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Biconvex lenses with high focal ratio, for sale

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#1 Tavi F.

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Posted 18 October 2012 - 03:29 PM

Main purpose: singlet lens objective for building a 17th century style non-achromatic refractor.
Glass used: BK7 and float soda-lime ("plate glass").

All the lenses are handmade, grinded and polished individual, and those on BK7 substratum comes with a Ronchi test certificate. Diffraction limited.

A. Optical glass BK7 lenses
Type 1. Specifications:

- focal length (nominal) in G-channel: F = 2400mm (+10/-5mm);
- total diameter: Dt = ~49.5mm;
- center thickness: tc = ~8mm;
- high precision optical diameter: Duseful = 40mm;
- relative opening ("focal ratio"): N = F/Du = 60;
- the chromatic aberration coefficient: x = N/Du = 1.5
General: http://img717.images...bk7prezgene.jpg
Ronchi tests: http://img811.images...ntile13567c.jpg
Airy disc, crop100%, unprocessed: http://img844.images...ala58mcr100.jpg
From "A to Z": http://img98.imagesh...rismelorfor.jpg

PRICE for one lens = 25 euro.
Two lenses are still available (no.1&3).

For a more attractive offer, I add a second smaller BK7 lens (type 2) in the package:
Type 2. Specifications:
- focal length in G-channel: F = 1250mm;
- total diameter: Dt = ~35mm;
- center thickness: tc = ~6.5mm;
- high precision optical diameter: Duseful = 28mm;
- relative opening ("focal ratio"): N = F/Duseful = 44.64;
- the chromatic aberration coefficient: x = N/Duseful = 1.59
General: http://img29.imagesh...trlunetajpg.jpg
Airy disc, crop100%, unprocessed: http://img809.images...ala241md28m.jpg
(notice the Airy disc; USlim means the resolving power)

PRICE [lens D28mm + lens D40mm] = 30 euro.

As a divagation, here is a Ronchi test (made two years ago, using the same screen) for a meniscus lens, F=1320mm. At that moment, the commercial lens was stopped at 32mm.
http://img585.images...32mmf1320mm.jpg
Just below are some more recent comparative pictures, entrance pupil: 28mm for both lenses (which were mounted on the same refractor).
Meniscus (commercial): http://img809.images...ne003redjpg.jpg
Biconvex (my lens): http://img171.images...100l2455pxr.jpg
The images speak for themselves!

B. Soda-lime glass, float "plate glass"
The glass of these lenses is ordinary plate glass, but the initial tests (by checking the plate in front of a concave mirror) had shown me a good optical homogeneity of the material.
Type 1'. Specifications:
- focal length (nominal) in G-channel: F = 5400mm (+100/+20mm);
- total diameter: Dt = ~69.5mm;
- center thickness: tc = ~7.5mm;
- high precision optical diameter: Duseful = 60mm;
- relative opening ("focal ratio"): N = F/Du = 90;
- the chromatic aberration coefficient: x = N/Du = 1.5
General: http://img687.images...mf5400mmjpg.jpg
The 18 feet long refractor (in provisional form): http://img717.images...letd60mmjpg.jpg
Moon, afocal set-up: http://img109.images...etad60mmjpg.jpg

PRICE for one lens = 23 euro.
Four lenses are available.

Type 2' (practical, these lenses gives the same image quality as the BK7 version).
Specifications:
- focal length (nominal) in G-channel: F = 2400mm (+10/-5mm);
- total diameter: Dt = ~49.3mm;
- center thickness: tc = ~7mm;
- high precision optical diameter: Duseful = 40mm;
- relative opening ("focal ratio"): N = F/Du = 60;
- the chromatic aberration coefficient: x = N/Du = 1.5
General: http://img13.imagesh...1/img5348cr.jpg
Ronchi tests using a distant terrestrial light source, wire thickness=0.11mm, inside-focus:
http://img689.images...ed40f2400mm.jpg
(This is just the final validation test, for the viewers. I also did another indoor optical test, during polishing, to establish the necessary strokes adjustments for both D40 and D60mm lenses.)
A few images which illustrates the manufacturing stages:
http://img267.images...scurilorjpg.jpg
http://img196.images...slefuirejpg.jpg
http://img585.images...4/sdvurijpg.jpg
http://img534.images...lafinalulsl.jpg
http://img534.images...olisareajpg.jpg
http://img407.images...img4645mod3.jpg

PRICE for one lens = 18.5 euro.
Six lenses are available.

