Jump to content


Photo

Measuring the Baader Glasspath correctors

  • Please log in to reply
30 replies to this topic

#1 Astrojensen

Astrojensen

    Fly Me to the Moon

  • *****
  • Posts: 5454
  • Joined: 05 Oct 2008
  • Loc: Bornholm, Denmark

Posted 23 May 2012 - 07:41 AM

Hello!

To satisfy my own curiosity, I decided to measure my Baader Glasspath Correctors (GPC's), to find out, just how much they magnify, when used with my Baader Maxbright binoviewer. For the sake of comfort and laziness, I decided to do so in the daytime. I set up my Zeiss 60/850mm refractor on a Zeiss TM mount and timed the drift of the tip of a distant antenna, as the motor drive rotated the scope and moved the field of view across the antenna. Sort of doing drift timing the backward way... But it worked just fine.

So, here's what I found:

1. 1.25x GPC, used in top of Zeiss T2 prism: 1.24x. Close to the listed figure.

2. 1.25x GPC, used in front of Zeiss T2 prism: 1.31x. No surprises. Difference very slight and barely visible, yet clearly gives more extra back focus.

3. 1.7x GPC, used in top of Zeiss T2 prism: 1.51x. What the hey?

4. 1.7x GPC, used in front of Zeiss T2 prism: 1.65x. What? Not even 1.7x here?


This is seriously surprising! This also means that many if the magnifications listed in my old observing reports are seriously in error and too high by a factor of about 15%! Where I thought I was using 204x, I was only at 180x and so on.

I also measured my old east asian barlow. With a 1.25" nosepiece on the Maxbright and into the barlow, it worked at 4x. With the barlow element unscrewed and threaded into the 1.25" nosepiece, it was at 3.6x.

This leaves a huge gap between 1.65x and 3.5x. Time to get that 2.6x Baader GPC!


Clear skies!
Thomas, Denmark

#2 Eddgie

Eddgie

    Voyager 1

  • *****
  • Posts: 13178
  • Joined: 01 Feb 2006

Posted 23 May 2012 - 09:51 AM

Thanks for posting this.

Just last night, I used the 1.3x GPC on top of my standard T2 diagonal. I was hoping to get a bit more magnificaiton in my C14 than I could get with my shortest eyepiece pair (12mm), but when I put it in, it seemed like the magnification was not quite as much as I had expected.

And it was your tip that got me to put the 1.3x GPC in front of my T2 when used in my 6" APO. The scope did not quite reach focus with the GPC behind the diagonal, but did reach with it in front. Only a couple of millimeters to spare, but that is all it takes. This kept me from going to the 1.7x (or should we say 1.5x) corrector...

Good idea for the test though, and thanks for posting the resluts.

#3 tomcody

tomcody

    Surveyor 1

  • *****
  • Posts: 1798
  • Joined: 06 Jul 2008
  • Loc: Titusville, Florida

Posted 23 May 2012 - 10:21 AM

So, here's what I found:

1. 1.25x GPC, used in top of Zeiss T2 prism: 1.24x. Close to the listed figure.

2. 1.25x GPC, used in front of Zeiss T2 prism: 1.31x. No surprises. Difference very slight and barely visible, yet clearly gives more extra back focus.

3. 1.7x GPC, used in top of Zeiss T2 prism: 1.51x. What the hey?

4. 1.7x GPC, used in front of Zeiss T2 prism: 1.65x. What? Not even 1.7x here?
Thomas, Denmark

Thomas,
I was just reading a thread (on the Yahoo AP users group) where Roland talks about the positioning of the correctors (which way they face) as the 2.6 is installed in the opposite direction as the other two on the Mark V's and how it must be due to the curvature of the lens.
It was mentioned on the thread that the 1.25 and 1.7 are installed opposite on the Maxbrights and no clear explanation was provided. Perhaps the 1.7 needs to be turned in the opposite direction to give the full 1.7x power on the Maxbrights? Roland mentioned removing the lens and reversing it in the cell (on Yahoo AP user group post # 30251)
http://tech.groups.y...?threaded=1&l=1
So maybe this is a design issue when using that corrector with the Maxbrights? Just a thought! :question:
Rex


#4 Astrojensen

Astrojensen

    Fly Me to the Moon

  • *****
  • Posts: 5454
  • Joined: 05 Oct 2008
  • Loc: Bornholm, Denmark

Posted 23 May 2012 - 12:04 PM

So maybe this is a design issue when using that corrector with the Maxbrights?


