Jump to content

  •  

CNers have asked about a donation box for Cloudy Nights over the years, so here you go. Donation is not required by any means, so please enjoy your stay.

Photo

Fluorite Refractors

  • Please log in to reply
314 replies to this topic

#226 HARRISON SCOPES

HARRISON SCOPES

    Vendor-Harrison Telescopes

  • *****
  • Vendors
  • Posts: 614
  • Joined: 05 Nov 2006
  • Loc: The Garden of England

Posted 10 September 2018 - 01:41 AM

Any doublet will likely have less scatter than a triplet it's 4 versus 6 surfaces. Obviously if both are air spaced and in the same class of manufacturing .

Edited by HARRISON SCOPES, 10 September 2018 - 01:42 AM.


#227 X3782

X3782

    Mariner 2

  • -----
  • Posts: 242
  • Joined: 11 Jun 2018
  • Loc: ---

Posted 10 September 2018 - 03:47 AM

The small microbubbles are only visible in the bright coherent light of a green laser, and the beam's brightness within the glass is faint compared to where it encounters surfaces. It's hard to imagine there is enough scatter within the glass to be noticeable, let along differentiate between a doublet or triplet with a single fluorite element from one with all glass elements. A lens using fluorite still has one or two glass elements. There are also far too many variables involved to point to a single one as causing a difference. 

 

The bubbles the Nikon article discusses appear to be larger bubbles, visible by eye, and certainly something consumers might object to. I've seen antique lenses with serious bubble problems. The article makes no mention of contrast. 

 

Clear skies, Alan

Scattering from microbubbles are visible with incoherent light too, a beam from a bright lamp will suffice. This effect tends to be much worse for fluorophosphate glass compared to the highest quality matching crown glass or calcium fluoride, the latter group tends to have much higher homogenity and lower inclusions.


Edited by X3782, 10 September 2018 - 04:18 AM.


#228 X3782

X3782

    Mariner 2

  • -----
  • Posts: 242
  • Joined: 11 Jun 2018
  • Loc: ---

Posted 10 September 2018 - 04:08 AM

>When a curved surface is polished into the fluorite crystal, the crystal planes come to the surface in concentric rings and this cannot be polished out.

>This results in surface scatter that can be easily measured.

 

The atomic crystal planes are spaced so close together compared to the optical wavelength that I cannot see how this will be the limiting effect. For calcium fluoride, the problem is that it is so awfully soft and brittle. Abrasive polishing creates a lot of sub-surface damage and micro-roughness which leads to scatter. More advanced polishing techniques can reduce this effect substantially, but it is too expensive for amateur use. Given the same level of abrasive polishing technique (well the details of the technique are actually different), fluorophopshate glass will tend to achieve a smoother polish and less surface defects than calcium fluoride, hence less surface scatter. If you just try to polish CaF2 in the normal way, you will see a lot of fogging and whitish imperfections on the surface. Improving the technique will reduce this, but it will not go down to zero, so some compromise is reached in what gets sent to the volume consumer. No optical material is perfect, some will scatter on the surface, some will scatter in the bulk.


Edited by X3782, 10 September 2018 - 04:28 AM.

  • Fomalhaut likes this

#229 Fomalhaut

Fomalhaut

    Surveyor 1

  • -----
  • Posts: 1,763
  • Joined: 16 Aug 2008
  • Loc: Switzerland

Posted 10 September 2018 - 04:49 AM

So I took the same diagonal, the same eyepiece, and aimed them at the same target, on the same night using my Twilight II mount.  The scatter was less in the FS-152 than the TSA -102.

 

May I ask if you are the owner of both (FS-152 and TSA-102)?

 

If yes waytogo.gif, then yours is exactly the way to exclude any owner's pride  -  which probably is

the main bias-booster.

 

=> Any visual comparison should be done by somebody who either owns both instruments to be compared

or none of them. 


Edited by Fomalhaut, 10 September 2018 - 09:18 AM.


#230 Alan French

Alan French

    Night Owl

  • *****
  • Posts: 6,041
  • Joined: 28 Jan 2005
  • Loc: Upstate NY

Posted 10 September 2018 - 06:45 AM

So I took the same diagonal, the same eyepiece, and aimed them at the same target, on the same night using my Twilight II mount.  The scatter was less in the FS-152 than the TSA -102.

OK. So how do you decide the difference is caused by the use of fluorite and its lack of scatter I the FS-152?  You have other significant differences in the two scopes.

