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azure1961p
Postmaster
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Reged: 01/17/09

Loc: USA
Re: Izar and Porrima new [Re: Bonco]
      #5793570 - 04/11/13 11:45 PM

Agreed. However if indeed the scope had been a 24mm aperture, Fred's points would stand well of course.

Pete


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fred1871
scholastic sledgehammer


Reged: 03/22/09

Loc: Australia
Re: Izar and Porrima new [Re: azure1961p]
      #5793735 - 04/12/13 02:19 AM

I thought it was a reference to a galileo scope, such as I've seen some folk experimenting with - rather than a single-lens eyepiece. William Herschel used such single-element eyepieces at times, though that's rare in post-Huyghens observing. Ok, so it's an eyepiece. I shall simply express myself puzzled about combining a later type of telescope with a primitive eyepiece. Which I think is why I misread the note.

Question suggested by my earlier ramble - what's the smallest aperture that anyone's seen Izar split with? We know that 60mm does it, and Buffham with ~48mm. The latter (1.875" aperture, unobstructed) has a Dawes Limit of ~2.4", which suggests it might be near the best possible. Of course, "resolved" as we've often discussed here can mean anything from separated by a black space to vaguely elongated. Any offers of splits need to spell that out.

Edited by fred1871 (04/12/13 02:26 AM)


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ziridava
super member


Reged: 08/17/12

Loc: Arad,Romania,Eastern Europe
Re: Izar and Porrima new [Re: fred1871]
      #5794938 - 04/12/13 05:15 PM

Please accept my apologies I was unclear and I created confusion.
I was just using a Galilean ocular of 24mm focus at full aperture of my 125mm Newtonian.
I cannot reach focus with Galilean eyepieces without using a Barlow lens.For now I have and sometime use three Galilean oculars of 27mm ,24mm and 18 mm focus.
I like to use them in a sort of reenactment.
Galilean eyepieces were used until the end of XIX Century.
The last famous person to use them was Thomas Grubb.
Apart of historical flavor,they are optically very good.
A good Galilean ocular is able to compete with an orthoscopic.

Off-topic:I start thinking on this forum there are mind-reading people
Once it was unveiled,I have to recognise:it is true,I'm on my way building a Galilean refractor ,this week I made some progress on it.This was supposed to be for a while a ''secret project'' ,meant to be a tribute to the memory of Giovanni Hodierna,a reenactment of his observations.

Mircea


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Bonco
Post Laureate
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Reged: 04/17/06

Loc: Florida
Re: Izar and Porrima new [Re: fred1871]
      #5795244 - 04/12/13 07:16 PM

Quote:

I thought it was a reference to a galileo scope, such as I've seen some folk experimenting with - rather than a single-lens eyepiece. William Herschel used such single-element eyepieces at times, though that's rare in post-Huyghens observing. Ok, so it's an eyepiece. I shall simply express myself puzzled about combining a later type of telescope with a primitive eyepiece. Which I think is why I misread the note.

Question suggested by my earlier ramble - what's the smallest aperture that anyone's seen Izar split with? We know that 60mm does it, and Buffham with ~48mm. The latter (1.875" aperture, unobstructed) has a Dawes Limit of ~2.4", which suggests it might be near the best possible. Of course, "resolved" as we've often discussed here can mean anything from separated by a black space to vaguely elongated. Any offers of splits need to spell that out.



Fred,
60mm/900mm telescope with 7mm .965 eyepiece = 128X. Izar perfectly resolved with dark space between the stars. 6mm resolved it too but better viewed with the 7mm.
Bill


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ziridava
super member


Reged: 08/17/12

Loc: Arad,Romania,Eastern Europe
Re: Izar and Porrima new [Re: Bonco]
      #5812874 - 04/21/13 11:48 AM

Soon I will be able to compare directly my 9mm Vixen orthoscopic to a brand new Galilean eyepiece of 9mm focus.

Coming back to double star observation,last night myself,with my 125mm F7 Dobsonian/ and my friend Emil with his 114mm F8.8 Bird-Jones Newtonian, were in front of the City Hall for a public star party as part of ISAN 6.

