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Eyepiece for f/4.2

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#1 Vedran

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Posted 25 November 2022 - 04:36 AM

Recently, I've ordered f/4.2 telescope and my plan is to sell off current eyepiece lineup. This is my current eyepiece lineup for 12" f/5 telescope which has been collected during last 15 years:

  • 23mm SkyWatcher Panorama (82°)
  • 17mm Baader Hyperion (68°)
  • 15mm SkyWatcher Panorama (82°)
  • 10mm Baader Hyperion (13mm tuned with rings to 10mm)
  • 7mm SkyWatcher Panorama (82°)
  • 6mm SkyWatcher Planetary (58°)
  • 5mm SkyWatcher Planetary (58°)
  • 3.2mm SkyWatcher Planetary (58°)

 

I really like exit pupils in range 1.5 do 2.5 mm. My primary observing interest are galaxies, which respond very well to mention exit pupil range. That's why for most of the time I'm using 10mm Hyperion or 7mm Panorama. Those eyepieces give me best combination of FOV, magnification and contrast.

 

My plan is to sell of current eyepiece collection and buy new, more streamlined collection. Wide field, low power eyepiece is low on priority list so I'm looking for recommendations in 1-4mm exit pupil range (4-17mm). I'm willing to spend about 200€ per eyepiece, maybe 300€ if there is big enough performance gain.

I'm also thinking of getting barlow lens for higher magnifications instead of buying short focal eyepieces.

My train of thought goes like this:

  • 18mm ES 82° Argon filled
  • 11mm ES 82° Argon
  • 8.8mm ES 82° Argon
  • 2.5x Barlow, still deciding between 2" or 1.25" form factor
  • and in far future 25mm ES 100° for wide field work

Do I need coma corrector for eyepieces in mentioned focal range (Baader MPCC Mk3)? Are there better, more cost-effective choices in mention focal range? How are ES 82° eyepieces responding to Barlow lens?

I'm also getting itched by Baader Morpheus, but they cost around 100€ more per eyepiece. Is this 50% price hike when compared to ES justified? If Morpheus works well at f/4.2 without coma correct, that could be a deal breaker and reason to switch from ES to Baader.

 

Many thanks

 

 



#2 izar187

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Posted 25 November 2022 - 05:36 AM

My vote here would be to get a coma corrector first, before selling off any ep's.

F/4.2 newt plus 82 degree field will not be as sharp as you hope for, without coma corrected.

 

Cool sketches too : )


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#3 Highburymark

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Posted 25 November 2022 - 06:05 AM

For info, the ES 82 degree line is available under the Opticstar brand in the UK (opticstar.com) from £125 - quite a saving on ES prices. They are the same eyepieces with EMD coatings.
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#4 Ernest_SPB

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Posted 25 November 2022 - 06:14 AM

"Recently, I've ordered f/4.2 telescope and my plan is to sell off current eyepiece lineup.

This is my current eyepiece lineup for 12" f/5 telescope which has been collected during last 15 years" 

 

so you are experienced observer, and most probably have own opinion...

 

Do you like your current set of eyepieces? In F4.2 it will work similar, representing just a bit more fiend aberrations.

 

"23mm SkyWatcher Panorama (82°)

17mm Baader Hyperion (68°)
15mm SkyWatcher Panorama (82°)
10mm Baader Hyperion (13mm tuned with rings to 10mm)
7mm SkyWatcher Panorama (82°)
6mm SkyWatcher Planetary (58°)
5mm SkyWatcher Planetary (58°)

3.2mm SkyWatcher Planetary (58°)"

 

For the first time it would be enough to try the new scope, evaluate by the way is it required for it a coma corrector. 

So, I suggest to be more conservative.

 

"18mm ES 82° Argon filled

11mm ES 82° Argon

8.8mm ES 82° Argon"

 

I have similar set (with replacement the first on 16mm Nagler. And I like it.

