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Why did Meade stop making the 18mm 82AFOV UWA 5000?

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#1 faackanders2

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Posted 22 July 2017 - 01:53 PM

Why did Meade stop making the 18mm 82AFOV UWA 5000?  With it being the widest TFOV 1.25" eyepiece, you would think it would have a niche; especially finders, binoculars, and binoviewers who shed their outer housings for IPD clearance.



#2 NOLAMusEd

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Posted 22 July 2017 - 02:53 PM

Someone may know the exact reason (isn't me), but my best guess is that it may have suffered from too many optical aberrations when compared against other focal lengths. For 82 degree eyepieces, the shortest focal length that you can design one with a 1.25" barrel without excessive distortion would be about 16mm. Look at Explore Scientific 18mm 82, it's a 2 inch EP. Same for the 1mm shorter 17 type 4 Nagler.

It's essentially the same reason the Ethos only goes up to 21mm even though the field stop is smaller than the max in a 2" barrel. (FS around 36mm, Max 46mm) You could make a 25mm 100 in a 2 inch (ES has done it), but you're going to have to deal with distortion or vignetting due to the design limitations.


Edited by NOLAMusEd, 22 July 2017 - 08:03 PM.

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#3 rowdy388

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Posted 23 July 2017 - 10:54 AM

Yeah, around 17-18mm focal lengths things gets more difficult to work through. Look at the 

delays that Baader is having getting their 17mm Morpheus just right.

 

Edit: Just a guess but I suspect the eventual 17 Morpheus will be a 2" only eyepiece or else

the weakest focal length of the series because of inherent limitations. I also suspect it will

cost substantially more than the others.


Edited by rowdy388, 23 July 2017 - 10:59 AM.


#4 starbase25

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Posted 23 July 2017 - 10:20 PM

Yeah, around 17-18mm focal lengths things gets more difficult to work through. Look at the 

delays that Baader is having getting their 17mm Morpheus just right.

 

Edit: Just a guess but I suspect the eventual 17 Morpheus will be a 2" only eyepiece or else

the weakest focal length of the series because of inherent limitations. I also suspect it will

cost substantially more than the others.

Baader is offering the 17.5mm at regular price when release date comes. (See near the end of the article). Looks like it will be a 1.25" as well.

 

http://www.baader-pl...field-eyepiece/


Edited by starbase25, 23 July 2017 - 10:20 PM.


#5 Starman1

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Posted 23 July 2017 - 11:53 PM

Why did Meade stop making the 18mm 82AFOV UWA 5000?  With it being the widest TFOV 1.25" eyepiece, you would think it would have a niche; especially finders, binoculars, and binoviewers who shed their outer housings for IPD clearance.

2 reasons:

1) significant vignetting, which is why the newer one is 2".

2) Meade changed companies, so their eyepieces are now made by a different company since 2011.


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#6 Starman1

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Posted 23 July 2017 - 11:55 PM

Yeah, around 17-18mm focal lengths things gets more difficult to work through. Look at the 

delays that Baader is having getting their 17mm Morpheus just right.

 

Edit: Just a guess but I suspect the eventual 17 Morpheus will be a 2" only eyepiece or else

the weakest focal length of the series because of inherent limitations. I also suspect it will

cost substantially more than the others.

1) it will be 1.25".

2) it will eventually be more expensive, but they will honor all earlier orders at the older prices.

So the first shipments will all be at the same price as the other focal lengths.

But the price will likely go up with every additional order.


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#7 aeajr

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Posted 27 July 2017 - 08:32 AM

Someone may know the exact reason (isn't me), but my best guess is that it may have suffered from too many optical aberrations when compared against other focal lengths. For 82 degree eyepieces, the shortest focal length that you can design one with a 1.25" barrel without excessive distortion would be about 16mm. Look at Explore Scientific 18mm 82, it's a 2 inch EP. Same for the 1mm shorter 17 type 4 Nagler.

It's essentially the same reason the Ethos only goes up to 21mm even though the field stop is smaller than the max in a 2" barrel. (FS around 36mm, Max 46mm) You could make a 25mm 100 in a 2 inch (ES has done it), but you're going to have to deal with distortion or vignetting due to the design limitations.

