Steve Napier
Carpal Tunnel
Reged: 05/10/04
Posts: 1559
|
|
Ive just read a post on the TeleVue forum and a member states that he has split e Bootis {Izar} using a 60mm scope at 120x.
It should be pointed out that he was using a TV 60 which is an APO.
I was wondering what would be the minimum of both aperture and magnification that could effectivley make this split?
I will certainly be making some inquiries in to the TV 60 as it sounds ideal for a travelscope.
The owner,who was making a first light report states that when the diagonal is removed the scope is only 10" long.
This would be very handy for the likes of me who uses public transport.
Steve.
|
Steve Napier
Carpal Tunnel
Reged: 05/10/04
Posts: 1559
|
|
I stopped my Oracle3 down to 60mm last night and I split Izar too.Very surprising as most books suggest a 3" refractor for the seperation.
I might go down to 50mm and if its clear try tonight.
Steve.
|
Steve Napier
Carpal Tunnel
Reged: 05/10/04
Posts: 1559
|
|
I tried at 50mm last night but,was unable to make the split.
Steve.
|
P_Nut
professor emeritus
Reged: 12/21/03
Posts: 659
Loc: Novo mesto, Slovenia, Europe
|
|
I tried splitting Izar with 70mm Celestron Firstscope one and a half year ago and was able to make the split, but it was pretty hard. But I was just a begginer then!
Edited by P_Nut (09/08/04 12:30 PM)
|
EdZ
Professor EdZ
Reged: 02/15/02
Posts: 12581
Loc: Cumberland, R I , USA42N71.4W
|
|
Izar, e Boo is 2.5-5.0/2.8".
Use Rayliegh Limit to determine what any scope is capable of splitting. Rayleigh Limit is the forumla which defines the size of an Airy disk produced by a scope. R.L. = 5.45/Dinches or 138/Dmm. That will give you the radius of the Airy disk to the first minimum, answer in arcseconds. Double it to get the diameter.
Faint stars have a bright central spot that takes up about 50% to 60% of the Airy disk diameter. The central bright spot for the brightest stars take up at maximum about 85% of the Airy disk diameter. No stars have a bright central spot that takes up the full diameter of the Airy disk. If all stars had a central bright spot equal to 50% the diameter of the full Airy disk, then any scope would be able to cleanly split any two stars when they are separated by just a hair more than one half the diameter, or the radius of the Airy disks they form. This is rarely true, as bright stars have a wider central spot.
Because one of the components of Izar is very bright, it has a wide central spot, possibly 70%-80% the full diameter of the Airy disk.. The other component is not so bright. It's central spot may be only 50%-60% the diameter. The central bright spots, the visible disks, need to be separated by sufficient measurement to see a black space. In this case it will be near about Rayleigh Limit for the scope times the factor for the diameter of the central bright spots, ((80+60)/50)/2 or (140/50)/2 = 2.8/2 = 1.4x. It could be as small as ((70+60)/50)/2 or 1.3x. Two normally equal 5th magnitude stars ends up being 1.2x R.L., so this is not out of the ordinary.
Color of the components can add to or reduce the difficulty of splitting two components. It takes more to split red stars. it is easier to split blue stars. All the values we calculate are based on yellow stars.
Typically an 80mm scope could split two mag 5-6 stars of 138/80 = 1.73". A 50mm scope could split 138/50 = 2.76", just about the size of Izar. Izar is 2.8" (measured center to center, not space between disks). But because of the magnitude of the stars involved, it must be factored by 1.4x or 1.3x. Then 2.8x1.4 = 3.9". Factored by 1.3x, you would need a scope than can split 3.6". If 138/Dmm = R.L., and you need 1.3x to 1.4x R.L., then you need 138x1.3/2.8 = 64mm to 138x1.4/2.8 = 69mm to split Izar.
My TV85 beats these type of calculations by only a few percent. My 150mm refractor can equal these type of calculations. Most of my other scopes fall within about 5-10% of the calculated values. None of the scopes I own can split stars better than the Rayleigh limit, although I suspected it once with my 150mm refractor on 16Vul 5.8-6.2/0.8" and once with my TV85 on 6.1-6.4/1.5".
I've seen Izar at 100x in a 76mm, 20 year old Swift Schmidt-Newtonian.
edz
--------------------
Teach a kid something today. The feeling you'll get is one of life's greatest rewards.
member#21
Edited by EdZ (09/09/04 08:01 AM)
|
Steve Napier
Carpal Tunnel
Reged: 05/10/04
Posts: 1559
|
|
Edz,your TV 85 is optically superior to my old Oracle 3,have you tried using a cardboard mask with a a 60/50mm cut out aperture to see if you can make the seperation?
