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Glasspath magnification factors, including the 2.6

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#1 Heavens Above

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Posted 18 November 2012 - 03:24 PM

As you may be aware the quoted magnification factor for the Baader 1.7x has been reported on CN as actually more like 1.4x. So I decided to check the magnification factor of all three of my Baader Glasspath correctors: 1.25x, 1.7x & 2.6x. Partially because I wanted to see if my 1.7x was also underpowered, but also to set my mind at rest as to what magnification factor I am getting with my 2.6x. Is this corrector also underpowered?

To do this I set the scope up in daylight and focused on a roof 3 miles away and used the number of tiles visible across the widest part of the eyepiece to judge the factor of magnification.

A slight complication factor is that my scope (Mewlon 210) has moving mirror focusing. This sort of focusing has the unfortunate consequence of changing the focal length of the scope dependent on the distance between the primary and secondary mirrors.

The end result of this is that I would expect to see the differences in magnification provided by the correctors slightly compressed in my scope. I would estimate that they should read as follows:

The 1.25x should in fact provide slightly less than 1.20x, 1.7X should provide approx 1.60x and the 2.6x should provide approx than 2.5x in my Mewlon and other moving mirror catadioptric scopes.

The actual results I obtained were:

1.25x = 1.18x. Exactly what I would have expected in a moving mirror scope. So it’s fair to say the 1.25x is a 1.25x.

1.7x = 1.38x!! So taking into account the focusing generated change of focal length in the Mewlon the 1.7x is in fact more like a 1.45x, which fits with other people’s observations.

2.6x = 2.4x. So the 2.6x I would guess is more like a 2.5x. Pretty close, which from my point of view is a relief?

But let’s get back to 1.7x. This corrector is way under powered. If I had known the true magnification factor of the 1.7x I would never have bought the 1.25x, they are just too similar. I think Baader (and Roland Christen of Astro Physicis, who designed them, and must know of this disparity) have some serious questions to answer. I know that Mr Christen sometimes responds to questions on CN. I would welcome a response from him.

This is all a shame as the correctors have fantastic optical quality, and the Baader MkV binoviewer is just the best. What Baader/Astro Physics should do now is change the rating on the 1.7x to 1.45x and release a new corrector with a 1.9x magnification, as the gap between 1.45x and 2.6x is just too large.

In all tests the correctors were used after the diagonal, and orientated in the correct direction.

#2 Eddgie

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Posted 22 November 2012 - 08:32 AM

I think your results may have been more influenced by the moving mirror than you realize. As the barlow factor increases you get much diffefent mirror seperation whice can skew the focal length.

I belive someone else did this test in a fixed focal length scope and got a much different result.

You might want to validate by testing in fixed focal length scope.

#3 10gauge

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Posted 23 November 2012 - 11:24 AM

The previously quoted magnification factors for the GPCs were based on the T2 prism diagonal in a refractor. With all newer MkVs, they only come with the T2 mirror diagonal. What will the magfnication factors will be with the mirror diagonal in place?

#4 Heavens Above

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Posted 23 November 2012 - 12:10 PM

I think your results may have been more influenced by the moving mirror than you realize. As the barlow factor increases you get much diffefent mirror seperation whice can skew the focal length.

I belive someone else did this test in a fixed focal length scope and got a much different result.

You might want to validate by testing in fixed focal length scope.

Hi Eddgie

If you look at this link CN Forum you will find just the opposite, other people who have tested get the same result as I did, that's what prompted me to test mine.

#5 Heavens Above

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Posted 23 November 2012 - 12:15 PM

Oops! Lets try that link again! First time i've tried inserting a link.

CN Forum

If this does not work try searching: Measuring the Baader Glasspath correctors

#6 Eddgie

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Posted 23 November 2012 - 12:17 PM

Well, I can't see the page for some reason, but it sounds like your work is consistent with what others have measured.

Sorry to hear that the published specs are so far in error.