 

"Do I need coma corrector for eyepieces in mentioned focal range"

 

I think so. Consider GSO CC. It is cheap and quite effective.

 

"How are ES 82° eyepieces responding to Barlow lens?"

 

It is interesting question. My measurements showed that Barlow makes AFOV of 82-deg. ES close to 100-deg!!! Without influence to effective FOV. So it is acceptable. But I prefer do not use Barlow. Fast Newtons do not like Barlowing.


Edited by Ernest_SPB, 25 November 2022 - 06:15 AM.

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#5 Vedran

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Posted 25 November 2022 - 06:58 AM

Thanks for responses.

I'm mostly satisfied with eyepieces that I own, especially Hyperions. Only SkyWatcher Panorama 23mm is so-so, it has mushy stars near the edge of FOV, probably due combinations of coma and EP astigmatism. 

My plan is to get coma corrector first. Baader MPCC Mk3 is on my wish list, but I will look into GSO CC.



#6 Jon Isaacs

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Posted 25 November 2022 - 09:01 AM

Thanks for responses.

I'm mostly satisfied with eyepieces that I own, especially Hyperions. Only SkyWatcher Panorama 23mm is so-so, it has mushy stars near the edge of FOV, probably due combinations of coma and EP astigmatism. 

My plan is to get coma corrector first. Baader MPCC Mk3 is on my wish list, but I will look into GSO CC.

 

My understanding is that the Baader is a photographic coma corrector, it's not designed for visual.  I'm not sure how well the GSO coma corrector works at F/4.2 but it's a place to start.

 

Jon


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#7 SeattleScott

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Posted 25 November 2022 - 11:07 AM

The cheaper coma correctors work pretty well as long as you don’t go crazy and go below F4 or something. It’s not like you are accustomed to perfect eyepieces and coma correction currently. But there is more complicated setup involved, especially if your eyepieces aren’t parfocal. And barlowing will make them not parfocal, so the parfocal ring you got for using the eyepiece without barlow won’t provide optimal correction with barlow, as I understand, unless you get a focal extender/Powermate. The 18mm ES won’t be parfocal with the 1.25” ones. Again this can be managed but barlowing would really throw a wrench in it I would think.

With Paracorr it has a tunable top so easier to adjust to different focus positions. But more expensive.

The ES 82s tend to bench test roughly the same as Morpheus. Morpheus have more eye relief for easier viewing. There are some people who swear Morpheus provide better views than ES, not just better ER. Maybe a difference in coating or baffling. I haven’t used a Morpheus myself. Either would certainly be an upgrade over your current set. Obviously the 2” ES 18mm goes wider than the Morpheus 17.5, if that matters.

Scott
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#8 Vedran

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Posted 25 November 2022 - 01:40 PM

Thanks Scott.

For sketching I acutally prefer narrower field of view. Less eye movement means better placement of details.

Also, when barlowing, coma shouldn't be a problem since FOV will be smaller. I wasn't planing of using coma corrector with Barlow lens.

 

 

My understanding is that the Baader is a photographic coma corrector, it's not designed for visual.  I'm not sure how well the GSO coma corrector works at F/4.2 but it's a place to start.

 

Jon

It is possible to buy Baader MPCC with tunable ring which enables visual use. It is sold with tunable ring to ensure 55 mm distance from coma correct to field stop lens of eyepiece. As I understant it, it should work for visual (or I got it something wrong).

I have an opportunity to borrow GSO coma corrector. I will test it before spending for something else.



#9 EsaT

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Posted 25 November 2022 - 04:58 PM

My understanding is that the Baader is a photographic coma corrector, it's not designed for visual.

Basic corrector is for photography only, but there's kit with 1.25" eyepiece attachment parts.
https://www.baader-p...tion_manual.pdf

 

As I understant it, it should work for visual (or I got it something wrong).

Depends on if you're going to get wide angle 2" eyepiece...

Whose wide view would benefit lot from coma correction.