I bet your skies are better than mine.
Steve.
|
EdZ
Professor EdZ
Reged: 02/15/02
Posts: 12581
Loc: Cumberland, R I , USA42N71.4W
|
|
I have a nice little 60mm scope that has proven itself very well. I'll give it a try.
edz
--------------------
Teach a kid something today. The feeling you'll get is one of life's greatest rewards.
member#21
|
David Knisely
Postmaster
Reged: 04/19/04
Posts: 6784
Loc: Beatrice, Nebraska
|
|
Quote:
Ive just read a post on the TeleVue forum and a member states that he has split e Bootis {Izar} using a 60mm scope at 120x.
It should be pointed out that he was using a TV 60 which is an APO.
I was wondering what would be the minimum of both aperture and magnification that could effectivley make this split?
I will certainly be making some inquiries in to the TV 60 as it sounds ideal for a travelscope.
The owner,who was making a first light report states that when the diagonal is removed the scope is only 10" long.
This would be very handy for the likes of me who uses public transport.
Steve.
I took a look at Izar a couple of nights ago with my 100mm f/6 refractor. At about 190x, despite a little color excess "haze" from the achromat, the double resolved very nicely with the bluish companion separated from the star and out of the inner brighter portions of the diffraction pattern. Then, I stopped my refractor down to 60mm and took a look at Izar at 190x. The companion appeared as merely a slightly brighter spot right on top of the first diffraction ring, so while it was visible, it was not well shown. The faintness of the companion and its close separation are reasons why at least a 3 inch aperture is often recommended for observing this colorful double. Clear skies to you.
--------------------
David W. Knisely
Hyde Memorial Observatory
http://www.hydeobservatory.info
|
Steve Napier
Carpal Tunnel
Reged: 05/10/04
Posts: 1559
|
|
Hi David.
I must admit,I had to stay at the eyepiece for a good few minutes before I was certain of the seperation but,it was definately there.
An astronomer split Sirius with only a 4" refractor in the Israeli desert,obviously seeing conditions were exceptional.
I dont trust most of the information one reads in books regarding what size aperture is needed to seperate a certain double,far better to read the experiences of observers out in the field.
Steve.
|
EdZ
Professor EdZ
Reged: 02/15/02
Posts: 12581
Loc: Cumberland, R I , USA42N71.4W
|
|
I tried Izar last night with my 60mm refractor. I spent at least an hour using 4 or 5 different magnifications. I could not even see the secondary component, let alone elongate it or split it. I had a very nice diffraction ring around the primary at 138x and 118x, but I believe diffraction complete overwhelmed the secondary.
The central visible disk had an appearance of being quite large. Considering the physics of the 60mm refractor, I suspect the central visible disk for Izar was broader than 3 arcseconds in diameter. That is compared to the central visible disk formed by my 5" scope, which produces a visible disk approximately 1.5 arcseconds in diameter for Izar.
After no success with Izar, I pointed the refractor up to zenith to try e1e2 Lyra. Even at magnifications of 118x and 104x, I was easily able to elongate and deeply notch both e1 and e2, although last night I did not see either as a clean split. Both of those are a challenge for a 60mm scope, but having primary components lees bright than Izar a bit easier.
edz
--------------------
Teach a kid something today. The feeling you'll get is one of life's greatest rewards.
member#21
|
David Knisely
Postmaster
Reged: 04/19/04
Posts: 6784
Loc: Beatrice, Nebraska
|
|
Quote:
I tried Izar last night with my 60mm refractor. I spent at least an hour using 4 or 5 different magnifications. I could not even see the secondary component, let alone elongate it or split it. I had a very nice diffraction ring around the primary at 138x and 118x, but I believe diffraction complete overwhelmed the secondary.
The central visible disk had an appearance of being quite large. Considering the physics of the 60mm refractor, I suspect the central visible disk for Izar was broader than 3 arcseconds in diameter. That is compared to the central visible disk formed by my 5" scope, which produces a visible disk approximately 1.5 arcseconds in diameter for Izar.
After no success with Izar, I pointed the refractor up to zenith to try e1e2 Lyra. Even at magnifications of 118x and 104x, I was easily able to elongate and deeply notch both e1 and e2, although last night I did not see either as a clean split. Both of those are a challenge for a 60mm scope, but having primary components lees bright than Izar a bit easier.
edz
It is possible that you weren't using enough power. I had no trouble noticing the companion at 190x with the Orion SkyView Pro 100 I have (used the 2.5x Tele Vue Powermate and my 5-8mm Speers Waler eyepiece). It was quite obvious, although the companion wasn't exactly all that bright. I used the scope's 60mm "hole" in the lens cap to get what would be the equivalent of a 60mm f/10 refractor while keeping the power the same. I knew the position angle of the companion from the earlier observations and it was easy to notice the brightening in the first diffraction ring which marked the location of the companion. When viewing doubles, all bets are off as far as the maximum usable magnification is concerned (I used over 1000x on Gamma Virginis with my NexStar 9.25 a few months ago). Clear skies to you.