#7 Heavens Above

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Posted 23 November 2012 - 12:20 PM

The previously quoted magnification factors for the GPCs were based on the T2 prism diagonal in a refractor. With all newer MkVs, they only come with the T2 mirror diagonal. What will the magfnication factors will be with the mirror diagonal in place?

As the Glasspaths should always be used after the diagonal the diagonal used will make no difference to magnification.

#8 tomcody

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Posted 23 November 2012 - 12:56 PM

The previously quoted magnification factors for the GPCs were based on the T2 prism diagonal in a refractor. With all newer MkVs, they only come with the T2 mirror diagonal. What will the magfnication factors will be with the mirror diagonal in place?

As the Glasspaths should always be used after the diagonal the diagonal used will make no difference to magnification.

Just a thought: as the GPC can be installed in either position 1 (screwed into the bottom of the Mark V) or position 2 (screwed into the top of the diagonal) that alone should cause about a 4mm difference in spacing in addition to the length of the Mark V quick change unit (which is listed as 11 MM). Total difference in spacing is about 15mm, I would think that that has to make a difference in magnification and might account for the varied magnifications reported.
Rex

#9 Astrojensen

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Posted 23 November 2012 - 02:18 PM

A slight difference between measured magnifications, such as 1.45x vs 1.5x for the (nominal) 1.7x GPC can be explained by rounding-off differences as well as slight differences in focal plane location in different eyepieces, as well as measuring errors and different methods.

As the Glasspaths should always be used after the diagonal

They don't have to be used after the diagonal. They can be used ahead as well, as long as one remembers to use them in the correct orientation, relative to the binoviewer. If they are set up to be used in a Mark V, with the rim of the cell facing the objective side of the light path, they can't be used ahead of the diagonal, unless you insert them backwards in the 2" nosepiece and secure them with a T2 male adapter ring. The normal thing is to insert them between the diagonal and 2" nosepiece and use the threads of the nosepiece to secure them, but then the rim has to face the eyepiece end of the light path and then you have to turn the lenses around in the cell, if you want to use them with the Mark V.

I often use my GPCs ahead of the diagonal or even stack them, with one in front of the diagonal and one after, to get higher magnification. No ill effects seen so far, quite the contrary.

Clear skies!
Thomas, Denmark

#10 Mark9473

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Posted 23 November 2012 - 03:12 PM

What eyepiece are you guys doing this measurement with? According to my measurements with the Baader 8-24 zoom, the Mark V binoviewer would have to have an optical length of less than 50 mm in order for the 1.7x Glasspath corrector to behave as a 1.5x lens. That is unrealistically short.

This was tested with the GPC in the housing of a T2 prism diagonal (in a refractor), and using various extension tubes between it and a 1.25" clicklock eyepiece clamp holding the eyepiece. No binoviewer. More details of the test in this old thread.

I would assume that Baader ortho's, which also require significant in-focus, give a similar result, but other eyepieces would be different.

#11 Astrojensen

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Posted 23 November 2012 - 04:19 PM

Hi Mark

Pretty odd, getting such widely discordant results. I have measure the magnification factor of my GPCs with the drift method and averaged the results, for best accuracy. There will be a small variation between different eyepieces, due to the slightly different location of the focal plane in their barrels. It seems that several observers have measured the 1.7x GPC to be close to 1.5x in the Mark V or the Maxbright, when used in the Mark V body or just in front of the Maxbright, in the top of the diagonal. This seems to be independent on eyepieces or binoviewer used, save for a small variation between 1.45x and 1.51x.

I used 25mm UO orthos for my measurements, BTW.

Clear skies!
Thomas, Denmark

#12 Mark9473

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Posted 23 November 2012 - 06:24 PM

Thomas, there would be a difference in optical path length between the Maxbrights and the Mark V's so I'd actually expect more difference among those that do the test with a binoviewer in place. Any explanation?