#10 Deep13

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Posted 25 November 2022 - 05:56 PM

I don't have any experience with ES eyepieces, so I can't help you there. I have heard good things about them.

My 7mm and 10mm eyepieces are Pentax XWs. My 14mm ep is a Televue Delos. I like the eye relief, 70° afov, and sharp, clear views I get from them.

I have an 11mm and 13mm TV type 6 Naglers. They also work really well. There's less eye relief, but the afov is wider. I'm thinking of getting a short focal length (<5mm) NT6 for planets.

They all work very well in my 12.5" f/5 Dob with no coma corrector. I also have a 15" f/4.5 Dob that has an early model TV Paracorr. Those eyepieces are good in that scope, too.

#11 Starman1

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Posted 26 November 2022 - 04:32 PM

Recently, I've ordered f/4.2 telescope and my plan is to sell off current eyepiece lineup. This is my current eyepiece lineup for 12" f/5 telescope which has been collected during last 15 years:

  • 23mm SkyWatcher Panorama (82°)
  • 17mm Baader Hyperion (68°)
  • 15mm SkyWatcher Panorama (82°)
  • 10mm Baader Hyperion (13mm tuned with rings to 10mm)
  • 7mm SkyWatcher Panorama (82°)
  • 6mm SkyWatcher Planetary (58°)
  • 5mm SkyWatcher Planetary (58°)
  • 3.2mm SkyWatcher Planetary (58°)

 

I really like exit pupils in range 1.5 do 2.5 mm. My primary observing interest are galaxies, which respond very well to mention exit pupil range. That's why for most of the time I'm using 10mm Hyperion or 7mm Panorama. Those eyepieces give me best combination of FOV, magnification and contrast.

 

My plan is to sell of current eyepiece collection and buy new, more streamlined collection. Wide field, low power eyepiece is low on priority list so I'm looking for recommendations in 1-4mm exit pupil range (4-17mm). I'm willing to spend about 200€ per eyepiece, maybe 300€ if there is big enough performance gain.

I'm also thinking of getting barlow lens for higher magnifications instead of buying short focal eyepieces.

My train of thought goes like this:

  • 18mm ES 82° Argon filled
  • 11mm ES 82° Argon
  • 8.8mm ES 82° Argon
  • 2.5x Barlow, still deciding between 2" or 1.25" form factor
  • and in far future 25mm ES 100° for wide field work

Do I need coma corrector for eyepieces in mentioned focal range (Baader MPCC Mk3)? Are there better, more cost-effective choices in mention focal range? How are ES 82° eyepieces responding to Barlow lens?

I'm also getting itched by Baader Morpheus, but they cost around 100€ more per eyepiece. Is this 50% price hike when compared to ES justified? If Morpheus works well at f/4.2 without coma correct, that could be a deal breaker and reason to switch from ES to Baader.

 

Many thanks

Will you need a coma corrector?  Yes.

An economical one that will work is the GSO.

82° eyepieces will work fine with a Barlow.  The main issue is using one with a coma corrector and maintaining coma correction spacing.

You don't say what size of f/4.2 scope you have on order, and the eyepiece recommendations would depend on the size and focal length of the scope.

 

I think you could easily get by with 5 eyepieces instead of 8.

In a 12", 60/120/180/240/300x would cover just about all observing except maybe very small PK planetaries or Uranus and Neptune.

In a 16", 70/140/210/280/350x

In a 20", 80/160/240/320/400x

Could you use more eyepieces?  Sure.  But do you NEED more eyepieces?  That's a tougher question.

 

Remember, aperture in mm ÷ magnification = exit pupil

That will give you a magnification range for your aperture with your preferred exit pupil requirements.

For 1.5-2.5mm exit pupil:

12": 122-203x

16": 162-271x

20": 203-339x

 

Also remember a GSO coma corrector multiplies the focal length of the scope by 1.1x.


Edited by Starman1, 26 November 2022 - 05:28 PM.


