Big apo news

[vlaiv]

I think we have established a standard for scatter control here

 

[sloz1664]

I've worked out that if I put £1 into an extremely large piggy bank every day, it will take me 9.38 years to acquire one. 😱

Steve

[JamesF]

26 minutes ago, sloz1664 said:

I've worked out that if I put £1 into an extremely large piggy bank every day, it will take me 9.38 years to acquire one. 😱

Steve

By which time it will have doubled in price

James

[Ben the Ignorant]

2 hours ago, joe aguiar said:

apm is too far from Canada

They have an official rep in the US now.

https://www.outdoorsportoptics.com/shop/telescopes_pw1_6_1.html

[Ben the Ignorant]

1 hour ago, ollypenrice said:

I heard it described on CN as 'A glorified achromat.'

(speaking of TEC's 140mm f/7 triplet)

Well, those who say that should know the facts can be found on the internet to prove them wrong. Rohr tested it and found less than 70µ chromatic spread:

A Vixen 130SS I looked through has 150µ chromatic spread and no fringe could be detected at all around the Moon, Jupiter and Mars. The W_gesamt 0.9381 value means the scope is an apo because it's under 1. Between 1 and 2 are the semi-apos, and achros are above 2.

[ollypenrice]

11 hours ago, Laurin Dave said:

The Esprit 150 is no slouch either! 
Dave

Indeed it isn't. It seems to be quite outstanding.

Olly

[fate187]

It is indeed consistency of quality of the scopes sold, collimation necessities but also after sale service. TEC has its reputation. TS does have one as well, granted they are only reseller. The new 140 looks nice, but ultimately one has to see and wait for reports also over a longer period of time to judge the quality. Fingers pressed to the potential buyers :).

 

best

michael

[gorann]

There are many high class apo triplets with just one ED lens. Actually I thought they all only had one ED lens. Does anyone know if there are any advantages with two ED lenses - seems to be the new trend, see:

 

[Alan White]

Another wonderful bit of kit, 
sadly one I will never be able to own, even though it shows as 'in stock'.
To whoever owns one, enjoy it and please share the joy and the eyepiece with us all.
 

Edited November 27, 2019 by Alan White

[John]

22 minutes ago, gorann said:

There are many high class apo triplets with just one ED lens. Actually I thought they all only had one ED lens. Does anyone know if there are any advantages with two ED lenses - seems to be the new trend......

 

I don't know the answer to this but its a very good question.

We are seeing more triplets (or more elements) that use more than one low dispersion glass element.

Such glass is expensive though (FPL-53 blanks are many times as much as more normal glass types) so you would assume that having those optical characteristics in more than one element does deliver optical performance benefits and is not just a marketing gimmick.

On another forum it was asked why all the lens elements in objectives are not FPL-53 or similar but that would not work of course. The refractive indexes of the glasses used in an objective need to compliment each other to achieve the best colour correction which is why a mix of glass types is what is required.

Then there is the figure, polish, coating, spacing and mounting of the lens elements all of which need to be very precise to ensure that the objective functions well. No wonder the good ones cost a lot !

 

[Alan White]

3 minutes ago, John said:

Then there is the figure, polish, coating, spacing and mounting of the lens elements all of which need to be very precise to ensure that the objective functions well.
No wonder the good ones cost a lot !

In reality they don't of course, when many of us started in this hobby,
a decent 80mm Achromatic was a dream scope and way beyond our means.
These days far more fine scopes and many very affordable to many.

The 5 -15k scopes are for the few who have the means and in terms of build must be quite something.
In the 1980's it would have been a professional instrument if available at all as way beyond almost all of us.

[vlaiv]

49 minutes ago, gorann said:

Does anyone know if there are any advantages with two ED lenses

I think it is best compared with eyepieces - you can get very good eyepiece with three of four lens elements. But if you want large AFOV, good eye relief and correction to the edge - you need to go with 6 or 7 or maybe even larger count of lens in a design.

Often wondered why there are no triplets made out of "regular" glass types as opposed to ED types and more exotic types. It all comes down to specs of the scope you want to build - what size of aperture you are going for and what F/ratio you want to achieve (probably even how flat field you want to get). One could probably design very good triplet at something like F/12 from regular glass types - but what would be the point? You can almost get very good color correction with achromatic doublet at that F/ratio (small aperture) and certainly with ED glass - although up until recently there were no slow ED scopes (there is now F/11 ED 4").

Combining more exotic glass types in triplet let's you optimize for particular scope design - fast with large aperture and relatively flat?