No. The lenses must always face the binoviewer the same way, even if the cell doesn't. If they don't, then the corrector lens introduces horrible chromatic aberration! Just try it. It is very easy to tell if the lens is facing the wrong way in the cell. There is clear instructions on this in the Baader manual.

The problem with the Mark V, is that the GPC's can be mounted in two different positions:

1. In the binoviewer itself, or

2. In the diagonal housing. Whether just in front of the bino or in front of the diagonal housing, the GPC always faces the same way. Therefore there is not three different positions.

In position 2, it must be turned 180°, compared to position 1. Add to this that the 2.6x GPC can also be mounted in both positions but is designed to be used in only position 2, and you've got one big mess. Add the fact that Baader had wrong instructions on their website for a while, and the confusion is total. Some could get the 2.6x to work, others couldn't. When I received the 1.7x - sorry, the 1.5x - GPC, the lens was mounted to be used in a Mark V in position 1. This was very obvious at first light. I just removed the retaining ring, flipped the lens, and put the retaining ring back. Done.

With the Maxbright, the GPC's can only be used in position 2, so there is less confusion.

It is very clear from all this, that the 1.7x GPC has always been a 1.5x GPC, also in the Mark V, unless used in front of the diagonal, in position 2. Then it would give close to 1.7x, but only with the Mark V.

I guess someone should make some illustrations to guide users through all this. Baader hasn't done a good job at it so far.


Clear skies!
Thomas, Denmark

#5 tomcody

tomcody

    Surveyor 1

  • *****
  • Posts: 1798
  • Joined: 06 Jul 2008
  • Loc: Titusville, Florida

Posted 23 May 2012 - 12:56 PM

No. The lenses must always face the binoviewer the same way, even if the cell doesn't. If they don't, then the corrector lens introduces horrible chromatic aberration! Just try it. It is very easy to tell if the lens is facing the wrong way in the cell. There is clear instructions on this in the Baader manual.


When I received the 1.7x - sorry, the 1.5x - GPC, the lens was mounted to be used in a Mark V in position 1. This was very obvious at first light. I just removed the retaining ring, flipped the lens, and put the retaining ring back. Done.

Thomas here is the Baader manual that I am using:
http://www.alpineast...nstructions.pdf
I can not find any instructions on reversing the lens in the cell or which way the lens should face (by its curvature) . Do you have different instructions available to you?
Rex

#6 junomike

junomike

    Surveyor 1

  • *****
  • Posts: 1987
  • Joined: 07 Sep 2009
  • Loc: Ontario

Posted 23 May 2012 - 12:56 PM

Thomas, Now I'm confused? Is the proper way to use the 2.6X GPC with the flange closest to the Binoviewer and the lens facing the Diagonal?

Mike

#7 tomcody

tomcody

    Surveyor 1

  • *****
  • Posts: 1798
  • Joined: 06 Jul 2008
  • Loc: Titusville, Florida

Posted 23 May 2012 - 01:05 PM

Thomas, Now I'm confused? Is the proper way to use the 2.6X GPC with the flange closest to the Binoviewer and the lens facing the Diagonal?

Mike

Yes, there is a diagram on the Astro-Physics site that shows the correct orientaton. Its on the AP site , Baader Mark V page, in the corrector paragraph.
Rex

#8 Astrojensen

Astrojensen

    Fly Me to the Moon

  • *****
  • Posts: 5454
  • Joined: 05 Oct 2008
  • Loc: Bornholm, Denmark

Posted 23 May 2012 - 01:13 PM

Is the proper way to use the 2.6X GPC with the flange closest to the Binoviewer and the lens facing the Diagonal?



Yes.

