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What optically are the differences between FPL55 and Flourite

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#1 rcg

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Posted 13 January 2019 - 05:03 PM

CFF uses FPL55 in their newer scopes. Others use Flourite, as I haven't seen FPL55 anywhere else specified does anyone know the differences/ advantages between FPL55 and Flourite.

 



#2 petert913

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Posted 13 January 2019 - 05:27 PM

.....and FPL53 !



#3 Bomber Bob

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Posted 13 January 2019 - 05:40 PM

In terms of Extra-Low Dispersion (ELD), CaF2 is superior to FPL-53, which is slightly better than FPL-55.  But remember, the glass types of the mated elements in the lens matter as well.  


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#4 Element79

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Posted 13 January 2019 - 05:40 PM

FPL53 and FPL55 are glasses whereas Fluorite is a crystal.  FPL55 is a newer glass than FPL55 and is supposed to supersede it.  It is supposedly cheaper and easier to work than FPL53 but maybe not quite as good.  Fluorite is a much better 'element' for use as the ED part of a lens but it is far more expensive than either of the glasses and much more difficult to work with.


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#5 james7ca

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Posted 13 January 2019 - 05:54 PM

Just Google something like the following:

 

  dispersion fpl-53 graph



#6 gezak22

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Posted 13 January 2019 - 07:15 PM

See this along with this and realize that you are comparing apples to oranges because glass type are just one parameter in a plethora of others.


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#7 Paul G

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Posted 13 January 2019 - 07:30 PM

Fluorite isn't necessarily "much better" than or "superior" to FPL-53, the differences are minor. FPL-53 is mostly fluorite with some additives melted in. Color correction is determined by the available mating glasses. The only thing fluorite allows the scope maker to do is to make a somewhat faster scope with similar color correction vs FPL-53. All kinds of other things have a greater effect on the image you see, including optical design, how well that design is executed, smoothness of polish, quality of the glass elements (bubbles, striae, nonhomogeneity, etc.), seeing, etc.


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#8 Jeff B

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Posted 13 January 2019 - 07:34 PM

Well, I've recently spent quite a bit of time with three excellent scope samples using FL, FPL-53 and FPL-55.  These were a TEC 140ED (FPL-53), a TEC 140FL, and a CFF 160 F6.5 (FPL-55).

 

All are excellent samples optically with little to choose between them visually except for the TEC 140FL having a slight "warmth" to its images of Jupiter and less so on the Moon and, with the CFF, the advantages associated with the extra aperture (slightly brighter and a just a little extra resolution).  All are basically equally sharp at high power. 

 

Only in DPAC on the bench and star testing did I see consistent differences between them.  But those differences to me were entirely due to the particular designs (how well the three glasses play with each other) and the execution of the designs in these particular samples rather than any one glass used for the center element being inherently "superior" to another.  In fact, I'm continually impressed with just how good the CFF is despite its use of the "inferior" FPL-55 glass.

 

So to me, I'm not really concerned about the center glass used (though I do find it interesting from a design point of view), what I'm really concerned about visually (not imaging wise) is how sharp the lens is at focus.   Which means, how well was it made.  Shoot, my old AP, pre-ED Starfires don't have an ED bone in their bodies and they give up a mild bit of "CA" in the deep red and blue, but boy, are they sharp.  Ditto with some of my achromats.

 

Jeff


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#9 Steve Allison

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Posted 13 January 2019 - 07:58 PM

Sharpness is everything to me. 

 

Less color but less sharp? No thanks.


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#10 Kunama

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Posted 13 January 2019 - 08:37 PM

...... I'm not really concerned about the center glass used (though I do find it interesting from a design point of view), what I'm really concerned about visually (not imaging wise) is how sharp the lens is at focus.   Which means, how well was it made.  Shoot, my old AP, pre-ED Starfires don't have an ED bone in their bodies and they give up a mild bit of "CA" in the deep red and blue, but boy, are they sharp.  Ditto with some of my achromats.