[John]

31 minutes ago, Alan White said:

In reality they don't of course, when many of us started in this hobby,
a decent 80mm Achromatic was a dream scope and way beyond our means.
These days far more fine scopes and many very affordable to many.

The 5 -15k scopes are for the few who have the means and in terms of build must be quite something.
In the 1980's it would have been a professional instrument if available at all as way beyond almost all of us.

True. "We have never had it so good"

I have some catalogues and price lists from the 1990's which plainly illustrate that the choice for the amateur astronomer was massively less than it is today and generally pricing was much higher relative to incomes back then.

 

 

 

 

 

[johnturley]

On 26/11/2019 at 14:51, Davey-T said:

https://www.teleskop-express.de/shop/product_info.php/info/p11814_TS-Optics-140-mm-f-6-5-Super-Triplet-Apo-mit-2-ED-Elementen.html

Or the version in English

https://www.teleskop-express.de/shop/product_info.php/info/p11814_TS-Optics-140-mm-f-6-5-Super-Triplet-Apo-with-2-ED-elements.html

I noticed that they also have the 152mm f8 on special offer at 3,395 EUR 

https://www.teleskop-express.de/shop/product_info.php/info/p10776_TS-Optics-PHOTOLINE-152-mm-f-8-Triplet-APO---3-7--RPA-focuser.html

John 

P.S. They were in English, but appear now to have switched to German for some reason.

P.P.S. You just have to click on the Union Jack icon top right hand, to get it to change back to English.

Edited November 28, 2019 by johnturley

[DaveS]

Even the original Cooke Photovisual Triplet from the very early 20th Century used some rather exotic (For the time) glasses, to the point that the first iterations came a cropper due to one especially unstable element. I think the first one made was a 9" f/15.

[John]

The TAL Apolar 125 used no exotic glass amongst it's 5 elements as far as I know. While the scope had some other issues, the colour correction achieved was really good.

Interesting that we are seeing some new large aperture refractors using lots of FPL-53 glass. Not so long ago it was rumoured that it was going out of production. Obviously Ohara decided to do some more melts of it

 

[johnturley]

2 minutes ago, John said:

The TAL Apolar 125 used no exotic glass amongst it's 5 elements as far as I know. While the scope had some other issues, the colour correction achieved was really good.

Interesting that we are seeing some new large aperture refractors using lots of FPL-53 glass. Not so long ago it was rumoured that it was going out of production. Obviously Ohara decided to do some more melts of it

 

I think that TEC stated that one reason why they switched to Fluorite in their APO Refractors, was due to shortage of FPL53 glass.

John 

[gorann]

1 hour ago, vlaiv said:

I think it is best compared with eyepieces - you can get very good eyepiece with three of four lens elements. But if you want large AFOV, good eye relief and correction to the edge - you need to go with 6 or 7 or maybe even larger count of lens in a design.

Often wondered why there are no triplets made out of "regular" glass types as opposed to ED types and more exotic types. It all comes down to specs of the scope you want to build - what size of aperture you are going for and what F/ratio you want to achieve (probably even how flat field you want to get). One could probably design very good triplet at something like F/12 from regular glass types - but what would be the point? You can almost get very good color correction with achromatic doublet at that F/ratio (small aperture) and certainly with ED glass - although up until recently there were no slow ED scopes (there is now F/11 ED 4").

Combining more exotic glass types in triplet let's you optimize for particular scope design - fast with large aperture and relatively flat?

But there are some great and relatively fast triplet apos with a single ED lens. Like Esprit 100 f/5.5; APM LZOS 130 f/6; CFF 140 f/6.5; Astro-Physics 130 f/6.3 (at least they do not advertise double ED elements).

I do not think the new TS 140 f/6.5 has a flatter field since they seem to recommend the same flattener/reducer (TS 0.79x 3") as for other telescopes, and they do not claim a flatter field.

[vlaiv]

2 minutes ago, gorann said:

But there are some great and relatively fast triplet apos with a single ED lens. Like Esprit 100 f/5.5; APM LZOS 130 f/6; CFF 140 f/6.5; Astro-Physics 130 f/6.3 (at least they do not advertise double ED elements).

I do not think the new TS 140 f/6.5 has a flatter field since they seem to recommend the same flattener/reducer (TS 0.79x 3") as for other telescopes, and they do not claim a flatter field.

There is more to objective lens than just color correction and field curvature. How does it behave off axis for example.

With all spherical design of the lens - you have following parameters (I could be wrong at this, so happy to be corrected): radius of curvature for each surface, thickness of each element, spacing between elements and refraction index of each element.