It was a nice surprise to be able to split Porrima and especially Izar at 140x/Faworski 10mm Plossl+1,8x Barlow in my 125mm Dobsonian,from that litle corner of Hell.
The complete list of stars on the double/multiple star menu of our ISAN 6 Star-Party were Alcor-Mizar,Castor,Porrima and Izar.
The light polution there is huge:only the Moon,Jupiter,Saturn were visible.I had to guess where to look for Porrima, Izar or Mizar.
After a while,by blind guessing ,I found also M44.
About 120-150 people had their first telescopic view of some heavenly bodies,including some very fine double stars.

Mircea


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Rutilus
Carpal Tunnel


Reged: 12/17/10

Re: Izar and Porrima new [Re: ziridava]
      #5813478 - 04/21/13 04:30 PM Attachment (33 downloads)

Last night I observed Izar with what I thought was a 60mm aperture mask on my 100mm f/13 Carton.
This morning I measured it again and found it to be 58mm. Still the companion was nicely seen with magnifications up to 260x.
The companion appeared to be extremely close to the inside edge of the first diffraction ring, with some light showing
up in the diffraction ring itself. Dark space clearly visible between the primary and companion.
Here is a quick drawing.


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fred1871
scholastic sledgehammer


Reged: 03/22/09

Loc: Australia
Re: Izar and Porrima new [Re: Rutilus]
      #5814326 - 04/21/13 10:35 PM

Good drawing, Rutilus - nicely shows the pair. Interesting, as you and Bill (Bonco) have now resolved this one with ~60mm at not much more magnification than Sissy Haas recorded with her 60mm refractor, but both of you got a clean separation which her description doesn't suggest she did. Better optics? Better atmospheric conditions? Who knows ....

No doubt the 60mm has a benefit from the placement of the first diffraction ring just outside where the secondary star is located. Interesting. I'll try Izar (Epsilon Bootis) again when my local weather improves. Maybe with my 80mm refractor, then stop it down to 60mm to see the difference (and, I hope, the companion). I don't think it's optically good enough to manage Izar at 50mm - but my very good 140mm refractor might be worth stopping down that far. Hmmm. Think I can hear an experiment suggesting itself.


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brianb11213
Postmaster
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Reged: 02/25/09

Loc: 55.215N 6.554W
Re: Izar and Porrima new [Re: fred1871]
      #5814627 - 04/22/13 04:20 AM

Quote:

I don't think it's optically good enough to manage Izar at 50mm



Stopping down an instrument usually results in the optics becoming near perfect even if they were a bit iffy at full aperture. Especially as the effects of "pinching" by the objective cell will disappear when the outer part of the objective is obscured. Also increasing the working focal ratio is beneficial given the very short focal ratios which seem to be fashionable these days ... it takes a pretty good eyepiece to work well at f/6 & even the better (more complex, well engineered) designs seem to work better at f/7 - f/8 than at shorter focal ratios.


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SeptemberEquinox
sage
*****

Reged: 01/29/12

Re: Izar and Porrima [Re: brianb11213]
      #5823880 - 04/26/13 09:28 AM

"diffraction ring"

what is diffraction ring? And in your photos what are those rings around the star?

I was able to split Epsilon Boo(Izar) at 220X ish clearly for the first time last night.


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Rutilus
Carpal Tunnel


Reged: 12/17/10

Re: Izar and Porrima new [Re: SeptemberEquinox]
      #5825071 - 04/26/13 06:53 PM

The diffraction ring - "Diffraction is an optical effect caused by the interference of light
waves in passing around or through any opening, such as a lens or your eye.
A point source is seen as a tiny disk, surrounded by one or more faint rings of light"

"This diffraction pattern consists (assuming a circular objective) of a central bright disc, termed
the spurious disc or Airy disc, surrounded by alternate concentric rings of light and darkness-
the diffraction rings and interspaces".

Quotes taken from from Sam brown's book All about Telescopes and Sidgwick's book Amateur
Astronomers Handbook.

The ring around the star in the drawing is the first diffraction ring. Only on nights of excellent seeing do
I see the ring as a solid circular patern. Usually due to the seeings conditions, the ring appears broken,
often appearing as arcs of light


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SeptemberEquinox
sage
*****

Reged: 01/29/12

Re: Izar and Porrima new [Re: Rutilus]
      #5825199 - 04/26/13 07:36 PM

So the light is playing trick to our eyes. it's an optical illusion or visual phenomenon?

