Jump to content

  •  

CNers have asked about a donation box for Cloudy Nights over the years, so here you go. Donation is not required by any means, so please enjoy your stay.

Photo

Televue 11mm Plössl vs 32mm with 3X

  • Please log in to reply
25 replies to this topic

#1 carl_g

carl_g

    Sputnik

  • -----
  • topic starter
  • Posts: 38
  • Joined: 23 Aug 2019
  • Loc: Vancouver, BC, Canada

Posted 02 February 2020 - 10:49 AM

Hi there, I find that my 32mm TV Plössl with 3x TV Barlow gives better eye relief and the same if not better view than my TV 11mm Plössl. I bought the 11mm thinking it would be better since there is less glass for the light to go through but I guess I wasted $.

#2 CrazyPanda

CrazyPanda

    Surveyor 1

  • *****
  • Posts: 1,984
  • Joined: 30 Sep 2012

Posted 02 February 2020 - 11:23 AM

Hi there, I find that my 32mm TV Plössl with 3x TV Barlow gives better eye relief and the same if not better view than my TV 11mm Plössl. I bought the 11mm thinking it would be better since there is less glass for the light to go through but I guess I wasted $.

I wish I could say "well yeah, no duh, what did you expect?", but I went down a similar path with my 11mm TV Plossl vs the 11mm TV DeLite, expecting a noticeable difference between the two. The reality is there isn't one (for my scope, skies, and eyes). Sold the 11 TVP after planetary season ended and I was confident that chasing photons through minimum glass isn't worth the loss of comfort.


  • BDS316, areyoukiddingme, 25585 and 1 other like this

#3 sg6

sg6

    Fly Me to the Moon

  • *****
  • Posts: 6,931
  • Joined: 14 Feb 2010
  • Loc: Norfolk, UK.

Posted 02 February 2020 - 11:37 AM

It's normal.

The eyepiece has about 20-22mm eye relief. The barlow changes the scope not the eyepiece, so you still have 20-22mm of eye relief.

 

A 32mm with a 3x barlow is a 32mm TV plossl in a scope of 3xstated focal length not a 11mm eyepiece.

 

Big mistake is talking of the eyepiece being reduced by a factor of 1/3, it is not. The scope is extended by 3x.


  • 25585 and carl_g like this

#4 25585

25585

    Fly Me to the Moon

  • *****
  • Posts: 7,478
  • Joined: 29 Aug 2017
  • Loc: In a valley, in the UK.

Posted 02 February 2020 - 11:44 AM

11mm pain v 32 x3 Barlow pleasure? 

 

32mm is useful inpendently, and with a x2, 16mm. With a x4 8mm. With a x5, 6mm. 


  • carl_g likes this

#5 Jon Isaacs

Jon Isaacs

    ISS

  • *****
  • Posts: 81,934
  • Joined: 16 Jun 2004
  • Loc: San Diego and Boulevard, CA

Posted 02 February 2020 - 11:50 AM

It's normal.

The eyepiece has about 20-22mm eye relief. The barlow changes the scope not the eyepiece, so you still have 20-22mm of eye relief.

 

A 32mm with a 3x barlow is a 32mm TV plossl in a scope of 3xstated focal length not a 11mm eyepiece.

 

Big mistake is talking of the eyepiece being reduced by a factor of 1/3, it is not. The scope is extended by 3x.

 

It depends on your point of view. If you think of the Barlow as part of the "ocular system" then it does reduce the focal length by a factor of 3.  But the eyepiece itself, is still a 32mm eyepiece, now it's just the positive section of a negative-positive eyepiece like any other short focal length ocular with decent eye relief.

 

The danger in thinking that the scope's focal ratio is increased by a factor of 3 is that some assume that this means aberrations like coma, field curvature, chromatic aberration are reduced accordingly.  That some how a 10 inch F/5 with a 3X Barlow now has the coma of a a 10 inch F/5.  The scope is still F/5, the coma is still the coma of an F/5.

 

Jon


  • SteveG, REC, BFaucett and 3 others like this

#6 Spikey131

Spikey131

    Apollo

  • *****
  • Posts: 1,166
  • Joined: 07 Feb 2017

Posted 02 February 2020 - 12:30 PM

Hi there, I find that my 32mm TV Plössl with 3x TV Barlow gives better eye relief and the same if not better view than my TV 11mm Plössl. I bought the 11mm thinking it would be better since there is less glass for the light to go through but I guess I wasted $.

 

Before modern optical coatings, losing light through multiple elements more of an issue.  So simple eyepieces with the fewest elements were noticeably better, especially with respect to contrast.  And many inexpensive barlows were uncoated and of dubious optical quality.

