mike bacanin
professor emeritus
Reged: 03/19/07
Posts: 638
Loc: united kingdom
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Could you please clarify what effect putting a barlow ahead of a binoviewer has on mag?
for example, a 2x barlow?
is there a formula to work it out for any barlow?
Thanks
Mike
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94bamf
professor emeritus
Reged: 12/15/08
Posts: 720
Loc: Kansas City,Mo
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On a purely visual guess, I would say my Celestron Ultima barlow is around 3 to 3.5x in front of my binoviewers. I also have a Zhumell 2x barlow that the lens assembly unscrews from the barlow, and screws directly on the front of the binoviewer. I would guess that one is around 2.5x to 3x. Basically my understanding is the further away the barlow lens is from the eyepieces, the more magnification.
Ken
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Telescopes:
Celestron C6 SCT on CG4 mount
Skywatcher 8 inch F/5 Newt on a GEM
Celestron 8 inch Starhopper Dob
Celestron Oynx 80ED
Celestron C130 Mak
Celestron C102HD
Binoculars:
Nikon 7x35 Action
Nikon 7x50 Action
Zen Ray Summit 10x42
Celestron 10x42 Noble
Orion 10x50 Scenix
Celestron 10x50 Noble
Pentax 12x50 PCF WP II
Celestron 15x70 Skymaster
Oberwerk 20x60
Zhumell 20x80
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Covey32
scholastic sledgehammer
Reged: 12/09/04
Posts: 921
Loc: Georgia
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The best bet for accuracy is to go with a dedicated optical corrector assembly which is designed to install that way.
You get an exact figure that way.
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Hank
12.5" Mag1 Portaball
Orion 120mm F5 Refractor
Skywatcher 120ED F7.5 Refractor
1982 Celestron C8 Orange tube
Celestron ED80 Refractor with Lunt 50mm HA
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Erik Bakker
professor emeritus
Reged: 08/10/06
Posts: 534
Loc: Haren, The Netherlands, Europe
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Hi Mike,
The only way to determine this magnification is to measure field of view with and without barlow. The magnification of a barlow is dependent on the distance between the glass elements of the barlow and the field stop of the eyepiece used. Hence the differnce between straight through, with diagonal and with binoviewer. The magnification stated on a barlow is usually that for the straight through (like in a Newtonian) situation. My Ap 2x barlow measures 2.15x straight through and 2.41x with the Baader 60 degree binoviewer. Hope this clarifies.
Clear skies,
Erik
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Visual astronomer, main instruments:
Fully mounted Questar 7 P-BB
Celestron C 102F f/8.8 fluorite
Vixen FL 70S f/8 fluorite
Celestron C 55F f/8 fluorite
Sets of Zeiss, TeleVue and Brandon eyepieces
Zeiss 7x50 Marine B/GA
Zeiss TM german equatorial
Gitzo 224 with Manfrotto 501 fluid head
Unitron alt-az mount
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mike bacanin
professor emeritus
Reged: 03/19/07
Posts: 638
Loc: united kingdom
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Thank you for all your responses.
Erik,would a Televue 2x give roughly about the same with the same 60 degree bino?
Mike
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Erik Bakker
professor emeritus
Reged: 08/10/06
Posts: 534
Loc: Haren, The Netherlands, Europe
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Hi Mike,
Not necessarily so, but someting between 2.2x and 2.6x should be a safe starting point. You might even end up with 2.4x ! However, you won't know without actually trying and measuring. Counting bricks in a distant wall works, be sure tu use ortho's or Ethoi because the don't suffer from angular magnification towards the edges of their fields.
Clear skies,
Erik
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Visual astronomer, main instruments:
Fully mounted Questar 7 P-BB
Celestron C 102F f/8.8 fluorite
Vixen FL 70S f/8 fluorite
Celestron C 55F f/8 fluorite
Sets of Zeiss, TeleVue and Brandon eyepieces
Zeiss 7x50 Marine B/GA
Zeiss TM german equatorial
Gitzo 224 with Manfrotto 501 fluid head
Unitron alt-az mount
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EdZ
Professor EdZ
Reged: 02/15/02
Posts: 14732
Loc: Cumberland, R I , USA42N71.4W
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My Denkmeier BV does not come to focus in my TV102 when used with the Denk adapter. So instead, I use my TV2x barlow. I've measured it at almost exactly 4x when used in front of the Denk. My Denk has a power switch on it, although this 4x is used with no PS lens in place, however it does add length and it is true the longer the distance from barlow to eyepiece the higher the power.
edz
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Teach a kid something today. The feeling you'll get is one of life's greatest rewards.
member#21
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mike bacanin
professor emeritus
Reged: 03/19/07
Posts: 638
Loc: united kingdom
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Erik,
The amplification with your AP barlow seems very low compared for example, to Edz' TV 2x barlow.
Am i right that the shorter the physical length of the barlow used in fron of the binoviewer, the less the amplification factor?