 

Using the same eyepiece means you are using almost half again as much magnification (49% increase) in the FS-152 than in the TSA-102. Your object and any glow from scatter cover a larger part of the field. 

 

The FS-152 has four air to glass surfaces while the TSA-102 has six. They are different designs and may vary in how scattered light ends up in the focal plane.

 

There may be differences depending on which lens is cleanest.

 

As I mentioned before, I did the laser test with my fluorite triplet. The beam is faint within the two outer glass elements. It is brighter and more obvious at the two air to glass surfaces. The beam is also brighter at where it passes from glass to fluorite and fluorite to glass, although not as much as at the air to glass surfaces. 

 

I have no doubt you see a difference in scatter. I just think you are too quick to conclude it is because of the lack of scatter within the fluorite. There are too many other possibilities, and more than one may increase the scatter in the TSA-102.

 

Clear skies, Alan


Edited by Alan French, 10 September 2018 - 08:23 AM.

  • Steve Allison likes this

#231 Erik Bakker

Erik Bakker

    Cosmos

  • *****
  • Moderators
  • Posts: 8,908
  • Joined: 10 Aug 2006
  • Loc: Netherlands, Europe

Posted 10 September 2018 - 08:05 AM

OK. So how do you decide the difference is caused by the use of fluorite and its lack of scatter I the FS-152?  You have other significant differences in the two scopes.

 

Using the same eyepiece means you are using almost half again as much magnification (49% increase) in the FS-152 than in the TSA-102. Your object and any glow from scatter cover a larger part of the field. 

 

The FS-152 has 6 air to glass surfaces while the TSA-102 has four. They are different designs and may vary in how scattered light ends up in the focal plane.

 

There may be differences depending on which lens is cleanest.

 

As I mentioned before, I did the laser test with my fluorite triplet. The beam is faint within the two outer glass elements. It is brighter and more obvious at the two air to glass surfaces. The beam is also brighter at where it passes from glass to fluorite and fluorite to glass, although not as much as at the air to glass surfaces. 

 

I have no doubt you see a difference in scatter. I just think you are too quick to conclude it is because of the lack of scatter within the fluorite. There are too many other possibilities, and more than one may increase the scatter in the TSA-102.

 

Clear skies, Alan

You probably meant it the other way around:

 

The FS-152 gas 4 air to glass surfaces, while the TSA-102 has 6. 



#232 Alan French

Alan French

    Night Owl

  • *****
  • Posts: 6,041
  • Joined: 28 Jan 2005
  • Loc: Upstate NY

Posted 10 September 2018 - 08:23 AM

You probably meant it the other way around:

 

The FS-152 gas 4 air to glass surfaces, while the TSA-102 has 6. 

Yes, thanks - typing in the morning is always dangerous. I'll correct it.

 

Alan



#233 Alan French

Alan French

    Night Owl

  • *****
  • Posts: 6,041
  • Joined: 28 Jan 2005
  • Loc: Upstate NY

Posted 10 September 2018 - 09:00 AM

Scattering from microbubbles are visible with incoherent light too, a beam from a bright lamp will suffice. This effect tends to be much worse for fluorophosphate glass compared to the highest quality matching crown glass or calcium fluoride, the latter group tends to have much higher homogenity and lower inclusions.

Do we have any evidence the scatter from microbubbles has any visible effect on the image? Telescope objective are rather simple, usually having only two or three elements. The consumer world includes much more complex optical systems, camera lenses, binoculars, and spotting scopes with built in erecting systems. These have increasingly used fluor-crown glasses and are often used under much brighter conditions than astronomical telescopes.

 

Modern binoculars, spotting scopes, and the increasingly complex eyepieces available for telescopes, in spite of their complexity, offer detailed, high contrast views. Modern camera lenses perform well. 

 

Clear skies, Alan


Edited by Alan French, 10 September 2018 - 09:01 AM.

  • 25585 likes this

#234 SandyHouTex

SandyHouTex

    Fly Me to the Moon

  • *****
  • Posts: 5,103
  • Joined: 02 Jun 2009
  • Loc: Houston, Texas, USA

Posted 10 September 2018 - 09:39 AM

OK. So how do you decide the difference is caused by the use of fluorite and its lack of scatter I the FS-152?  You have other significant differences in the two scopes.

 

Using the same eyepiece means you are using almost half again as much magnification (49% increase) in the FS-152 than in the TSA-102. Your object and any glow from scatter cover a larger part of the field. 

