Big Brother of my Kowa TSN-99a (1 Viewer)

[paperweight]

I recently got a s/h Takahashi TOA 130 telescope, and yesterday I mounted my TSN-99a together with that huge refractor on my AOK Swiss AYOdigi II mount with a Vixen style dovetail bar. The AYO allows a fine adjustment on the left side, so I can really have the two glasses show the same objects (of course with a small deviation).

My first observation yesterday in daylight proved the TSN-99a is the superior glass for terrestrial observation in daylight. I use a Pentax XW 30 eyepiece on the TOA 130 (which results in about 35x magnification), so the 40x of the TE 80 eyepiece on the TSN-99a was about the same.

Over the next weeks, I'll get two or three other eyepieces for the TOA (about 15, 7 and 4mm). For the TSN-99a, I have got two 1.6 extenders which will take the TE 80 to about 100x and the TE 11 to an insane 180x. So there will be some nice comparisons. For the TOA, I will either stay with Pentax XW or try Televue Radian, Delos, Nagler or even Ethos.

 

[Binastro]

I can only suppose that the Seeing was poor or the Takahashi was not temperature stabilised.

During the daytime Seeing can vary drastically from awful to good or better.

Have both scopes been star tested?

In very good conditions I have used 180x during the day and higher at night.

Regards,
B.

 

[paperweight]

@Binastro: seeing was poor with temperatures of about 26° and a lot of air movement. But I loved the contrast and the depth of colour in the TSN 99a. My first comparison is far away from any kind of judgement.

 

[Tringa45]

What diagonal were you using?
At f/7,7 a prism diagonal would not contribute much SA or CA and might have less scatter than a dielectric mirror.

John

 

[Binastro]

Today should be interesting for testing here.

40C in the next few hours is forecast.

Regards,
B.

 

[paperweight]

@john: I bought the TOA 130 in a package with additional gear. It came with this Mirror Diagonal by TS-Optics:

TSZS2D TS 2" Zenith Mirror - 99% reflection - ring clamping - 2" connection

TSZS2D TS 2" Zenith Mirror - 99% reflection - ring clamping - 2" connection: TS 2" zenith mirror - 99% reflection A zenith mirror of the upper class ...

www.teleskop-spezialisten.de

I can't really tell if it's fine or mediocre because this is my first step into astronomy, I'm a total newbee. I just knew I wanted a fine refractor and had known about the TOA for years.

@Binastro: I had thought about keeping the unit out in the open overnight. But the sky last night did not provide good seeing, it was a bit overcast, and since today and tomorrow will be very warm with hight clouds, I decided to disassemble the unit. So, at the moment, everything is back in their boxes. Besides, I have no chance to take pictures with the TOA at the moment. I can with the TSN 99.

 

[Binastro]

In the autumn I expect that the Takahashi can be used visually in good Seeing at up to 330x on planets and double stars.

The problem is Jupiter and Mars are low in high northern latitudes.
Starting at 150x.

An altazimuth mount is fine with a finder, or just use a low power eyepiece in the telescope as the finder.

I don't know if the Takahashi has collimating screws.

Regards,
B.

P.S.
Mars and Jupiter are now quite high in the sky when south.
The problem is Saturn, which is still low.

When a planet is due south tracking with an altazimuth mount is only needed left to right not up and down.

P.P.S.
I see in the photo that the Takahashi does have a finder scope mounted.

 

[paperweight]

@Binastro: it's better to have the Takahashi experts work on the collimation if necessary.

 

[henry link]

Using such a low magnification (33.3X) with a 130mm scope in daylight results in a 3.9mm exit pupil. In bright daylight the eye is probably closed to about 2.5 mm, which means only 2.5 mm of the 3.9mm exit pupil can be accepted by the eye. The result is an effective aperture for the 130mm Tak of about 83mm. On the other hand the Kowa 99 at 40x has an exit pupil of about 2.5mm, so it's effective aperture in daylight is its full 99mm aperture. In this test set-up it's actually the Kowa that is effectively the larger scope. The lowest magnification that would allow the full aperture of the Tak to be used in bright daylight would be 52x or even higher if the observer's eye is closed to less than 2.5mm.

 

[paperweight]

@henry link : thanks for the very precise and logical explanation. My "old eyes" (about 72) won't be able to profit from a large exit pupil even at night.

 

[henry link]

I think if you take the magnification to 70x or more (and provided the Tak is at least as well corrected as the Kowa) you won't have any trouble seeing a better image through the Tak in steady air.

