105 replies to this topic

[Jae]

Yeah... I had the Tasco (Towa 339) re-brand; and, the leg slats are pretty thin.

The mount base is pretty wide, with some thicker legs maybe there a chance.

[Jon Isaacs]

 

 

It triplets are made right, there shouldn't be any worries, certainly no increased worries.

 

Bob

 

I read of people sending their A-P scopes to Roland for collimation.. I've read that the centering tolerances on triplets can be as little as 5 microns..

 

Drop a triplet, it may need to collimation.. More likely than with a doublet. 

 

Jon

[bobhen]

I read of people sending their A-P scopes to Roland for collimation.. I've read that the centering tolerances on triplets can be as little as 5 microns..

 

Drop a triplet, it may need to collimation.. More likely than with a doublet. 

 

Jon

I'm sure a very small percentage of refractors from high-end makers has needed a collimation touchup. But if the refractor has collimation adjustment screws, you don't have to send it back. You can collimate the scope at home.

 

As I said in my earlier post, my AP 152mm (not a small scope) rolled off the couch and dropped to the floor without needing collimation. So I guess it depends on how high the fall. But dropping any scope from a decent height can cause more issues than needing collimation.

 

Lens de-centering (which is different than a collimation issue) is also very rare with well-made triplets. Off the top of my head, the only refractors that come to mind that had serious lens de-centering issues were Meade's old 178mm EDs. And that was a "doublet". And the market is very well aware of that issue. There have been long threads here on CN about it.  I believe the first Takahashi Sky 90s had some lens de-centering issues as well. That refractor was also a "doublet".

 

Because they were doublets, in order to reduce chromatic aberration to triplet levels, the lenses had very steep curves that were more sensitive to de-centering. Just shipping Meade's 178 would cause lens de-centering. In both cases, the designers probably should have used a triplet design.

 

Bob

Edited by bobhen, 30 April 2025 - 12:27 PM.

[Jon Isaacs]

I'm sure a very small percentage of refractors from high-end makers has needed a collimation touchup. But if the refractor has collimation adjustment screws, you don't have to send it back. You can collimate the scope at home.

 

As I said in my earlier post, my AP 152mm (not a small scope) rolled off the couch and dropped to the floor without needing collimation. So I guess it depends on how high the fall. But dropping any scope from a decent height can cause more issues than needing collimation.

 

Lens de-centering (which is different than a collimation issue) is also very rare with well-made triplets. Off the top of my head, the only refractors that come to mind that had serious lens de-centering issues were Meade's old 178mm EDs. And that was a "doublet". And the market is very well aware of that issue. There have been long threads here on CN about it.  I believe the first Takahashi Sky 90s had some lens de-centering issues as well. That refractor was also a "doublet".

 

Because they were doublets, in order to reduce chromatic aberration to triplet levels, the lenses had very steep curves that were more sensitive to de-centering. Just shipping Meade's 178 would cause lens de-centering. In both cases, the designers probably should have used a triplet design.

 

Bob

 

Have you ever tried to align a triplet that has been dropped?  My friend and I tried.  We could not do it.  He had to send it back to the factory.   The "collimation" screws on triplets and on many doublets, they are center the lenses. Collimation involves both tilt and alignment of the optical axes of the various components. 

 

That's why Newtonians are so easy to collimate, they only have one curved optical component so collimation just involves aligning the optical axis of the focuser with the optical axis of the primary mirror. 

 

Jon 

[bobhen]

Have you ever tried to align a triplet that has been dropped?  My friend and I tried.  We could not do it.  He had to send it back to the factory.   The "collimation" screws on triplets and on many doublets, they are center the lenses. Collimation involves both tilt and alignment of the optical axes of the various components. 

 

That's why Newtonians are so easy to collimate, they only have one curved optical component so collimation just involves aligning the optical axis of the focuser with the optical axis of the primary mirror. 

 

Jon 

I have collimated a triplet, inside and using a Cheshire collimating "eyepiece".

 

The screws on most triplets and doublets tilt the complete cell so collimation can be accomplished.  However, if one of the lenses on say a triplet becomes de-centered, you can collimate all day and it won't help. Lens de-centering is a different issue than when the lens "cell" is out of collimation.  That was the problem with the Meade 178. The lenses IN the cell would become de-centered – even when the lens cell itself was collimated. The lens cell tolerances were not designed and made well enough to keep the lens elements with their steep curves aligned. 

 

In later production models, Meade added screws around the cell that if turned would nudge the individual lenses back in alignment. Those screws were NOT cell collimation screws they were individual lens element alignment screws.

 

If triplet makers couldn't keep the lenses aligned after some moderate or even some bumpy handling, they wouldn't be around long. The Meade 178 didn't last long after the problems with the scope's lens alignment issues got out.

 

A Newtonian might be easier to collimate. But in the 22-years that I owned my large 6" triplets and the 20-years that I owned a 105mm fast F6.2 triplet and a 120mm F7.5 triplet, they "never needed" collimation. But in the 11-years that I owned my 2, 15" Newtonian reflectors, they both needed collimation every night!  And sometimes they needed collimation during the night! 

 

Bob  

Edited by bobhen, 05 May 2025 - 08:57 AM.

[danielgolite]

   Couple of simple cellphone photos I posted recently on a TeleVue thread in the Refractors Forum. My Ranger- set up as a solar scope, using a black polymer solar filter from Thousand Oaks Optical. Did well on the April 2024 total solar eclipse as pictured. An amazing event and a lot of people looked through the little scope. Our skies along Lake Erie in northeast Ohio were really clear then cloudy before totality then cleared up enough just at the right time.

 

     Seems like it is more common today to buy a scope, use it for a little while, and then get rid of it and move on to something else. I am not talking about the non-astronomical public, I am talking about "us," more serious astronomy observers. I guess it is human nature not to be satisfied for very long. Now that my Ranger has been with me for 18 years and some special events, we have a "history" together.

 

   I was not prepared for how special the moment would be during totality when I removed the solar filter and for the first time "looked" at the sun (safely covered by the Moon) straight through using the Ranger. The view was amazing but the thought that this might be a once in a lifetime look really hit home. Same with the Venus Transit in June, 2012. 

 

    What I like about TeleVue scopes is their solid build. Some now are classics and the rest will be in the future.

 

 

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