#12 Starman1

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Posted 26 November 2022 - 04:39 PM

Thanks Scott.

For sketching I actually prefer narrower field of view. Less eye movement means better placement of details.

Also, when Barlowing, coma shouldn't be a problem since FOV will be smaller. I wasn't planning of using coma corrector with Barlow lens.

 

 

It is possible to buy Baader MPCC with tunable ring which enables visual use. It is sold with tunable ring to ensure 55 mm distance from coma correct to field stop lens of eyepiece. As I understand it, it should work for visual (or I got it something wrong).

I have an opportunity to borrow GSO coma corrector. I will test it before spending for something else.

The Baader accessory for a helical focusing on the MPCC only works with 1.25" eyepieces.

To use the MPCC on 2" eyepieces, it is attached directly to the eyepiece, and there is usually a spacer in between the eyepiece and MPCC and the spacer thickness needed varies from eyepiece to eyepiece.

 

The visibility of coma in the eyepiece is not related to focal length of eyepiece, it is related to the apparent field of the eyepiece.

50° eyepieces will display the same coma at all magnifications, as will 100° eyepieces.  It's just that 100° eyepieces see coma at twice the apparent size as the 50° eyepieces.


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#13 sixela

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Posted 26 November 2022 - 04:53 PM

I’d get a GSO before I’d get an MPCC (not that good at f/4.2, adds spherical aberration visible even at medium power) but frankly at f/4.2 you want either a Paracorr or an ES HR CC (careful, you need 32mm of focuser in-travel for the latter).

Once you splurge on that the 9 and 13mm APM XWAs are a no-brainer ;-). Or the Baader Morpheus, depending on taste.

Edited by sixela, 26 November 2022 - 05:00 PM.

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#14 EsaT

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Posted 26 November 2022 - 05:13 PM

Remember, aperture in mm ÷ magnification = exit pupil
That will give you a magnification range for your aperture and preferred exit pupil requirements.

Usually faster way for getting exit pupil is dividing focal length of the eyepiece by focal ratio of the telescope.

 

And for getting eyepiece focal length for the wanted exit pupil equation becomes exit pupil multiplied by focal ratio.



#15 Starman1

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Posted 26 November 2022 - 05:27 PM

Usually faster way for getting exit pupil is dividing focal length of the eyepiece by focal ratio of the telescope.

 

And for getting eyepiece focal length for the wanted exit pupil equation becomes exit pupil multiplied by focal ratio.

Yes, but I was relating the magnification range to the overall magnification range I was recommending for each size of scope.

You can also simply divide to get focal length:

Eyepiece focal length = Telescope focal length ÷ magnification

 

If you start with the focal length of eyepiece, figuring out the exit pupil is better done your way, with FL/f-ratio = E.P.

If you start with magnification, then figuring out focal lengths of eyepieces is easy with the formula above.  FL = TFL/M

If you simply start with desired exit pupil, eyepiece focal length is the exit pupil x the f/ratio as you mention. FL = E.P. x F/rat.

 

It just depends on where you start.



#16 Vedran

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Posted 27 November 2022 - 11:40 AM

Thanks all for input. After reading answers I've decided first to get coma corrector, probably GSO, and the see wich EPs are redundant or don't work well with telescope.

 

You don't say what size of f/4.2 scope you have on order, and the eyepiece recommendations would depend on the size and focal length of the scope.

20" f/4.2


Edited by Vedran, 27 November 2022 - 11:41 AM.


#17 Starman1

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Posted 27 November 2022 - 12:34 PM

Thanks all for input. After reading answers I've decided first to get coma corrector, probably GSO, and the see wich EPs are redundant or don't work well with telescope.

 

20" f/4.2

20"?  I would pay for a Paracorr for that large a scope, but setting up a GSO isn't going to be too problematic.

See this thread:

https://www.cloudyni...coma-corrector/


Edited by Starman1, 27 November 2022 - 12:35 PM.

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