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Meade Series 5000 MWA has arrived....

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#1 Dave Bush

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Posted 18 December 2014 - 06:12 PM

Got the 21mm today.  Interesting that though I ordered directly from Meade's website, it came from OPT.

 

So here are my initial impressions...

 

  • It's smaller and lighter than I expected.  It's about the same size and weight as my 20mm Meade 5000 UWA
  • Eye relief.  Though I can't measure it it is indeed longer than the 20mm UWA.  That one is spec'ed at 17mm.  With the eyecup extended I can easily see the whole field and still be able to blink my eye with no eyelash contact (and I have long lashes much to my wife's dismay). 
  • FOV.  Now I've never looked through a 100º eyepiece so this might be due to that but, when I compare it with the 20mm UWA it seems to me to be maybe 10º wider instead of nearly 20.  I'll leave it to someone else to actually measure it.
  • The field stop is sharp/in focus with an ever so slight blue ring.
  • Because someone was curious on the other thread, the eye lens measures almost exactly 30mm in diameter.

I will try to get the scope out and give it a quick look.  Skies are clear now but I won't have a lot of time.  I'll of course post my impressions later tonight.   

 

Here are a some pics...

Attached Thumbnails

  • MWA1.jpg

Edited by Dave Bush, 18 December 2014 - 06:19 PM.

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#2 Dave Bush

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Posted 18 December 2014 - 06:13 PM

Second Pic...

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  • MWA2.jpg


#3 Dave Bush

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Posted 18 December 2014 - 06:14 PM

Third pic...

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  • MWA3.jpg

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#4 dyslexic nam

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Posted 18 December 2014 - 06:19 PM

Lots of folks are curious to hear your impressions.



#5 russell23

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Posted 18 December 2014 - 07:51 PM

I'll be interested to hear if you see any EOFB.

 

Dave



#6 Starman1

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Posted 18 December 2014 - 08:28 PM

With a 30mm eye lens and zero distortion, the apparent field with a 17mm eye relief would be 82.8 degrees.

Since distortion is definitely present in all widefield eyepieces, I see no reason to disbelieve it could be as large as 85 degrees.

If it's 100 degrees, the eye relief is a lot shorter.

 

Now, as for evaluation, here are some points:

 

Eyepiece Aberrations
2. Chromatic Aberration-axial, lateral and fringe.  Be sure to hold your eye properly.  Sometimes you see some, but it's due to looking through the eyepiece at the wrong angle.
3. Field Curvature-negative and positive and scope interaction.  Is the center in focus when the edge is and vice-versa.  If not, this could be FC in the eyepiece, but if the scope is a refractor shorter than 2000mm in focal length, or a reflector shorter than 1000mm focal length, it could be the scope.
4. Angular Magnification Distortion (+/-).  Look at a double star.  Is the apparent separation the same at the center and edge?  Then no AMD.  If yes, how much is present?
5. Rectilinear Distortion a) pincushion b) barrel and relationship to astigmatism.  Does the edge focus sharply?  If not, and it isn't simple coma, then the eyepiece has astigmatism in whatever f/ratio scope the test scope is.  Do straight lines curve in or out as they near the edge (they will, and it's probably better to have them bow in)
6. Spherical aberration.  This is if and only if you know what's in the scope.  If other eyepieces have taught you that, then you can take a shot at the eyepiece.  Otherwise, forget this point.
7. Transmission anomalies by Frequency: coloration (tint) and overall transmission.  Does the image appear bright or dim compared to other eyepieces, and is the Moon yellow or white or blue-white?  Can you see the color difference between Saturn's rings and disc?
8. Light loss due to  a) reflection b) absorption c)scatter d)internal vignetting.  Is the edge dimmer than the center when you hold the eyepiece up to the daytime sky?  Do you see a lot of light scatter at night when pointed near the Moon?  Do bright stars outside the field create streaks inside the field?  Is the edge brighter than the center?
9. Spherical Aberration of the Exit Pupil and relationship to eye relief.  Can you hold the eye steady and see the field edge with peripheral vision at the same time you can see the center with direct vision?
10. Chromatic aberration of the exit pupil (Ring of fire).  If used in the daytime, do you see only a tiny thin line of color at the edge, or is the outer 10% of the field tinted yellow or orange?
11. Coma in off-axis light.  Ignore this one.  You won't find it in this eyepiece.
12. Vignetting (loss of edge brightness) due to improper lens diameters, barrel diameter, normal design.  Is the edge dimmer than the center when holding the eyepiece up to a bright sky?  It may indicate a reduced illumination at the edge on purpose in the design.
13. Astigmatism a) tangential and sagittal b) tilted elements c) wedge d)relationship to focal ratio of scope e)relationship to astigmatism of objective.  Can you see astigmatism at the edge when the scope is cooled to ambient temperature?  Do stars focus into radial slots on one side of focus and circumferential slots on the other side of focus and then down to  a tiny + sign in focus?
14. Wavefront aberration a) poor polish  b) poor figure  c) result of more surfaces in eyepiece.  Is the center star sharp in focus, or somewhat soft compared to other eyepieces?  If sharp, does that change as the star is moved away from the center?  If so, where, and how much?
15. Light Scatter:
a. Surface scatter-roughness (creates a fog around bright stars.  Careful: moisture on the glass or mirrors will do this.
b. Reflections: lens(edge and surface-polish and coatings), and barrel (ghosting).  Do you see ghost images of planets or bright stars elsewhere in the field when viewing them?
c. Lateral rays (lens edge and barrel and low incidence scatter by coatings).  Do you see reflections at the edge of the field?  Does the edge get brighter as a bright star approaches it?
16. Design Flaws
a. Field stop not in focus.  Look directly at the field edge.  Is the stop in focus and sharp or somewhat vague?
b. Critical f/ratio too high (inadequate off-axis ray handling).  Does it work great in an f/10 scope but poorly in an f/5 dob?
c. Improper internal ray handling, causing vignetting or reflections.  Ignore this.
d. Wrong glass refractive index used.  Ignore this one.
17. Thermal issues  due to size, improper housing.  As the eyepiece cools, does the image quality improve or get worse?  Some large eyepieces have to be cooled just like an objective lens to yield the best image quality.
18. Blur circle and spot diagrams and focus of different colors.  Is there any chromatic change in the centered star image as you move it in and out of focus in either direction?

