New Takahashi eyepieces announced

[John]

8 hours ago, F15Rules said:

That's SGL speak, loosely translated in normal parlance as  "he's a tight old...." (insert your preferred adjective😉☺️😂)

Dave

He can't be that tight - he has developed a taste for Ethos now 😉

[JeremyS]

2 hours ago, John said:

He can't be that tight - he has developed a taste for Ethos now 😉

Not to mention the excursion into Apollo territory. Thankfully there is only one….at the moment 🤣

[Bivanus]

I didn't understand what Don was saying about the 90° so I look it up...Wow ! Takahashi Ultra Wide/Flat Field 1.25" 90° at 3.3/5.7/7/10mm...All of a sudden the TOE line lost it's charm...

[MalcolmM]

Just wondering if anyone is going to get one of these,  or even better, already used one?

Does anyone know if the outer 50% of the FOV is likely to be similar/better/worse than the Abbes or LEs?

Malcolm 

[F15Rules]

35 minutes ago, MalcolmM said:

Does anyone know if the outer 50% of the FOV is likely to be similar/better/worse than the Abbes or LEs?

Malcolm 

Well, based on my own Tak Abbe 12.5mm orthos, I can't see how the outer 50% of the FOV could be any better to my eyes..

Ok, so I'm using them at F8, in a Tak scope..maybe a faster scope, say F5, would show something different, but for my scope they show me the best view optically that I can detect, within the limitations of their designed FOV.😉.

Dave

[JeremyS]

2 hours ago, MalcolmM said:

Just wondering if anyone is going to get one of these,  or even better, already used one?

Does anyone know if the outer 50% of the FOV is likely to be similar/better/worse than the Abbes or LEs?

Malcolm 

I thought @Highburymark had volunteered to take one for the SGL team 🤔

🤣

[MalcolmM]

9 hours ago, F15Rules said:

Well, based on my own Tak Abbe 12.5mm orthos, I can't see how the outer 50% of the FOV could be any better to my eyes..

That's my worry! I think the Tak Abbe's must be incredibly hard to best! But here's hoping 🙂

Malcolm 

[JeremyS]

Well there’s more to worry about, @MalcolmM.
I hesitate to raise this spectre, but I saw on a US website a photo someone posted of their new TPLs, but it seems Tak has changed the design of their EP boxes. Instead of a liftoff lid, it’s a flap. 
I’m not sure I can take this change.

Naturally, we will have to wait until @Highburymark takes delivery of his 3 TPLs (or was it 6 for binoview?) to see if the UK is subjected to this change.

But at least the boxes are still blue, with the lovely Tak writing.

[MalcolmM]

45 minutes ago, JeremyS said:

Well there’s more to worry about, @MalcolmM.
I hesitate to raise this spectre, but I saw on a US website a photo someone posted of their new TPLs, but it seems Tak has changed the design of their EP boxes. Instead of a liftoff lid, it’s a flap. 
I’m not sure I can take this change.

Naturally, we will have to wait until @Highburymark takes delivery of his 3 TPLs (or was it 6 for binoview?) to see if the UK is subjected to this change.

But at least the boxes are still blue, with the lovely Tak writing.

Flapping heck, that sounds like a major drop in standards. You can't beat a nice blue lid!

Malcolm 

[Louis D]

On 16/07/2023 at 08:30, vlaiv said:

or comparison F/10 4" objective will have size of airy disk at 221.6" or 3.7 arc minutes - about x287 larger circle than presented in the image.

If indeed Tak has managed to reduce the aberration spot size by a factor of 287 over a typical improved Plossl (TV, Clave, Brandon), I will be insanely impressed.

[vlaiv]

7 hours ago, Louis D said:

If indeed Tak has managed to reduce the aberration spot size by a factor of 287 over a typical improved Plossl (TV, Clave, Brandon), I will be insanely impressed.

That is not quite what I've said (nor was it claimed by Tak).

I'll need a bit of an introduction that you and anyone else reading this explanation may already know - then consider this as a reminder and setting the context for what will be said.

Telescope is a projection device - it projects angles onto a focal plane.

Eyepiece is "inverse" of above - it takes image from focal plane and turns it into output rays at certain angles.

When we combine the two we get system that magnifies the image - or increases incident rays by some factor.

To understand what I meant by factor of x287 over airy disk of F/10 scope

Quote

For comparison F/10 4" objective will have size of airy disk at 221.6" or 3.7 arc minutes - about x287 larger circle than presented in the image. -

we need to think of eyepiece as magnification lens - much like regular magnifying lens.

