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Posts Made By: Mark Nevitt

August 18, 2005 07:59 PM Forum: Refractors

Vixen ED Refractors

Posted By Mark Nevitt
According to the Vixen web site. Their ED refractors have an ED lens and a Kruz Flint lens. Does anyone know what glass types are used and what level of color correction is achieved?

Mark

December 8, 2005 10:56 PM Forum: Refractors

Stellarvue 102BV

Posted By Mark Nevitt
I was at the Stellarvue website reading a description of their
102BV. In the descpition they state the 102 optical system provides excellent color correction thanks to high dispersion ED lens. I may be wrong butI thought that ED glasses were low
dispersion.

Mark

September 3, 2006 02:09 PM Forum: Refractors

OTA Diameter

Posted By Mark Nevitt
I was at the Orion website looking at the ED120 ota. The tube rings listed for this scope are 116mm ID. This is a 120mm scope shouldn't the ota be at least 120mm in diameter and ideally larger than the 120mm diameter of the objective.

Mark

August 12, 2007 05:26 PM Forum: Refractors

AP color correction curves

Posted By Mark Nevitt
On the Astro-Physics web site under the link for optical design, they have links to the color correction curves for various scopes. My question is how do you interpet these graphs.


Thanks

Mark

August 20, 2007 05:35 PM Forum: Refractors

FK5 glass

Posted By Mark Nevitt
Is there any advantages to designing an achro that uses Fk5 and a lanthanum mate glass. I thought tht lanthanum was used for eyepieces.

Mark

October 5, 2007 02:36 AM Forum: Refractors

Achro Design

Posted By Mark Nevitt
If a scope is called a Fraunhofer doublet with BK7 and F2 glass does it have to have CeF correction or can the correction be something different. IF the correction is different is it still a Fraunhofer.

Mark

May 16, 2008 11:06 PM Forum: Refractors

Edge of field performance

Posted By Mark Nevitt
Lets say you had 2 refractors. One was a 6" f/8 and the other a 3" f/8. The true field size in the 3" scope would be 2x larger than the 6" scope with the same eyepiece. What is the best way to compare the edge of field performance of the objective. With the same eyepiece in the scopes or with different eyepieces in each scope of the same design(Nagler)that would show the same true field.

Mark

June 1, 2008 04:29 PM Forum: Refractors

Antares Achros

Posted By Mark Nevitt
Recently I was reading the description of various Antares refractors. I came across some terms used to describe them. "Vixen Spec", "LDA(low dispersion achro)", "ULDA(ultra low dispersion achro)", and "well corrected". Do any of these terms actually have a meaning? I would think that only Vixen could use the term "Vixen Spec" to describe its refractors.

Mark

May 16, 2009 04:36 PM Forum: Refractors

using a barlow

Posted By Mark Nevitt
Does using a barlow change the size of the airy disk produced by a refractor. If you put a 2x barlow in an f/10 scope does it produce an airy disk of the same diameter as a f/20 scope of the same aperture

Mark

August 15, 2006 02:14 AM Forum: Refractors

What are the challenges for making fast APO refrac

Posted By Mark Nevitt
I not positive but I think spherochromatism puts a limit on how fast you can make a lens.

Mark Nevitt

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