 

Jeff

bow.gif   This is good advice waytogo.gif


Edited by Kunama, 13 January 2019 - 09:30 PM.

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#11 Bomber Bob

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Posted 13 January 2019 - 09:00 PM

Visually, my fluorite refractors present star colors closest to what I see unaided, compared to ED types.  On some extended objects, the differences are less obvious.



#12 glend

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Posted 13 January 2019 - 09:56 PM

FPL-55 offers advantages to the manufacturer, as it is easier to polish than FPL-53, or so I an hearing.  Workability is important to them as it reduces waste, rework, etc. It may mean lower cost. I don't have a problem with change over to FPL-55, and as has been mentioned elsewhere the mating element is important. Lanthanum gets mentioned often. 



#13 rcg

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Posted 13 January 2019 - 10:25 PM

I have heard of some scopes with 2 ED elements, Lanthanum has been mentioned but I have only seen this in small scopes to date … imaging ...



#14 peleuba

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Posted 14 January 2019 - 11:04 AM

FPL-55 offers advantages to the manufacturer, as it is easier to polish than FPL-53, or so I an hearing.  Workability is important to them as it reduces waste, rework, etc. It may mean lower cost.

 

I had not ever heard of this - FPL55 being "easier" to polish then FPL53.  Can you site this so I can read about it?  The properties of both glasses have much more in common then what differentiates them.  When you speak about "ease of polish" you are really talking about the hardness of the substrate.  The harder the glass is, the faster the polisher can go.  Most flavors of ED glass are considered "soft" as their prime "ingredient" is Fluorite.  Fluorite needs to be polished slowly over a longer period of time to achieve a given level of polish I can't imagine that there would be an appreciable difference in polish time between FPL53 and FPL55.  

 

Usually when, when a glass manufacturer tweaks the recipe of an existing glass type to come up with a new formula, its to satisfy environmental concerns; to improve optical qualities (dispersion, index of refraction, homogeneity); or, simply, the market dictates a change.  Amateur optical telescope production is not a large enough market to drive anything, we are at the mercy of digital and smart phone camera industry.

 

Best Regards.  


Edited by peleuba, 14 January 2019 - 11:06 AM.

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#15 vahe

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Posted 14 January 2019 - 11:41 AM

I had not ever heard of this - FPL55 being "easier" to polish then FPL53.  Can you site this so I can read about it?  

http://www.ohara-inc...ew/s-fpl55.html

.

Vahe


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#16 glend

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Posted 14 January 2019 - 03:42 PM

And note the Abbe number of FPL-55 on that spec sheet. The human eye cannot discriminate between, FPL-55, 53, and Flourite. 


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#17 peleuba

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Posted 14 January 2019 - 04:29 PM

 

 

Thanks Vahe!

 

I have read this several times over the last couple of months and don't recall seeing the phrase: "...similar to FPL53, with advantage of improved polishing characteristics".  But there it is.

 

I think these improved polishing characteristics are only beneficial to the digicam manufacturers who polish ED glass in batches on high speed polishers using relatively hard synthetic polishing pads (instead of pitch).  See the attached picture. 

 

I don't think its meaningful to the top tier, boutique manufacturers who polish slower and in some cases hand figure/aspherize the optics for our telescopes.  As an example, other then CFF no one has embraced FPL55 (improved polishing characteristics or not).  They either continue to use FPL53; have gone to FCD100; or have gone to all Fluorite crystal designs.   

 

Admittedly, I am getting a little far afield here but I am certain that Roland, Yuri, Catalin/Pal did not come together and appeal to Ohara to develop a more refined grade of ED glass for the sole benefit of enhancing/speeding up the polishing phase of optical fabrication.  The amount ED glass that these shops use won't move the needle within the larger optical glass market.

 

So, at the end of the day, after reading the literature, I stand by what I said a few post above - that FPL55 was developed for the digicam industry because of the need to lay down a fine polish on a lot of smaller blanks in the shortest possible time frame.

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Edited by peleuba, 14 January 2019 - 04:30 PM.

