13165 replies to this topic

[25585]

Do you have a single-speed or dual-speed on your NS?

Single.

[alceo]

And it makes the Sun slightly sharper too. Best white light filter IMO - though I haven’t used the 7.5nm before. Mine’s the previous 10nm - shouldn’t make a difference for visual

I also have a 10nm filter in 2" and visually I don't see any difference, I haven't compared it in photography.

[quilty]

Which is the highest estimated Takfrac in 4 to 5 inch size? Is it the TSA 120?

Edited by quilty, 31 March 2025 - 11:21 AM.

[Lagrange]

The TOA-130 is just over 5" (3mm more).

[quilty]

The TOA-130 is just over 5" (3mm more).

Ok thanks, but just for the larger aperture or for the better lens?
Both are triplets, both FPL53 or similar air spaced.
Why is it TOA and TSA and not the same letters?

Edited by quilty, 31 March 2025 - 11:27 AM.

[norvegicus]

Which is the highest estimated Takfrac in 4 to 5 inch size? Is it the TSA 120?

Highest estimated what?  Price?  Aperture?  Optical performance?

[25585]

Ok thanks, but just for the larger aperture or for the better lens?
Both are triplets, both FPL53 or similar air spaced.
Why is it TOA and TSA and not the same letters?

TOA has two SD lenses, TSA has only one. The TOA is heavier, noticibly. The TSA can be considered light for a 120mm triplet. TOAs are aimed more at imagers, the TSA can be imaged with as well though, but its more general purpose.

[quilty]

Why is the 120 called "TSA" and the 130 "TOA"?

Apart from weight and number of SD lenses, which one is considered best at contrast and detail/aperture.
Does the price difference just display the aperture difference or an optical superiority of the TOA, too?

"Highest estimated what? Price? Aperture? Optical performance?"

Sorry that I don't answer this, maybe you can find out by yourself

Edited by quilty, 31 March 2025 - 12:49 PM.

[Lagrange]

The TOA (Triplet Ortho-Apochromat) models use a more sophisticated lens design that's significantly more expensive to manufacture, but it reduces spherochromatism to levels far below typical triplet apos and even less than some catadioptric scopes. It's a modified Cooke Triplet design which uses two positive S-FPL53 elements with a negative S-BSL7 element in between, all separated by very wide air gaps. The design performs incredibly well but it's very sensitive to misalignment so the lens cell has to be very robust (hence the weight) and manufactured to extreme precision. One 6" S-FPL53 lens is expensive enough, so having two makes it a costly scope to produce.

 

The TSA (Triplet Super-Apochromat) is a conventional air-spaced triplet with very small air gaps and only a single positive element of S-FPL53 sandwiched between two negative elements of S-BSL7. Its manufacturing cost is much lower and it doesn't require the very large, heavy lens cell of the TOA design.

 

I've not looked through either scope so I can't say how visible any differences would be, but the TOA is reputed to be about as good as a refractor gets for its aperture. The TSA might not be as sophisticated or quite as well corrected but I've never read of anyone who was disappointed in its performance either.

[jrazz]

According to the published graphs the TOA is nearly perfect. Looking through a TOA the view is, indeed perfect. It’s as color free as any reflector while having the awesome contrast of a refractor.

However, at this level your sky conditions matter far more than the telescope. On a perfect night I could convince myself I see the difference between the TOA and my 4” FC. On most nights the limiting factor was the atmosphere. Additionally, the FC cools down significantly faster making it much nicer to use overall. Not to mention the weight.

So yeah, TOA is optically perfect. It’s “the” Takahashi to have but I sold mine and kept the FC.

[skyops]

* 

 

Stated during an interview with the U.S. importer, the TOA-130 produces a spot-size smaller than any pixel currently produced, and smaller than any other scope manufacturer, so if imaging is your bag you know what to do.

 

I enjoy visual-only.

 

 

 

 

.

[quilty]

Ok, thanks for this information. Triplet Super Apo and Triplet Ortho Apo.

The TOA then seems to need much a longer acclimatisation time with wide air gaps and that delicate at perfect adjustment.
It's much heavier, 6 vs. 10 kg but it's not that much more expensive. About 5 k vs. 6.5 k

The TOA is obviously considered as the optically best possible 5" refractor and the TSA not much behind. Neither scope needs a flourite element.

Edited by quilty, 31 March 2025 - 04:08 PM.

[Scott in NC]

Single.

The reason I asked is that my NS version came with a MEF-3 dual speed focuser. I do have an extra FTF3545 plus appropriate adapter for my TOA-130, but the original focuser is nice enough that I haven’t made the upgrade yet. You could get a MEF-3 much more easily and less expensively than a whole 4” NFB-type focuser, if all you’re looking for is dual-speed capability.