I need a little help understanding this.   Not challenging it as I am not qualified to challenge.  Seeking to learn and understand.

 

I have 1.25" ES 82 8.8, 6.7 and they make a 4.7.    Are you saying these have serious distortion, in your opinion?    

 

I am no eyepiece expert.  I am not even moderately knowledgeable.  I only know what I have experienced and haven't studied the science of eyepiece design.   Those ES 82s and a Meade 5000 UWA 82  5.5 mm and a Baader Hyperion Zoom  are my "best" eyepieces.  So those are my reference points.    I have never stood them up against the TV line in my scope.

 

So help me understand what you are saying since others seem to be agreeing with your assessment.



#8 Jon Isaacs

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Posted 27 July 2017 - 09:13 AM

I need a little help understanding this.   Not challenging it as I am not qualified to challenge.  Seeking to learn and understand.

 

 

Ed:

 

Good catch.  

 

The author meant to say:

 

"For 82 degree eyepieces, the longest focal length that you can design one with a 1.25" barrel without excessive distortion would be about 16mm."

 

jon


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#9 Starman1

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Posted 27 July 2017 - 09:27 AM

 

Someone may know the exact reason (isn't me), but my best guess is that it may have suffered from too many optical aberrations when compared against other focal lengths. For 82 degree eyepieces, the shortest focal length that you can design one with a 1.25" barrel without excessive distortion would be about 16mm. Look at Explore Scientific 18mm 82, it's a 2 inch EP. Same for the 1mm shorter 17 type 4 Nagler.

It's essentially the same reason the Ethos only goes up to 21mm even though the field stop is smaller than the max in a 2" barrel. (FS around 36mm, Max 46mm) You could make a 25mm 100 in a 2 inch (ES has done it), but you're going to have to deal with distortion or vignetting due to the design limitations.

I need a little help understanding this.   Not challenging it as I am not qualified to challenge.  Seeking to learn and understand.

 

I have 1.25" ES 82 8.8, 6.7 and they make a 4.7.    Are you saying these have serious distortion, in your opinion?    

 

I am no eyepiece expert.  I am not even moderately knowledgeable.  I only know what I have experienced and haven't studied the science of eyepiece design.   Those ES 82s and a Meade 5000 UWA 82  5.5 mm and a Baader Hyperion Zoom  are my "best" eyepieces.  So those are my reference points.    I have never stood them up against the TV line in my scope.

 

So help me understand what you are saying since others seem to be agreeing with your assessment.

 

The field stop diameter of an 18mm 82° eyepiece might not fit in a 1.25" barrel depending on design.

So, if you wanted to make that, there are some alternatives:

1) place the field stop above the barrel and allow quite a bit more light drop off at the edge of the field.  This is commonly done, as in the 35mm "pseudo-Masuyama" eyepieces from the '80s and '90s,

or in the 32mm König 1.25" eyepiece, etc.

2) allow more distortion at the edge of the field to "shoehorn" the larger field of view in a smaller space.  Note that this does not typically expand the field stop diameter, merely the true field.

 

Shorter focal lengths would have field stops that easily fit in a 1.25" barrel, so this would not apply to them.

Note that Explore Scientific (the maker of the Meade 18mm 82° eyepiece in 1.25") specifies a 25.3mm field stop in their 18mm 82° 2" eyepiece.  Since that field stop size is under the size that would fit in a 1.25" barrel, the expansion of the light after passage through the field lenses must have dictated the larger barrel to avoid serious vignetting and to provide a more stable mounting for the eyepiece barrel diameter above the insertion barrel.  They used a 2" barrel on the 14mm 100° eyepiece for the same reason.

 

It's also possible the newer 18mm is a different internal design than the older one.


Edited by Starman1, 27 July 2017 - 09:31 AM.


#10 NOLAMusEd

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Posted 27 July 2017 - 10:03 AM

 

I need a little help understanding this.   Not challenging it as I am not qualified to challenge.  Seeking to learn and understand.