Mike
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EdZ
Professor EdZ
Reged: 02/15/02
Posts: 14732
Loc: Cumberland, R I , USA42N71.4W
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Here's the measures from another barlow.
This is from my ad when I sold it thru CN classifieds.
Celestron 2x standard 1.25" barlow, Fully Multi-coated,
very good condition, both caps, generic box
Get a barlow and a BV adapter all in one.
nosepiece works as a 2.8x BV adapter
gives a very nice 56x in my 80/500 when using long 25mm eyepieces.
The front nose-piece of this barlow contains the barlow elements. It screws into the front end of the 1.25" barrel sleeve threads. This nose-piece is similar to the Burgess BV (OCA) adapter and the Stellervue BVA adapter. It will screw into the front chrome sleeve of both these binoviewers. Actually, this barlow element has 2mm larger clear aperture than the Stellervue adapter. It works well in either of these binoviewers. Used in this manner, it provides about 40% higher magnification than the standard BV adapter. In my Megrez 80 500mm refractor, it has a factor of about 2.8x vs 2.1x for the standard BV issue adapter. But, it allows focus with the telescope draw tube about 1" further out. So, if you've had a problem reaching focus with your BV because you need more in-focus, this barlow nosepiece will give you about an extra inch of travel.
You could just insert the BV into the whole barlow, just like you would an an eyepiece, which provides focus even further out, but at the expense of a magnification factor around 3.5x. Best used in the BV by just screwing the Barlow nose-piece into the BV nose for 2.8x.
So barlow / BV adapter all-in-one
3.5x if used as barlow, 2.8x if you just use the nosepiece with the barlow element.screwed onto your BV.
edz
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Teach a kid something today. The feeling you'll get is one of life's greatest rewards.
member#21
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Erik Bakker
professor emeritus
Reged: 08/10/06
Posts: 534
Loc: Haren, The Netherlands, Europe
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Hi Mike,
The difference in effective magnification between my and Ed's example is mostly in the length the light travels through the binoviewer before it reaches the fieldstop of the eyepiece. This a great advantage of the 60 degree Baader bino's compared to "normal" bino's that need a stardiagonal in a refractor: you can use them in almost any refractor WITHOUT barlow = wide fields! So if you use them WITH barlow, there is less glasspath wich results in less effective magnification. It may help you to visualize the barlow as a beamer (or projector) and the eyepiece as the screen. The further the screen is from the projector, the bigger (more magnified) the image with the same projectorlens.
Clear skies,
Erik
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Visual astronomer, main instruments:
Fully mounted Questar 7 P-BB
Celestron C 102F f/8.8 fluorite
Vixen FL 70S f/8 fluorite
Celestron C 55F f/8 fluorite
Sets of Zeiss, TeleVue and Brandon eyepieces
Zeiss 7x50 Marine B/GA
Zeiss TM german equatorial
Gitzo 224 with Manfrotto 501 fluid head
Unitron alt-az mount
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EdZ
Professor EdZ
Reged: 02/15/02
Posts: 14732
Loc: Cumberland, R I , USA42N71.4W
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The Baader Maxbright BV, either with or without the 60° nose, is no shorter than any other standard binoviewer. Therefore, I fail to see how it could be considerably lower in power when using a barlow.
The 90° star diagonal does not come into play in any of these instances, when trying to determine the power factor of a barlow. If in use it is in front of the barlow and has no affect on power. it would only affect in/out travel.
edz
http://www.alpineastro.com/Binoviewers/binoviewers.htm
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Teach a kid something today. The feeling you'll get is one of life's greatest rewards.
member#21
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mike bacanin
professor emeritus
Reged: 03/19/07
Posts: 638
Loc: united kingdom
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Edz,
This is the Baader/Celestron unit Erik is referring to.
http://www.teleskop-service.se/produkter/eng/baader/accessories/accessories.html#bino
Its the one halfway down the page.
Mike
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Rick
Post Laureate
Reged: 04/12/05
Posts: 3047
Loc: Tokyo, Japan
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While I don't want to disagree with the Baader sales rap, that style of binoviewer was definitely lifted from microscopes. Tak made one too. Kinda of cludge really.
They work OK but the 60deg configuration is not optically "ideal" and I believe you have to constantly re-adjust the IPD as you refocus.
cheers,
Rick
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www.japanastro.com
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Erik Bakker
professor emeritus
Reged: 08/10/06
Posts: 534
Loc: Haren, The Netherlands, Europe
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Hi Rick,
This an older no longer available item. If you change IPD, you have to refocus. It's great for unbarlowed widefield viewing in refractors. For high magnifications, a Baader/Zeiss Mark iV or Mark V binoviewer will be sharper and has the benefit of individual focus adjustments for left and right. On smaller scopes, the 60 degree bino is easy to balance and they have excellent build quality.