 

Modern coatings have reduced light loss and scatter to the point of being negligible for most uses. Barlows from respected manufacturers like Tele Vue are virtually invisible optically.  There are those who still invest in quality Abbe orthoscopic eyepieces and put up with the narrow FOV and short eye relief to get the utmost clarity and contrast.  I am not among them because any slight advantage is hard for me to see and not worth putting up with the downsides.


  • Jon Isaacs, REC, BFaucett and 2 others like this

#7 REC

REC

    Voyager 1

  • *****
  • Posts: 11,644
  • Joined: 20 Oct 2010
  • Loc: NC

Posted 02 February 2020 - 12:48 PM

Hmmm to this post? I hardly ever use my 2x barlow thinking seperate focal length will always be better. I don't have a really good barlow, just a 2x shorty Meade. Have to give it a try with my Brandon 32mm barlowed vs the Brandon 16mm.


  • carl_g likes this

#8 carl_g

carl_g

    Sputnik

  • -----
  • topic starter
  • Posts: 38
  • Joined: 23 Aug 2019
  • Loc: Vancouver, BC, Canada

Posted 02 February 2020 - 12:50 PM

Thanks everyone for the responses! I think I will list the 11mm Plössl in the classifieds lol
  • Jon Isaacs and 25585 like this

#9 Jon Isaacs

Jon Isaacs

    ISS

  • *****
  • Posts: 81,934
  • Joined: 16 Jun 2004
  • Loc: San Diego and Boulevard, CA

Posted 02 February 2020 - 01:14 PM

Hmmm to this post? I hardly ever use my 2x barlow thinking seperate focal length will always be better. I don't have a really good barlow, just a 2x shorty Meade. Have to give it a try with my Brandon 32mm barlowed vs the Brandon 16mm.

Shorty Barlows are not a good match for long focal length eyepieces.  Very likely there will be vignetting and some other off-axis issues. 

 

The TeleVue 3X Barlow that Carl used is not a Shorty, it's closer to an old style long Barlow. 

 

  Barlow_right.jpg

 

I use shorty Barlows but with medium and short focal length eyepieces. I have a 2X TeleVue as pictured above. It's the Barlow I use when I want the best possible views and need a Barlow.

 

Jon


  • Joe1950, cookjaiii and carl_g like this

#10 carl_g

carl_g

    Sputnik

  • -----
  • topic starter
  • Posts: 38
  • Joined: 23 Aug 2019
  • Loc: Vancouver, BC, Canada

Posted 02 February 2020 - 04:39 PM

I wish I could say "well yeah, no duh, what did you expect?", but I went down a similar path with my 11mm TV Plossl vs the 11mm TV DeLite, expecting a noticeable difference between the two. The reality is there isn't one (for my scope, skies, and eyes). Sold the 11 TVP after planetary season ended and I was confident that chasing photons through minimum glass isn't worth the loss of comfort.


Agreed eye relief comfort is very important. It almost seems like it’s hard to take in the whole 50° field of view

#11 25585

25585

    Fly Me to the Moon

  • *****
  • Posts: 7,478
  • Joined: 29 Aug 2017
  • Loc: In a valley, in the UK.

Posted 02 February 2020 - 05:52 PM

What Barlows/Extenders can do is flatten the FoV. Some are more dedicated to an eyepiece or range, others to telescopes.   



#12 CeleNoptic

CeleNoptic

    Apollo

  • *****
  • Posts: 1,336
  • Joined: 20 Dec 2007
  • Loc: Mid-Atlantic, Bortle 7

Posted 02 February 2020 - 09:33 PM


What Barlows/Extenders can do is flatten the FoV. Some are more dedicated to an eyepiece or range, others to telescopes.   

 

Nope. You can't combine them, IMO. Extenders yes, they do, but Barlows can flatten to some extent or can do just opposite depending on Barlow and objective.


Edited by CeleNoptic, 02 February 2020 - 09:38 PM.


#13 REC

REC

    Voyager 1

  • *****
  • Posts: 11,644
  • Joined: 20 Oct 2010
  • Loc: NC

Posted 04 February 2020 - 01:16 PM

Shorty Barlows are not a good match for long focal length eyepieces.  Very likely there will be vignetting and some other off-axis issues. 

 

The TeleVue 3X Barlow that Carl used is not a Shorty, it's closer to an old style long Barlow. 

 

  Barlow_right.jpg

 

I use shorty Barlows but with medium and short focal length eyepieces. I have a 2X TeleVue as pictured above. It's the Barlow I use when I want the best possible views and need a Barlow.

