New WO73 fpl53 glass.

[25585]

9 minutes ago, FLO said:

The ED element is only part of the story, the matching Crown element is equally as important and manufacturing quality is, arguably, most important. There are doublets that out-perform triplets, and triplets with FPL51 that out-perform similar models using FPL53. 

Buying a refractor that boasts a particular ED element, that doesn't mean you are out of the woods. 

Steve 

Steve do you know what the number after FPL signifies? Is it a measurement of some kind?

[John]

This might help:

https://www.oharacorp.com/o1.html

 

[25585]

15 minutes ago, John said:

This might help:

https://www.oharacorp.com/o1.html

 

Thank you

@FLOput a SW leaflet in with my Equinox. The refractor ranges are just 2 - black & whites going from 102 to 150 (BK15012EQ6), all on tripod+mount and Esprits from 80 to 150 "FPL53" stipulated, OTA only. 

[25585]

[John]

S-FPL53 will be used for one of the elements. As Steve said, the glass used for the other "mating" elements is just as important as is figure, polishing and lens cell design.

 

[Adam J]

Interesting scope F5.9 is a little fast for a doublet though? Will have to wait and see some RGB images to see how well corrected it is...not that the 61 looks bad at all. 

[Chris]

3 minutes ago, Adam J said:

Interesting scope F5.9 is a little fast for a doublet though? Will have to wait and see some RGB images to see how well corrected it is...not that the 61 looks bad at all. 

I'd say F5.9 is pretty standard for small ED's in the 60 to 80mm range. The Equinox 80mm is f6 with fpl53 glass and that gets some praise for it's imaging ability. I should imagine the WO73 would be very close to the WO61. This is my bet.

 

[ronin]

3 hours ago, Adam J said:

Interesting scope F5.9 is a little fast for a doublet though? Will have to wait and see some RGB images to see how well corrected it is...not that the 61 looks bad at all. 

WO seem to always go for claiming n.9 refractors. They seem to operate of the idea that people like to see "fast" refractors, appeals toi imagers more. There is a new Astro Tech that came out the same time as the WO 61, same glass same focal length but AT have said it is 60mm dia so that make it an f/6 scope not an f/5.9.

The ZS61 is another example and I think even the older Megrez 90 was the same, cannot recall the GT81 but would half suspect that to be another that was an f/n.9 scope.

Willing to bet the WO and the AT are exactly the same. When everyone brought out a 100 degree eyepiece I recall one manufacturer designated theirs as 101 degrees - may have been WO or Meade.

If you look at the link to the melt frequency then FPL-53 is fairly low whereas FPL-51 is one of the highest melt frequency they do. So I would doubt that FPL-51 may be phased out.

FPL-55 is now more frequent then FPL-53.

Isn't Schott FCD-100 an almost direct replacement for FPL-53 now. Which may be why ES use it and not FPL-53, if there are concerns that FPL-53 may slowly get removed.

 

[Chris]

12 minutes ago, ronin said:

WO seem to always go for claiming n.9 refractors. They seem to operate of the idea that people like to see "fast" refractors, appeals toi imagers more. There is a new Astro Tech that came out the same time as the WO 61, same glass same focal length but AT have said it is 60mm dia so that make it an f/6 scope not an f/5.9.

The ZS61 is another example and I think even the older Megrez 90 was the same, cannot recall the GT81 but would half suspect that to be another that was an f/n.9 scope.

Willing to bet the WO and the AT are exactly the same. When everyone brought out a 100 degree eyepiece I recall one manufacturer designated theirs as 101 degrees - may have been WO or Meade.

If you look at the link to the melt frequency then FPL-53 is fairly low whereas FPL-51 is one of the highest melt frequency they do. So I would doubt that FPL-51 may be phased out.

FPL-55 is now more frequent then FPL-53.

Isn't Schott FCD-100 an almost direct replacement for FPL-53 now. Which may be why ES use it and not FPL-53, if there are concerns that FPL-53 may slowly get removed.

 

Altair also have the same scope labelled 60mm f/6. Whether 60mm or 61mm or f5.9 or f/6 it's all the same to me.

https://www.altairastro.com/60EDF-ED-R-Refractor-Telescope.html

[John]

48 minutes ago, ronin said:

Isn't Schott FCD-100 an almost direct replacement for FPL-53 now....

 

I think FCD-100 is a Hoya product. It is close to FPL-53 in terms of specification and a little less expensive as well.

[Adam J]

18 hours ago, John said:

I think FCD-100 is a Hoya product. It is close to FPL-53 in terms of specification and a little less expensive as well.

More to it than just the quoted color correction specifications, i.e bubbles and inclusions are not specified in either case...at least not to the public. One of the things that most people dont realize is that there are multiple grades of FPL-53 that cost more or less depending on these largely unacknowledged factors. 

[Skyline]

FCD-100 is a Hoya product:

https://refractiveindex.info/?shelf=glass&book=HOYA-FCD&page=FCD1

[Ben the Ignorant]

On ‎11‎/‎12‎/‎2017 at 15:04, John said:

I've heard mention of a glass called FPL-55 which sits somewhere between FPL-51 and 53 but much closer to the latter.

Time will tell ....