--------------------
David W. Knisely
Hyde Memorial Observatory
http://www.hydeobservatory.info
|
Steve Napier
Carpal Tunnel
Reged: 05/10/04
Posts: 1559
|
|
I used a 10.5mm TV Plossl and a 2.5x TV Barlow to produce a magnification of 133x times and I could make the split.
Edz,try again using your TV 85.
Steve.
|
EdZ
Professor EdZ
Reged: 02/15/02
Posts: 12581
Loc: Cumberland, R I , USA42N71.4W
|
|
The TV85 is too much for what we are trying to check, smallest aperture. Last night I had my AT1010 78mm and again the 60mm set up, but never saw Izar through the clouds. I have only a one hour window of time before it dips below th trees.
I could not bring the 60mm to focus easily even at 138x. That's a 0.965" Vixen 6mm orhto in a Vixen barlow. This is a 415mm refractor.
On previous occasions, I split or noticed Izar's secondary at magnifications of 100x in a 3" and 96x in a 5" and just recently at 90x with a 15mm RKE in my 5" SCT on a very cold 50° June night. So I know I can see it at those magnifications on a good night. But I think the 60mm is not enough scope. Considering David's success, could be just this 60mm scope. may have been seeing the other night as it wasn't all that easy to see e1e2 lyra either, and I've done that one at lower magnifications.
Maybe I'll try a paper mask on the TV85 at 70mm 65mm and 60mm. Focus is so easy on that scope at any power, it would improve chances.
--------------------
Teach a kid something today. The feeling you'll get is one of life's greatest rewards.
member#21
|
Steve Napier
Carpal Tunnel
Reged: 05/10/04
Posts: 1559
|
|
Yes Edz,thats what I was meaning,try your TV 85 with a 60mm aperture cut out mask,Im sure that will make the seperation for you.
Steve.
|
EdZ
Professor EdZ
Reged: 02/15/02
Posts: 12581
Loc: Cumberland, R I , USA42N71.4W
|
|
Hi Steve,
While I didn't yet make a mask and try the TV85, I did make an effort again yesterday with my 60mm/415mm f7 and with my 78mm/ 480mm f6.2 AT1010.
I discovered the AT1010 has a problem that shows diffraction not concentric. That prevented me from seeing e Boo with that scope.
Seeing was much better than two nights ago.
I remounted my 60mm and I had a much easier time with steady focusing. I used magnifications of 104x, 118x, 138x, 166x and 208x, using an 8mm RKE, and 7mm, 6mm, 5mm and 4mm orthos in a Vixen 2x barlow. But I still had no success seeing a split. I barely noticed elongation of the components at magnifications of 138x and 166x. 208x was way too much for this scope. I had great difficulty focusing and the image was distorted at the edges of the bright visible disk.
The best view was at 138x. I suspected elongation at about PA 330°. The 60mm scope did show one very clear symetric diffraction ring at magnifications of 104x, 118x and 138x, but the elongation I noticed was not in the ring, it was on the central bright spot. That would mean the secondary is appearing inside the first diffraction ring on the central bright spot. That would not happen in a 60mm scope.
A 60mm scope has an Airy disk radius of 2.3", with the first diffraction ring being outside that radius. E Boo is 2.8", just about right for the secondary to fall on the first diffraction ring. The only way that I could be seeing elongation of a 2.8" double ON the central bright visible disk, inside the first diffraction ring, is if this 60mm scope is internally stopped down to something slightly smaller than 60mm. There is a stop half way down to the focuser. It may be stopping down the aperture to eliminate distortion at the edges. If I'm correct that I saw elongation on the visible disk then this scope appears it may be operating closer to 50mm.
The view through this scope is real nice, but dim. Afterwards I viewed M13 at 118x, 104x and 70x. While 104x still showed quite a bit resolved, 70x was quite a bit brighter and more enjoyable.
I'll still have to try the TV85 at 60mm. This should prove whether this other scope is stopped down. I'm really curious to see if the secondary falls on the ring. If so, that's proof enough for me.
edz
--------------------
Teach a kid something today. The feeling you'll get is one of life's greatest rewards.
member#21
Edited by EdZ (09/13/04 03:44 PM)
|
David Knisely
Postmaster
Reged: 04/19/04
Posts: 6784
Loc: Beatrice, Nebraska
|
|
Quote:
Hi Steve,
While I didn't yet make a mask and try the TV85, I did make an effort again yesterday with my 60mm/415mm f7 and with my 78mm/ 480mm f6.2 AT1010.
