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Olivier Biot
Amused
*****

Reged: 04/25/05

Loc: 51°N (Belgium)
Comparison of 24mm-26mm Eyepieces
      #5076852 - 02/17/12 11:36 AM

Comparison of 24mm-26mm Eyepieces

By William Paolini.

Edited by jrcrilly (02/17/12 11:40 AM)


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dyslexic nam
Carpal Tunnel
*****

Reged: 01/28/08

Loc: PEI, Canada
Re: Comparison of 24mm-26mm Eyepieces new [Re: Olivier Biot]
      #5076853 - 02/17/12 11:38 AM

Yay

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jrbarnett
Eyepiece Hooligan
*****

Reged: 02/28/06

Loc: Petaluma, CA
Re: Comparison of 24mm-26mm Eyepieces new [Re: dyslexic nam]
      #5076928 - 02/17/12 12:16 PM

An absolute gold mine of interesting data.

A few initial observations:

1. Not all "orthos" are created equal.

2. Televue knows edge correction.

3. On a budget? Think UO Abbe Ortho or Sterling Plossl.

4. And, most importantly, Brandon FTW!

Regards,

Jim


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Doug Culbertson
Post Laureate
*****

Reged: 01/06/05

Re: Comparison of 24mm-26mm Eyepieces new [Re: jrbarnett]
      #5076930 - 02/17/12 12:18 PM

Wow, what an amazingly well done comparison. I must admit that there were some surprises, along with some expected results. A thoroughly enjoyable read!

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WarrenM
member


Reged: 07/27/11

Loc: Clovis, Calif., USA
Re: Comparison of 24mm-26mm Eyepieces new [Re: dyslexic nam]
      #5076958 - 02/17/12 12:32 PM

Wow! Now thats what I call a well done comprehensive review. Well done William!

Warren


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Sean Cunneen
Let Me Think
*****

Reged: 08/01/07

Loc: Blue Island Illinois
Re: Comparison of 24mm-26mm Eyepieces new [Re: WarrenM]
      #5076966 - 02/17/12 12:37 PM

Fantastic! A round of applause!

now I am off to Google Sterling...
Sean


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BDS316
Carpal Tunnel


Reged: 09/16/09

Loc: Sol 3
Re: Comparison of 24mm-26mm Eyepieces new [Re: Sean Cunneen]
      #5076984 - 02/17/12 12:48 PM

One take-home message is that you don't have to spend a lot of money to get a great eyepiece. This point was made with STERLING clarity.

Would have been interesting to have seen how well a generic Asian plossl, such as a Synta or GSO would have done...


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Jason B
Proud father of 5!!
*****

Reged: 06/21/04

Loc: Mid-Michigan
Re: Comparison of 24mm-26mm Eyepieces new [Re: Sean Cunneen]
      #5076987 - 02/17/12 12:49 PM

Very well done. The wealth of information is staggering.

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coutleef
Post Laureate
*****

Reged: 02/21/08

Loc: Saint-Donat, Quebec, Canada
Re: Comparison of 24mm-26mm Eyepieces new [Re: Jason B]
      #5077001 - 02/17/12 12:56 PM

Well done Bill. We were waiting for that review for a while and it was definitely worth waiting for.

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Scott99
Carpal Tunnel
*****

Reged: 05/10/07

Loc: New England
Re: Comparison of 24mm-26mm Eyepieces new [Re: coutleef]
      #5077143 - 02/17/12 02:02 PM

great job Bill! That's a lot of work and it's much appreciated.

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Starman1
Vendor (EyepiecesEtc.com)
*****

Reged: 06/24/03

Loc: Los Angeles
Re: Comparison of 24mm-26mm Eyepieces new [Re: Scott99]
      #5077246 - 02/17/12 03:11 PM

This review is exhaustive and much attempt is made to make comparisons valid.

