Plossl

[Daniel3]

Hi what is the difference between a plossl and a super plossl also can someone recommend a good 15 mm plossl thanks 

[Merlin66]

The classical plossl has four glass elements in two groups. Usually each pair is symmetrical.

The "super" version has an additional single lens between the pairs - supposed to improve the performance.

I've been using TV plossls for the past twenty years - a good investment; they will outlast my eyes.

 

 

[John]

Just to add to the good information above, many plossls today have "Super Plossl" printed on them but are the standard 4 element in 2 groups design. Don't assume that just because the "Super" word is there that they have 5 elements or are in any way different to the standard plossl design.

 

[Charic]

There is a 12mm Super Plössl for £16.20  available on Astroboot?

Its not the 15mm you desire, but at that price who cares, but hey, I turned down Meade and TeleVue Plössls in favour of their GSO built Revelation Astro EP's.

Daniel3, you don't mention for which scope, that may have a bearing on which EP you could/should choose, but the dearer EPs  above produced no favours for me on my f/6 scope!

If you can afford TeleVue Plössl's, their there for the taking, some at reasonable prices second hand, if you check the right places, and loads of folk love them. I still think based on sales and feed back, TeleVue are one of the better brands out there, but you'll pay for the premium.
Ive tried them but on my scope, those  premium optics are  just not needed or essential to get great views.
Only issue I'm having with great views at present  is weather related!

 

[Mak the Night]

These 9mm eyepieces are often described as 'Super Plossls'. The Bresser above has five lens elements and a 60͒ FOV.

The 9mm GSO above described as a Super Plossl is a four element 50͒ FOV standard Plossl.

[MarsG76]

If you go with TeleVue eyepieces, you will not regret it.. sure they are pricey but worth it...

 

[Mak the Night]

These are often referred to as Super Plossls or even just Plossls. They're five element Erfles really. In scopes f/8 and slower they are as good as anything in my opinion. They still aren't really Plossls though.

[YKSE]

To make things more complicated, there's another "definition" difference of plossl vs super plossl, in addition to mentioned by Merlin and John, as shown in these links:

https://www.teleskop-express.de/shop/product_info.php/info/p3957_TS-Optics-1-25--Ploessl-Eyepiece---10-mm-focal-length--50--apparent-field-of-view.html

https://www.teleskop-express.de/shop/product_info.php/info/p152_Super-Ploessl---9mm-Focal-Length---1-25----52--FOV---FMC.html

Where "plossl" means "multi-coated", i.e. only the two lens' outer surfaces are multi-coated, while "super" means "fully multi-coated", i.e. all the lens surfaces are multi-coated. The impact is the "fully multi-coated" will have better light through put than the "multi-coated".

[Louis D]

And to add to the confusion, most mass produced "Plossls" are really symmetrics because they're cheaper to make since the two doublets are identical.  Televue Plossls are not symmetrical, are a modification of the original Plossl design, and are patented in their own right.  Brandons are also a modification of the Plossl design and are definitely not symmetrical, employing three different glass types.  The five element "Plossls" are closer the Zeiss Astroplan design than an Erfle since they were going for improved correction in a narrow field of view over mediocre correction over a wider field of view as in a typical Erfle design.

[YKSE]

14 minutes ago, Louis D said:

And to add to the confusion, most mass produced "Plossls" are really symmetrics because they're cheaper to make since the two doublets are identical.  Televue Plossls are not symmetrical, are a modification of the original Plossl design, and are patented in their own right. 

Where in the patent saying Televue plossls are not symmetrical?

[Stu]

47 minutes ago, YKSE said:

Where in the patent saying Televue plossls are not symmetrical?

This is the patent image I found, seems to be symmetrical.

