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85° Masuyama's ?


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2 hours ago, mikeDnight said:

Thanks Louis,

I've just ordered a 5mm Pseudo in the form of an Ultrascopic from ENS Optical, which should sooth the itch for a while. If only these 85° were 50° or even 40°, id have probably bitten long before now. Its interesting what you say about the purely positive design. Im going to have to read up in more depth about these and similar designs. ☺

I'll be interested to see what you think of that one Mike.

It was interesting that Orion commissioned the manufacturer to add a lower lens set with the 5mm and 3.8mm in their versions of this pseudo-Masuyama range. I presume this is to give better eye relief. I used to have the 5mm Celestron Ultima which did not use a lower lens set and the eye relief was pretty tight. Very nice optically though. There was never a Celestron Ultima 3.8mm - perhaps without a lower lens set the eye relief would have been virtually zero !

Edit: Actually I think the 5mm Ultrascopic is the same as the 10mm but with a 2x amplifier in the eyepiece barrel.

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2 hours ago, mikeDnight said:

Thanks Louis,

I've just ordered a 5mm Pseudo in the form of an Ultrascopic from ENS Optical, which should sooth the itch for a while. If only these 85° were 50° or even 40°, id have probably bitten long before now. Its interesting what you say about the purely positive design. Im going to have to read up in more depth about these and similar designs. ☺

Very decent of you Mike to take temptation away from others,
good chap 😉

Now about that 82 degree Masuyama...... 

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6 hours ago, mikeDnight said:

Thanks Louis,

I've just ordered a 5mm Pseudo in the form of an Ultrascopic from ENS Optical, which should sooth the itch for a while. If only these 85° were 50° or even 40°, id have probably bitten long before now. Its interesting what you say about the purely positive design. Im going to have to read up in more depth about these and similar designs. ☺

This is a function of design,  The TeleVue Delites are designed to have a 1µ spot size on axis and 1.5µ at the edge of the field.  Both figures are smaller than the Airy disc in amateur scopes.

And some positive-only eyepiece designs are horrible.  So it's not whether it's a positive-only, or negative-positive lens arrangement, it's a matter of design.

And there are good and bad eyepieces in both camps.

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4 hours ago, Don Pensack said:

This is a function of design,  The TeleVue Delites are designed to have a 1µ spot size on axis and 1.5µ at the edge of the field.  Both figures are smaller than the Airy disc in amateur scopes.

And some positive-only eyepiece designs are horrible.  So it's not whether it's a positive-only, or negative-positive lens arrangement, it's a matter of design.

And there are good and bad eyepieces in both camps.

I was thinking more in terms of 80+ degree designs that seem to sacrifice central sharpness for overall correction.  There are simple UWA eyepieces out there without a negative group that appear sharper in the center than negative/positive designs such as Naglers and ES-92s.  Their downfall is outside that central 30 to 40 degrees of ultra-crispness.  The Delites are generally judged to be slightly behind the simpler, positive only designs like the ZAOs, TOEs, XOs, HRs, etc. in terms of contrast, but perhaps not in sharpness.

I would love for a negative/positive design to match those specialist eyepieces for sharpness, contrast, stray light control, etc. and still yield an 80 degree, 20mm eye relief design, but it hasn't happened yet.  The designs are getting closer, that's for certain, but there is still a slight gap.  My hat's off to Tele Vue for their work toward eyepiece perfection, pushing the industry forward and out of the eyepiece stagnation of the 1970s and earlier.  I'm just saying we haven't achieved eyepiece nirvana just yet, despite marketing claims to the contrary (think Nirvana branded eyepieces).

Edited by Louis D
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Hi 

I also had to scratch that itch.

It is certainly one of my favourite eyepieces, eye relief bit tight but manageable.

Views excellent  on axis better than my es 92 17mm.

Will  certainly buy more in the range even though have all the eyepieces I really need.

 

59B7A4EC-B738-4397-B35F-F371A55E14EF.jpeg

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2 minutes ago, Sweep said:

imageproxy.php?img=&key=127fb0a7147957bfHi 

I also had to scratch that itch.

It is certainly one of my favourite eyepieces, eye relief bit tight but manageable.

Views excellent  on axis better than my es 92 17mm.

Will  certainly buy more in the range even though have all the eyepieces I really need.

 

59B7A4EC-B738-4397-B35F-F371A55E14EF.jpeg

What scope / scopes do you use it with and how is the edge sharpness ?

It is a heck of a lot smaller than the ES 92 / 17 that/s for sure !

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3 minutes ago, John said:

What scope / scopes do you use it with and how is the edge sharpness ?

It is a heck of a lot smaller than the ES 92 / 17 that/s for sure !

It is tiny, but perfectly formed.

I’m using in a 130mm Apo, and currently trying to decide whether  to buy a 11” act or 10” classical cassegrain.

Edge of field not perfect on axis best of my collection, which include 

Es 40mm 68

Es 30mm 82

Es 17mm 92

Es 12mm 92

Televue delete 7mm

Wo 4mm Uwan

Vixen 3.5mm ssw

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16 minutes ago, Sweep said:

It is tiny, but perfectly formed.

I’m using in a 130mm Apo, and currently trying to decide whether  to buy a 11” act or 10” classical cassegrain.

