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Comparing FPL-53 and CaF2

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#151 gnowellsct

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Posted 05 June 2018 - 08:56 AM

This month's Sky & Tel had an short article that said that the Webb's launch will now be in 2020 rather than 2019 because extensive testing has lasted longer than expected.  So let's hope that they get it right this time!

It's a very complex design (the unfolding business).  I'm worried that it'll screw up.


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#152 Terra Nova

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Posted 18 June 2018 - 11:15 AM

Perkin-Elmer didn’t really perish, they just ceased making optics for the astrophysical and surveillance science industries, and re-organized to focus on instrumentation for genetics, medicine, and biotechnology. God help us all! :lol:


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#153 starcanoe

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Posted 18 June 2018 - 12:09 PM

This month's Sky & Tel had an short article that said that the Webb's launch will now be in 2020 rather than 2019 because extensive testing has lasted longer than expected.  So let's hope that they get it right this time!

 

Maybe their Protostar flocking still hasn't come in yet...


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#154 gnowellsct

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Posted 20 June 2018 - 03:18 PM

Maybe their Protostar flocking still hasn't come in yet...

Flocking?  No way.  They still haven't gotten the secondary support.


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#155 Jeff B

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Posted 22 June 2018 - 01:56 PM

Flocking?  No way.  They still haven't gotten the secondary support.

I wonder who's making the dew shield.


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#156 Nippon

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Posted 22 June 2018 - 04:51 PM

Tele Vue I believe has never identified what glass they use in their scopes. Everyone seems sure it is FPL 53 but who knows, could be some magic Nagler pixie dust Al puts in the air space. Point is everyone seems happy with their Tele Vue refractors. FPL53 and Fluorite in ads or around lens rings is more marketing than anything. Like "dual overhead cams" on the top of your cars valve cover.


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#157 gnowellsct

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Posted 22 June 2018 - 05:22 PM

Tele Vue I believe has never identified what glass they use in their scopes. Everyone seems sure it is FPL 53 but who knows, could be some magic Nagler pixie dust Al puts in the air space. Point is everyone seems happy with their Tele Vue refractors. FPL53 and Fluorite in ads or around lens rings is more marketing than anything. Like "dual overhead cams" on the top of your cars valve cover.

They do perform and have an avid fan base.  At the high end I prefer machined knife edge baffles to sandpaper, but that's just me.    There are two in my club and they do what an apo oughta.  Greg N


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#158 Nippon

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Posted 23 June 2018 - 12:07 PM

They do perform and have an avid fan base.  At the high end I prefer machined knife edge baffles to sandpaper, but that's just me.    There are two in my club and they do what an apo oughta.  Greg N

I indeed was happy with my TV85 but just got to the point I wanted something larger. The TV 101 was just to expensive and a little to short on focal length. All I knew about the Vixen ED103  I bought was that it had ED glass. I found out it uses FPL 53 because there was a Vixen catalog packed in the box with the scope that stated that the ED81, 103, and 115 were FPL53. Since I remember Vixens in the past had either the word Fluorite or letters ED in large print on the tube I thought it strange that they now were so discreet about it. Just the other day I saw photos of a brand of 102 that had the words synthetic fluorite etched on the front cell retaining ring. That is clearly an attempt to suggest that their scope is not just another ED scope in a sea of ED scopes. In the text they tell you it's FPL53. The refractor companies know that their target market believes the only way a refractor can be any good is if it uses fluorite, especially fluorite, or FPL 53. I have often wondered if when Takahashi dropped the TSA102 and replaced it with a fluorite doublet chose to use fluorite because it was that much better or they just knew it would sell better. I think it is safe to say that they wanted to introduce a less expensive 4" scope but would an FPL53 version have been perceived as a cheap Takahashi compared to a perception of them bringing back a legend. 


Edited by Nippon, 23 June 2018 - 12:07 PM.

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#159 gnowellsct

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Posted 23 June 2018 - 01:23 PM

I indeed was happy with my TV85 but just got to the point I wanted something larger. The TV 101 was just to expensive and a little to short on focal length. All I knew about the Vixen ED103  I bought was that it had ED glass. I found out it uses FPL 53 because there was a Vixen catalog packed in the box with the scope that stated that the ED81, 103, and 115 were FPL53. Since I remember Vixens in the past had either the word Fluorite or letters ED in large print on the tube I thought it strange that they now were so discreet about it. Just the other day I saw photos of a brand of 102 that had the words synthetic fluorite etched on the front cell retaining ring. That is clearly an attempt to suggest that their scope is not just another ED scope in a sea of ED scopes. In the text they tell you it's FPL53. The refractor companies know that their target market believes the only way a refractor can be any good is if it uses fluorite, especially fluorite, or FPL 53. I have often wondered if when Takahashi dropped the TSA102 and replaced it with a fluorite doublet chose to use fluorite because it was that much better or they just knew it would sell better. I think it is safe to say that they wanted to introduce a less expensive 4" scope but would an FPL53 version have been perceived as a cheap Takahashi compared to a perception of them bringing back a legend. 

Well I am these days inclined to believe that 60 or 70% of the performance of a high end refractor is in the design and closely monitored production of the lens cell to extremely tight specifications, and close attention to the installation and adjustment of the lens in the cell.  I think I'd rather have "cheap" glass (such as FPL 51) and a an Astro-physics or TEC level lens cell than expensive glass in a poorly executed lens cell.  This is assuming that high levels of automation give the glass good figures, about which I know very little except that automated lens and mirror production today is a good deal better than it was fifty years ago.

 

Lens cells are less appealing to talk about.  But high end glass and a high end lens cell often go together.  I speculate that often times what we attribute to the magic of glass is in fact the magic of glass that is spaced 3/1000th of an inch more accurately than the low end rival.  

 

Greg N


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#160 Scott in NC

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Posted 23 June 2018 - 08:51 PM

 

Lens cells are less appealing to talk about.  But high end glass and a high end lens cell often go together.  I speculate that often times what we attribute to the magic of glass is in fact the magic of glass that is spaced 3/1000th of an inch more accurately than the low end rival.  

 

I think you've hit the nail on the head here, Greg.  And it's not just the fact that it's spaced more accurately.  It's also that the lens cell is robust enough to hold that precise spacing despite extensive use of the scope over an extended period of time.


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#161 photoracer18

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Posted 05 August 2020 - 08:08 PM

I wonder why Yuri still aspherises his oiled triplets when he could get away with an all spherical design?  I am sure there is a reason but since I don't have an advanced degree in optical engineering I will just have to live with the fact that he feels that it's necessary.

Yes but that quoted text mentioned that an aspherised 140mm oil-spaced triplet would have zero spherochromatism and at F7 would be better corrected for that than a TOA-130 at F7.7 an optic with all spherical surfaces. But expensive due to the amount of aspheric correction needed (-.5). Which is why Roland mentioned highly skilled optical workers as they would be needed to get the needed amount of aspheric correction I am betting. So everyone of importance knows what must be done but not all are willing to do it for the costs. The actual difference might not be that visible depending on what the scope was designed to be used for. So each does it their way. I am not an optical expert but I used to own a 1st run TEC140ED.




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