[YKSE]

Thanks stu, I've read that patent a couple of times through the years

[Mak the Night]

1 hour ago, Louis D said:

And to add to the confusion, most mass produced "Plossls" are really symmetrics because they're cheaper to make since the two doublets are identical.  Televue Plossls are not symmetrical, are a modification of the original Plossl design, and are patented in their own right.  Brandons are also a modification of the Plossl design and are definitely not symmetrical, employing three different glass types.  The five element "Plossls" are closer the Zeiss Astroplan design than an Erfle since they were going for improved correction in a narrow field of view over mediocre correction over a wider field of view as in a typical Erfle design.

Yes, I believe you're right about the Astroplanokular design. Which was a modified Erfle I believe.

[John]

My understanding of the TV plossl design is that the "difference" was the slight concave figure to the outer surfaces (R1 and R6) of the two groups to improve edge sharpness in faster scopes

That, and Al's magic dust of course

There are rumours that the Vixen NPL's have a similar feature but I've no evidence of that.

 

 

[Louis D]

1 hour ago, John said:

My understanding of the TV plossl design is that the "difference" was the slight concave figure to the outer surfaces (R1 and R6) of the two groups to improve edge sharpness in faster scopes

That, and Al's magic dust of course

There are rumours that the Vixen NPL's have a similar feature but I've no evidence of that.

 

 

I stand corrected.  I remember the concave figure as you describe, but I was thinking it was applied to only one of the outer surfaces rather than both.  Al probably went the symmetrical route to reduce costs because he was trying to fund his ultrawide field designs with some sales of lower cost eyepieces in the beginning.

[Louis D]

2 hours ago, Stu said:

This is the patent image I found, seems to be symmetrical.

Good catch.  I misremembered the details.  I wonder if correction would have been even better with asymmetrical doublets.

[Charic]

I'm sure I read in the past that TeleVue had not paid a fee so their Plössl patent has lapsed, but that does not make their eyepiece any inferior.

[Louis D]

1 hour ago, Charic said:

I'm sure I read in the past that TeleVue had not paid a fee so their Plössl patent has lapsed, but that does not make their eyepiece any inferior.

Patents expire 17 years after the date of issuance in the U.S.  There is no option to renew a patent here like a copyright or trademark.  How do patents work in the UK?

[Daniel3]

Hi guys I have just bought a sky watcher explorer 130ps  az5 telescope, sky watcher 2x De-luxe Achromatic Barlow lens and Meade series 400015mm super plossl eyepiece......

[Charic]

3 minutes ago, Daniel3 said:

 Meade series 400015mm super plossl eyepiece......

I wanted to build a set of Meade 4000's, but in comparison favoured the Revelations.

 

[John]

5 minutes ago, Daniel3 said:

Hi guys I have just bought a sky watcher explorer 130ps  az5 telescope, sky watcher 2x De-luxe Achromatic Barlow lens and Meade series 400015mm super plossl eyepiece......

Congratulations - I hope you really enjoy using your new kit

[Charic]

2 hours ago, Louis D said:

Patents expire 17 years after the date of issuance in the U.S.  There is no option to renew a patent here like a copyright or trademark.  How do patents work in the UK?

Its my understanding that patents expire after 20 Years from the date of filing, but require re-newal fees from Year 5 onwards!
Having a patent description in your  sales brochure is no bad thing especially if what you have patented makes for an improvement, and the patent  itself prevents further redevelopment by other parties?

[John]

Patents are only worthwhile if you can afford the considerable legal costs of defending them. I think that was the problem that Tele Vue had as a relatively small company. My cousin is a business patent lawyer and earns big money, really big money 

 

 

[YKSE]

Read the online patent, you'll how the maintenensce fee pays to extend a patent:

https://www.google.com/patents/US4482217

There're many unik eyepiece designs protected with patents, whether or not  worth to apply for patents or keep the patent in effect, it's different business decisions, I'd guess.

[Daniel3]

Feel like a kid in a sweet shop, just had my delivery of my first telescope and bits and bobs all I need is a nice clear sky  then the learning begins