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Delos Dilemma: 17.3mm Delos or 17mm Vixen LVW?

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#51 hottr6



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Posted 07 August 2014 - 08:07 AM

To the OP, if you examine the used-eyepiece market, used Delos' appear in the classifieds almost every day. Used LVWs are rarer than transits of Titan. What is this suggesting?
1) Production quantities of Delos' are more than a magnitude greater than LVWs?
2) Delos owners prefer their Naglers?
3) LVWs are keepers?

Occams Razor suggests #3.
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#52 Eric38


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Posted 07 August 2014 - 08:44 AM


Bottom line here:
The 17mm Vixen LVW is much better in a fast scope, (correction-wise), than the 17.3mm Delos.

"Is" would mean that it's an objective truth.



"It depends on what your definition of "is" is"

#53 JustaBoy



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Posted 07 August 2014 - 11:21 AM

Ok Bill.

#54 Starman1


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Posted 07 August 2014 - 11:59 AM

Well, if two good eyepieces display different amounts of coma in the same scope, and it's certainly possible they do, the reasons could be:

--one eyepiece has a narrower apparent field than the other.  Narrower apparent fields = smaller comatic image at the edge.

--one eyepiece has edge of field vignetting.  Since the outer edges of the comatic star images are considerably fainter than the inner points, rolling off the brightness would make the comatic star images appear shorter

--one eyepiece could have more field curvature than the other.  Nothing makes a comatic star image appear worse than making it a little bigger through de-focusing.

--one eyepiece has more chromatic aberration than another.  Comatic stars differ in size by color.  If the worst coma is accented by chromatic aberration, it will appear worse

--one eyepiece has more astigmatism.  This can spread the comatic star image in length, or in width.  At the worst, become a seagull.  At any rate, it doesn't help hide coma.

--one eyepiece has a higher transmission than another by a big enough margin to make the outer edges of the comatic star images more visible.

--one eyepiece has angular magnification distortion that either shrinks or expands the comatic star images at the edge.


Now, at f/4.7, the comatic star image, with no eyepiece issues added, is about 10X as long as the Airy Disc in a radial direction in a 40mm field, about the size of a 35 Panoptic or 34mm 68 degree ES.

At low power, the resolution of that small an image may be moot.


So if one low power eyepiece displays noticeably more evidence of coma than another, look to the above for reasons.  That doesn't mean you don't see it, just explaining WHY you might see it.

With the Delos, we can rule out astigmatism, and, compared to the LVW, we can rule out field size.  And we can rule out chromatic aberration.

That leaves a few possibles.

#55 Scanning4Comets



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Posted 07 August 2014 - 12:25 PM



Bottom line here:
The 17mm Vixen LVW is much better in a fast scope, (correction-wise), than the 17.3mm Delos.

"Is" would mean that it's an objective truth.



"It depends on what your definition of "is" is"



What kind of mystery is that supposed to be?


This IS an Objective analysis, not a Subjective one, as I did put both in the same scope. Sometimes I get a good laugh at people in here. :roflmao:

Edited by Scanning4Comets, 07 August 2014 - 12:26 PM.

#56 eklf



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Posted 07 August 2014 - 01:02 PM

"It depends on what your definition of "is" is"


Bill should have inhaled...

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