Edge of field not perfect on axis best of my collection, which include 

Es 40mm 68

Es 30mm 82

Es 17mm 92

Es 12mm 92

Televue delete 7mm

Wo 4mm Uwan

Vixen 3.5mm ssw

Thanks. That's interesting to know :icon_biggrin:

 

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3 hours ago, Sweep said:

It is tiny, but perfectly formed.

I’m using in a 130mm Apo, and currently trying to decide whether  to buy a 11” act or 10” classical cassegrain.

Edge of field not perfect on axis best of my collection, which include 

Es 40mm 68

Es 30mm 82

Es 17mm 92

Es 12mm 92

Televue delete 7mm

Wo 4mm Uwan

Vixen 3.5mm ssw

Pretty much validates what I said about negative-positive designs not matching a purely positive design.  Of that list, only the 40mm ES-68 is a purely positive design.  I have the 40mm Meade 5000 SWA version of it, and it's not as sharp in the center as the even simpler 40mm Meade 5000 Plossl which is very sharp only in the inner 30 degrees.  Another example is my 30mm Agena UWA 80 degree Wide Scan clone that is sharper in the center than my 30mm ES-82.  However, it has field curvature and astigmatism outside the inner 40 degrees.

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On 27/05/2020 at 02:36, mikeDnight said:

 Its interesting what you say about the purely positive design. I'm going to have to read up in more depth about these and similar designs. ☺

http://astro-talks.ru/forum/viewtopic.php?f=32&t=1483

You'll see a list of eyepieces tested at f/4 and f/10.  Look at the size of the aberrations in each and you'll see that whether the eyepiece has small aberrations on axis or large is independent of whether it has a Smyth or Barlow lens as a field group (negative field group).  Most of the very best eyepieces tested do have a negative field group.  As I said before, axial sharpness has little to do with whether the eyepiece has a negative field group.  

Sharpness off axis, however, does.  

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2 hours ago, Alan White said:

Telvue Delete, that's a new one @Sweep 😉

 

1 hour ago, Timebandit said:

 

 

Must be a new Range Televue have released, look forward to the reviews on these 😁

 

Only pulling your leg Sweep, welcome to SGL 👍

 

 

Blasted school teachers are lurking on this forum as well.🧑‍💻🧑‍💻

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2 minutes ago, Sweep said:

Blasted school teachers are lurking on this forum as well.🧑‍💻🧑‍💻

That's funny, my smelling is too awful...... 🤣  
Who we need is Olly Penrice to come and correct us propper like e duz sometimz!!

I was more concerned it was a Freudian comment on DeLites to be honest.

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  • 11 months later...
20 minutes ago, Commanderfish said:

RESURRECTION!

Does anyone actually have the Masuyama 26mm 85?  How is the performance in F7.4 scopes and over?  I mostly run F7.4 Fracs and F10 CCs.

Would be interesting to see how it would compare to the now discontinued Tele Vue 26mm Nagler eyepiece, I don't suppose that there would be any comparison in an f5 Newtonian.

I can't understand why Tele Vue decided to discontinue their 26mm Nagler, leaving a large gap between the 22mm and the 31mm.

John  

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2 hours ago, johnturley said:

I can't understand why Tele Vue decided to discontinue their 26mm Nagler, leaving a large gap between the 22mm and the 31mm.

They probably ran out their existing stock and decided that it wouldn't be economical to start another run given past sales performance.  They would also probably have to raise the price as well to cover new, higher manufacturing costs to such a point it probably wouldn't be at all competitive.

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2 hours ago, johnturley said:

Would be interesting to see how it would compare to the now discontinued Tele Vue 26mm Nagler eyepiece, I don't suppose that there would be any comparison in an f5 Newtonian.

I can't understand why Tele Vue decided to discontinue their 26mm Nagler, leaving a large gap between the 22mm and the 31mm.

John  

I can see it from TeleVue's position: you have an eyepiece that barely sells (as a dealer I can tell you that only the 2.5mm Nagler sold less), and you need to reorder and there is a minimum of 300 pieces to get a price that allows the wholesale and retail price to stay the same.

It's going to be many tens of thousands of dollars that would better be spent in another product, like the 22mm, for instance, that is a good seller.

So you slowly discontinue the ones that really don't sell--the 26mm, 20mm, 12mm, 11mm, 2.5mm and let them run out.

That still leaves you with a fairly complete 82° lineup--31, 22, 17, 16, 13, 9, 7, 5, and 3.5mm.  That's still 2 more focal lengths in an ultrawide line than any other seller.

The 31mm to 22mm jump is not large at all--only 39x to 55x in a 1200mm focal length, a difference of 16x, or a 41% increase, which is commensurate with TeleVue's position about having a 40% difference between magnifications.

In case you wonder where that comes from, it turns out the true field, if all eyepieces have the same apparent field, is exactly 1/2 the size by area when magnifications increase by a factor of 1.414 between eyepieces.

Starting with the 31mm as a low power, the next focal length in a set would be 22mm, which is probably why the 26mm never sold well.

Plus the fact that the magnification difference between the 31mm and 22mm is small in most scopes.  My scope is longer (1826mm), yet I never use a 31mm or 22mm on the same night--they're both low powers.

 

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Oddly enough the 26mm Nagler was my favourite of the longer focal length Naglers. Just hit the sweet spot for me. Second hand 26mm Naglers do seem to sell very quickly and bring a high price at least in the UK.

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