[james7ca]

* 

Stated during an interview with the U.S. importer, the TOA-130 produces a spot-size smaller than any pixel currently produced, and smaller than any other scope manufacturer, so if imaging is your bag you know what to do.

 

I enjoy visual-only.

Practically speaking that's kind of meaningless since the smallest spot size (i.e. the Airy disk) that a telescope can produce is based solely on the f-number and the wavelength of light and you'd need something like an f/1 lens to produce an Airy disk smaller than the smallest pixel that is currently available in a camera. Now, the geometrically ray-traced spot size can be infinitely small, but that's not what a telescope actually produces.

 

It could, however, be correct (or possible) that the ray-traced spot size is smaller than the theoretical Airy disk. But, the TOA-130 is an f/7.7 scope and the Airy disk produced by that system in green light can be no smaller than 10.3um.

 

If you want to see how the linear size of the Airy disk varies with f-number here is a good reference:

 

  https://www.edmundop...AhUK9Qj2xwMsqt_

 

The reason why camera pixels can be so small is that the manufacturing process uses UV light of a very short wavelength in combination with very "fast" (high numerical aperture) optical systems.

Edited by james7ca, 31 March 2025 - 05:46 PM.

[Jay_Reynolds_Freeman]

It could, however, be correct (or possible) that the ray-traced spot size is smaller than the theoretical Airy disk.

I believe that is a common design goal for the designers of high-end refractor objectives: If the spot size is indeed substantially smaller than the theoretical Airy disc, and if the lens can be fabricated as designed, then one can assert in good faith that the objective is truly diffraction-limited.

 

 

Clear sky ...

[james7ca]

… if the lens can be fabricated as designed…

 

Clear sky ...

Yes, but that’s an important qualifier since manufactures (including, IMO, Takahashi) can have difficulty in routinely achieving that goal. However, it may be true that many of their scopes are “good enough” to the typical user (note that I said “to” and not “for” the typical user, that makes a difference).

 

[UPDATE]

If I had said "for" my meaning would have been for a more critical, absolute, or technical evaluation, whereas my use of "to" is meant to be more casual or just an everyday type of experience.

[/UPDATE]

 

In any case, determining what four or five inch Takahashi is the “best” for visual use depends on more than what the on-axis, ray-traced spot diagram looks like. For example you may want to consider what the off-axis performance looks like and the TOA’s may not be the best in that regard unless you include a field corrector.

Edited by james7ca, 31 March 2025 - 10:04 PM.

[Jay_Reynolds_Freeman]

Yes, but that’s an important qualifier [...]

I agree, it certainly is, that's why I mentioned it ...  :-)  :-)  :-)

[Phil Cowell]

The FT dual speed is a joy to use if you go that path.

 

Single.

Edited by Phil Cowell, 31 March 2025 - 07:39 PM.

[25585]

The reason I asked is that my NS version came with a MEF-3 dual speed focuser. I do have an extra FTF3545 plus appropriate adapter for my TOA-130, but the original focuser is nice enough that I haven’t made the upgrade yet. You could get a MEF-3 much more easily and less expensively than a whole 4” NFB-type focuser, if all you’re looking for is dual-speed capability.

In the UK, only FSQs have OE MEF focusers, apart from TSA-120s with the FT fitted.

 

I use heavy eyepieces - ES92s, long FL + Barlows etc, so thought a Tak 2.7" might not always be strong enough. The 92s are OK, but a 4x Powermate with a ES68 34mm + 2" diagonal, might be too much.

[Scott in NC]

The Tak 2.7” focuser with MEF on my TOA-130NS works well for visual use with an AP 2” Maxbright and 21 Ethos or 31T5 Nagler.

[TerryWood]

It's so nice to see the sky again...the winter was nothing but clouds and bad seeing. I have a window of opportunity tonight before the rain comes back tomorrow. So, the 1999 FSQ-106 is set up and ready to go. I have Tak prism turret with the short adapter on there and it works great!

 

V/R

 

Terry

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[helpwanted]

It's so nice to see the sky again...the winter was nothing but clouds and bad seeing. I have a window of opportunity tonight before the rain comes back tomorrow. So, the 1999 FSQ-106 is set up and ready to go. I have Tak prism turret with the short adapter on there and it works great!

 

V/R

 

Terry

I love your view so much I barely noticed the telescope.

[TerryWood]

I love your view so much I barely noticed the telescope.

Hey, thanks! I'm out in the sticks. Here's a wider view.

 

V/R

 

Terry

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[Kitfox]

It sure looks like Appalachians to me...mid-Atlantic...

 

The turret leaves a lot of in-travel to spare...I need to try that!

Edited by Kitfox, 01 April 2025 - 08:13 PM.

[TerryWood]

It sure looks like Appalachians to me...mid-Atlantic...

 

The turret leaves a lot of in-travel to spare...I need to try that!

You called it right! West Virginia, about 30 miles from the Pennsylvania border. 

 

V/R

 

Terry