You'd need a reflector or well-corrected triplet or quadruplet apo refractor to judge this one.

 

Just some of the things you'd look for in judging an eyepiece.

Oh, in case you wondered, #1 above was:

 

1. Contrast (how it’s many factors and why it will be difficult to measure—why AF relates to perceived contrast—how critical dark adaptation is—how cataracts affect--):

Contrast in an eyepiece is tied to the suppression of scattered light.  To this end, blackening of the lens edges, full multi-coating, very dark internals in the barrel and blackened threads and bottom edge may all help.  The best way to test this is to put a very bright star just outside the FOV.  If spikes or ghosts of the star are visible in the field, the eyepiece gets an F.  If a brightening of the field is noticed at the edge just inside the field from the bright star and it's quite bright at the edge, then the eyepiece gets a D.  If you can tell which direction of the compass the bright star lies outside the field, but little evidence of the star's brightness is inside the field, the eyepiece gets a C.  If you can tell there is a bright object outside the field of view, but it's uncertain what direction is lies, the eyepiece gets a B.  If you literally cannot tell there is a bright star outside the field, the eyepiece gets an A.  One caveat: newtonians with great contrast, used in dark skies, will show the spikes from a bright star in the FOV if the star is still in the field of the telescope, but just happens to be outside the FOV of that eyepiece.  In that case, seeing the spikes might indicate terrific contrast in the eyepiece.

Narrow fields of view may allow a perceived improvement in contrast, but this is not certain.

It is critical to evaluate eyepiece contrast when fully dark adapted.  Otherwise, a dark background may simply be an indication of a lack of dark adaptation.  If the site is so bright you cannot dark adapt, I would argue you cannot accurately assess the contrast in the eyepiece.

Cataracts in the eye's lens scatter light and cause anomalous flares and glare, too, so obviously this would make it very difficult to assess the contrast in the eyepiece.

Many factors influence contrast.  Some have already been mentioned.  Also important are polish on the lens surfaces, good design, good adherence to design, induced aberrations from the f/ratio of the scope, chromatic aberration, and a host of other issues.  Superior contrast requires a high level of quality on all aspects of design and manufacturing.  Generally, if the eyepiece performs well in all the other factors, it'll do well in this one (as nebulous a term as contrast is, it's like pornography--we all know it when we see it, but it's really hard to define :grin: )


Edited by Starman1, 19 December 2014 - 01:46 AM.

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#7 Dave Bush

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Posted 18 December 2014 - 08:43 PM

Geeez Don.  I feel like I'm going to be taking a test.   lol

 

Well, as it turns out it just got overcast so I may not be going out tonight.  

 

I was initially just going to do an overall "how does it look" type of evaluation.  I will want to make sure I have good clear, steady skies and more time to look at/for all the things you mentioned.  I'll try but don't expect that detailed of an evaluation soon.   haha.

 

Quick question.  You said with 17mm eye relief the AFOV would be 97.2 degrees.  What would it be if indeed this eyepiece has the 20mm of eye relief they claim?