 

Jon

Thanks for that explanation, would never had thought of it!



#14 Tank

Tank

    Skylab

  • *****
  • Posts: 4,016
  • Joined: 27 Jul 2009
  • Loc: Stoney Creek, Ontario, CANADA

Posted 05 February 2020 - 07:49 AM

Be careful with Barlow's
Usually there not running exact 3x as indicated
It's all based on the EP fieldstop your using
So when comparing you maybe higher or lower magnification
This may sway your results one way or another
FYI

#15 Miranda2525

Miranda2525

    Vanguard

  • *****
  • Posts: 2,060
  • Joined: 12 Jul 2016

Posted 05 February 2020 - 07:58 AM

Hi there, I find that my 32mm TV Plössl with 3x TV Barlow gives better eye relief and the same if not better view than my TV 11mm Plössl. I bought the 11mm thinking it would be better since there is less glass for the light to go through but I guess I wasted $.

A 32mm Plossl has eye placement issues to start with. Adding any kind of barlow will only make it harder to use.



#16 RFeaster

RFeaster

    Lift Off

  • -----
  • Posts: 18
  • Joined: 02 Aug 2019
  • Loc: Southern Indiana

Posted 05 February 2020 - 10:58 AM

I have Plossls 32, 25, 20, 17, 15, & 13.  I also have 2x, 3x, 5x [4] element barlows (telecentric).  I don't barlow the 32 & 25 due to redundancy, but the others I do.  This setup gives me 38x to 462x with about 18% increments and good (for me) eye relief.  From what I have read here on CN, the eye relief doesn't change when using telecentric barlows.  The views look pretty good to me, but I'm a noob...so what do I know.   


  • Jon Isaacs and eros312 like this

#17 Jon Isaacs

Jon Isaacs

    ISS

  • *****
  • Posts: 81,934
  • Joined: 16 Jun 2004
  • Loc: San Diego and Boulevard, CA

Posted 06 February 2020 - 01:09 PM

The views look pretty good to me, but I'm a noob...so what do I know.

 

 

You know what you see. The rest is just stuff to argue about.  :ubetcha:

 

Jon


  • bdcmd, Lenard, clearwaterdave and 2 others like this

#18 Bigzmey

Bigzmey

    Vostok 1

  • *****
  • Posts: 177
  • Joined: 25 Sep 2015
  • Loc: San Diego

Posted 07 February 2020 - 03:32 PM

Thanks everyone for the responses! I think I will list the 11mm Plössl in the classifieds lol

But what if you need 3mm or 5mm EP? laugh.gif



#19 carl_g

carl_g

    Sputnik

  • -----
  • topic starter
  • Posts: 38
  • Joined: 23 Aug 2019
  • Loc: Vancouver, BC, Canada

Posted 08 February 2020 - 11:21 PM

That’s a good point thanks!

#20 Bigzmey

Bigzmey

    Vostok 1

  • *****
  • Posts: 177
  • Joined: 25 Sep 2015
  • Loc: San Diego

Posted 08 February 2020 - 11:51 PM

I have also noticed that sometimes barlowing let's say 20mm Plossl produces cleaner image than using 10mm Plossl, and sometimes the other way around. Nice to have both options.


  • wrnchhead and RFeaster like this

#21 MartinPond

MartinPond

    Fly Me to the Moon

  • *****
  • Posts: 5,255
  • Joined: 16 Sep 2014

Posted 09 February 2020 - 02:09 AM

A 32mm Plossl has eye placement issues to start with. Adding any kind of barlow will only make it harder to use.

Aha!

Now I know why there is a 'well' going down to the eye lens these days,

  for many 25mm----35mm.    Makes sense now.

That makes placement much easier, although for glasses you need the 30-35mm.  


Edited by MartinPond, 09 February 2020 - 02:09 AM.

  • 25585 likes this

#22 Miranda2525

Miranda2525

    Vanguard

  • *****
  • Posts: 2,060
  • Joined: 12 Jul 2016

Posted 09 February 2020 - 03:55 AM

Aha!

Now I know why there is a 'well' going down to the eye lens these days,

  for many 25mm----35mm.    Makes sense now.

That makes placement much easier, although for glasses you need the 30-35mm.  

???



#23 MartinPond

MartinPond

    Fly Me to the Moon

  • *****
  • Posts: 5,255
  • Joined: 16 Sep 2014

Posted 14 February 2020 - 12:51 AM

???

 

It is not unusual for eyepieces

   (for telescopes or binoculars) with sensitive eye placement

   or 'kidney-beaning' to have an adjustable height eyecup

   or a deep fixed eyepiece.