Whatever is placed at focal plane of eyepiece - we will be able to see it magnified.

Now, back to original TAK diagram and their claim

They claim that single spot at focal plane produces above image. Not star image thru a telescope - but single spot. Think of it as single atom of light emitting phosphorus or something like that in focal plane. That single point will produce object that is up to 4 micro radians to our eyes or 0.825 arc seconds. Now in perfect system - single dot, no matter how magnified will still be single dot - but this eyepiece "blurs" that perfect dot into something that has angular size like say one of the moons of Jupiter - viewed by the naked eye.

Now, let's for the moment say we have perfect eyepiece - one that introduces no aberrations. 4" F/10 telescope will produce airy disk 2.77 arc seconds. Such telescope has 1000mm focal length and if we pair it with perfect 12.5mm eyepiece - image will be magnified by 1000/12.5 = x80

To our eye - star, or rather its airy disk will look like it is 2.77" * x80 = 221.6 arc seconds large

So perfect spot in focal plane with Tak eyepiece will be presented to us like 0.825" large circle (in worst case at edge of the field) while

4" F/10 scope with perfect eyepiece (in fact both can be perfect optical system) - will present star image to our eyes that is 221.6 arc seconds large.

Difference between these two images is 221.6 / 0.825 = x268 (I obviously made a typo or copy error in initial calculation - as result is 268 not 287).

The way one needs to interpret that would be - perfect eyepiece in 4" F/10 scope will produce around 221.6" airy disk size to our eyes, but with Tak eyepiece that size will be increased by roughly 1/268th of that to 222.4" - at the edge of the field.

Or in simple words - blur that eyepiece adds to perfect airy disk (for 4" F/10 scope) is about 1/268 of the size of that airy disk - of we could say insignificant.

Hope this makes sense now.

[Highburymark]

15 hours ago, JeremyS said:

Well there’s more to worry about, @MalcolmM.
I hesitate to raise this spectre, but I saw on a US website a photo someone posted of their new TPLs, but it seems Tak has changed the design of their EP boxes. Instead of a liftoff lid, it’s a flap. 
I’m not sure I can take this change.

Naturally, we will have to wait until @Highburymark takes delivery of his 3 TPLs (or was it 6 for binoview?) to see if the UK is subjected to this change.

But at least the boxes are still blue, with the lovely Tak writing.

I might be tempted by a pair of 12.5s.  Must confess to having an huge amount of 25mm/20mm/18mm eyepieces, especially orthos, so the 12.5mm TPLs are the most attractive. Going to have a big eyepiece cull in next few weeks.

[Don Pensack]

Takahashi identifies those circles as 4 milliradians, which translates to 13.75' in apparent size.

That is not a great lateral sharpness, but is typical for a well-corrected 4-element Plössl.

They admit that the edge deteriorates, and given the specs, I'm sure it does.

But they also don't identify the f/ratio that yields those spot diagrams, so the actual performance of the eyepieces will depend on that factor.

[Mr Spock]

What we need is someone gullible enthusiastic enough to test them 

[vlaiv]

2 hours ago, Don Pensack said:

Takahashi identifies those circles as 4 milliradians, which translates to 13.75' in apparent size.

Image says 4 micro radians - not milliradians - that is x1000 less.

 

[Louis D]

3 hours ago, Don Pensack said:

Takahashi identifies those circles as 4 milliradians, which translates to 13.75' in apparent size.

I just google image translated it as 4 microradians (see below), which again would be astonishing if it is 1000x better corrected than an improved Plossl.

Why would they use an Airy disk, which is typically in the 2.5 to 5 milliradians range, for the upper images, and then switch to 4 microradians, 1/1000ths of a typical airy disk, for the lower images?  An apples to oranges comparison is very confusing.

Text:

Center spot diagram comparison
LE12.5

The circle is an Airy disk, 11 wavelengths
from 436mm to 656nm are synthesized,
and the objective is an aplanatic optical system.
(C) TAKAHASHI SEISAKUSHO Ltd.
TPL-12.5 Spot Diagram
Apparent field of view
(half angle)
0°
5.5°
11°
16.5°
22°
A circle is 4 microradians
Afocal calculation of 11 wavelengths
from 436mm to 656nm
(C) TAKAHASHI SEISAKUSHO Ltd.