 

The FS-152 has four air to glass surfaces while the TSA-102 has six. They are different designs and may vary in how scattered light ends up in the focal plane.

 

There may be differences depending on which lens is cleanest.

 

As I mentioned before, I did the laser test with my fluorite triplet. The beam is faint within the two outer glass elements. It is brighter and more obvious at the two air to glass surfaces. The beam is also brighter at where it passes from glass to fluorite and fluorite to glass, although not as much as at the air to glass surfaces. 

 

I have no doubt you see a difference in scatter. I just think you are too quick to conclude it is because of the lack of scatter within the fluorite. There are too many other possibilities, and more than one may increase the scatter in the TSA-102.

 

Clear skies, Alan

One of the things I've learned as a Mechanical Engineer for a large government aerospace organization is that you cannot dispute actual, empirical evidence.  But go ahead and keep trying.  You are free to believe whatever you want too.


Edited by SandyHouTex, 10 September 2018 - 09:40 AM.

  • doctordub, Jeff B, Fomalhaut and 1 other like this

#235 Jeff B

Jeff B

    Fly Me to the Moon

  • *****
  • Posts: 7,156
  • Joined: 30 Dec 2006

Posted 10 September 2018 - 09:51 AM

Over the years I've enjoyed incredible planetary views in Newtonians, apochromats, Mak-Casses, and Mak-Newts. The biggest three factors, by far, have been aperture, high quality optics, and steady skies.

 

Clear skies, Alan

Amen, and I'd like to add, thermally stable and collimated (especially for the ones with mirrors).

 

Jeff



#236 peleuba

peleuba

    Mercury-Atlas

  • *****
  • Posts: 2,627
  • Joined: 01 Dec 2004
  • Loc: North of Baltimore, MD

Posted 10 September 2018 - 10:03 AM

 

As I mentioned before, I did the laser test with my fluorite triplet. The beam is faint within the two outer glass elements. It is brighter and more obvious at the two air to glass surfaces. The beam is also brighter at where it passes from glass to fluorite and fluorite to glass, although not as much as at the air to glass surfaces. 

 

 

The picture below of my TEC160FL and the green laser test highlights (what I think is) exactly what you are saying vis-a-vis behavior of the laser.  

 

Agree that you cannot really determine what the causes the lack of scatter between the telescopes.

Attached Thumbnails

  • TEC160FL 009.JPG


#237 Jeff B

Jeff B

    Fly Me to the Moon

  • *****
  • Posts: 7,156
  • Joined: 30 Dec 2006

Posted 10 September 2018 - 10:09 AM

One of the things I've learned as a Mechanical Engineer for a large government aerospace organization is that you cannot dispute actual, empirical evidence.  But go ahead and keep trying.  You are free to believe whatever you want too.

Good point Sandy and we would say "Never be afraid of the data.  We may not like it, but it's there to help us".  But we would still argue over how the data was taken and what it meant.  In other words, the validity of the test or how the data was gathered and its consequences on what we were trying to achieve.  

 

Also I have found there is subjective data too that's completely valid.  I saw on-axis coma, for example.  I can't say precisely how much was there in terms of a wave front number, or, importantly, its source, but I did indeed observe it.  

 

Nice discussions and one of these days, I'm going to have to actually live with a fluorite refractor.

 

Jeff 



#238 Fomalhaut

Fomalhaut

    Surveyor 1

  • -----
  • Posts: 1,763
  • Joined: 16 Aug 2008
  • Loc: Switzerland

Posted 10 September 2018 - 01:54 PM

When it comes down to belief, then
I sincerely do believe Takahashi has the closest access to Canon-Optrons (longest and most advanced) experience world-wide to produce the purest-possible Fluorite blanks and the most refined techniques of grinding, polishing and coating those blanks to a paramount quality-level.

All the others (except Vixen and Borg, who seem to have found their own access to Canon-Optron) still have to do a lot of work developing their own way to an Optron-like level of highest Fluorite-Art.
Unless they would also be supplied by that Japanese Company which however obviously doesn't sell their objectives to everybody abroad...

And this high quality is clearly visible to me and hence also distinguishable, period.

Amen


Edited by Fomalhaut, 11 September 2018 - 05:31 AM.

  • doctordub and Erik Bakker like this

#239 Alan French

Alan French

    Night Owl

  • *****
  • Posts: 6,041
  • Joined: 28 Jan 2005
  • Loc: Upstate NY

Posted 10 September 2018 - 02:17 PM

One of the things I've learned as a Mechanical Engineer for a large government aerospace organization is that you cannot dispute actual, empirical evidence.  But go ahead and keep trying.  You are free to believe whatever you want too.