FPL-55 is only one quarter of one percent inferior to FPL-53 (from Ohara's own site) in its Abbé number, the most critical property of glass for making apos. And it costs 15% less, plus it's easier to polish. CFF is already using it. Those who are afraid 55 will not match 53 didn't read the specs. A "53" scope with 40µ chromatic spread would have 39.9µ chromatic spread if switched to "55". No one will see the difference, and even lab instruments will have a tough time detecting it, which will be drowned in other tolerances, anyway.

[John]

3 hours ago, Ben the Ignorant said:

... No one will see the difference, and even lab instruments will have a tough time detecting it, which will be drowned in other tolerances, anyway.

FPL-53 is even closer to Fluorite than FPL-55 is in terms of Abbe Number but there are subtle differences in the performance scopes that use FPL-53 and Fluorite which even a klutz such as me can see. I think you are underestimating observers perhaps ?

Have you compared similarly specced scopes using FPL-55 and FPL-53 glass in their objectives Ben ?

Perhaps you could share your findings ?

[John]

6 hours ago, Adam J said:

More to it than just the quoted color correction specifications, i.e bubbles and inclusions are not specified in either case...at least not to the public. One of the things that most people dont realize is that there are multiple grades of FPL-53 that cost more or less depending on these largely unacknowledged factors. 

Quite correct. Having seen the specifications that APM / TMB use for LZOS glass used in their triplet apchromats it is clear to me that there are many aspects to glass quality apart from the abbe number. The higher the stipulations of the specs, the more the glass manufacturer will charge for the products that meet it. 

[Ben the Ignorant]

6 hours ago, John said:

Have you compared similarly specced scopes using FPL-55 and FPL-53 glass in their objectives Ben ?

Perhaps you could share your findings ?

Have you compared all the optics you ever talked about?

Perhaps you could share your findings? 

[Stu]

3 minutes ago, Ben the Ignorant said:

Perhaps you could share your findings? 

Do you ever read SGL?

[Chris]

17 hours ago, Ben the Ignorant said:

Have you compared all the optics you ever talked about?

Perhaps you could share your findings? 

This is John we're talking about here, comparing optics especially eyepieces is what he does 

[Chris]

23 hours ago, John said:

FPL-53 is even closer to Fluorite than FPL-55 is in terms of Abbe Number but there are subtle differences in the performance scopes that use FPL-53 and Fluorite

I've never owned a fluorite scope, although the general jist I get from others when comparing say a Fluorite Tak to a Synta ED is that the fluorite is slightly brighter, sharper, and more neutral in tone.

I believe it was your self that said you 100mm fluorite performs similarly to you 120mm fpl53.. 

Whether that's worth the extra premium is down to the individual, but the longer you're in this game the more discerning you become I've found  

 

[F15Rules]

57 minutes ago, Lockie said:

On 15/12/2017 at 17:39, John said:

 

I've never owned a fluorite scope, although the general jist I get from others when comparing say a Fluorite Tak to a Synta ED is that the fluorite is slightly brighter, sharper, and more neutral in tone.

Hi Chris,

Having been fortunate enough to acquire my first fluorite scope (probably my only one!), the FS128, I'd say the main features I've noted as compared to FPL53 scopes I've owned (ED120, ED100s) is improved contrast and reduced light scattering.

Saying that, I've had precious few sessions with the Tak so far, which is why I haven't yet posted a more detailed first light report.. If I've learned one thing about the performance of high end glass (by which I include Fluorite, FPL53, and top end long achromats like D&G), it's that the differences are relatively small on most nights and that local seeing and sky conditions will often have far more effect on the views than the type of glass in your scope.

Having lived in Lincolnshire now since March, I really believe we have a micro climate here: yes, skies are a good deal darker than where we came from, but the seeing is much more variable.  We live in a valley surrounded by low hills, and I'm convinced we get "ripples" of unsteady air flowing down to us: often, even the Tak won't take above x100 or so magnification (same for  the ED103s), although early in the year I got  a couple of "etching like" views of Jupiter  that hinted at what the Tak  is capable of..it's not all  bad news though, I think this shimmering effect lessens as the night goes on, and air temperatures equalise..unfortunately, as I still have to work at the moment I don't get the chance for many late night observing sessions. But several times recently, when called by nature to the bathroom in the middle of the night, I've noticed through a velux window how simply stunning the night sky has looked at c3am in the evening. I am SO looking forward to retirement with no work to get up for! ?

Back to the glass, the fact is that we are very lucky today to have access to affordable high quality optics, whatever the glass type. If we could reduce light and air pollution a lot, then ALL our scopes could give of their best, more often..

Dave

PS dare I say it's looking promising outside tonight?!

[25585]

Being retired is what re-kindled my viewing. Sleeping in after a night of viewing & watching summer night constellations rising "still there", is a luxury I longed for. 

Not so many reviews on the Takahashi Flourite TSA-120 yet. (Huge price difference between it & the 130). 

[Chris]

Thanks Dave, I'm guessing more care is taken with the figure of high end fluorite scope lenses which would contribute to the sharper/less scatter also, so maybe not all down to glass type? You're right though, seeing conditions trump any of these differences when using moderate to high mags. 

The 128 does sound like an ultimate retirement scope when you can make use of those 3am skies, certainly something to look forward to other than not having to go work