Fixing the distance makes the other eye placement much easier.

I have glued collars onto several eyepieces to stabilize eye placement.

Of course....I have to take off my glasses.  

 

So..I am guessing that the deep well on the 26mm 4000 is to

  avoid nuisance and complaints.  Unless someone has strong astigmatism..

Unfortunately, the well exists on other 26mm Plossls as well...

   ...probably because they are the same design..


Edited by MartinPond, 14 February 2020 - 12:52 AM.


#24 Bigzmey

Bigzmey

    Vostok 1

  • *****
  • Posts: 177
  • Joined: 25 Sep 2015
  • Loc: San Diego

Posted 14 February 2020 - 03:00 PM

It is not unusual for eyepieces

   (for telescopes or binoculars) with sensitive eye placement

   or 'kidney-beaning' to have an adjustable height eyecup

   or a deep fixed eyepiece.

Fixing the distance makes the other eye placement much easier.

I have glued collars onto several eyepieces to stabilize eye placement.

Of course....I have to take off my glasses.  

 

So..I am guessing that the deep well on the 26mm 4000 is to

  avoid nuisance and complaints.  Unless someone has strong astigmatism..

Unfortunately, the well exists on other 26mm Plossls as well...

   ...probably because they are the same design..

Having adjustable eyeguards is the right way to go. Unfortunately, most Plossls don't have them. This is why I like smoothies. I make sliding eyeguards for them and can set them to the level I need for eyeglasses or no eyeglasses.


  • RFeaster and j.gardavsky like this

#25 BillP

BillP

    Hubble

  • *****
  • Posts: 19,137
  • Joined: 26 Nov 2006
  • Loc: Spotsylvania, VA

Posted 14 February 2020 - 03:24 PM

Modern coatings have reduced light loss and scatter to the point of being negligible for most uses. Barlows from respected manufacturers like Tele Vue are virtually invisible optically.  There are those who still invest in quality Abbe orthoscopic eyepieces and put up with the narrow FOV and short eye relief to get the utmost clarity and contrast.  I am not among them because any slight advantage is hard for me to see and not worth putting up with the downsides.

This is all very true.  Modern quality Barlows are exceedingly good...it is hard not to be good as talking only 2 elements, and when they are cemented and multicoated then we only have 2 air-glass interfaces that we are adding so impacts will be "virtually" meaningless (note that tone changes might be noticeable as well al off-axis issues like lateral color sometimes induced by the Barlow).  But for the most part, if you buy a quality Barlow or amplifier like TV Powermate or Siebert Telecentrics, then there is little to concern over IME.

 

However...yes there is always a however...when one adds glass to the train there will always be some impact.  But the question is if the impact will rise to the threshold of becoming visible?  And if it does become visible, then will it be meaningful?  So there are levels here and whether going thru these levels is important of not is entirely dependent on things like if the rest of the optical system is optimized to the point that the small addition of scatter and such by the extra glass will fall out or be overwhelmed by the other components in the optic chain.  And when one has a very highly optimized optic with least scatter possible, will any degradation from extra glass be meaningful?  This is trickier to determine as one would need to know if the observer routinely observes the portions of a target that might be impacted by those small difference or not.  And finally if it will have an impact, is that impact important for that observer?  Only way to know is by knowing oneself.  No one else can answer that question or say that the small gain is "small" in terms of importance to the observer and their individual needs.  If it is, then the typical downsides of the highly optimized minimal glass eyepieces, like smaller afovs and tight eye relief, may well be not just worth it, but critical.  And of course for others that have equipment still excellent but not so optimized for scatter, who observe critically but not in areas where small gains will have much impact, well for them it is a waste and better to get something more comfortable.  Both ways are good and admirable.  And like anything else, once one regularly uses something they become adept at it and there is no longer any discomfort or strain to use small ER and small AFOV eyepieces.  So nothing given up for the improvement that is small in nature but large in meaning for the particular observer when using highly optimized minimum glass eyepieces.  So basically it is ALL good, but it all doesn't necessarily fit every person.  And when it doesn't fit, does not make it bad or seemingly crazy or extreme, just means what we always know, that everyone is different and we should be happy that the market is able to cater to such a broad range of needs.


Edited by BillP, 14 February 2020 - 03:24 PM.

  • eros312 likes this


CNers have asked about a donation box for Cloudy Nights over the years, so here you go. Donation is not required by any means, so please enjoy your stay.


Recent Topics






Cloudy Nights LLC
Cloudy Nights Sponsor: Astronomics