FPL-53 FLUORITE

[Solar B]

You know me Tony...easily pleased...can you read it again copy the important

bits and paste it here 8)

BTW i here your not going to Kielder HOW NO

Brian

[Whippy]

Sorry Brian, it appears that CN removed the thread. Probably because Televue owners couldn't face having an inferior scope to whatever 'won'....

Yeah, I can't do Kielder this year mate . Really wanted to go too but alas, things have conspired against me. I'm already making plans for next Autumn though...

Tony..

[John]

..... I love the way people have to justify their purchases by getting approval from people they've never met....

Thats only because our families show no interest whatsoever Tony ! (or at least mine does not .... )

John

[NickH]

LOL

I find it funny when people get so defensive about kit...if someone says "X is better than Y", then great...that's what they think...personally, I don;t really care much, if people had a pot at any gear I owned...that's fine/cool and their personal opinion.

Kit is kit... it's not family

[Coco]

This is an interesting thread, the content probably stands arguably more so today than back in 2008, what now with other self branded importers slapping there named brand on the tube and making claims of optical perfection, how do you actually know that your scope has got FPL-53 glass apart from the word of the importer?

In my ordinary day job we’ve have had made 7075 alloy wheel nuts made in Taiwan (2004-12-), just recently in the last few months we have come across a few quality control issues and tested some of these nuts, its turned out that the factory ''manager who has now been sacked'' (oh really) changed the alloy stock from 7075 to 6075, not life threatening but cheaper quality. The switch was very obvious but I doubt with fpl-51/53 - FDC1 glass you would notice.

Some of these ED80 triplets on the market have near identical tubes and likely Identical manufacturer, some have the same focuser too, yet some are FDC-1 some FPL-53

ie:Explore Scientific/Meade 5000 ED80 (FDC1) Altair Astro/Telescope Services ED80 (FPL-53) and so on.

What’s to stop the latter being fitted with FDC-1 and the factory manager gets his bonus?

I doubt there is a scope for life unless you get a TEC or Tak, so when making a purchase decision its quite likely you may base it on ‘what’s it worth if I sell it’ & therefore ‘I’d better go with the crowd’

[Brian Nordstrom]

I agree Steve on that , as everyone has their own way of descerning what they see , me well I have a little 60mm Takahashi FS60C with 1 element of " Flourite " , the other lense is un specified by Takahasaki , but what ever it is it gels so well with the flourite it amazing .

At 355mm focal length and an easy 200x the coulor correction and sharpness are perfect , amazing for a 60mm scope with only 355mm to play with .

I was using my Tak with a William Optics 3mm planetary eyepiece and 2x Celestron barlow giving 235x on Saturn last night and the image was not breaking down , a little dimm but still Tak ( pun intended ) sharp ,, as I said , an Amazing scope .

I also have an ED80 with FPL53 and at 600mm fl its ability to reach higher magnifactions easily 200x , because of its longer F/L is the only differance , Yes the 60mm TAK gives better views , given its 20mm less apateaure and 245mm less F/L .

My ED80 is no slouch , either .

There is definatly something about " Flourite " .

My eyes tell me so .

Brian.

[E621Keith]

The Tak 'Flourite' is CaF2 crystal, a crystalline material where all the ED glass try to emulate. FPL53 is suppose to be the closest optically. FPL53 also have a few advantages over the fluorite crystal including durability, easier to figure and coat.

However that's only half the story, the crown element is also very important. I'm not aware anyone make any statement about the crown element (may be apart from Skywatcher - Schott glass (not sure which one)).

However, I doubt the difference between your FS60 and ED80 is due to the material. I'd say it's more to do with the quality of the figure, the polish, the coating, the QC and every other details manufacturers don't put on the specs.

[Brian Nordstrom]

You are right there Keith , I regually put my little Tak at 60mm and 355 mm f/l up against my Zeiss 63mm Telementor 840mm f/l , its fun to do especially because I have a good eyepiece collection using Orthoscopics , 4-24mm and Vixen Lanthiums 2.5 - 20mm and using my 2x Ultima barlow can duplicate almost all magnifactions in my Tak , Zeiss , TV Pronto and ED80 and it always boils down to the TAK and the Zeiss , because of there superior polish and figure , not to say the Pronto of ED80 are not good I am talking 200x + and the Pronto and ED hit the wall not much past that 200x perhaps around the 220 x , whereas on good nights both the TAK and Zeiss will hit 280x and thats where it get interesting .

Sometimes the Zeiss has the better result and sometimes the TAK .

I am sure that I can go higher but my 2,5mm Vixen and 2x ultima is 284x in the Tak is as high as I can get , and 3mm WO in the Zeiss at 280x and I wont go any higher , It takes a driven GEM for these times and stupid magnifications , but its still amazing that my 2 , 60mm scopes acheave this . So much fun .

This only happens on those good nights that we get lots of here in the Northern Territory of Australia this time of the year . So I make the most of it , almost time to go out now .

Yep its about QUALITY !!! .

Brian

[ollypenrice]

Random refractions...