 

 

Ed:

 

Good catch.  

 

The author meant to say:

 

"For 82 degree eyepieces, the longest focal length that you can design one with a 1.25" barrel without excessive distortion would be about 16mm."

 

jon

 

Jon, you're exactly right. My mistake! grin.gif

 

Ed, sorry to worry you, but nothing is wrong with your 82 degree eyepieces! What I was trying to say was that every AFOV class of eyepiece has a limit on how long a focal length you can fit into a 1.25" barrel. The maximum field stop size available in 1.25" format is about 27mm.

 

For 52 deg. eyepieces, the limit is about 32mm (this is why a 1.25" 40mm plossl has a 42 deg AFOV)

For 68 deg., the limit is around 24mm

For 82 deg., the limit is essentially 16mm

For 100 deg., the limit is 13-14mm

 

Attempting an optical design that goes beyond these boundaries is sure to have its consequences. Good results can still be achieved, but you might have to deal with with excessive edge distortion or vignetting. The vignetting especially true for eyepieces that use a negative element for the field lens, which puts the field stop somewhere within the eyepiece. This is why a 32mm plossl and 24mm/68 use the maximum 27mm field stop, but eyepieces like the 16mm Type 5 and 13mm Ethos have field stops of 22.1 and 22.3mm respectively. Almost 5mm of available space in the 1.25"  barrel cannot be used in the two aforementioned due to the way the light cone diverges once it passes through the negative field lens.



#11 aeajr

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Posted 27 July 2017 - 10:27 AM

Thanks everyone.

 

I try to follow all you smart guys in these conversations so I can learn.  When something seems off I am apt to ask for an explanation as either someone made a type, as happened here, or I am very lost in my understanding of how things work.    I did study physics in college so I am not clueless about this stuff, but the finer points sometimes escape me.    

 

And, of course there is the sorting of facts vs. opinions which can be a bit more challenging.

 

 

Thanks for the clarification. 


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#12 Jon Isaacs

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Posted 27 July 2017 - 10:33 AM

Thanks everyone.

 

I try to follow all you smart guys in these conversations so I can learn.  When something seems off I am apt to ask for an explanation as either someone made a type, as happened here, or I am very lost in my understanding of how things work.    I did study physics in college so I am not clueless about this stuff, but the finer points sometimes escape me.    

 

And, of course there is the sorting of facts vs. opinions which can be a bit more challenging.

 

 

Thanks for the clarification. 

 

:waytogo:

 

Ed:

 

A good student asks questions when they do not understand something..

 

We're all students..

 

Jon


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#13 The night's watch

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Posted 27 July 2017 - 10:37 AM

Hi im a newbie here, can anyone suggest a good telescope for a beginner like me?

i kinda like this one - http://www.meade.com...scope-60mm.html

Have anyone tried this one before?

 

Anyway thank you in Advance guys!.



#14 Richard Whalen

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Posted 27 July 2017 - 10:48 AM

I think there are as wide or wider 1-1/4 eyepieces out there than the 18mm 82, for instance the PaNoptic 24mm or even the old TV wide field 24 is a hair wider.



#15 aeajr

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Posted 27 July 2017 - 10:49 AM

Hi im a newbie here, can anyone suggest a good telescope for a beginner like me?
i kinda like this one - http://www.meade.com...scope-60mm.html
Have anyone tried this one before?
 
Anyway thank you in Advance guys!.



Welcome Night's Watch.   We are happy to have you join our Cloudy Nights community.
 
My I suggest that you repost this question in a new discussion in the beginners forum.  People will flock to help you.
https://www.cloudyni...eginners-forum/
 
This is the eyepiece forum and your question will be buried here in a completely unrelated topic and you won't get the benefit of the general community. I will look for your post there and be happy to jump in to help.

Edited by aeajr, 27 July 2017 - 10:50 AM.

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#16 Jon Isaacs

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Posted 27 July 2017 - 11:01 AM

I think there are as wide or wider 1-1/4 eyepieces out there than the 18mm 82, for instance the PaNoptic 24mm or even the old TV wide field 24 is a hair wider.