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#8 zsb04

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Posted 18 December 2014 - 08:46 PM

i think all of CN is awaiting this review hahaha


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#9 Scanning4Comets

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Posted 18 December 2014 - 09:55 PM

Now that I think of it, it very well will be close to 20mm of eye relief because the ES and other Meade has a recessed eye lens. This one that Dave has doesn't have a recessed top eye lens.

 

https://www.astronom...large/19754.jpg

 

https://www.google.c...ve.html;550;405


Edited by Scanning4Comets, 18 December 2014 - 09:56 PM.

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#10 csrlice12

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Posted 18 December 2014 - 10:22 PM

Maybe Sunny's getting serious....



#11 Bill Steen

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Posted 18 December 2014 - 11:17 PM

I think I need to print out Don's post and stick it in my valuable astronomy papers file.


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#12 Dave Bush

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Posted 18 December 2014 - 11:23 PM

Well, sorry folks.  No observing report tonight.  Clouded out.  Next best shot will be Saturday night.  <sigh>   



#13 range88

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Posted 18 December 2014 - 11:34 PM

If that eye lens diameter measurement is correct and the eye lens nearly flat, I'm afraid the eye relief will be less than 13mm.
The calculation is simple, er=30/2/tg50.

#14 Bill Steen

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Posted 18 December 2014 - 11:34 PM

Since I am a Meade Fan, I will have to pay attention.  I had not noticed the pictures on their website.  Those are pretty things!  If they are as light as a UWA 20 mm, then I could use them in my Infinity 102 and not point to the sky.  I can use a 24 mm UWA and the mount can just barely control it.

 

I do not think they should have called them Mega Wide Angle.  They should have used the term Extreme and saved Mega for greater than 120 degrees.  That way, they could save the term Giga Wide Angle for the eyepieces where you can see the back of your head!


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#15 Dave Bush

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Posted 18 December 2014 - 11:43 PM

If that eye lens diameter measurement is correct and the eye lens nearly flat, I'm afraid the eye relief will be less than 13mm.
The calculation is simple, er=30/2/tg50.

 

The eye lens is slightly concave.


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#16 csrlice12

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Posted 19 December 2014 - 01:04 AM

Hey Dave, just looked outside....the clouds have gone and Jupiter and Orion are available for your viewing pleasure.....and don't forget Don's short list....



#17 Starman1

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Posted 19 December 2014 - 01:44 AM

Geeez Don.  I feel like I'm going to be taking a test.   lol

 

Well, as it turns out it just got overcast so I may not be going out tonight.  

 

I was initially just going to do an overall "how does it look" type of evaluation.  I will want to make sure I have good clear, steady skies and more time to look at/for all the things you mentioned.  I'll try but don't expect that detailed of an evaluation soon.   haha.

 

Quick question.  You said with 17mm eye relief the AFOV would be 97.2 degrees.  What would it be if indeed this eyepiece has the 20mm of eye relief they claim?

Without distortion: it's 82.8 degrees with 17mm eye relief (had the numerator and denominator reversed before--sorry.  I'll edit my post)

With 20mm eye relief, it'd be 73.7 degrees.

Distortion could add up to 5% or so to the AFOV, but for a 100 degree apparent field, the eye lens would have to be around 48mm without distortion and a few mm smaller with distortion.

To have a 100 degree field with a 30mm eye lens, the eye relief would be around 13mm, as mentioned.  Add distortion, and the eye relief could be a mm or so longer.



#18 range88

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Posted 19 December 2014 - 02:12 AM


If that eye lens diameter measurement is correct and the eye lens nearly flat, I'm afraid the eye relief will be less than 13mm.
The calculation is simple, er=30/2/tg50.


The eye lens is slightly concave.

Then the eye lens should be very very concave to justify the 7mm difference.

#19 Darren Drake

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Posted 19 December 2014 - 09:23 AM

Does anyone here happen to know the diameter of the eyelens on the 13 Ethos?  Starting to think I might have jumped the gun ordering the 15mm thinking it really has 20 mm of er.  Had I seen the pic of the eyelens I would of held off till some real user reports came in.



#20 BillP

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Posted 19 December 2014 - 09:48 AM

Well, sorry folks.  No observing report tonight.  Clouded out.  Next best shot will be Saturday night.  <sigh>   

 

I don't understand...aren't there any houses down the street with Christmas lights you can observer? Star light Christmas light, what's the difference :lol:


Edited by BillP, 19 December 2014 - 09:48 AM.

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#21 russell23

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Posted 19 December 2014 - 09:55 AM

Does anyone here happen to know the diameter of the eyelens on the 13 Ethos?  Starting to think I might have jumped the gun ordering the 15mm thinking it really has 20 mm of er.  Had I seen the pic of the eyelens I would of held off till some real user reports came in.