Special offers:
PRICE [lens D40mm + lens D60mm] = 35 euro.
PRICE for two lenses D40mm = 32 euro.


Note: to all effective prices, I will add the shipping cost and the PayPal fee.
For more information, please contact me at e-mail: tavi.florian@gmail.com

#2 Ira

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Posted 18 October 2012 - 05:07 PM

Stupid question. Are there any plans that might show how to build a 17th century-style telescope from these lenses? I'd love to try.

/Ira

#3 Tavi F.

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Posted 19 October 2012 - 03:07 AM

Here, on CN, is at least another subject on making the 17th century style refractors:
http://www.cloudynig...5/o/all/fpart/1
(I have posted some thoughts there)

At the following link, you can see a good article about medium sized non-achromatic refractors:
http://www.jdso.org/...r4/binder47.pdf

A brief history of refracting telescope (including images):
http://www.aip.org/h...-telescopes.htm
- Hevelius, 60 feet telescope - http://cnx.org/conte...escope_60ft.gif
- Huygens's tubeless telescope - http://cnx.org/conte...l_telescope.gif

Beyond the optical components, for a (precise) mechanical replica the main materials should be wood, ropes and paper (cardboard).
- In case of relative short focal lengths (up to 2 or 2.5 meters), we may consider the Galileo's solid primary tube + the focusing eyepiece tube.
http://galileotelescope.org/
- For longer focus objectives, we may chose:
1. the telescopic solution (2..4 segments);
http://cnx.org/conte...s_telescope.gif
2. long and solid wooden tube, like Alan Binder's replica;
3. or simply tubeless design, Huygens style.
The simplest ocular is a Kepler eyepiece (a single plan-convex lens), but the better one is a Ramsden or Huygens evolution.

Hopefully, these links are useful to get some ideas.

L.E.: Pics with my D28mm and D40mm refractors:
- D28mm: http://img209.images...td28mmf1250.jpg
- D40mm (in action): http://img542.images...td40mminobs.jpg
and the lens cell http://img838.images...lasimpletd4.jpg

#4 Tavi F.

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Posted 24 October 2012 - 01:25 PM

A region of the Moon, 23rd oct. Picture taken through the D40mm (plate glass) refractor + Plossl f25mm eyepiece + Canon A530 (movie mode) with its objective set at 23.2mm f.l.
800 frames stacked and processed, single point alignment:

Posted Image

#5 Tavi F.

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Posted 07 December 2012 - 08:17 AM

New offers available only this month, until the end of the year:

BK7 lenses:
- PRICE [lens D28mm + lens D40mm] = 26 euro.

Plate glass lenses:
- PRICE [lens D40mm + lens D60mm] = 30 euro.
- PRICE two lenses D40mm = 28 euro.

Note: to all effective prices, I will add the shipping cost and the PayPal fee.

Happy holidays!

P.S.: A brighter version of the previous photo (+ other details):
http://img805.images...0mm800cmod3.jpg

#6 Tavi F.

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Posted 12 June 2013 - 11:25 AM

Update: All the D40mm/BK7 lenses were sold out (three of them in my home country; two worldwide- Italy and USA). But I still have some D40mm/plate glass lenses and also the largest singlet objective made by me, D60mm.

Here is the new price list:

Unit price:
1. - lens D40mm, F2400mm = 16.5 euro;
2. - lens D60mm, F5400mm = 21 euro.

Prices for sets of two lenses:
1. - [lens D40mm+lens D60mm] = 28 euro;
2. - [two lenses D40mm] = 26 euro.
3. - I can add a 3rd lens (the D28mm/BK7 lens) for a 5 extra euros, at each set. Two D28mm lenses are still available.

Note: to all effective prices, I will add the shipping cost and the PayPal fee.
*********

And now I want to study the myth of allowable "loose tolerances in long focus singlet lenses". Bi-convex shape vs. meniscus. I started from a particular glasses lens which I own. This lens has R2=106mm and a focal length F=~1300mm, and so it resulted the remaining data. I don't know any other largely available source of meniscus convergent lenses, but the glasses.
Useful (imposed) aperture, D=30mm.

