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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.






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