There are a few quibbles I have with his test procedures however:

1) Comparing a 68 degree eyepiece's edge correction with a 50 degree eyepiece's edge correction would seem to be valid, given that the widefield user will be looking for definition at or near the edge of the field just like the narrower field user. However, if we assume that the edge correction of a 50 degree eyepiece is less than perfect at the edge, while a 68 degree eyepiece is perfect at the same 50 degree point in the field, but deteriorates more at the edge, then which eyepiece actually has the better correction? To give a valid comparison, I would want to see the correction obtained at 20, 25, 30, and 34 degrees off axis for each. It could be the widefield eyepiece yields a better-corrected 50 degree field than the 50 degree eyepiece. If so, the edge correction would have to be "field size compensated" to yield a relative ranking.

2) Bill seems to have some confusion about rectilinear distortion and angular magnification distortion and which aberration causes what in the image. Perhaps a good way to think about these two distortions is to picture map projections. If you reduce a globe to a flat representation, then there will be geometric distortions in the map, worst at the edges. We see this all the time in standard flat maps of the world. This is similar to what we would see as rectilinear (geometric) distortion.
If the globe itself is presented and rotated, a country will come around the edge of the globe, come toward you, and move away from you, changing size as it goes, but it will not be geometrically distorted. yet, it will appear to change in size.
Case one represents rectilinear distortion, while case two represents (it's an inexact analogy, I admit)) angular magnification distortion.

Would we want the planet to appear smaller at the edge of the field than the center? Probably not, though this wouldn't seem to be an issue in a driven scope with the planet's image held in the center. So, in the undriven scope, angular magnification distortion would not appear to be a desirable trait, especially in star fields or for viewing double stars.

But, the wider the field, the more the correction of one aberration leads to more of the other, so an eyepiece corrected for AMD will, necessarily, have RD. Since our eyes tend to have a little barrel distortion (positive RD)(it's a brain thing) when viewing the edge of a field, some amount of negative RD (pincushion) seems to result in an undistorted image to our eyes.
If there is too much RD, the object will appear to stretch and change shape as it nears the edge, similar to that Mercator map projection we talked about.

So what's ideal?
Well, in an undriven scope, a low level of AMD for sure. And for the least distortion visible to our eyes in images, a certain amount of RD. Not surprisingly, many good eyepieces are designed this way.

But what about the person who pans across the field? Well, if there is AMD in any significant amount it would appear as if the image is rolling across the surface of a globe. I have a kaleidoscope that does this--the edge appears farther away than the center because the object changes in size as it crosses the field and our brains tell us we are watching a globe rotating.

With a lot of RD and no AMD? Well, we'd see the object change its shape as it moves across the field, but the field could still appear flat. And if the RD amount is chosen to leave only a tiny bit of AMD in the field, we might see very little distortion in the field.

But, extend the field even more, to 82 degrees, or 90 or 100 or 110 degrees. The curves of solution for AMD and RD diverge even more. Having that *just right* about of RD in the field will result in noticeable AMD. So, a designer could solve for AMD and let RD be a larger amount. Given that most of these eyepieces are deep-sky eyepieces, that is probably the right choice. Used as terrestrial eyepieces, the edge of the field would appear quite distorted because we know how tree trunks and building edges are supposed to appear.
We might even tolerate that, though, if the eyepiece was free from astigmatism and the edge was sharp.

But it does indicate that the demands of designing the perfect astronomical eyepiece and perfect terrestrial eyepiece can be quite different.

I refer you to the discussions of RD and AMD which exist on the web, especially as they relate to binoculars and terrestrial usage.

3) Bill also missed the opportunity to discuss astigmatism and field curvature in the eyepieces. Field curvature's visibility might be related to the scope in which the eyepiece is used, but astigmatism is not. Since most of these eyepieces have narrow fields, where astigmatism should be tightly controlled, this could have been an illuminating comparison. I suppose some of that could be garnered from the comparison with Paracorr used, since, if coma and field curvature are more or less corrected, what's left is astigmatism [excluding chromatic aberrations].

All-in-all, a good step toward trying to be fair in comparisons. It was illuminating to see some highly-touted eyepieces come in down the list, and I applaud Bill's lack of that annoying drone about "tinted" eyepieces.