 

Richard:

 

There are.. The difference is that eyepiece's like the 24 mm Panoptic have no optics in the barrel so they can use field stops nearly as large as the inner barrel diameter.

 

82 degree eyepieces have a negative Smyth section in the barrel so fitting the optics and retainers in the barrel becomes a challenge.

 

The 16 mm Type 6 Nagler has an effective field stop of 22.2 mm. An 18 mm would require a 25.0 mm field stop with sufficient clear aperture, not an easy fit into a 28 mm diameter barrel.

 

Jon


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#17 Starman1

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Posted 27 July 2017 - 12:40 PM

An eyepiece can easily have lenses in the insertion barrel and have a 27mm field stop.

The bottom lenses, however, cannot be excessively diverging.

Example: APM 24mm 65° eyepiece with 30.2mm field stop and negative lens in insertion barrel:

cross section: https://www.cloudyni...gree/?p=7769970

Not a high magnification figure on the bottom lens.

And there are many eyepieces with lenses in the insertion barrels that have field stops of 24mm and larger, especially widefield eyepieces like Erfles.


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#18 Jon Isaacs

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Posted 27 July 2017 - 02:25 PM

An eyepiece can easily have lenses in the insertion barrel and have a 27mm field stop.

The bottom lenses, however, cannot be excessively diverging.

Example: APM 24mm 65° eyepiece with 30.2mm field stop and negative lens in insertion barrel:

cross section: https://www.cloudyni...gree/?p=7769970

Not a high magnification figure on the bottom lens.

And there are many eyepieces with lenses in the insertion barrels that have field stops of 24mm and larger, especially widefield eyepieces like Erfles.

 

Don:

 

If the clear aperture of the barrel is smaller than the effective field stop,  it seems that there must be vignetting.   The drawing of the eyepiece you refer to has a 27 mm clear aperture which requires some careful machining to fit that into a 1.25 inch barrel. When retaining rings are included,  that means a wall thickness of about 1 mm with a ring with about 1 mm wall. 

 

A 24mm with a 65 degree AFoV implies a 27.2 mm effective field stop.  The 30.2 number suggests the negative lens has a 30.2/27.2 = 1.11x magnification factor. 

 

As far as Erfle's go, the field stop is in front of the optics..  

 

???

 

Jon



#19 Starman1

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Posted 27 July 2017 - 03:25 PM

Yes, but the field lens in Erfles is mildly negative and the light expands to the next lens, so the "insufficient space" issue could exist.

And yes, in the APM eyepiece, there could be vignetting, but it depends on whether the lateral rays are cut off by the barrel, which is not clear in the cross section.

Remember, other eyepieces with larger than 28.5mm field stops do vignette, but that's because the field stop is below the field lens and above the barrel (example: 24mm Hyperion). 


Edited by Starman1, 27 July 2017 - 03:34 PM.

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#20 Jon Isaacs

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Posted 27 July 2017 - 03:43 PM

Yes, but the field lens in Erfles is mildly negative and the light expands to the next lens, so the "insufficient space" issue could exist.

And yes, in the APM eyepiece, there could be vignetting, but it depends on whether the lateral rays are cut off by the barrel, which is not clear in the cross section.

Remember, other eyepieces with larger than 28.5mm field stops do vignette, but that's because the field stop is below the field lens and above the barrel (example: 24mm Hyperion). 

 

Don:

 

There Erfles I have seen have the field stop in the barrel,  the optics in the main body.. 

 

How it all works out is complicated.   The legendary 20 mm Type 2 Nagler has a 27.2 mm field stop but a massive field lens that fills the 2 inch barrel..  Probably not much vignetting there. 

 

Being the heaviest ever TeleVue eyepiece,  it's compact and not a good one to drop on your toe. 

 

Jon



#21 Peter Besenbruch

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Posted 29 July 2017 - 08:48 PM

Being the heaviest ever TeleVue eyepiece,  it's compact and not a good one to drop on your toe.

