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Equipment Discussions >> Binoviewers

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Keith-in-Texas
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Reged: 10/16/06

Loc: Stephenville, TX
Re: TEC 140 and MK V bino..... [Re: HowardK]
      #6142059 - 10/16/13 11:37 PM

I read in an older thread on the Mark V bino that using it without a GPC can cause some unwanted reflections due to the GPC not being present to cover some highly reflective internal components.

In the same thread there was mention by some they purchased an extra GPC and removed the optics and used the GPC without optics to eliminate the internal reflections.

I always use a GPC in my Mark V to avoid this potential issue.

Best regards,

Keith


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Stellarfire
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Reged: 07/10/11

Loc: Switzerland
Re: TEC 140 and MK V bino..... new [Re: Keith-in-Texas]
      #6144986 - 10/18/13 02:20 PM

Yes, the Mark V with empty GPC's is discussed here (see posts #6081488 - 15/09/13 03:50 AM, and #5664676 - 06/02/13 06:02 AM)

I am the Swiss guy who uses two Baader Mark V binoviewers without GPC's.
I do this since I consider the small GPC's as the potentially weakest part in the entire optical train. My 6" f/7.3 APO refractor / Mark V combo comes with most eyepieces to focus without a GPC. So - in this particular case - to me there is no real need for a GPC. I therefore use both Mark V's with empty black GPC frames put in place. This way the chromed ring on inside of the Mark V just behind the T-2 Quick Changer is covered and no reflections are degrading the image.

For high power observations, the wanted increased focal length is achieved by a 2" Powermate, an A-P BARCON or BARADV, or the Baader FFC. Any additional GPC in the light path makes no sense to me.


Stephan


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t.r.
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Reged: 02/14/08

Loc: Upstate NY
Re: TEC 140 and MK V bino..... new [Re: Stellarfire]
      #6145062 - 10/18/13 03:03 PM

If I remember correctly the old Barcon barlow acts as a 1.7x compensator, correct?

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mark8888
Carpal Tunnel


Reged: 09/24/10

Re: TEC 140 and MK V bino..... new [Re: Stellarfire]
      #6145096 - 10/18/13 03:27 PM

Quote:

I do this since I consider the small GPC's as the potentially weakest part in the entire optical train.




I'm interested in this comment, including "potentially"... have you compared the views using the GPCs (for example the 1.7) to views using a BARCON or BARADV (without a GPC installed) and found that the GPCs are inferior? If so, how? Or are you assuming that the view would somehow be worse because they are so small?


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Stellarfire
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Reged: 07/10/11

Loc: Switzerland
Re: TEC 140 and MK V bino..... new [Re: t.r.]
      #6145124 - 10/18/13 03:47 PM

In combination with the long light path of the Mark V binoviewer, the BARCON (placed in front of the diagonal) yields slightly over 2.5x

Tammy provided us with following BARCON focal ratio figures when used without additional GPC (see his post #5664099 - 05/02/13 06:14 PM):

Quote:


2.52x BARCON-AP16T-T2Mirror-QC-MarkV-Delos-10

2.59x BARCON-AP16T-T2Mirror-QC-MarkV-Docter-UWA-12.5




Stephan


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Stellarfire
Pooh-Bah


Reged: 07/10/11

Loc: Switzerland
Re: TEC 140 and MK V bino..... new [Re: mark8888]
      #6145180 - 10/18/13 04:24 PM

Quote:

Quote:

I do this since I consider the small GPC's as the potentially weakest part in the entire optical train.




I'm interested in this comment, including "potentially"... have you compared the views using the GPCs (for example the 1.7) to views using a BARCON or BARADV (without a GPC installed) and found that the GPCs are inferior? If so, how? Or are you assuming that the view would somehow be worse because they are so small?




I use most of the time a T-2 Prism Diagonal and prefer to achieve the desired focal length before the diagonal, instead of afterwards (as a GPC does).

And yes, your last line describes exactly what I am thinking. Looking at the small dimensions of the 2-element lens of the GPC which sells at $118.00 retail, one can imagine the required high level of precision and polish of this critical part...
I did some comparos on Luna and found that differences with GPC against no GPC (substituted by a high quality Barlow or Powermate element placed in front of diagonal) are subtle, but become visible at high powers over 400x. At low powers, there is no visible difference of image quality.

Stephan

Edited by Stellarfire (10/19/13 02:30 AM)


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RAKing
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Reged: 12/28/07

Loc: West of the D.C. Nebula
Re: TEC 140 and MK V bino..... new [Re: t.r.]
      #6145282 - 10/18/13 05:28 PM

Quote:

If I remember correctly the old Barcon barlow acts as a 1.7x compensator, correct?




That is correct if you just use it as a Barlow with an eyepiece.

For binoviewing, we unscrew the Barcon from the eyepiece holder and thread it directly to the front of the T2 diagonal - replacing the AP nosepiece. Used this way, the Barcon was said to achieve a 2.4x magnification factor.

It looks like Tammy is keeping the AP nosepiece in place and threading the Barcon to the front of that, which will boost the magnification factor even more.

Cheers,

Ron


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tomcody
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Reged: 07/06/08

Loc: Titusville, Florida
Re: TEC 140 and MK V bino..... new [Re: Stellarfire]
      #6146257 - 10/19/13 09:14 AM

Quote:

Quote:

Quote:

I do this since I consider the small GPC's as the potentially weakest part in the entire optical train.




I'm interested in this comment, including "potentially"... have you compared the views using the GPCs (for example the 1.7) to views using a BARCON or BARADV (without a GPC installed) and found that the GPCs are inferior? If so, how? Or are you assuming that the view would somehow be worse because they are so small?




I use most of the time a T-2 Prism Diagonal and prefer to achieve the desired focal length before the diagonal, instead of afterwards (as a GPC does).

And yes, your last line describes exactly what I am thinking. Looking at the small dimensions of the 2-element lens of the GPC which sells at $118.00 retail, one can imagine the required high level of precision and polish of this critical part...
I did some comparos on Luna and found that differences with GPC against no GPC (substituted by a high quality Barlow or Powermate element placed in front of diagonal) are subtle, but become visible at high powers over 400x. At low powers, there is no visible difference of image quality.

Stephan



I also notice a small difference in quality of view in favor of the Barcon over the GPC when using a Baader/ Ziess prism, I was wondering why? but now I think it is not a quality difference between the Barcon and GPC, rather only a difference of magnifying before or after the prism!
I also do not notice any difference between the two when using a Maxbright mirror instead of the prism.
Rex


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