Clear skies,
Erik
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Visual astronomer, main instruments:
Fully mounted Questar 7 P-BB
Celestron C 102F f/8.8 fluorite
Vixen FL 70S f/8 fluorite
Celestron C 55F f/8 fluorite
Sets of Zeiss, TeleVue and Brandon eyepieces
Zeiss 7x50 Marine B/GA
Zeiss TM german equatorial
Gitzo 224 with Manfrotto 501 fluid head
Unitron alt-az mount
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EdZ
Professor EdZ
Reged: 02/15/02
Posts: 14732
Loc: Cumberland, R I , USA42N71.4W
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Mike, that is exactly the same BV I pointed to on Alpine Astros page.
Note this in the specs.
Quote:
Optical Length
The optical length of this binocular viewer is approximately 110mm.
That is almost identical to the numerous Chinese binoviewers all over the market.
Therefore, this BV will have almost exactly the same power factor when used with a barlow as almost any other BV.
edz
--------------------
Teach a kid something today. The feeling you'll get is one of life's greatest rewards.
member#21
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Erik Bakker
professor emeritus
Reged: 08/10/06
Posts: 534
Loc: Haren, The Netherlands, Europe
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Hi Ed,
The bino you point to is different. I included a picture of the 60 degree Baader bino to clarify. Regardless, the situation you describe holds true for a Newton. In a refractor, the MaxBright or Mark V need a diagonal to work comfortably, adding another ca. 2 inches of lightpath to that of the bino compared to none ADDED in case of the 60 degree Baader bino.See this link http://www.cloudynights.com/item.php?item_id=12 for a nice report on several binos including the 60 degree Baader/Celestron.
CS,
Erik
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Visual astronomer, main instruments:
Fully mounted Questar 7 P-BB
Celestron C 102F f/8.8 fluorite
Vixen FL 70S f/8 fluorite
Celestron C 55F f/8 fluorite
Sets of Zeiss, TeleVue and Brandon eyepieces
Zeiss 7x50 Marine B/GA
Zeiss TM german equatorial
Gitzo 224 with Manfrotto 501 fluid head
Unitron alt-az mount
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EdZ
Professor EdZ
Reged: 02/15/02
Posts: 14732
Loc: Cumberland, R I , USA42N71.4W
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Quote:
In a refractor, the MaxBright or Mark V need a diagonal to work comfortably, adding another ca. 2 inches of lightpath to that of the bino compared to none ADDED in case of the 60 degree Baader bino.
I addressed this in my comments in my post above.
The shape of this binoviewer makes no difference. And the need to add a 90° diagonal has no affect on the resultant power of putting a barlow in front of the BV. Rarely would anyone put the diagonal between the barlow andd the binoviewer, so the diagonal, almost always being placed IN FRONT of the barlow, adds no length at all to the light path for determination of barlow power factor.
edz
--------------------
Teach a kid something today. The feeling you'll get is one of life's greatest rewards.
member#21
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Erik Bakker
professor emeritus
Reged: 08/10/06
Posts: 534
Loc: Haren, The Netherlands, Europe
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I have a different point of view here. I put my barlow in front of the diagonal, mostly from a mechanical = torque perspective.
YMMV,
CS,
Erik
--------------------
Visual astronomer, main instruments:
Fully mounted Questar 7 P-BB
Celestron C 102F f/8.8 fluorite
Vixen FL 70S f/8 fluorite
Celestron C 55F f/8 fluorite
Sets of Zeiss, TeleVue and Brandon eyepieces
Zeiss 7x50 Marine B/GA
Zeiss TM german equatorial
Gitzo 224 with Manfrotto 501 fluid head
Unitron alt-az mount
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suburbanskies
sage
Reged: 12/18/04
Posts: 253
Loc: New Jersey, USA
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Quote:
I have a different point of view here. I put my barlow in front of the diagonal, mostly from a mechanical = torque perspective.
YMMV,
CS,
Erik
I also put my barlow in front of my diagonal for the same reason.
Mike: I'm not surprised that the AP barlow produces a lower magnification with a given distance between the barlow and the field stop of the eyepiece. The AP barlow's focal length is -127mm which is longer than many other barlows out there.
Amplification depends on two main factors: the focal length of the barlow and the distance between the barlow and the eyepiece's focal plane.
Mark
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EdZ
Professor EdZ
Reged: 02/15/02
Posts: 14732
Loc: Cumberland, R I , USA42N71.4W
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Quote:
I have a different point of view here. I put my barlow in front of the diagonal, mostly from a mechanical = torque perspective.
YMMV,
CS,
Erik
Quote:
Mike: I'm not surprised that the AP barlow produces a lower magnification with a given distance between the barlow and the field stop of the eyepiece. The AP barlow's focal length is -127mm which is longer than many other barlows out there.
Then you should state from the very beginning the arrangement and the uniqueness of your equipment, as these might preclude your's from being a standard upon which someone could get reliable answers regarding what to expect with a barlow in front of a binoviewer.
edz
--------------------
Teach a kid something today. The feeling you'll get is one of life's greatest rewards.
member#21
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