Tele Vue APO Design and Build “Secrets”

[KingClinton]

http://televue.com/notamnomen/2019/08/0 ... OSecrets01

[JayTee]

Thanks Clinton,

This falls right in line with my post on the very same subject. It's nice when we all agree.. viewtopic.php?f=65&t=2478

Cheers,
JT

[DeanD]

Thanks Clinton,

I like the philosophy that one person builds each scope from start to finish: and the home-workshop look of their benches, telescope cradles etc. I reckon I could cope with a job like that!

I love Al's definition of an Apo too: "we consider any instrument APO quality if no blue fringing is seen on Sirius, in focus, at 200x"... That sorts out all the arguments nicely I reckon!

Cheers!

Dean

[Lowjiber]

...I love Al's definition of an Apo too: "we consider any instrument APO quality if no blue fringing is seen on Sirius, in focus, at 200x"... That sorts out all the arguments nicely I reckon!

Al has always been one to cut-to-the-chase... no hocus-pocus nonsense.

[notFritzArgelander]

I'm not a fan of this definition of an apochromat. I prefer an actual quantitative definition like the one found here

https://www.telescope-optics.net/apo_refractor.htm

That's a real definition. Without doing the work to show Al's definition is as good or better I'll just have to regard it as highly effective marketing hype. It's distasteful to me but obviously effective.

[dghent]

...I love Al's definition of an Apo too: "we consider any instrument APO quality if no blue fringing is seen on Sirius, in focus, at 200x"... That sorts out all the arguments nicely I reckon!

Al has always been one to cut-to-the-chase... no hocus-pocus nonsense.

However eyepieces can also introduce CA and other effects. By his measure, a telescope could go from being an APO to not being an APO depending on the type and quality of the eyepieces being used to look at Sirius. This is not a quantitative analysis of the telescope's optics alone. At best, it's a field test with several expensive predicates.

[Lady Fraktor]

A nice read but sales must be dropping a bit to turn up the marketing scheme again.

[DeanD]

...I love Al's definition of an Apo too: "we consider any instrument APO quality if no blue fringing is seen on Sirius, in focus, at 200x"... That sorts out all the arguments nicely I reckon!

Al has always been one to cut-to-the-chase... no hocus-pocus nonsense.

However eyepieces can also introduce CA and other effects. By his measure, a telescope could go from being an APO to not being an APO depending on the type and quality of the eyepieces being used to look at Sirius. This is not a quantitative analysis of the telescope's optics alone. At best, it's a field test with several expensive predicates.

True, but as a field test it is a pretty extreme one and can really sort out the "apo" quality of a scope if you use the same eyepieces in a comparison. As a matter of interest, my TV76 struggles (read: "fails") with this test with any of my high-power eyepieces (including the Nagler 3-6), while my Tak TSA 102 passes with flying colours... (To be fair, asking a 76mm scope to run at 200x is also a bit extreme.)

I like the definition because it is something that can be done by anyone and gives a very good idea of the "apo" credentials without using the equipment needed for the "quantitative" tests. Sure, eyepieces can introduce CA -although even the cheapest are pretty well controlled in the centre of the field- but you can easily swap out an eyepiece to check if that is the "problem".

Personally, I am a fan of field testing in general: a field test of a star image can tell you an awful lot about the quality of a scope, an eyepiece, seeing conditions etc. without having to lab-test. After all, it is the view in the field that we all want.

And wrt Gabby's comment about sales: I suspect she is right: TV doublets are quite expensive in comparison to the Chinese competition, and optically they wouldn't be any better than the best of the Chinese ones. I suspect my TV76 is around 1/6-1/8 wave... (from my field testing! )

- Dean

(PS: Optics aren't everything though: we pay for mechanical/build quality too, and here the TV scopes are pretty good, and very solid! As an aside, years ago I ran my old ETX90 head to head with a Questar and optically it was a draw with high-power views of Jupiter: both scopes showed very similar contrast and the same detail in the GRS on Jupiter. Mechanically and build-wise though it was a Rolls Royce vs an early VW beetle. Cost-wise the Questar was over 10x as much. But still, I want a Questar!!!)

[Lady Fraktor]

TeleVue does make a good quality refractor, I just find them a bit over priced nor would I place them in the ranks of AP, TEC, Tak, CFF etc.
They remind me more of the Vixen apochromatic with a heavier build to them. More a "poor mans Tak"

[notFritzArgelander]

TeleVue does make a good quality refractor, I just find them a bit over priced nor would I place them in the ranks of AP, TEC, Tak, CFF etc.
They remind me more of the Vixen apochromatic with a heavier build to them. More a "poor mans Tak"

I agree on performance. On OTA cost the price of a 4" Tak is less than the price of a 4" TV.

https://www.takahashiamerica.com/takaha ... scope.html

https://www.highpointscientific.com/tel ... O8QAvD_BwE

Tak accessories to make it flat field will narrow the price gap but more than a 1K$ will remain.

[Lady Fraktor]

I did a comparison between the TV-76 ($1650USD) and Tak FS-78 ($1200USD) a few years ago, I felt the Tak put up slightly better views for planetary.
The TV makes a great widefield telescope and I also found it excellent as a daytime birding telescope, colour rendition was superb.

[notFritzArgelander]

I did a comparison between the TV-76 ($1650USD) and Tak FS-78 ($1200USD) a few years ago, I felt the Tak put up slightly better views for planetary.
The TV makes a great widefield telescope and I also found it excellent as a daytime birding telescope, colour rendition was superb.

That fits with my impressions from quick views through other folks' scopes.

[DeanD]

I did a comparison between the TV-76 ($1650USD) and Tak FS-78 ($1200USD) a few years ago, I felt the Tak put up slightly better views for planetary.
The TV makes a great widefield telescope and I also found it excellent as a daytime birding telescope, colour rendition was superb.

That fits with my impressions from quick views through other folks' scopes.

Me too. It doesn't like going over ~ 150x, but gives great lower-power views.