison, Michigan
Re: My tale of Trapezium F - finally new [Re: Bonco]
      #5722612 - 03/09/13 04:38 PM

i can definitely say I didn't see black space. I wasn't fully convinced about elongation either since I couldn't even pick a most likely position angle.

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WRAK
scholastic sledgehammer


Reged: 02/18/12

Re: My tale of Trapezium F - finally new [Re: buddyjesus]
      #5723393 - 03/10/13 05:35 AM

If +11.6mag STF748F would be a single star without nebula you would be able under else perfect conditions so resolve it with a 60mm scope as the TML for 60mm is theoretical +11.6mag.
Given that F is near glaring C and within a nebula then under not so perfect conditions (Pickering 7, NEML 4.5, M42 below 45 altitude, some haze ...) I think it also impossible to resolve it with a 100mm scope with a theoretical TML of +12.7mag as the TML-loss due to these conditions is certainly larger than 1.2mag.
With some more light pollution as it usual near or on the fringe of big cities means NEML about +3mag even a 140mm scope will no longer resolve a +11.6mag star regardless if double or not and certainly not in competition with a glaring primary.
Wilfried


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fred1871
professor emeritus


Reged: 03/22/09

Loc: Australia
Re: My tale of Trapezium F - finally new [Re: WRAK]
      #5723467 - 03/10/13 07:36 AM

Wilfried, I think you're right about 60mm telescopes. But NEML isn't as bad as 3.0 on the fringe of every city, even large ones. It varies a lot.

From a suburban area with 2 million city population, where I was observing some years ago, I could see mag 4.5 normally on moonless nights. Another example - outer suburb, local population 400,000, NELM 5.0-5.5 on moonless nights.

Worst case from my recent experience - in outer parts of Sydney I can see mag 4-4.5 stars from some locations (moonless). Sydney area, 4+ million. Now there are areas of (suburban) Sydney that are overlit, so NELM of 3.0 would apply there.

But there's no universal level of light pollution in cities. I'm sure other people will make the same point. Obviously, you're in a difficult location for light pollution. What's your local population total? High, I'd expect, given your NELM figure often being around 3. That makes Trapezium F very difficult even with 140mm.


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WRAK
scholastic sledgehammer


Reged: 02/18/12

Re: My tale of Trapezium F - finally new [Re: fred1871]
      #5723481 - 03/10/13 08:12 AM

Fred, I am located in the southern part of Vienna/Austria and my average NEML is about +3mag (on very transparent nights 3.5 and on hazy ones about 2.5).
Wilfried


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hazilim
sage
*****

Reged: 09/11/08

Loc: Arizona
Re: My tale of Trapezium F - finally new [Re: WRAK]
      #5737808 - 03/17/13 12:39 AM

Just saw F. I've tried many times before, without success. I didn't do anything different than previously:
Celestron 8SE (C8) reasonably well collimated.
Nagler 13mm T6.
Moon was not far away (1st quarter).
Maybe the seeing was better than usual - I don't know!
E was a cinch, while F was harder, but definitely there.
For E & F, perseverance seems to be the key.
Bob


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