HOWEVER! Baader, at some time, offered to make 2.6x GPC's for the Mark V, that were designed to be threaded into the bino, just like the 1.25x and 1.7x GPC's!!! But just observe something with it, perhaps the Moon or something, and it will be very obvious if the lenses are facing one way or the other. The image will suffer noticeably, if the lens faces the wrong way. With the Mark V, you can use the cell in either position 1 or 2, so there really is no problems. With the Maxbright, the situation is worse, if the 2.6x GPC is accidentally turned the wrong way at the factory, since it can be used only in position 2, in the diagonal. That could be a problem, because:

ON NO ACCOUNT should you take the 2.6x GPC apart!!! It has air-spaced lenses and is carefully adjusted at the factory. If you own a Maxbright and is sent a 2.6x GPC with the lenses facing the wrong way, you have to send it back. It is probably not a trivial thing to adjust such a small air-spaced lens.


Clear skies!
Thomas, Denmark

#9 Astrojensen

Astrojensen

    Fly Me to the Moon

  • *****
  • Posts: 5454
  • Joined: 05 Oct 2008
  • Loc: Bornholm, Denmark

Posted 23 May 2012 - 01:17 PM

Yes, there is a diagram on the Astro-Physics site that shows the correct orientaton. Its on the AP site , Baader Mark V page, in the corrector paragraph.
Rex


Thanks to Rex. Here's a link:

http://www.astro-phy...th 12-20-11.pdf


Clear skies!
Thomas, Denmark

#10 Astrojensen

Astrojensen

    Fly Me to the Moon

  • *****
  • Posts: 5454
  • Joined: 05 Oct 2008
  • Loc: Bornholm, Denmark

Posted 23 May 2012 - 01:26 PM

Thomas here is the Baader manual that I am using:
http://www.alpineast...nstructions.pdf
I can not find any instructions on reversing the lens in the cell or which way the lens should face (by its curvature) . Do you have different instructions available to you?
Rex



Hi Rex

Yes, I have a German pamphlet about the T2 system, in which the different positions of the GPC's are explained. The convex side of the lenses must face the objective of the telescope. The instructions about reversing the lenses in their cells are as detailed as: "Loosen retaining ring, flip lens, tighten ring. Enjoy." And: "Don't mess with the 2.6x GPC!"


Clear skies!
Thomas, Denmark

#11 tomcody

tomcody

    Surveyor 1

  • *****
  • Posts: 1798
  • Joined: 06 Jul 2008
  • Loc: Titusville, Florida

Posted 23 May 2012 - 02:09 PM

Thanks, Thomas
Rex

#12 Astrojensen

Astrojensen

    Fly Me to the Moon

  • *****
  • Posts: 5454
  • Joined: 05 Oct 2008
  • Loc: Bornholm, Denmark

Posted 23 May 2012 - 02:36 PM

You're welcome. Am working right now on a series of drawings that show how much each GPC magnifies in the different positions and what goes where.


Clear skies!
Thomas, Denmark

#13 junomike

junomike

    Surveyor 1

  • *****
  • Posts: 1987
  • Joined: 07 Sep 2009
  • Loc: Ontario

Posted 23 May 2012 - 04:08 PM

Thanks guys, that clarifies things!

Mike

#14 ewave

ewave

    Apollo

  • *****
  • Posts: 1241
  • Joined: 16 May 2009
  • Loc: northwest NJ

Posted 23 May 2012 - 05:50 PM

Thanks Thomas! I was hoping that I can use the 1.25x gp for my TMB-92L instead of the 1.7 (er..um. 1.5x) yet still reach focus......cant wait to see your diagrams.

#15 Scott99

Scott99

    Mercury-Atlas

  • *****
  • Posts: 2933
  • Joined: 10 May 2007
  • Loc: New England

Posted 24 May 2012 - 01:55 PM

Thomas - thanks for posting, it's very useful information. In fact, this reminded me of a thread posted on the AP Yahoo group from years ago, where someone used a tape measure, he came out w/ very similar results. Looks like the specs need to be updated on these!

http://tech.groups.y...g/message/33096

1.25x corrector - 1.2x
1.70x corrector - 1.5x
Barcon lens threaded to prism diagonal - 2.5x
Barcon lens + 1.25x corrector - 2.8x
Barcon lens + 1.7x corrector - 3.2x
Barcon used with extension tube - 2.9x (approximate, need another
extension tube to reach focus)
TV Big Barlow - 3.9x (used the Barcon extension tube to reach focus)

#16 Tamiji Homma

Tamiji Homma

    Gemini

  • *****
  • Posts: 3141
  • Joined: 24 Feb 2007
  • Loc: California, USA

Posted 24 May 2012 - 03:51 PM

I've measured Barlow factor of various combinations that I use.