You have observed that there is less scatter in your FS-152 than in your TSA-102, so you have one piece of evidence saying the 152 has less scatter than the TSA-102. 

 

If you're claiming the reduced scatter is due to the use of fluorite in the FS-152, I'd like to know how you came to that conclusion, 

 

Clear skies, Alan


Edited by Alan French, 11 September 2018 - 01:05 PM.


#240 HARRISON SCOPES

HARRISON SCOPES

    Vendor-Harrison Telescopes

  • *****
  • Vendors
  • Posts: 614
  • Joined: 05 Nov 2006
  • Loc: The Garden of England

Posted 10 September 2018 - 02:34 PM

Doublets have less scatter than triplets in like for like designs. Simple.

Then take out the diagonal and there will less again!

Edited by HARRISON SCOPES, 10 September 2018 - 02:35 PM.

  • Alan French and Jeff B like this

#241 Peter Besenbruch

Peter Besenbruch

    Fly Me to the Moon

  • *****
  • Posts: 7,446
  • Joined: 21 Aug 2014
  • Loc: Oahu

Posted 10 September 2018 - 03:07 PM

Over the years I've enjoyed incredible planetary views in Newtonians, apochromats, Mak-Casses, and Mak-Newts. The biggest three factors, by far, have been aperture, high quality optics, and steady skies.

What was that last one again? ;)


  • Jeff B likes this

#242 Paul G

Paul G

    Cosmos

  • *****
  • Posts: 9,022
  • Joined: 08 May 2003
  • Loc: Freedonia

Posted 10 September 2018 - 04:20 PM

You have observed that there is more scatter in your FS-152 than in your TSA-102, so you have one piece of evidence saying the 152 has less scatter than the TSA-102. 

 

If you're claiming the reduced scatter is due to the use of fluorite in the FS-152, I'd like to know how you came to that conclusion, 

 

Clear skies, Alan

IIRC, Yuri, who makes scopes with both types of glass, says the difference in scatter is not visible at the eyepiece.


  • peleuba likes this

#243 payner

payner

    Vanguard

  • *****
  • Posts: 2,177
  • Joined: 22 Mar 2007
  • Loc: Bluegrass & Cumberland Valley Regions, Kentucky

Posted 10 September 2018 - 05:10 PM

The sound you just heard is the TAK FS crowd pounding away at the keyboard Googling for something/anything that would dispute this.

Hi Paul: Not poor me; I'm quite happy observing and enjoying my FS refractors, including the one I fortunately picked up from you.  With the views and enjoyment I get from these telescopes I require no validation elsewhere.  Happy with them, even when compared to others.

 

Randy


  • doctordub and 25585 like this

#244 peleuba

peleuba

    Mercury-Atlas

  • *****
  • Posts: 2,627
  • Joined: 01 Dec 2004
  • Loc: North of Baltimore, MD

Posted 10 September 2018 - 07:41 PM

Hi Paul: Not poor me; I'm quite happy observing and enjoying my FS refractors, including the one I fortunately picked up from you.  With the views and enjoyment I get from these telescopes I require no validation elsewhere.  Happy with them, even when compared to others.

 

 

Randy - Hope your well.   That was a fun day meeting you, having lunch and saying goodbye to my FS152.   I think that was nearly 10 years ago...  The FS152 was the telescope that showed me what 6" of unobstructed aperture can do.

 

My comment was absolutely not directed at you and was written tongue-in-cheek.  Nevertheless, there are a few of the "Fluorite Always/Fluorite Forever" believers who, probably, are not thrilled that the scatter in the mating elements can wipe out any benefit that a reduction in scatter using Fluorite may offer. 

 

Anyway, my comment was an attempt to make folks laugh.  Hope it worked.

 

Best Regards.


  • payner likes this

#245 payner

payner

    Vanguard

  • *****
  • Posts: 2,177
  • Joined: 22 Mar 2007
  • Loc: Bluegrass & Cumberland Valley Regions, Kentucky

Posted 10 September 2018 - 09:26 PM

Paul: That was a fun day driving up to WV to purchase the FS-152.  It was pleasant meeting someone in person to make this purchase, having lunch and talking about telescopes and eyepieces.  It will be 10 years this next February; hard to believe how the time has seemingly flown by.  Well, I meant what I said, I feel fortunate to have made the purchase before someone else snatched it up.

