SW Evostar 150ED / FPL53

[Solar B]

Don’t know , much about it but it is a 53 so betters the APM 150 as its a 51 

 

https://www.primalucelab.com/astronomy/apo-refractors/skywatcher-evostar-ed150-apochromatic-refractor.html

 

 Brian 

[John]

There is a fair amount of discussion on this exciting new scope here:

Not FPL-53 though, something else.

Note: Schott does not make FPL-53 glass, it's an Ohara product. So the PrimaLuce Lab piece is incorrect on two counts there.

[Solar B]

Ah right thanks John , I’m not up to date on my Refractors at all then !! 

Do we know what / which glass is being used by Ohara , I do think that a 150mm 53 could have been a game changer.

 

Brian 

[John]

6 minutes ago, Solar B said:

Ah right thanks John , I’m not up to date on my Refractors at all then !! 

Do we know what / which glass is being used by Ohara , I do think that a 150mm 53 could have been a game changer.

 

Brian 

Ohara still produces FPL-53 and 51 as far as I know. Synta/Skywatcher have decided to use an alternative, undisclosed, glass combination for the ED150 which they seem confident will perform to the standard that we have come to expect from their ED doublet refractors. They are working very hard to get this scope "right" from what I hear, including ditching a whole batch of glass because it did not meet their requirements for this scope.

 

[Solar B]

I see , I do think that if one were to be spending near on 2K for a scope they do deserve to know which glass is 

being used , if this info is now being withheld , (72ED) then I’m not impressed regardless of performance.

 

Brian 

[DRT]

Sorry for the slight thread-drift, but can someone explain what the 51/53 designation actually means? {not being smart here, I really just don't know!}

[Solar B]

Mmmmm , 53s definitely better than 51 , as to why who knows , from my own experience you can normally get away with

a 53 doublet but to achieve similar performance a 51 has to sit in a triplet configuration and here is often slightly better.

pure fluorite CaF2 in a doublet probably still offers the best performance/contrast though.

F,Fluorite,P,Lead,L,Low dispersion.

 

Brian 

 

 

[John]

There are also triplets that use an FPL-51 (or equivalent) element that show more CA than some FPL-53 doublets.

There is more to a good refractor than just the glass types used. The match of the glass types, their figure, coating, baffling and mounting (ie: lens cell design) all play an important part in the eventual optical performance.

This is a complex subject though and there are reams of posts on the web about the topic. Those by Roland Christen and Thomas Back are well worth searching out

APM do not specify FPL-51 for their 152mm ED doublet by the way. Here is a quote from their website:

"...The new 152-1200ED features a Doublet lens cell using ED glass equivalent to FPL-51..."

[RayD]

As John notes, Schott and fpl53 are made by different people, but my understanding is that SW are not and will not be releasing the specifications for any of their objectives as they feel it is the performance that matters, not what the name is.

I think this idea is liked by some (me) and not by others, but I suspect the suppliers noting it as fpl53 are taking a wild stab in the dark as the information simply isn't available. 

[Victor Boesen]

According to Skywatcher USA on their instagram they claim that there is a "DX" version as well. I don't know what the difference will be?

[John]

2 hours ago, Victor Boesen said:

According to Skywatcher USA on their instagram they claim that there is a "DX" version as well. I don't know what the difference will be?

Photos on the web elsewhere seem to show that the DX version will have a larger, better quality focuser and CNC tube rings. Whether there are other changes from the base scope I don't know. 

[Rick_It]

As for the ED element, from the good to the ugly those are the possible options:

FPL55 (O'Hara)

FCD100 (Hoya)

FPL51 (O'Hara)

FCD1 (Hoya)

HK61 (CDGM)

If indeed SW has decided for the FPL55, it's really beyond my understanding why the have decided not to declare the ED element.

 

[25585]

Kind of binocular maker approach where only prism type and coatings (sometimes) are disclosed. ED at most for lenses. They can chop & change as long as performance stays constant (for price) or improves. 

Bins are made in fixed magnifications with fixed eye lenses though so less flaws would be obvious than with refractors going up to much higher numbers. 

Perhaps @FLO could offer an optional E S Reid test for the 150. 

[25585]

1 hour ago, John said:

Photos on the web elsewhere seem to show that the DX version will have a larger, better quality focuser and CNC tube rings. Whether there are other changes from the base scope I don't know. 

DX is on a Losmandy D dovetail, standard on Vixen. 

[FLO]

43 minutes ago, 25585 said:

Perhaps @FLO could offer an optional E S Reid test for the 150. 

We could but I doubt it will be necessary, Sky-Watcher's doublet cells are normally bomb-proof. 

Steve 

[Solar B]

Glass classification is a very emotive subject , and I’ve just viewed some scary posts from me 10 yrs ago here on this very topic !

But hey it’s “Solar Time” now so I don’t care about any glass types  ... forgetaboutit ? ☀️?

 

Brian 

 

[DaveS]

On ‎17‎/‎04‎/‎2018 at 23:30, Solar B said:

Mmmmm , 53s definitely better than 51 , as to why who knows , from my own experience you can normally get away with

a 53 doublet but to achieve similar performance a 51 has to sit in a triplet configuration and here is often slightly better.

pure fluorite CaF2 in a doublet probably still offers the best performance/contrast though.

F,Fluorite,P,Lead,L,Low dispersion.

 

Brian 

 

 

No, there's no lead in FPL-5x, indeed there's no lead in any modern glass.

FPL, Fluoro-Phoshate, Light.

I think Ohara have stopped making, or are stopping making, FPL53, replacing it with FPL55. Which is why TEC switched their 140 apo to use fluorite in the central component.

[25585]

11 minutes ago, DaveS said:

No, there's no lead in FPL-5x, indeed there's no lead in any modern glass.

FPL, Fluoro-Phoshate, Light.

I think Ohara have stopped making, or are stopping making, FPL53, replacing it with FPL55. Which is why TEC switched their 140 apo to use fluorite in the central component.

Another reason to buy a FPL-53 while still available.