 

[paperweight]

@henry link : your profile does not allow personal messages. I don't want to turn this thread into a Tak-thread, but attached you will find the pdf of the test my TOA 130 was put to by Wolfgang Rohr, an expert in Germany. Of course it's about 14 years old, so collimation might have suffered. I will of course have a look at 70x....as soon as I have a 14mm eyepiece. If things work out fine, I'll soon have a Televue Ethos 13mm that will do the job.
Back to the Kowa TSN-99a: this relatively new model has seen some criticism and doubt. I enjoy its performance and can only recommend it, especially with the new TE80 wide angle eyepiece.

 

[Binastro]

For the planets with an undriven mount I would use a Nagler eyepiece of about 7mm giving 140x or 150x.
There are lower price options.

Then higher powers as necessary.

Regards,
B.

 

[DRodrigues]

...
My first observation yesterday in daylight proved the TSN-99a is the superior glass for terrestrial observation in daylight. I use a Pentax XW 30 eyepiece on the TOA 130 (which results in about 35x magnification), so the 40x of the TE 80 eyepiece on the TSN-99a was about the same.
...

You have to explain on what the Kowa was superior...
Besides Henry explanation, you might be biased by the fact that XW30 is a 70º AFOV ep and TE80 is a 80º AFOV ep...

 

[paperweight]

I felt the Kowa was superior because of colour and contrast. But this is very individual and spontaneous judgement that will have to be verified yet. Today, at about 40° C I preferred staying indoors to putting the two candidates to the test.

 

[henry link]

@henry link : your profile does not allow personal messages. I don't want to turn this thread into a Tak-thread, but attached you will find the pdf of the test my TOA 130 was put to by Wolfgang Rohr, an expert in Germany. Of course it's about 14 years old, so collimation might have suffered. I will of course have a look at 70x....as soon as I have a 14mm eyepiece. If things work out fine, I'll soon have a Televue Ethos 13mm that will do the job.
Back to the Kowa TSN-99a: this relatively new model has seen some criticism and doubt. I enjoy its performance and can only recommend it, especially with the new TE80 wide angle eyepiece.

How lucky you are to have such a thoroughly vetted telescope. I googled that review and came up with the page below that cuts to the chase: 1/6.3 waves Peak to Valley, 1/41.5 waves RMS, 0.977 Strehl Ratio. You can see that the Peak to Valley error is not really that damaging since the highest errors cover only a small area at the edge of the lens.

The two TSN-99s I tested would not have been much optical competition for your Tak.

 

[jring]

Hi,

congratulations to a new toy! Although the TOA series are usually used as high performance imaging scopes they will certainly offer a great view visually too - although the amount of color correction they offer is probably not needed fro visual.

The results from Mr. Rohr were measured with a very good scope which should deliver near identical diffraction patterns in a star test. I would not normally expect a Tak refractor to get out of collimation unless badly abused. They are not exactly known for shoddy mechanics...

But please wait for a relatively cool early morning for your star test and leave the scope time to get to ambient temperature - I would expect this to take an hour or two with such a massive instrument. Or make an artificial star and use that on an cool and overcast morning (again let the scope get to ambient temp).

As for eyepieces I personally would look at eyepieces around 80 degrees afov for a non-driven mount, which is about what is useful for me. I can't really use the 100 deg of an Ethos without extensive eye gymnastics... so I'd rather buy two 80 deg EPs instead of one Ethos.

Btw, do you have to wear glasses for observing (because you have astigmatism in your eye)? If yes, you can probably scratch Nagler and Ethos series from your list...

Joachim

 

[Tringa45]

Btw, do you have to wear glasses for observing (because you have astigmatism in your eye)? If yes, you can probably scratch Nagler and Ethos series from your list...

Dioptrix seem to be compatible with most Naglers and Ethos: DIOPTRX™

John

 

[paperweight]

Still rehearsing and trying to get some routine with the Kowa 99a and the TOA 130. There are so many things to take care of and to have in mind when working in the darkness.
I have just done two pictures of the 99a and the TOA. It's not that I really want to judge, I'll keep both instruments anyway. I used a Pentax XW 7 eyepiece (resulting in 143x magnification) on the TOA and the Kowa TE 11 Zoom eyepiece with two stacked Kowa 1.6 extenders on the 99a. I tried to find the matching magnification by twisting the zoom to an estimated 56x to achieve 143x.
My "camera" was my iPhone 6s in a Kowa TSN-IP6 Photo Adapter which of course did not fit the diameter of the Pentax. So I had to somehow hold it in place.
This is no serious comparison. There is a lot of air movement at the moment (25° C) and I do hope the air will be cool and calm later on to allow me a look at Saturn in the South around 11pm.

TOA 130



99a

 

[Binastro]

Saturn is low, but may show some moons.
If higher I would expect 5 possibly 6 within reach of the Takahashi.

The Cassini division should be possible.

A better bet is Jupiter and later Mars, as these reach higher elevations.

Regards,
B.