See the OSLO print-screens:
A. Biconvex lens: http://www.astronomy...mm_f1300mm_5...
Residual spherical aberration is lambda/248 PV wavefront at best focus.

B. Meniscus lens:
http://www.astronomy...f1300mm_588n...
Residual spherical aberration of the glasses meniscus is lambda/2.2 PV wavefront at best focus!! So, even a perfect executed meniscus will "perform" below the Rayleigh (L/4) criterion!

Back to real life:
More pictures taken in afocal set-up, unprocessed:
A. Biconvex lens, D28mm; F1250mm:
http://img850.images...rtfbiconvex.jpg
B. Meniscus lens, D28mm; F1310mm:
http://img703.images...rtfmeniscjp.jpg

Artificial stat tests:
A. http://www.astronomy...ala_jpg_182.jpg
B. http://www.astronomy...ea_artificia...

~Monochromatic light:
A. http://www.astronomy...a_r_jpg_113.jpg
B. http://www.astronomy...a_r_jpg_856.jpg

A vs. B' - Ronchi test, double pass through the tested lens, autocollimation on a flat mirror:
http://www.astronomy...od2_jpg_136.jpg

B'- the same meniscus before cutting, stopped at D32mm.

#7 Tavi F.

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Posted 05 August 2013 - 10:41 AM

Up!

#8 Tavi F.

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Posted 15 September 2013 - 11:08 AM

Up.

#9 Tavi F.

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Posted 16 November 2013 - 09:43 AM

Up.

New offer: three lenses D40mm = 33 euro.

#10 Tavi F.

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Posted 01 December 2013 - 05:33 PM

New prices for the remaining lenses:

Unit price:
1. - lens D40mm, F2400mm = 11.5 euro;
2. - lens D60mm, F5400mm = 13.5 euro.

Prices for sets of two lenses:
1. - [lens D40mm+lens D60mm] = 23 euro;
2. - [two lenses D40mm] = 21 euro.

#11 Tavi F.

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Posted 02 March 2014 - 11:54 AM

Up.

At the following link is a older capture of the Sun (from 10th of July 2012), taken afocally through the 40mm aperture singlet lens objective:

http://www.flickr.co...in/photostream/

Just 9 frames of each type stacked multipoint in AutoStakkert. These photos being the results of a recent reprocessing using that software.

#12 Tavi F.

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Posted 23 July 2014 - 02:01 AM

Still valid.

#13 Tavi F.

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Posted 15 October 2014 - 02:13 AM

Up.

In order to cut drastically the shipping cost, I can send the lenses in a registered letter.

 

The update from 1st of December 2013 is the lowest selling list price. Even myself think these are cheap, but it's not possible to offer them for nothing (not now or in the near future).
The lenses are not consumable, they last more than a human lifetime!!

 

More information only in PM.
Thanks.

 

LE: Sorry for the lost images hosted on Imageshack. They mix up the links, and seems to be a unreliable site. Some other time, I should post again a few images.


Edited by Tavi F., 15 October 2014 - 11:06 AM.


#14 meade4ever

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Posted 16 October 2014 - 07:56 AM

Do you still offer BK7 lenses ?

 

Can you grind custom lenses w/ much bigger diameter ?



#15 Tavi F.

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Posted 16 October 2014 - 09:31 AM

No, the BK7 lenses were sold out. In my country, it is quite hard to find optical glass (BK7). Probably for the larger and more important projects (achromatic doublets), I will search world wide for much needed glass.

Practically, the modern float glass (soda-lime) is a very proper substrate for singlet lens objectives. No detectable defects, just a tiny light loss through a given aperture. 

 

And for this moment, I do not make custom lenses. Maybe in a distant future. These three types (D28, 40 and 60mm) were designed to fit my personal needs, first of all... and then extended to small production.


Edited by Tavi F., 16 October 2014 - 09:33 AM.


#16 Simon Alderman

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Posted 22 October 2014 - 05:59 PM

Pm'ing you for the 60mm...








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