36 replies to this topic

[SandyHouTex]

Thanks for posting these links, Sandy.

 

Referring to my post above to Matt (#15) I surmised that the mating element on the TSA series was BK7 as its time tested, readily available in uber high quality, and mates well with FPL53. 

 

I was suprised in reading your post that in fact, the TSA mate is BSL-7.  I was wondering how I could have gotten this wrong as I was not at all familiar with BSL-7 as a mating element to FPL-53.  I did some additional research combing through some glass catalogs archived on my home server and found this Optical Glass Equivalents Table.  It can also be found here: 

 

https://www.edmundop.../optical-glass/

 

At least I can sleep easy tonight knowing that I was not completely off-base...   BK7 is the Schott equivalent to Ohara BSL7. 

It appears that your memory served you well.

[MikiSJ]

I had the joy of owning an APM/TMB 152/1200 triplet. Does anyone here know what the optical characteristics of the lens combination is?

 

BTW, I sold a TAK FS-152 to get the APM.

[n2068dd]

I had the joy of owning an APM/TMB 152/1200 triplet. Does anyone here know what the optical characteristics of the lens combination is?

 

BTW, I sold a TAK FS-152 to get the APM.

Hi,
Reading from Mr. Thomas Back explanation, it looks traditional design like in the EDF 155 by AP. Recent optic from Russia could be different, though to see some test reviews it looks not so changed.

http://airylab.net/c...011_05006_A.pdf

https://www.airylab....015-35002-a.pdf

In there, you can see the crossing point at height 0.7 to 0.8. It's the same type of design like TSA-120.

[n2068dd]

I always thinking, Most important matter is in the production. Maybe, most of all triplet design in the market is not so different. Except TOA or FOA, the triplet design is not changed in 100 years when Zeiss had introduced. In early '70, Zeiss introduced ED and followed Ohara or Nikon. At that time, ED had some compromise than fluorite.In late '90 Ohara ruled the world of ED, though triplet design is still in old fashioned style. Considering the element of only three, it may be hard to find another method. TOA or FOA could be, though very difficult in production. In reality, no other company can't follow them. To change the stand point, we can accept with ED doublet in common use for most of the target. Only in AP which have the issue of blue halo matter will needs ED triplet, I may think. Such like planet in visual, most important matter is air turbulence in first and optic precision in next I strongly feel.

[DavidNealMinnick]

Agreed. My best view, ever, of Jupiter was through my C-9.25 SCT, hardly a planetary scope, but the seeing that night was perfect.

 

Made all the difference.

 

I still wish Takahashi would market a new 5-inch class doublet.

[teashea]

I guess someone forgot to tell Mr Yuyama at Takahashi Seisakusho that it can't be done.......

 

I don't think Takahashi have ever disclosed the actual mating glasses to their ED or CaF2 designs. 

The TSA has one FPL53 element between two unknown elements, 

The original TOA130 had an FPL53 at the front, unknown in the middle and FPL52 at G3,

The later TOA130 and the TOA150 have FPL53 at G1 and G3 and another 'mystery' glass in between..... 

 

The only doublet that comes close is the FOA60.

Takahashi says that the FOA60 optics are the finest optics they have ever produced.  

[SandyHouTex]

I always thinking, Most important matter is in the production. Maybe, most of all triplet design in the market is not so different. Except TOA or FOA, the triplet design is not changed in 100 years when Zeiss had introduced. In early '70, Zeiss introduced ED and followed Ohara or Nikon. At that time, ED had some compromise than fluorite.In late '90 Ohara ruled the world of ED, though triplet design is still in old fashioned style. Considering the element of only three, it may be hard to find another method. TOA or FOA could be, though very difficult in production. In reality, no other company can't follow them. To change the stand point, we can accept with ED doublet in common use for most of the target. Only in AP which have the issue of blue halo matter will needs ED triplet, I may think. Such like planet in visual, most important matter is air turbulence in first and optic precision in next I strongly feel.

Well I do think it’s quite unusual for Tak to use 2 flint glasses in their premium designs.  

[LDW47]

So I have heard, but cannot verify that the TSA uses FPL-53 sandwiched between two IDENTICAL flints.  In the case of the TOA objective, I’ve heard it’s two pieces of FPL-53 on the outside with a flint on the inside.

 

So now let’s go to “Telescope Optics”, by Rutten and van Venverooij, page 312.  The figure there, and the text states, that to design the best doublet possible, you need to pick elements as far apart as possible, and as close to a horizontal line possible.  However the two designs above are triplets, so let’s flip to page 324 and Fig. 21.21.  Here and in the text it says you need to pick elements such that a triangle is created, with the largest area, for the best possible correction.

 

Now if the TSA and TOA have elements as stated above, they will not create a triangle at all, but only a line, like a doublet.  Therefore, they cannot have any better correction than a doublet, and in that case, it makes NO SENSE to make a triplet at all.

 

And just for the record, of all of the triplet designs I’ve seen, they used three DIFFERENT glasses for the objective.

 

A long time ago, I was proficient in a DOS ray tracing program, and actually traced a 16 inch Buchroeder Tri-Schiefspiegler and an FPL-53 doublet.  Currently, I don’t have the time or inclination to learn OSLO or ZEMAX.  So what am I missing, if anything.  This conundrum is driving me crazy.

Rest assured you are no more confused than Vinny Barbarino was way back when !

[Alan French]

Well I do think it’s quite unusual for Tak to use 2 flint glasses in their premium designs.  

Remind me, where does Tak use two flint glasses in their design, and what glass are you referring to?

 

Clear skies, Alan

[mtminnesota]

Takahashi says that the FOA60 optics are the finest optics they have ever produced.

That's the FOA-60Q.

[n2068dd]

Well I do think it’s quite unusual for Tak to use 2 flint glasses in their premium designs.  

It's a difficult word to use 'premium designs'. I think 'premium designs' means not to use expensive material nor adding many lens material. Rather I do think using less expensive and less piece and perform better aberration than others should be called as 'premium designs'. To using stable and easy production lens material is the best way for many.

 

TSA is designed as budget from TOA which is heavy and ultra low aberration. Though, for most of the users, TSA has enough performance than other triplets. It's the Mr. Yuyama's way of design method. I may think. He never used fluorite to out perform FCT-125.

[edif300]

That is called skill. A genius designer in action.

Edited by edif300, 24 February 2021 - 03:57 AM.