 

No offense taken.  It is sometimes with a chuckle that I read some of the posts, and could see the humor in yours.  With the fine telescopes virtually everyone has that participates on these forums we are all a fortunate bunch, and truly splitting minuscule hairs which can become humorous in itself when one puts it in this context.  But that is what transpires with a group of folks in any subject matter that is a passion.

 

Hope you are doing well, too.  Keep enjoying the hobby.

 

Best wishes,

Randy



#246 X3782

X3782

    Mariner 2

  • -----
  • Posts: 242
  • Joined: 11 Jun 2018
  • Loc: ---

Posted 11 September 2018 - 02:45 AM

Do we have any evidence the scatter from microbubbles has any visible effect on the image? Telescope objective are rather simple, usually having only two or three elements. The consumer world includes much more complex optical systems, camera lenses, binoculars, and spotting scopes with built in erecting systems. These have increasingly used fluor-crown glasses and are often used under much brighter conditions than astronomical telescopes.

 

Modern binoculars, spotting scopes, and the increasingly complex eyepieces available for telescopes, in spite of their complexity, offer detailed, high contrast views. Modern camera lenses perform well. 

 

Clear skies, Alan

 

"Fluor-crown" is a term that existed for > century and doesn't refer to any particular composition of material. We are instead speaking of quite modern and specific materials like FPL-53 and FPL-55. Scatter in glass does decrease contrast and was a major reason why CaF2 was used in the past (e.g., consumer lenses in the 1970's despite the high cost); as better replacement glass material grades with less inclusions and scattering centers have been gradually introduced over the last decades, they have been more widely adopted in place of CaF2. It is a gradual evolutive process you see. If you want to argue that "now I subjectively see no difference between CaF2 and the latest FPL-5X offerings", that's a matter of personal opinion. 25 years ago with the material quality available at that time you may have felt differently, 25 years from now you will also feel differently as the material quality will steadily improve. Objectively a measuring device will observe more or less bulk scattering, whether the light source is coherent or incoherent. The probability of this scattering is not incident-light intensity dependent because it is a linear process.


Edited by X3782, 11 September 2018 - 03:11 AM.


#247 LewisM

LewisM

    Surveyor 1

  • *****
  • Posts: 1,737
  • Joined: 23 Jan 2013
  • Loc: Somewhere in the cosmos...

Posted 11 September 2018 - 05:13 AM

Fluorite is junk for this junky :)

 

Recently traded my only ED glass 'scope for it's older fluorite equivalent.



#248 25585

25585

    Voyager 1

  • *****
  • Posts: 10,361
  • Joined: 29 Aug 2017
  • Loc: In a valley, in the UK.

Posted 11 September 2018 - 05:24 AM

The Baader CaF2 Travel Companion is more expensive than a Tak or Borg or Vixen for 90 - 100 class.

 

Is there a special reason such as optical or OTA component for its cost? The TV NP101 costs more but it's more intricate optically.



#249 nicknacknock

nicknacknock

    A man of many qualities, even if they are mostly bad ones

  • *****
  • Administrators
  • Posts: 14,502
  • Joined: 20 Feb 2012
  • Loc: Nicosia, Cyprus

Posted 11 September 2018 - 06:02 AM

Usual Tak / Borg / Vixens in 90 to 100mm are doublets. The Baader is a triplet.

 

Also, labor cost in Europe are much higher, resulting in a much more expensive scope. Still much more expensive relative to other brands. Here's a quick price comparison.



#250 garret

garret

    Surveyor 1

  • ****-
  • Posts: 1,649
  • Joined: 26 Jul 2009
  • Loc: Netherlands

Posted 11 September 2018 - 11:48 AM

 

Usual Tak / Borg / Vixens in 90 to 100mm are doublets. The Baader is a triplet.

 

Also, labor cost in Europe are much higher, resulting in a much more expensive scope. Still much more expensive relative to other brands. Here's a quick price comparison.

Despite high price there is a very long waiting list for the Baader: they don't even accept new pre-orders!

https://www.baader-p...-companion.html

 

AP put you on a 10 year waiting list...


Edited by garret, 11 September 2018 - 11:50 AM.



CNers have asked about a donation box for Cloudy Nights over the years, so here you go. Donation is not required by any means, so please enjoy your stay.


Recent Topics






Cloudy Nights LLC
Cloudy Nights Sponsor: Astronomics