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Porrima (small scope)

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#1 Marty0750

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Posted 06 April 2021 - 12:13 AM

View in the 3.5-inch ETX90 Maksutov Cassegrain.195x. The airy rings most of the time seem to be divded into three arcs dancing around the pair (due to seeing effects). The pair are now 3" apart.

 

Martin

 

Porrima-fx-1-web.jpg


Edited by Marty0750, 06 April 2021 - 12:13 AM.

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#2 mdowns

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Posted 06 April 2021 - 06:45 AM

Fine report and drawing Martin.Thanks for posting this!



#3 flt158

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Posted 06 April 2021 - 07:27 AM

Hello, Martin. 

 

These 2 sketches are utterly sublime as you saw Porrima at 195X. applause.gif  

 

Maybe I'm missing something here. 

 

I'm sure I can take it the zoomed-in sketch you used 195X - which is indeed great

But what about the larger sketch without the airy discs?

What magnification did you have then?

I do find it stunningly good looking! waytogo.gif 

That's because the 2 stars appear much closer. 

 

I wish you clear skies down under from Aubrey.  


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#4 AdmiralAckbar

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Posted 06 April 2021 - 10:39 AM

Very pretty sketch of this double!



#5 niteskystargazer

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Posted 06 April 2021 - 10:43 AM

Martin,

 

Good sketch of Porrima (small scope) smile.gif .

 

CS,KLU,

 

thanx.gif ,

 

Tom



#6 frank5817

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Posted 06 April 2021 - 11:22 AM

Martin,

 

Nice sketch of what looks like distant headlights. They are a fine equal pair and continue to open up. Nine years back they we pretty close  less than 2" apart.

 

Frank :)


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#7 Marty0750

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Posted 07 April 2021 - 10:46 PM

The inset is an enlargement of Porrima drawn in the wide view - ie both 195x . Due to CN 500k limit the Porrima detail was lost in reduction. So I digitally copied, enlarged and pasted just Porrima as inset so to show that is was drawn with airy detial in the original wide wiew.

 

Hello, Martin. 

 

These 2 sketches are utterly sublime as you saw Porrima at 195X. applause.gif  

 

Maybe I'm missing something here. 

 

I'm sure I can take it the zoomed-in sketch you used 195X - which is indeed great

But what about the larger sketch without the airy discs?

What magnification did you have then?

I do find it stunningly good looking! waytogo.gif

That's because the 2 stars appear much closer. 

 

I wish you clear skies down under from Aubrey.  

 


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#8 flt158

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Posted 08 April 2021 - 10:23 AM

Thank you for your clarification, Martin.

 

Very best regards from Aubrey. 



#9 Uwe Pilz

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Posted 17 April 2021 - 10:30 AM

Many years ago, around 2005, I observed it with my 12 inch Dob. It was at periastron and I had problems splitting it. Now it is an easy target. Thank you for sharing.


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#10 dUbeni

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Posted 17 April 2021 - 12:04 PM

Hi Martin, you probably have seen this one before on other topics, but here is a link to my sketch of Porrima with a 55mm f/5.5 telescope at 121x with a 2.5mm eyepiece:

https://www.cloudyni...5095_143769.jpg

 

CS

Bernardo


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#11 rerun

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Posted 18 April 2021 - 03:12 PM

Great sketch , I like it very much and inspired me to watch porrima with my 60mm refractor yesterday , too. A fine pair .Thank you for sharing with us.


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#12 Marty0750

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Posted 18 April 2021 - 08:17 PM

Hi Martin, you probably have seen this one before on other topics, but here is a link to my sketch of Porrima with a 55mm f/5.5 telescope at 121x with a 2.5mm eyepiece:

https://www.cloudyni...5095_143769.jpg

 

CS

Bernardo

Indeed. CS I even see split airy rings in one of your sketches

 

I viewed Porrima in a friend's 12-inch a week ago and it was mushy (large aperture seeing effects) . There is something about the airy disk and rings in a small aperture that give the pair that sublimine optical quality. As we know we are seeing them as limited by wave optics itself! 

 

Interestingly in a dicussing with another observer we conlcuded that the seperation between the pair can be measured to far better accuracy than the diffration limit of the scope itself. (1.8" for 2.4-inch). If the airy disks are magnified enough (high power eyepiece) so they are large enough one only need to measure the speration between the centres of the disks with a micrometer. It theoretically should then be possible to measure the sepration of Porrima to fraction of an acrsecond with a 2.4 inch refractor!

 

Any posters comment on this?


Edited by Marty0750, 18 April 2021 - 08:19 PM.

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#13 dUbeni

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Posted 19 April 2021 - 08:33 AM

Interestingly in a dicussing with another observer we conlcuded that the seperation between the pair can be measured to far better accuracy than the diffration limit of the scope itself. (1.8" for 2.4-inch). If the airy disks are magnified enough (high power eyepiece) so they are large enough one only need to measure the speration between the centres of the disks with a micrometer. It theoretically should then be possible to measure the sepration of Porrima to fraction of an acrsecond with a 2.4 inch refractor!

Hello Marty0750, I was surprised when I did this observation with the small Vixen FL55SS, specially because it has only 300mm focal length, I usually use it as a wide field telescope.

The first thing I noticed was that it is less affected by seeing, and the Airy disks and first ring were very stable. I haven't done other double star observations with it, but I must try some more.

The theoretical limit for this telescope is 2.11" Dawes, and 2.51" Rayleigh. So Porrima at 2.81" is feasible.

I don't know what you mean by a micrometer, but I do have an astrometric eyepiece that I haven't used in quite a while, mainly because I think it's accuracy depends on magnification, meaning that greater magnifications will give better results.

Here is a sketch done a few years ago using the astrometric eyepiece:

STF2863 AB Xi Cep

The star is barely visible on the sketched scale, but it's there cool.gif

 

The SD number is obtained after running a star several times through the central scale, and averaging the time of the runs. It gives you the true size of the scale for the telescope in use.

From what we can see here a 2.8" separation needs a lot more magnification and a larger aperture to be more accurately measured. 

 

Bernardo




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