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Tele Vue 102 v's other Apo's?

bond19

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bond19

bond19

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 I'm going to purchase either a Tele Vue 102 or something like an Explore Scientific 102. I will be using the score for visual and looking at planets, moon and bright DSO.

Is there really that much of a difference in quality of image in the eyepiece all other things being equal? I have no experience with ANY apo refractor, but I have experience when comparing a quality camera lens v's a Leica lens or equivalent. I know both will produce great photographs, but the Leica will produce photos with 'personality' that others lens cannot match. Is this is fair comparison? Please let me know if the premium cost is worth it (I understand the quality of the scope many vary between brands)

Thanks
Chris Hurst

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John

John

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Here is a comparison of a few different scopes including the Televue 102 for you to look at:

http://www.wlcastleman.com/equip/reviews/100mm_refractors/index.htm

Interesting comparison that one. The Vixen ED100SF is basically the same scope as the Skywatcher ED100. The Skywatcher branded versions can be picked up used for around 25%-30% of the cost of a used TV102.

The overall build of the TV would be in a different class though.

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JRWASTRO

JRWASTRO

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Yes, if you have the cash, go for quality.

I do not know about Televue but I have owned refractors like The TOA150 made by Takahashi and Astrophysics. Buy a Takahashi 'scope. Put down your name on the wait list for an Astrophysics 130mm refractor and wait.

About eyepieces: The bigger APO refractors by AP and Tak are so well corrected that they make most eyepieces look good! Get eyepieces with the minimum number of elements. The test is to look at the very faint stars in a well known , not too dense, star cluster. I use the kappa Crucis star cluster ( Jewell Box) for my tests. This test will reveal how poor are some of the famous wide fov eyepieces because of the light attenuation due the the number of optical elements. In these telescopes dense star clusters look quite dim due to the focusing and optical correction.

Jeremy.

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John

John

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.... This test will reveal how poor are some of the famous wide fov eyepieces because of the light attenuation due the the number of optical elements. In these telescopes dense star clusters look quite dim due to the focusing and optical correction.

Jeremy.

I'm not sure thats always the case. The Nagler 16mm Type 5 was only fractionally behind the light transmission of the Zeiss Ortho 16mm in some tests I saw recently. The difference was somewhat less than 1%.

Maybe you were thinking of some other famous wide field eyepieces ?

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nicoscy

nicoscy

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This test will reveal how poor are some of the famous wide fov eyepieces because of the light attenuation due the the number of optical elements. In these telescopes dense star clusters look quite dim due to the focusing and optical correction.

Jeremy.

Actually with modern coatings these days, the difference is not so material. I would rather have a large field of view rather than feel like looking down a soda straw.

And if the need arises for that extra marginal brightness, a set of 2-3 orthos does the trick.

But it would be a pity to get the Teleview which provides a corrected flat field due to its Petzval design and not mate it with eyepieces that provide a wide field of view...

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JRWASTRO

JRWASTRO

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Greetings John and Nicos,

Just raising the issue of using a medium sized apochromatic refractors.

I would expect to see an undistorted AFOV when one uses an EP with a large field stop.

With ultra-wide eyepieces there is always field distortion (positive or negative curvature).

The disappearance of the dimmer stars is obvious in some cases. Eg. When doing a comparative test between Takahashi LE, Pentax oculars, University optics and the TMB 30mm Paragon.

When looking at the larger globular clusters the point would be to present the image on a flat field of a size where the object may be appreciated in its entirety.

For open clusters one would expect to see a max number of stars and the disappearance of the dimmer stars becomes obvious.

For observation of planets a 45 degree flat field high contrast view is all that may be required.

I ask the question: What is the point of using a very wide AFov eyepiece when observing / splitting doubles?

There's my two bob's worth,

Cheers and Beers,

Jeremy.

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nicoscy

nicoscy

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Hi Jeremy,

I don't want to sound contrarian and I do concede that there is a small advantage to low glass eyepieces, but:

The Televue is a Nagler-Petzval design. Meaning it has two elements in the front and two in the back, presenting a completely flat field and having a suitably short F ratio, making it perfect for both astrophotography as well as using ultra wide field of view eyepieces without any significant field distortion.

One does not buy a Televue NP for spillting doubles only. You are best served for doubles and planetary with a nice Maksutov Cassegrain. One buys the TV for the fact that you can both push the magnification but also enjoy wide field of views and for the flat field it provides.

As for the fact that there is a *marginal* dimming, as I mentioned a set of low glass eyepieces can take care of that in a very inexpensive way. BGOs are an excellent solution in this respect.

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nicoscy

nicoscy

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Chris,

Congrats on the purchase.

Pooling the posts made by Jeremy and myself, if you are indeed a critical observer - which I expect given your expertise in photography - you should pair the scope with a mix of ultra-wides and narrow FOV low glass eyepieces to get the best of everything this telescope can offer  :grin:

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Stu

Stu

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Hi Jeremy,

I don't want to sound contrarian and I do concede that there is a small advantage to low glass eyepieces, but:

The Televue is a Nagler-Petzval design. Meaning it has two elements in the front and two in the back, presenting a completely flat field and having a suitably short F ratio, making it perfect for both astrophotography as well as using ultra wide field of view eyepieces without any significant field distortion.

One does not buy a Televue NP for spillting doubles only. You are best served for doubles and planetary with a nice Maksutov Cassegrain. One buys the TV for the fact that you can both push the magnification but also enjoy wide field of views and for the flat field it provides.

As for the fact that there is a *marginal* dimming, as I mentioned a set of low glass eyepieces can take care of that in a very inexpensive way. BGOs are an excellent solution in this respect.

Hi Nicosy,

The TV 102 is actually an ED doublet similar to the 85, rather than a Nagler-Petzval like the Genesis/NP101 etc which have the reducer/flattener doublet at the rear.

The 102 is f8.6, vs f5 to 5.4 ish for the NP scopes so is a very different beast. I would expect it to excel on planets and doubles whereas the Petzvals are much better suited to widefield views.

Always wanted a 102 but can't see a gap in my kit where it would make much difference. I have a 106mm triplet f6.5 which probably gives similar results.

Cheers,

Stu

Sent from my iPhone using Tapatalk

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nicoscy

nicoscy

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Stu, absolutely right! Typing posts in between work breaks makes for errors!

Jeremy, apologies for my post, it is not valid. We all make errors (me first apparently).

But I still stand by my eyepiece comments re transmission, i.e. a blend of high glass ultra wides and low glass narrow field eyepieces will maximise the use of the scope under any scenario.

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John

John

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Thanks to Olly and everyone else for your help. I'm excitedly collecting a Tele Vue 102 later today (so I apologies in advance for the continued bad weather)

Cheers

Chris

Congratulations on the TV 102 Chris :smiley:

I'll look forward to reading your first light report on it.

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bond19

bond19

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Now for some decent eyepieces.. I'd welcome specific recommendations. Maybe some that will also compliment a 10" dob later down the line. 

Thanks everyone, I appreciate your input in helping me get the most of out the scope.

Chris

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