You play with those to get characteristics of your scope - color correction, correction of aberrations on/off axis but also there is one more point - tolerance. You need to know how much can manufacturing process deviate from ideal figure or thickness or spacing to still be within optical requirements that you set as a designer. Different combination of above parameters will have different level of "resilience" to errors.

I suspect that as manufacturing process is being automated - optical designers need to consider what sort of errors they can expect from machines doing figuring as well as tolerances on glass purity and account for those in their design process. On top of all of that - you need to be cost effective and have a market for your product.

Btw, I believe that we are pretty much at stage where computer can do it all - just wonder if software has been written for it - you input available types of glass, expected manufacturing errors, parameters of scope (possibly a few more specs like cost and time to grind/polish) and hit "optimize" button - and software gives you optimal solution - if it says to use two ED types of glass - who are we to argue

 

[Space Hopper]

1 hour ago, johnturley said:

I think that TEC stated that one reason why they switched to Fluorite in their APO Refractors, was due to shortage of FPL53 glass.

John 

Thats correct. They had become very difficult to get hold of.

[Ben the Ignorant]

3 hours ago, gorann said:

There are many high class apo triplets with just one ED lens. Actually I thought they all only had one ED lens. Does anyone know if there are any advantages with two ED lenses

An ED lens gives optical designers a large advantage, especially with FPL-53 and FPL-55 glass but these are very costly, and the two other lenses matter immensely. I think they have a choice between twenty or thirty glass types, so if a triplet can be great with lenses of less radical properties but lesser cost, they should go that road. It's probably what they did here, the two ED elements have got to be the more affordable type. Straight Ronchi lines and a white star test are all that matter in a triplet apo, anyway, what glasses do it doesn't count a bit.

By the way, it's a shame all these new scopes are not advertized with their Ronchi picture and their star test for everyone to see. A Ronchi grating cost 40€ and a star test costs nothing so there is no excuse.

[gorann]

16 minutes ago, Ben the Ignorant said:

An ED lens gives optical designers a large advantage, especially with FPL-53 and FPL-55 glass but these are very costly, and the two other lenses matter immensely. I think they have a choice between twenty or thirty glass types, so if a triplet can be great with lenses of less radical properties but lesser cost, they should go that road. It's probably what they did here, the two ED elements have got to be the more affordable type. Straight Ronchi lines and a white star test are all that matter in a triplet apo, anyway, what glasses do it doesn't count a bit.

By the way, it's a shame all these new scopes are not advertized with their Ronchi picture and their star test for everyone to see. A Ronchi grating cost 40€ and a star test costs nothing so there is no excuse.

Good point Ben about the types of ED glass used. Nothing is mentioned about it on the TS site and I expect they would tell us loudly if there were two FPL-53 elements in there. Maybe two FPL-51 (or similar) are cheaper than one FPL-53, or easier to get hold of.

Edited November 27, 2019 by gorann

[The Admiral]

17 hours ago, vlaiv said:

I think we have established a standard for scatter control here

 

Perhaps on that basis my "cheapo" 102mm Altair Wave Super ED triplet APO should come near the top of the pile!

Given that this was taken with an ALT-AZ mount and the exposures confined to 30s, perhaps it actually says as much about the exposure conditions as the 'scope?

Ian

[joe aguiar]

6 hours ago, gorann said:

 Actually I thought they all only had one ED lens. Does anyone know if there are any advantages with two ED lenses - seems to be the new trend, see:

 

well  USING 2 ED lens will be very expensive BUT you could make it like f/6 to 6.5 and have the same colour correction as a triplet with 1 ed lens at f7.7 

to some people this may be work it having something that short and less weight, you can use a bit smaller mount verses something 12 to 16" longer

joejaguar

Edited November 27, 2019 by joe aguiar

[gorann]

6 hours ago, joe aguiar said:

well  USING 2 ED lens will be very expensive BUT you could make it like f/6 to 6.5 and have the same colour correction as a triplet with 1 ed lens at f7.7 

to some people this may be work it having something that short and less weight, you can use a bit smaller mount verses something 12 to 16" longer

joejaguar

What I tried to say above is that you have some really great triplet apos with low f-values that apear to only use one ED element, like Esprit 100 f/5.5; APM LZOS 130 f/6; CFF 140 f/6.5; Astro-Physics 130 f/6.3, so could it be that using two cheaper ED elements (like FPL-51 or FCD-1) is novel way of makig great triple apos, if that is what TS and FLO are doing (they do not state what ED glass they are using)?