Especially in Hawaii, where the toe is frequently uncovered. gaah.gif



#22 faackanders2

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Posted 30 July 2017 - 06:50 AM

 

Yes, but the field lens in Erfles is mildly negative and the light expands to the next lens, so the "insufficient space" issue could exist.

And yes, in the APM eyepiece, there could be vignetting, but it depends on whether the lateral rays are cut off by the barrel, which is not clear in the cross section.

Remember, other eyepieces with larger than 28.5mm field stops do vignette, but that's because the field stop is below the field lens and above the barrel (example: 24mm Hyperion). 

 

Don:

 

There Erfles I have seen have the field stop in the barrel,  the optics in the main body.. 

 

How it all works out is complicated.   The legendary 20 mm Type 2 Nagler has a 27.2 mm field stop but a massive field lens that fills the 2 inch barrel..  Probably not much vignetting there. 

 

Being the heaviest ever TeleVue eyepiece,  it's compact and not a good one to drop on your toe. 

 

Jon

 

Isn't the 21mm Ethost the heaviest TV eyepiece?



#23 faackanders2

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Posted 30 July 2017 - 06:56 AM

 

Why did Meade stop making the 18mm 82AFOV UWA 5000?  With it being the widest TFOV 1.25" eyepiece, you would think it would have a niche; especially finders, binoculars, and binoviewers who shed their outer housings for IPD clearance.

2 reasons:

1) significant vignetting, which is why the newer one is 2".

2) Meade changed companies, so their eyepieces are now made by a different company since 2011.

 

Thanks Don,  Switching companies and redesigning for 2" 18mm 82 AFOV are probably the most likey reasons they discontinued the 18mm 82 AFOV 1.25".  Little reason to have two 18mm 82AFOV aside from the fact they could be used in 1.25" finders, binoviewers, binoculars, and 1.25" only telescopes.



#24 junomike

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Posted 30 July 2017 - 07:48 AM

 

 

Yes, but the field lens in Erfles is mildly negative and the light expands to the next lens, so the "insufficient space" issue could exist.

And yes, in the APM eyepiece, there could be vignetting, but it depends on whether the lateral rays are cut off by the barrel, which is not clear in the cross section.

Remember, other eyepieces with larger than 28.5mm field stops do vignette, but that's because the field stop is below the field lens and above the barrel (example: 24mm Hyperion). 

 

Don:

 

There Erfles I have seen have the field stop in the barrel,  the optics in the main body.. 

 

How it all works out is complicated.   The legendary 20 mm Type 2 Nagler has a 27.2 mm field stop but a massive field lens that fills the 2 inch barrel..  Probably not much vignetting there. 

 

Being the heaviest ever TeleVue eyepiece,  it's compact and not a good one to drop on your toe. 

 

Jon

 

Isn't the 21mm Ethost the heaviest TV eyepiece?

 

According to TV Specs the discontinued  20T2 clocks in at a honking 36.8 oz followed closely by the 21E @ 36 oz and then the 31T5 @ 35.2 oz as well as the 41 Pan @ 33.6 oz.



#25 Starman1

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Posted 30 July 2017 - 10:36 AM

 

 

Yes, but the field lens in Erfles is mildly negative and the light expands to the next lens, so the "insufficient space" issue could exist.

And yes, in the APM eyepiece, there could be vignetting, but it depends on whether the lateral rays are cut off by the barrel, which is not clear in the cross section.

Remember, other eyepieces with larger than 28.5mm field stops do vignette, but that's because the field stop is below the field lens and above the barrel (example: 24mm Hyperion). 

 

Don:

 

There Erfles I have seen have the field stop in the barrel,  the optics in the main body.. 

 

How it all works out is complicated.   The legendary 20 mm Type 2 Nagler has a 27.2 mm field stop but a massive field lens that fills the 2 inch barrel..  Probably not much vignetting there. 

 

Being the heaviest ever TeleVue eyepiece,  it's compact and not a good one to drop on your toe. 

 

Jon

 

Isn't the 21mm Ethost the heaviest TV eyepiece?

 

2.3 lbs for the 20mm T2 versus 2.25 lbs for the 21 Ethos.




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