Thank you for explaining


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Bonco
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Reged: 04/17/06

Loc: Florida
Re: Izar and Porrima new [Re: SeptemberEquinox]
      #5826697 - 04/27/13 04:36 PM

Quote:

So the light is playing trick to our eyes. it's an optical illusion or visual phenomenon?

Thank you for explaining



It's an artifact from the optical system. Bill


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Ain Soph Aur
professor emeritus
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Reged: 08/11/11

Loc: West Tennessee
Re: Izar and Porrima new [Re: Bonco]
      #5831212 - 04/29/13 10:11 PM

Izar nicely split tonight with the Carton 100mm f/13 aperture reduced to 50mm f/26. Companion cleanly split sitting on the first diffraction ring.

I have a nested aperture reduction system in 10mm increments from 90mm to 50mm, I kinda wish I had also had 40mm and 30mm reduction rings made too. 1.2" f/43 could be fun just to see what it is capable of splitting....


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BuffaloTri
member


Reged: 04/23/12

Re: Izar and Porrima new [Re: Kon Dealer]
      #5835976 - 05/02/13 10:29 AM

I took my first attempt at Izar last night with my CT 102mm f/11. The seeing was bad - Arcturus was twinkling to the naked eye, and I was in a white zone.

I tried it at 32x, 110x, and 220x. At 32x I wondered if I was on the right star because there wasn't even a hint of a split. There were occasional hints of the secondary at 110x. I had a clean split at 220x; the primary looked yellow/orange and the secondary was blue. It was not a crisp image because of the poor seeing. The primary itself was boiling and fragments of a diffraction ring would appear and disappear. Still, it was fun to split this double. Hopefully tonight I'll be able to try some magnifications in between 110-220 and find the minimum I need for a clean split.

I also like the idea of an aperture mask. I've always assumed I needed aperture to overcome the LP, but maybe that isn't the case.


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Bill Boublitz
super member


Reged: 05/04/13

Re: Izar and Porrima new [Re: Kon Dealer]
      #5846909 - 05/07/13 11:47 PM

I saw your post and couldn't help responding. Izar is one of my favorites! Sort of like and old friend. It was the first double of any challenge I split through a scope. I view it almost every year. I have always seen the companion more grey-green than blue. But I attribute the color to the particular set of oculars I was given to work with. Most log the companion as blue. I first viewed it with a 101 mm refractor at x145. Truly beautiful object. I never tire of it. Happy to read your post! Thanks.

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aquariusnic
newbie


Reged: 05/11/13

Re: Izar and Porrima new [Re: Bill Boublitz]
      #5854778 - 05/12/13 03:08 AM

Hi,

That was last may 7th, after seeing the double Algieba - very nice - in Leonis i had no problem splitting Porrima in Virgo on my balcony. The seeing was excellent (9/10) and my Tasco 60/900 showed it very well at 90X and better at 144X (12,5mm barlowed) like two close little diamonds. But I never saw the Izar companion with this.


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StarDusty
sage


Reged: 10/02/07

Loc: Parsippany, NJ
Re: Izar and Porrima new [Re: aquariusnic]
      #5855541 - 05/12/13 01:55 PM

I have not looked at Izar this year yet, but imaged it last summer. (Sorry, not in color.)

For a black and white image go here:

http://www.clearskyobserver.com/index.php/component/jce/?view=popup&tmpl=...


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grom
member


Reged: 02/23/09

Loc: Spain
Re: Izar and Porrima new [Re: StarDusty]
      #5860232 - 05/14/13 03:32 PM

A few days ago, with good seeing. Porrima two Airy discs were touching or almost-touching in a 80mm APO.

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Silver Bear
member


Reged: 04/02/13

Loc: Brazos Valley in Texas
Re: Izar and Porrima new [Re: grom]
      #5863042 - 05/15/13 07:55 PM

Two nights ago, I viewed Porrima, saw the color differences, but could not quite split the double under high magnification due to wind blowing against my light little telescope. Still, a very nice sight.

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Bill Boublitz
super member


Reged: 05/04/13

Re: Izar and Porrima new [Re: Silver Bear]
      #5878654 - 05/22/13 05:39 PM

My customary small instrument is a 101 mm refractor. Last night, I stopped it down to 60 mm with an aperture mask and split Izar quite easily. 1. The image was dimmer (than full aperture) 2. Colors seemed more vivid, more pronounced. 3. Prominent diffraction ring around primary - which is hardly noticeable at full aperture. Magnification was x225.

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