[vlaiv]

15 minutes ago, Louis D said:

Why would they use an Airy disk, which is typically in the 2.5 to 5 milliradians range, for the upper images, and then switch to 4 microradians, 1/1000ths of a typical airy disk, for the lower images?  An apples to oranges comparison is very confusing

Eyepiece aberration adds to that of telescope.

They presented combined spot diagram for Aplanatic optical system + each of their eyepieces to show improvement on axis compared to already existing lines.

In lower row - they wanted to show that there is in fact difference between on axis and edge performance of the new eyepiece - but in fact it is so small (both fall in 4 micro radians category) that it is negligible and essentially edge performance is as good as center as far as this eyepiece is concerned.

At least that's how I'm reading the diagrams.

[Don Pensack]

3 hours ago, vlaiv said:

Image says 4 micro radians - not milliradians - that is x1000 less.

 

That would make the circle 0.01375', or 0.825", and the spot size a small fraction of that

I think they made an error.  

That would make the star image essentially diffraction limited near the edge of the field.

I've seen that in several eyepieces at f/10, but none with a 4 element construction.

[vlaiv]

2 minutes ago, Don Pensack said:

That would make the circle 0.01375', or 0.825", and the spot size a small fraction of that

I think they made an error.  

That would make the star image essentially diffraction limited near the edge of the field.

I've seen that in several eyepieces at f/10, but none with a 4 element construction.

Agree on diffraction limited near the edge part, but have no idea if they made an error - my first impression was that it is legit, but who knows.

[vlaiv]

6 hours ago, Don Pensack said:

Takahashi identifies those circles as 4 milliradians, which translates to 13.75' in apparent size.

That seems too much for premium eyepiece?

It is the same as 2mm at arms length (500mm). I'm now looking at ruler at that distance - and I'd be surprised to see a star that size in the eyepiece to be honest.

[Don Pensack]

2 hours ago, Louis D said:

I just google image translated it as 4 microradians (see below), which again would be astonishing if it is 1000x better corrected than an improved Plossl.

Why would they use an Airy disk, which is typically in the 2.5 to 5 milliradians range, for the upper images, and then switch to 4 microradians, 1/1000ths of a typical airy disk, for the lower images?  An apples to oranges comparison is very confusing.

Text:

Center spot diagram comparison
LE12.5

The circle is an Airy disk, 11 wavelengths
from 436mm to 656nm are synthesized,
and the objective is an aplanatic optical system.
(C) TAKAHASHI SEISAKUSHO Ltd.
TPL-12.5 Spot Diagram
Apparent field of view
(half angle)
0°
5.5°
11°
16.5°
22°
A circle is 4 microradians
Afocal calculation of 11 wavelengths
from 436mm to 656nm
(C) TAKAHASHI SEISAKUSHO Ltd.

And if the lower circle was a lot smaller than the upper circle, wouldn't the spot sizes be larger instead of smaller?

That's one reason I think they meant milliradians in the bottom row, not microradians.

[Don Pensack]

2 minutes ago, vlaiv said:

That seems too much for premium eyepiece?

It is the same as 2mm at arms length (500mm). I'm now looking at ruler at that distance - and I'd be surprised to see a star that size in the eyepiece to be honest.

If you look at Ernest Maratovich's tests of many eyepieces, you'll see that many many eyepieces yield edge of field apparent stellar sizes in excess of 10'.

http://astro-talks.ru/forum/viewtopic.php?f=32&t=1483#p41976

start with the 4th post on that thread.

[vlaiv]

1 minute ago, Don Pensack said:

And if the lower circle was a lot smaller than the upper circle, wouldn't the spot sizes be larger instead of smaller?

They show different thing.

Upper circle is telescope + eyepiece, lower circle (at least I believe so) is just eyepiece with point source at focal plane - so not airy disk of optics in front of the eyepiece.

BTW - 12mm Vixen NLV has 5' star image at the edge of the field (comparable field size and comparable focal length) - it turns out that Vixen NLV performs much better than this eyepiece so why pay more?

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

[Louis D]

I think this eyepiece line aims for high contrast and sharpness on axis with low scatter and stray light, similar to the Vixen HR line.  I'm guessing they accomplish this through use of glass with very little bubbling or surface roughness from polishing.  They probably also have carefully designed light traps to reduce stray light.  If none of this is true, I, too, would wonder what makes them worth the premium price.

[Mr Spock]

According to that chart we should all be using a Svbony 7-21 zoom 

How about we do the old fashioned thing and look through stuff instead of getting tied up on technical voodoo