#13 thesubwaypusher

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Posted 24 November 2012 - 10:57 PM

or even stack them, with one in front of the diagonal and one after, to get higher magnification. No ill effects seen so far, quite the contrary.

Clear skies!
Thomas, Denmark

I have never understood why folks need to know the magnification in a given setup. If the image looks good, what's the difference? Unless it's just simple curiosity. Then I guess that makes sense. Because we are all need-to-knowers.

Thomas, I agree with you, and I don't quite understand how these little contraptions can work so well. For example, I was out with the FSQ-106 the other night and first had the extender screwing with the light path, then the 2.6 gpc, then the 1.25gpc. One would think that all this manipulation of the LP would distort it in some way, but Jupiter was perfectly sharp and detailed with all these things installed. In fact, I compared that setup with comparable eyepieces and could not tell the difference.

Thanks, Chris

#14 tomcody

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Posted 25 November 2012 - 09:29 AM

Thomas, there would be a difference in optical path length between the Maxbrights and the Mark V's so I'd actually expect more difference among those that do the test with a binoviewer in place. Any explanation?

The MarkV's (with the quick coupling) are listed on the Baader site as 123mm.
The Maxbrights at 110mm, the quick coupling at 11mm, total 121mm.
So if you use both with the quick coupling, there is only 2mm difference, more without it.
Rex

#15 10gauge

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Posted 25 November 2012 - 09:42 AM

Knowledge of magnification factors can give you an idea of how to chart a series of magnifications that won't be redundant and yet give you magnification range up to 300x with only two EP pairs. It could help determine what set of EP pairs to buy for bino use. I already own the 24 PO, I am trying to determine what to get as the second pair...

#16 Eddgie

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Posted 25 November 2012 - 01:31 PM

Don't tell this to the "Less Glass is better" crowd on the Eyepiece forums.

Heck to listen to them, anyone that is looking though a Nagler is looking though a Coke bottle bottom.

Modern coatings and manufacturing machines make multiple element configurations work exceptionally well.

#17 thesubwaypusher

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Posted 01 December 2012 - 02:53 PM

Knowledge of magnification factors can give you an idea of how to chart a series of magnifications that won't be redundant and yet give you magnification range up to 300x with only two EP pairs. It could help determine what set of EP pairs to buy for bino use. I already own the 24 PO, I am trying to determine what to get as the second pair...

Gottcha!

#18 thesubwaypusher

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Posted 01 December 2012 - 02:53 PM

Modern coatings and manufacturing machines make multiple element configurations work exceptionally well.

I agree.

#19 Mark9473

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Posted 21 February 2013 - 05:30 PM

I'm digging up this thread to report my own measurements from an evening spent looking at delta Orionis.

Equipment used:
- APM 107 mm f/6.5 apo; FL = 700 mm
- Baader T2 prism "T2P" (the Zeiss prism with 34 mm clear aperture) with 2" nosepiece ("NP")
- Baader 2.6x and 1.7x GPC
- Baader Maxbright binoviewer ("MBBV") without nosepiece, threaded directly on the prism housing
- Circle T volcano top 18mm ortho EP
- an 18mm extension ("ext") that threads into the eyepiece (to simulate effect of eyepieces having different focus position)

Configurations tested and drift timing results:
(1) 2" NP / T2P / MBBV / EP --> t = 256 sec
(2) 2" NP / T2P / MBBV / ext / EP --> will not focus
(3) 2" NP / 2.6x GPC / T2P / MBBV / EP --> t = 84 sec MAG = 3.05x
(4) 2" NP / 2.6x GPC / T2P / MBBV / ext / EP --> t = 77 sec MAG = 3.32x
(5) 2" NP / T2P / 2.6x GPC / MBBV / EP --> t = 104 sec MAG = 2.46x
(6) 2" NP / T2P / 2.6x GPC / MBBV / ext / EP --> t = 94 sec MAG = 2.72x
(7) 2" NP / 1.7x GPC / T2P / MBBV / EP --> t = 167 sec MAG = 1.53x
(8) 2" NP / 1.7x GPC / T2P / MBBV / ext / EP --> t = 159 sec MAG = 1.61x
(9) 2" NP / T2P / 1.7x GPC / MBBV / EP --> t = 185 sec MAG = 1.38x
(10) 2" NP / T2P / 1.7x GPC / MBBV / ext / EP --> t = 176 sec MAG = 1.45x

If the weather cooperates in coming days, I'll do these tests again with my Mewlon to see the effect of mirror focussing, and I would also like to do some tests with the AP Barcon.