 

I think you will be fine.  Dave said the eye relief of the 21mm was longer than the 20mm Meade UWA - which has 17mm of eye relief.  I had the 20mm Meade UWA and I was able to see the entire field with glasses on but the top was so wide it was difficult to get the exact placement that made that possible.  With a smaller diameter top and a longer usable eye relief you hopefully will be just fine with the 15mm.  I'm looking forward to your report.  A 15mm with enough eye relief is exactly what I would like - as long as it does not suffer from significant EOFB.  Heck - even if it only had an 85 deg AFOV I would be happy if the eye relief was sufficient.

 

Dave



#22 ibase

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Posted 19 December 2014 - 10:08 AM

Ain't she a beauty, or are my eyes just off tonight? :lol: On the other hand, never met an eyepiece I didn't like, 75 of them now. :)

 

Nice pics, thanks for posting, looking forward to more impressions, thanks.

 

Best,



#23 Starman1

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Posted 19 December 2014 - 11:08 AM

Does anyone here happen to know the diameter of the eyelens on the 13 Ethos?  Starting to think I might have jumped the gun ordering the 15mm thinking it really has 20 mm of er.  Had I seen the pic of the eyelens I would of held off till some real user reports came in.

If the calculations hold true, and the 13 Ethos has 15mm of eye relief, it should have an eye lens of 35.75mm diameter

It's about 28-1/2mm.  Either the eyepiece has an apparent field of <90 degrees, the eye relief is really 12mm,  or I think we haven't figured out some very important fact.

The apparent field of the eyepiece isn't related directly to the diameter of the eye lens if the light rays from the next lens in come into the eye lens

at oblique angles.

In other words, the ability to see 100 degrees is determined more by the diameter of the lenses below the eye lens.

And we are assuming a flat field in the eyepiece, and no angular magnification distortion.

 

BUT, the eye relief should be directly calculable from the eye lens diameter and apparent field.

If you know the apparent field, the tangent of 1/2 the apparent field equals 1/2 the diameter of the eye lens divided by the eye relief.

Solving for eye relief gives:

ER = 0.5eyelens diameter/tan0.5AFOV

 

What we're missing here is beyond me.  Lines of eyepieces with constant eye lens diameters and constant AFOVs should have constant eye reliefs through the series.

But I don't get the manufacturer's stated eye relief on any of them if I measure the diameters of the eye lenses and trust the manufacturer's claims

for AFOV.  So, do the manufacturers lie about eye relief, AFOV, or both?

 

Or is there something being missed?


Edited by Starman1, 19 December 2014 - 11:13 AM.


#24 bgi

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Posted 19 December 2014 - 11:29 AM

Hi, Don,

 

Call me crazy, but unless the light rays bend after exiting the eye lens, then the AFOV, Eye lens diameter, and ER relationships are fixed by the formula you posted above.  However, the manufacturers seem to clam ER as measured from the center of the eye lens, so the deeper the lens is curved, the smaller the diameter will be.  Correct?  The formula needs a little tweak to adjust for the eye lens curve:

 

ER - eyelens concavity= 0.5eyelens diameter/tan0.5AFOV



#25 Starman1

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Posted 19 December 2014 - 11:39 AM

Follow my logic, here:

1) You hold your eye at the proper eye relief distance from the eyepiece and look at the edge of the field.

2) A straight line from your pupil to the edges of the eye lens subtends an angle.  We'll call this the Calculated Apparent Field since it follows from

the angles to the edge of the eye lens and the eye relief distance.

3) But the light path, when looking at the edge of the eye lens diverges very strongly below the eye lens so that the point you are looking at when

you look at the edge of the lens is actually farther off axis than the angle at which you look at the edge of the lens.  In other words, the field being

looked at is wider than the eye lens would allow had there been no divergence.

4) draw a straight line from the edge of the visible field to the eye.  The apparent field seen, which we'll call the Effective Apparent Field.

is wider than the Calculated Apparent Field derived from the diameter of the eye lens and the eye relief.

5) Ergo, one cannot directly calculate the eye relief from the Effective Apparent Field (what we actually see) and the eye lens diameter.

6) Ergo, there is no contradiction between the manufacturer's eye relief claim and their apparent field claim since the Effective Apparent Field

will depend on the divergence of rays in the eye lens.

 

A simpler way to look at it is that the lenses under the eye lens are a telescope and the eye lens is a barlow.  It extends the eye relief, and makes the apparent field

seem narrower than it is because the rays are more parallel.  Plus, it allows a narrower cone of light to the eye to see a wider field.

 

Please shoot holes in my logic.  It does explain the eye lens diameter on a lot of 82 degree and wider eyepieces.


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