I attached a file. If you are interested, take a look :)

Tammy

Attached Files



#17 Astrojensen

Astrojensen

    Fly Me to the Moon

  • *****
  • Posts: 5454
  • Joined: 05 Oct 2008
  • Loc: Bornholm, Denmark

Posted 25 May 2012 - 04:29 AM

Hi Tammy

Lots of excellent info. I'll chew on it a bit and see what I can use in my diagrams. May also send you a PM later about some of it.


Clear skies!
Thomas, Denmark

#18 Moonglum

Moonglum

    Viking 1

  • -----
  • Posts: 576
  • Joined: 01 Jun 2008

Posted 25 May 2012 - 02:05 PM

Anyone without kids and not working overtime measure the 2.6 actual magnification yet?

#19 Astrojensen

Astrojensen

    Fly Me to the Moon

  • *****
  • Posts: 5454
  • Joined: 05 Oct 2008
  • Loc: Bornholm, Denmark

Posted 25 May 2012 - 03:02 PM

That would be very welcome info. I plan a purchase.


Clear skies!
Thomas, Denmark

#20 ewave

ewave

    Apollo

  • *****
  • Posts: 1241
  • Joined: 16 May 2009
  • Loc: northwest NJ

Posted 25 May 2012 - 04:34 PM

OK can someone tell me what this is:

Part # ORJ-R : 2" Refractor/SCT 1.8X Glasspath Corrector (needs T2 Diagonal) NEW * Low Stock $252

#21 Astrojensen

Astrojensen

    Fly Me to the Moon

  • *****
  • Posts: 5454
  • Joined: 05 Oct 2008
  • Loc: Bornholm, Denmark

Posted 25 May 2012 - 05:01 PM

OK can someone tell me what this is:

Part # ORJ-R : 2" Refractor/SCT 1.8X Glasspath Corrector (needs T2 Diagonal)



It's this one:

http://www.baader-pl...56305_gross.jpg

A 2", 1.8x GPC for fast refractors and SCT's. Haven't tried it. Perhaps Tammy has one?


Clear skies!
Thomas, Denmark

#22 Tamiji Homma

Tamiji Homma

    Gemini

  • *****
  • Posts: 3141
  • Joined: 24 Feb 2007
  • Loc: California, USA

Posted 25 May 2012 - 05:30 PM

Hi Thomas,

Yes, I have one.

I use this with refractors:
Posted Image

I use this configuration with MakNewt MN-86:
Posted Image

Tammy

#23 ewave

ewave

    Apollo

  • *****
  • Posts: 1241
  • Joined: 16 May 2009
  • Loc: northwest NJ

Posted 25 May 2012 - 06:14 PM

wow...ok the 2" looks like it will add quite a bit of focus travel? Perhaps will work with my fast APO?
Tammy, any travel distance numbers figured out yet for the 1.8x?

#24 Tamiji Homma

Tamiji Homma

    Gemini

  • *****
  • Posts: 3141
  • Joined: 24 Feb 2007
  • Loc: California, USA

Posted 25 May 2012 - 07:17 PM

wow...ok the 2" looks like it will add quite a bit of focus travel? Perhaps will work with my fast APO?
Tammy, any travel distance numbers figured out yet for the 1.8x?


When you attach the 1.8x Barlow lens, it pushes focuser about 65mm outward to reach focus.

I use it with f/5.5 refractor. It works well.

Tammy

#25 tomcody

tomcody

    Surveyor 1

  • *****
  • Posts: 1798
  • Joined: 06 Jul 2008
  • Loc: Titusville, Florida

Posted 25 May 2012 - 07:43 PM

OK can someone tell me what this is:

Part # ORJ-R : 2" Refractor/SCT 1.8X Glasspath Corrector (needs T2 Diagonal)



It's this one:

http://www.baader-pl...56305_gross.jpg

A 2", 1.8x GPC for fast refractors and SCT's. Haven't tried it. Perhaps Tammy has one?


Clear skies!
Thomas, Denmark


Here is a link to it on Alpine Astro:
http://www.alpineast...viewers.htm#ORJ
Rex






Cloudy Nights LLC
Cloudy Nights Sponsor: Astronomics