The Tak FSQ85ED that I use has no flourite and is the best colour corrected refractor - based on practical imaging experience - that I've ever used. I believe the earlier Tak FSQs had fluorite in the mix and the design was changed to eliminate it. The colour correction was, however, improved. So it does seem to me that the presence of one magic word, out of context, is so much hot air. However, it clearly has marketing pull since the magic letter 'F' was seen by Tak as essential. It stands for, er...Flatfield. Yeah, right. It's like 'Turbo' which will appear in your washing machine, your hairdryer, your toothpaste dispenser, your shoe brush, blah blah blah!

The Meade 127, at the eyepiece, gave a stunningly well corrected image for the price but in imaging the blue stars bloated. Other budget triplets that I've tested beat it convincingly with a CCD attached. I honestly don't care a jot what any of these scopes was made of. I look at the pictures they give.

I fairly recently sold a very early 'Pearl River' Genesis dating back to the late eighties or very early nineties. There was no issue with the fluorite. It was still a cracking good scope and I miss it.

The TEC 140 is fabulous but the budget scopes run it remarkably close, optically. Close but not equal. Mechanically they don't get near it and that does matter in years to come when you want to sell it. Sell it? Made that mistake with the old Genesis!

The Tak FS60 is another sweetie visually but it bloats in the blue with a CCD, really quite badly.

Olly

[E621Keith]

Random refractions...

The Tak FSQ85ED that I use has no flourite and is the best colour corrected refractor - based on practical imaging experience - that I've ever used. I believe the earlier Tak FSQs had fluorite in the mix and the design was changed to eliminate it. The colour correction was, however, improved. So it does seem to me that the presence of one magic word, out of context, is so much hot air. However, it clearly has marketing pull since the magic letter 'F' was seen by Tak as essential. It stands for, er...Flatfield. Yeah, right. It's like 'Turbo' which will appear in your washing machine, your hairdryer, your toothpaste dispenser, your shoe brush, blah blah blah! ....

Olly

Wow, that's new, I always thought 'F' in Takahashi scope stands for fluorite and that's why non fluorite scopes such as (TSA and TOA) didn't get the 'F' designation. It's good to know FSQ doesn't use fluorite, it is another good example why the lens material doesn't tell you the whole story.

[johninderby]

The following by Roland Christen is worth a read.

John

******************************************************************************************************************************************************

Roland Christen, ASTRO-PHYSICS

"Is it true that there is range of achromat glass (crown/flint) and there is a range of ED glass and there is a range of flourite lenses as well? By "range", I mean the degree that the glass can correct chromatic aberration (leaving everything else such as spherical aberrations as equal)."

The answer is NO and YES. NO, there is no range of achromat color correction. Achromats are made fromordinary glasses that have no special dispersion characteristics. An achromatis made with a crown positive element and a flint negative element. Theseglasses are made with various oxides, which give them their strength anddurability. Normal dispersion glasses will correct the colors from C to Fto 1 part in 2000, or the focal length will vary by .05% from red to green toblue, and approximately .25% for violet. The amount of color halo you see around astar with any aperture will be inversely proportional to the focal ratio.Thus an f15 scope will have half the color halo of an F7.5. A 20"F15 achromatscope will have the same size color halo as a 4"f15 achromat, but because the 20"has 1/5 the size Airy disc, the color relative to the Airy disc max resolutionwill be 5 times worse for the 20" vs. the 4" scope. What happens if you add athird element? Nothing, the color correction is still 1 part in 2000. You canadd 50 elements, and you won't gain anyhting.

YES, there is a difference between various ED and Fluorite scopes, but it isnot really the ED or Fluorite that governs the amount of correction, but themating element. Normally, even the worst ED design will have 4 times bettercolor correction than a normal achromat, but it could easily be 20 timesbetter simply by choosing a different mating element. The more expensive the ED,the easier it is to mate it to a corresponding negative element to achieveperfect color correction. You can make an ED lens with an ED positive element,and a flint negative element just like an achromat, but the color correction willnot be very good, perhaps a semi-apo. By choosing a Short-Flint or Crown-Flintyou can get better correction, but not perfect cancellation of secondary color -perhaps 4 to 6 times reduction depending on the combination. To get perfectcancellation over a wide wavelength range you would mate the ED with a negativeelement made with Crown glass. These are the most difficult to make, so commercial Apo makers avoid these.

What gives the ED material the ability to correct color? It is the chemicalcomposition of the material which is based on fluorides instead of oxides.Fluoride based glasses have a different dispersion characteristic caused byabsorption bands that are further away in the ultraviolet (this also allowsthem to pass UV light more readily). The drawback of fluoride based glass is that the bonds that fluoride formswith other materials are weak (oxide compounds are very strong and superhard). The fluoride material is hard to polish and stains more readily in somecases. One more comment, it is possible to make a so-called "ED" lens and have normalachromat correction of 1 part in 2000. There is one glass that some call ED -FK5, which will produce the same correction as any normal achromat combo. It'salso exceedingly cheap. Schott has given FK5 the designation FK (fluoro-crown),but it has no particular color correcting properties in the normal visualwavelength range.

Very confusing, yes?*

[Coco]

It's like 'Turbo' which will appear in your washing machine, your hairdryer, your toothpaste dispenser, your shoe brush, blah blah blah!

Hahah... one of the better analogies .. so true