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Minimum power to split Porrima.

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#26 Nucleophile

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Posted 03 June 2019 - 10:14 PM

Charlie,

 

That jibes with my observation with the 60mm scope (i.e., 60x was not quite enough).

 

-Mark M

 

( I have a few other little scopes around here to try out--if only a clear night were in the works)


Edited by Nucleophile, 03 June 2019 - 10:15 PM.

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#27 Nucleophile

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Posted 05 June 2019 - 09:57 PM

I had another look tonight at Porrima, this time with a few other small scopes.

 

1)  Stellarvue SV60 refractor finderscope (f/3.35.)  56x (UO 4mm) gave the same result I presented above:  elongated with possible hints of notch; 90x (Pentax 2.5XO) shows the pair right on the border of split, but it just won't.  Too little glass  and too short a tube, I suspect.

 

2) Bushnell 90mm Mak Cas f/14.4  65x (TV 20mm plossl) shows the pair as just split


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#28 CharlieB

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Posted 06 June 2019 - 07:08 AM

We have a few clear nights promised by the local weather forecast, so I'm going to try Porrima with a few 40mm scopes.  I have an f/20 SPI, an f/17.5 Unitron and f/12.5 Astro Optical, so it should be interesting to see how each of these do.  I'm expecting to have to push the magnification up to at least 120x for a clean split.  That's a lot of magnification for a 40mm scope.  Maybe too much.


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#29 Thomas Marshall

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Posted 06 June 2019 - 03:02 PM

We have a few clear nights promised by the local weather forecast, so I'm going to try Porrima with a few 40mm scopes.  I have an f/20 SPI, an f/17.5 Unitron and f/12.5 Astro Optical, so it should be interesting to see how each of these do.  I'm expecting to have to push the magnification up to at least 120x for a clean split.  That's a lot of magnification for a 40mm scope.  Maybe too much.

Wow! 40mm scope, - less than 2" dia. lens. 120X, - that should be interesting. This is "Aperture Fever" in 'Reverse', - big time. If this trend continues, the Scope Manufacturers could lose some dough$. 



#30 CharlieB

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Posted 06 June 2019 - 04:26 PM

The 40/500 may not be up to the task, but the other two should be OK.  Looks like tonight will be fairly clear. Here are the contenders.

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#31 Nucleophile

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Posted 06 June 2019 - 06:49 PM

So now I am tempted to try the Galileoscope.  lol.gif


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#32 John Fitzgerald

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Posted 09 June 2019 - 08:35 AM

Last night I split Porrima cleanly at 83x with a 90x500 (ST 90) Achro.


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#33 flt158

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Posted 09 June 2019 - 09:26 AM

Well done, John. 

 

Have you any ideas about the colours?

Just wondering, 

 

Aubrey. 



#34 John Fitzgerald

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Posted 09 June 2019 - 10:33 AM

Well done, John. 

 

Have you any ideas about the colours?

Just wondering, 

 

Aubrey. 

Looks white-white to me.


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#35 flt158

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Posted 09 June 2019 - 11:18 AM

Thank you very much for replying to my question, John. 

I just wanted to know how someone with a achromatic refractor would see Porrima. 

It is interesting that www.stelledoppie.it sees both stars as yellow -white. 

 

Personally my 158 mm apochromatic sees both as yellow -white also. 

 

But everyone sees doubles differently -and that's okay. 

 

Kind regards from Aubrey. 


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#36 Don Taylor

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Posted 10 June 2019 - 10:50 PM

Was observing the moon for a while tonight but then looked at a few stars and stumbled on Porrima. Using a de-forked ETX90 (with Wegat Optical back & GSO dielectric diagonal) and it clearly split with a 12mm BST FF (104x) - clearly double but no clean separation with 19mm (66x).

 

On a whim - switched to the Borg 77 Achro - 500mm fl and clearly split with 6mm L-P LER (83x). Then put the turret & 4, 6, 9, 12.5mm KK Fujiyama Orthos on and again clearly split with 6mm (83x) and clearly double but no clean separation with 9mm (56x)


Edited by Don Taylor, 10 June 2019 - 10:55 PM.

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#37 Nucleophile

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Posted 12 June 2019 - 09:32 AM

This thread may be morphing into 'minimum aperture to split Porrima' (perhaps more apt?)

 

I tried again with the SV60 the other night--I helped the f/# along a bit with the 5x Powermate to give f/16.8 and again used the 11 mm TV plossl (102x).  To reduce glare with hopes of increasing contast, I screwed my orange filter onto the plossl.

 

The result was very much elongated, occasionally displaying as notched--it really wanted to split into two but it just never did.

 

I feel this split should be possible with a 60mm objective--I just don't possess the quality glass to do the job.

 

CharlieB:  do you have any data from your 40mm scopes?


Edited by Nucleophile, 12 June 2019 - 09:34 AM.

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#38 Redbetter

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Posted 12 June 2019 - 02:04 PM

I am surprised the 60 isn't at least showing a strong deep notch.  My impression from earlier in the thread was:

 

I brought out the AT60ED and was able to see the double lobe at 60x, beginning to clearly resolve at 72x, and fully resolved by 90x.

 

The interesting part was when I stopped down the 80 f/5 to 42mm:

Out of curiosity I again used the Meade 80 f/5 achro and could see some indications of the split at 57x and it was definitely beginning to resolve at 67x and cleanly resolved beyond that. But what I really wanted to test was stopping it down, so I put the lens cover on and removed the central cap to achieve an effective aperture of 42mm.  This was showing elongation at only 67x, and showing a double lobe at 80x.  At 100x the impression was of two overlapping disks.  Each alternately appears a little brighter/in front of the other, and this contact binary appearance remains at 133x.

 

I suspect different folks can/will perceive substantially different things in the exact same conditions.  That is certainly true of high delta magnitude doubles, but I think it is at play on some of these close equal pairs too.  After all, the diffraction rings and spurious disk are not even stripes and a circle (step changes), they are wave functions of undulating intensity.  Judging elongation, notching, overlap, full resolution, etc. are all somewhat subjective near resolution limits.  That is without even factoring in seeing, aperture, and the nature of the instrument (short achro, long achro, SCT, apo, good figure, poor figure, etc.) 

 

The fully resolved part vs. touching is one aspect that I don't obsess about.  At one magnification something can appear to be touching and at a higher power appear to be resolved...although this latter part is relative too, since "resolved" does not mean that the intensity between the two stars drops to zero or even anywhere close to that.   


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#39 Kon Dealer

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Posted 12 June 2019 - 03:29 PM

Enjoy reading because I haven’t managed to get out again because of horrid weather.



#40 CharlieB

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Posted 12 June 2019 - 06:42 PM


 

CharlieB:  do you have any data from your 40mm scopes?

Not yet.  The weather hasn't been very cooperative and when it was, Porrima was in the trees by the time it got dark enough.  I am surrounded by 100+ ft pine trees.  Maybe tonight...



#41 John Fitzgerald

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Posted 13 June 2019 - 11:13 PM

Tonight (June 13) Using an ED80 f/6 triplet, saw that Porrima is double at 60x (notched), deeply notched at 80x, and very cleanly split at 120x.


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