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Equipment Discussions >> Eyepieces

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Sarkikos
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Reged: 12/18/07

Loc: Suburban Maryland, USA
Re: Suggestions for 2' Erecting Diagonals/Prisms new [Re: Jon Isaacs]
      #5621014 - 01/13/13 03:03 PM

My 70mm finder scope with a 20mm illuminated eyepiece gives me 4.7 degrees TFOV. That's plenty for rich field open clusters and such, and great for star hopping. Never seen the bright line, never seen vignetting. It works very well.

Mike


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ensign
professor emeritus


Reged: 12/16/08

Loc: Southwestern Ontario
Re: Suggestions for 2' Erecting Diagonals/Prisms new [Re: Sarkikos]
      #5621168 - 01/13/13 04:30 PM

I have a William Optics 2" erecting diagonal and have used it in a 110mm refractor and am currently using it with an Equinox 80. The copy on the WO website used to say that this diagonal was designed specifically for astronomical use. I have compared the views side by side with my WO 2" dialectric diagonal and noted that the views are essentially identical, except, of course that one is mirror-reversed. I noted no difference in brightness and no lines bisecting any of the views.

I have to admit that this diagonal was a tad on the expensive side at around $240. They don't appear to be available new any more.


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Sarkikos
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Reged: 12/18/07

Loc: Suburban Maryland, USA
Re: Suggestions for 2' Erecting Diagonals/Prisms new [Re: ensign]
      #5621252 - 01/13/13 05:10 PM

Yes, I've also wanted a good 2" true erecting prism, with no reversed image. I know there are some 2" erecting prisms which reverse the image, and are considered good for astronomy. Some think they are better than mirror diagonals, at least for some telescopes. There are threads about this on the Refractor Forum.

But a true 2" erecting prism with no reversed image is something else.

Mike


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DRodrigues
super member


Reged: 08/08/11

Re: Suggestions for 2' Erecting Diagonals/Prisms new [Re: Jon Isaacs]
      #5621303 - 01/13/13 05:38 PM

Quote:

Consider the NP-101 + 31mm Nagler, it's a wonderful richest field scope but a correct image prism would vignette the 4.5 degree TFoV.




At http://www.pt-ducks.com/cr-telescopes.htm#Nikon_FSA-L2 I tested the Nikon FSA-L2 and it doesn't vignette with a 30mm UWA that has a similar field stop of the Nagler 31mm...
You loose a bit of brightness and contrast but you gain a 3.5x zoom!!!


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Jon Isaacs
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Re: Suggestions for 2' Erecting Diagonals/Prisms new [Re: Sarkikos]
      #5622169 - 01/14/13 06:24 AM

Quote:

My 70mm finder scope with a 20mm illuminated eyepiece gives me 4.7 degrees TFOV. That's plenty for rich field open clusters and such, and great for star hopping. Never seen the bright line, never seen vignetting. It works very well.

Mike




Did you look at the erecting diagonal to see what the clear aperture is? At least look at it. As I said, I measured my Orion at 20.0mm, I have seen them much smaller but generally on inexpensive scopes.

Jon


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Jon Isaacs
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Re: Suggestions for 2' Erecting Diagonals/Prisms new [Re: ensign]
      #5622170 - 01/14/13 06:28 AM

Quote:

I have a William Optics 2" erecting diagonal and have used it in a 110mm refractor and am currently using it with an Equinox 80. The copy on the WO website used to say that this diagonal was designed specifically for astronomical use. I have compared the views side by side with my WO 2" dialectric diagonal and noted that the views are essentially identical, except, of course that one is mirror-reversed. I noted no difference in brightness and no lines bisecting any of the views.

I have to admit that this diagonal was a tad on the expensive side at around $240. They don't appear to be available new any more.




Have you tried splitting close double stars it? In another thread on this subject, someone with both the Baader and the WO said the WO had a large clear aperture but did not hold up at high magnifications. The Baader did well at high magnifications but had something closer to 32mm clear aperture.

Jon


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Sarkikos
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Reged: 12/18/07

Loc: Suburban Maryland, USA
Re: Suggestions for 2' Erecting Diagonals/Prisms new [Re: Jon Isaacs]
      #5622369 - 01/14/13 10:04 AM

Jon,

Quote:

Quote:

My 70mm finder scope with a 20mm illuminated eyepiece gives me 4.7 degrees TFOV. That's plenty for rich field open clusters and such, and great for star hopping. Never seen the bright line, never seen vignetting. It works very well.

Mike




Did you look at the erecting diagonal to see what the clear aperture is? At least look at it. As I said, I measured my Orion at 20.0mm, I have seen them much smaller but generally on inexpensive scopes.

Jon




I'll do that. But even if the CA indicates that there should be vignetting - even if I don't see it - I think I'll still use the erecting prism diagonal. When I'm star hopping, that rightsideup-nonreversed image is more important to me than a little lost light.

Mike


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ensign
professor emeritus


Reged: 12/16/08

Loc: Southwestern Ontario
Re: Suggestions for 2' Erecting Diagonals/Prisms new [Re: Jon Isaacs]
      #5622411 - 01/14/13 10:17 AM

Quote:

Quote:

I have a William Optics 2" erecting diagonal and have used it in a 110mm refractor and am currently using it with an Equinox 80. The copy on the WO website used to say that this diagonal was designed specifically for astronomical use. I have compared the views side by side with my WO 2" dialectric diagonal and noted that the views are essentially identical, except, of course that one is mirror-reversed. I noted no difference in brightness and no lines bisecting any of the views.

I have to admit that this diagonal was a tad on the expensive side at around $240. They don't appear to be available new any more.




Have you tried splitting close double stars it? In another thread on this subject, someone with both the Baader and the WO said the WO had a large clear aperture but did not hold up at high magnifications. The Baader did well at high magnifications but had something closer to 32mm clear aperture.

Jon




I am currently using the diagonal in an 80mm refractor as a combination wide-field scope/finder, having sold the 110. I could switch nospieces and try to split some tight doubles with my 9.25 Edge but, unfortunately, in Southern Ontario, cloudy nights is not only a web site but a continuing reality.


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Jon Isaacs
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Reged: 06/16/04

Loc: San Diego and Boulevard, CA
Re: Suggestions for 2' Erecting Diagonals/Prisms new [Re: Sarkikos]
      #5622422 - 01/14/13 10:27 AM

Quote:

I'll do that. But even if the CA indicates that there should be vignetting - even if I don't see it - I think I'll still use the erecting prism diagonal. When I'm star hopping, that rightsideup-nonreversed image is more important to me than a little lost light.

Mike




Mike:

If you prefer the correct images it makes sense to use the correct image diagonal you have, particularly since it is works for you. It's also good to know one's equipment so looking to see the clear aperture of the diagonal is worthwhile.

Vignetting is usually not so easily seen, that suggests that it may not be so important unless it is severe... In this case, the aperture stop is quite near the focal plane so it could actually be restricting the TFoV.

Jon


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