I discovered the AT1010 has a problem that shows diffraction not concentric. That prevented me from seeing e Boo with that scope.
Seeing was much better than two nights ago.
I remounted my 60mm and I had a much easier time with steady focusing. I used magnifications of 104x, 118x, 138x, 166x and 208x, using an 8mm RKE, and 7mm, 6mm, 5mm and 4mm orthos in a Vixen 2x barlow. But I still had no success seeing a split. I barely noticed elongation of the components at magnifications of 138x and 166x. 208x was way too much for this scope. I had great difficulty focusing and the image was distorted at the edges of the bright visible disk.
The best view was at 138x. I suspected elongation at about PA 330°. The 60mm scope did show one very clear symetric diffraction ring at magnifications of 104x, 118x and 138x, but the elongation I noticed was not in the ring, it was on the central bright spot. That would mean the secondary is appearing inside the first diffraction ring on the central bright spot. That would not happen in a 60mm scope.
A 60mm scope has an Airy disk radius of 2.3", with the first diffraction ring being outside that radius. E Boo is 2.8", just about right for the secondary to fall on the first diffraction ring. The only way that I could be seeing elongation of a 2.8" double ON the central bright visible disk, inside the first diffraction ring, is if this 60mm scope is internally stopped down to something slightly smaller than 60mm. There is a stop half way down to the focuser. It may be stopping down the aperture to eliminate distortion at the edges. If I'm correct that I saw elongation on the visible disk then this scope appears it may be operating closer to 50mm.
The view through this scope is real nice, but dim. Afterwards I viewed M13 at 118x, 104x and 70x. While 104x still showed quite a bit resolved, 70x was quite a bit brighter and more enjoyable.
I'll still have to try the TV85 at 60mm. This should prove whether this other scope is stopped down. I'm really curious to see if the secondary falls on the ring. If so, that's proof enough for me.
edz
The center of the first diffraction ring lies about 1.763*Lambda/D, or for visible light and a 60mm scope, at a radius of 3.3 arc seconds from the center of the diffraction pattern. The width of that ring could be large enough to pretty much wipe out a much fainter star at a separation of 2.8 arc seconds. However, I remeasured the stop for my 100mm f/6 and it is *53mm* not 60mm. This would have put the companion on the inside of the first diffraction ring. This has added even more confusion to the mix, although it would also mean that the companion would be far enough just inside the ring to be visible. I will have to try this one again. Clear skies to you.
--------------------
David W. Knisely
Hyde Memorial Observatory
http://www.hydeobservatory.info
|
Steve Napier
Carpal Tunnel
Reged: 05/10/04
Posts: 1559
|
|
I will look tonight if I get the chance.
I cant remember if the companion was on the inside or actually on the diffraction ring itself.
Steve.
|
EdZ
Professor EdZ
Reged: 02/15/02
Posts: 12581
Loc: Cumberland, R I , USA42N71.4W
|
|
I can try to determine the effective aperture of my little 60mm scope. I know it's focal length is 415mm. I can roughly check that, see if it comes up close.
If I open up the tube I can measure the distance from the objective to the baffle, and I can measure the opening in the baffel. I can determine how far down the light path the baffle is placed and how big the hole should be. I can determine how much of the light cone is being clipped by the baffle. By geometry, I can work backwards and determine the effective aperture. If it's as I suspect David, I should be coming up with something smaller than your 53mm.
edz
note: I t did turn out this little 60mm refractor was operating at a lot less than 60mm. there is a post in the forum title "What aperture is your scope operating at?" that is the results of performing these tests. Found HERE
--------------------
Teach a kid something today. The feeling you'll get is one of life's greatest rewards.
member#21
|
Steve Napier
Carpal Tunnel
Reged: 05/10/04
Posts: 1559
|
|
Have any of you two gentlemen viewed Izar again to determine exactly where the companion is in relation to the difraction ring?
I have had cloudy nights this past week.
Steve.
|
EdZ
Professor EdZ
Reged: 02/15/02
Posts: 12581
Loc: Cumberland, R I , USA42N71.4W
|
|
I've been unable to get out agian since my discovery of the 60mm deficiencies. I'm hoping to get a view with the TV85, but my view is now down to about 30minutes before it disappears behind the trees. Hope to get a chance.
edz
--------------------
Teach a kid something today. The feeling you'll get is one of life's greatest rewards.
member#21
|
Previous
Index
Next
Threaded
Edit
Reply
Quote
[Re: 