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mercedes_sl1970
professor emeritus
*****

Reged: 12/02/05

Loc: Canberra, Oz
Re: Comparison of 24mm-26mm Eyepieces new [Re: Starman1]
      #5077493 - 02/17/12 06:20 PM

An impressive and thoughtful review. Thank you!

Andrew


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KidOrion
professor emeritus


Reged: 07/07/07

Loc: Carbondale, IL
Re: Comparison of 24mm-26mm Eyepieces new [Re: mercedes_sl1970]
      #5077528 - 02/17/12 06:50 PM

I'm going to go give my $99 24mm SWA a hug.

Great work, Bill!

Edited by KidOrion (02/17/12 06:50 PM)


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Arizona-Ken
Pooh-Bah


Reged: 08/31/08

Loc: Scottsdale, Arizona
Re: Comparison of 24mm-26mm Eyepieces new [Re: KidOrion]
      #5077613 - 02/17/12 07:57 PM

An outstanding review.

An excellent attempt at describing the subtle differences among very good eyepieces and enough detail to allow both beginners to understand the differences and also to allow one to understand why some eyepieces are a bit better for different kinds of objects than others.

Here at CN we get good people to provide great insights on equipment but this is an order of magnitude above most efforts.

Congratulations, Bill.

Arizona Ken


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Doc Bob
professor emeritus
*****

Reged: 02/27/09

Loc: Maryland, USA
Re: Comparison of 24mm-26mm Eyepieces new [Re: Arizona-Ken]
      #5077878 - 02/17/12 11:28 PM

Bill,
Excellent review !! It helps me to now understand what is important when considering purchasing an eyepiece and that my set of Sterlings ain't half bad!!

Regards,
Bob


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Jim Rosenstock
Postmaster
*****

Reged: 07/14/05

Loc: MD, south of the DC Nebula
Re: Comparison of 24mm-26mm Eyepieces new [Re: Olivier Biot]
      #5078066 - 02/18/12 05:34 AM

A dizzying amount of information that I've just skimmed.

I like the way the information is broken down and laid out. It's instructive how an eyepiece can become a personal favorite, and still perform poorly in categories that aren't a personal concern.

I'll be spending more time with this review....and wondering how it would extrapolate to other focal lengths. Anybody else feeling a 12mm shootout?











Jim


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Joe Bergeron
Vendor - Space Art


Reged: 11/10/03

Loc: Upstate NY
Re: Comparison of 24mm-26mm Eyepieces new [Re: Olivier Biot]
      #5078186 - 02/18/12 08:53 AM

What happened to that poor Brandon? It looks like someone sanded the anodized finish off the barrel and added some kind of crude label? Almost as jarring as that putting green atop the Meade.

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rguasto
scholastic sledgehammer
*****

Reged: 11/18/10

Loc: Long Island, NY
Re: Comparison of 24mm-26mm Eyepieces new [Re: Jim Rosenstock]
      #5078194 - 02/18/12 09:01 AM

The 12mm shoot out results;
(read the 24mm shoot out) ...in conclusion all the 12mm EP's show twice the mag and 1/2 the TFOV


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csa/montana
Den Mama
*****

Reged: 05/14/05

Loc: montana
Re: Comparison of 24mm-26mm Eyepieces new [Re: Olivier Biot]
      #5078232 - 02/18/12 09:43 AM

Bill, an absolutely amazing Review!

This review is the ultimate for both beginners and long-time viewers; as it's in terms easily understood.

We all owe you a huge thank you for the time & effort you put into this, to benefit all of us here on CN.

Thank you, Bill!


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waskeyc
journeyman
*****

Reged: 06/27/08

Loc: Virginia
Re: Comparison of 24mm-26mm Eyepieces new [Re: Olivier Biot]
      #5078238 - 02/18/12 09:45 AM

And Bill hits one out of the park!

Great job Bill, fantastic review with scads of useful information.


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