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#18 Paul G

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Posted 14 January 2019 - 04:55 PM

I have heard of some scopes with 2 ED elements, Lanthanum has been mentioned but I have only seen this in small scopes to date … imaging ...

 

Roland on lanthanum/FPL-51 doublets from the AP Users Group:

https://groups.yahoo.../messages/77557

 

In the link at the bottom I have compared the designs of 4 different lenses in various combinations which can show the performance differences...

 

In the early 1990's Meade introduced an affordable doublet in 4", 6" and 7" sizes. These were based on Ohara FPL51 - KF3 glasses ...

 

At the same time a Japanese optical designer suggested to use a lanthanum element with FPL51 to achieve a similar visual apo performance with less steep curves...

 

What can be done today with Lanthanum and first generation FPL51 ED glass? Nothing really has changed, ...

 

In the posted images below, I have included for comparisons the original Meade ED design (top left in each posted image), as well as an ideal best possible SD doublet design using FPL55 and a very special short flint Schott mating element (bottom left) and finally a 155 GTX F8.35 design based on our 130 GTX upsized to 155mm. ...

 

 

https://groups.yahoo...ormance curves/

 

 

 


Edited by Uwe Pilz, 20 February 2019 - 08:23 AM.

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#19 csrlice12

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Posted 14 January 2019 - 08:04 PM

Thanks for finding and posting this.waytogo.gif 



#20 Marcsabb

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Posted 20 February 2019 - 03:15 AM

Is it possible to re-post the file here for those who are not members of the AP Yahoo group? Thanks!


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#21 Alan French

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Posted 20 February 2019 - 08:14 AM

This puzzles me. If folks are interested in AP scopes, why aren't they on the AP Yahoo group? (Ditto for other manufacturers and their groups.)

 

Nice to get first hand information from companies of interest. 

 

Clear skies, Alan



#22 Marcsabb

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Posted 20 February 2019 - 08:58 AM

This puzzles me. If folks are interested in AP scopes, why aren't they on the AP Yahoo group? (Ditto for other manufacturers and their groups.)

 

Nice to get first hand information from companies of interest. 

 

Clear skies, Alan

The linked file is about a comparison of different designs. (I'm particularly interested in what R-C calls "ideal best possible SD doublet design using FPL55 and a very special short flint Schott mating element")



#23 SandyHouTex

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Posted 20 February 2019 - 10:27 AM

This puzzles me. If folks are interested in AP scopes, why aren't they on the AP Yahoo group? (Ditto for other manufacturers and their groups.)

 

Nice to get first hand information from companies of interest. 

 

Clear skies, Alan

I actually try to limit my digital footprint.  I still pay my bills by mail to avoid having all of my info on the web.



#24 vahe

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Posted 20 February 2019 - 12:43 PM

Regarding FPL-53 and its availability, here is a recent comment by Roland:

.

Ohara FPL53 blanks of 6" size are very expensive now, and they discourage their use by anyone. Blank size is restricted now to only 150mm because they tell me that yield is low when the blanks are made larger and they have to throw out too much glass. Delivery time is also very long. With a 150mm blank you can make a 140 lens, but not a 6".

.

Perhaps this explains why many use FPL-55 particularly in 6" and larger apertures.

.

Vahe



#25 moshen

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Posted 20 February 2019 - 04:53 PM

Regarding FPL-53 and its availability, here is a recent comment by Roland:

.

Ohara FPL53 blanks of 6" size are very expensive now, and they discourage their use by anyone. Blank size is restricted now to only 150mm because they tell me that yield is low when the blanks are made larger and they have to throw out too much glass. Delivery time is also very long. With a 150mm blank you can make a 140 lens, but not a 6".

.

Perhaps this explains why many use FPL-55 particularly in 6" and larger apertures.

.

Vahe

This makes me wonder how Stellarvue is able to obtain FPL-53 and make the 152mm scopes (currently shipping). It uses a FPL-53 element and it'd have to be larger than 150mm to get a full 152mm clear aperture.

 

https://www.stellarv...plet-refractor/




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