#20 Mark9473

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Posted 04 March 2013 - 05:31 PM

I wanted to add some more data but I'm too late to edit my previous post.
For starters, I'm adding the focus position to some of the below configurations. The zero point is the 18 mm VT ortho used without a binoviewer (in the same Baader T2 prism, but with a 1.25" clicklock eyepiece clamp). Theses measurements are read from the focusser drawtube and therefore +/- 1 mm.

Equipment used:
- APM 107 mm f/6.5 apo; FL = 700 mm
- Baader T2 prism "T2P" (the Zeiss prism with 34 mm clear aperture) with 2" nosepiece ("NP")
- Baader 2.6x and 1.7x GPC
- Baader Maxbright binoviewer ("MBBV") without nosepiece, threaded directly on the prism housing
- Circle T volcano top 18mm ortho EP
- an 18mm extension ("ext") that threads into the eyepiece (to simulate effect of eyepieces having different focus position)

Configurations tested and drift timing results:
(1) 2" NP / T2P / MBBV / EP --> t = 256 sec
focus position = 78 mm inward compared to mono-viewing.

(2) 2" NP / T2P / MBBV / ext / EP --> will not focus

(3) 2" NP / 2.6x GPC / T2P / MBBV / EP --> t = 84 sec MAG = 3.05x
focus position = 12 mm outward so brings binoviewer focus out by 90 mm.

(4) 2" NP / 2.6x GPC / T2P / MBBV / ext / EP --> t = 77 sec MAG = 3.32x

(5) 2" NP / T2P / 2.6x GPC / MBBV / EP --> t = 104 sec MAG = 2.46x
focus position = 19 mm inward so brings binoviewer focus out by 59 mm.

(6) 2" NP / T2P / 2.6x GPC / MBBV / ext / EP --> t = 94 sec MAG = 2.72x

(7) 2" NP / 1.7x GPC / T2P / MBBV / EP --> t = 167 sec MAG = 1.53x
focus position = 32 mm inward so brings binoviewer focus out by 46 mm.

(8) 2" NP / 1.7x GPC / T2P / MBBV / ext / EP --> t = 159 sec MAG = 1.61x

(9) 2" NP / T2P / 1.7x GPC / MBBV / EP --> t = 185 sec MAG = 1.38x
focus position = 50 mm inward so brings binoviewer focus out by 28 mm.

(10) 2" NP / T2P / 1.7x GPC / MBBV / ext / EP --> t = 176 sec MAG = 1.45x

Focus position is obviously dependent on the eyepieces used. With my particular set-up the 18mm VT orthos in the binoviewer without GPC focus at 15 mm off the end of the focusser drawtube (meaning it's almost fully racked in). The 25mm VT orthos are 2 mm further in, and my 25mm Circle-T Erfles are 11 mm further in from the 18mm VT (so a mere 4 mm before the end). My 12.5mm BGO's don't come to focus.

I drift timed the 25mm Erfles at 7min 13sec on delta Ori so they give me a 1.8° TFOV at 28x magnification - not bad I think! Their field stop size is specified at 22.3 mm so a good match for my MaxBright binoviewer. In my Mewlon (FL = 2560mm effective) they give 0.48° TFOV at 102x magnification (assuming the 1.25" prism without binoviewer gives the native 2415mm FL so 97x magnification - drift time here gives 0.51° TFOV).

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