Telescope Reviews: Biconvex lenses with high focal ratio, for sale

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.imageshack.us/img717/7834/lentilad40mmbk7prezgene.jpg
Ronchi tests: http://img811.imageshack.us/img811/1826/ronchitestlentile13567c.jpg
Airy disc, crop100%, unprocessed: http://img844.imageshack.us/img844/5671/steaartificiala58mcr100.jpg
From "A to Z": http://img98.imageshack.us/img98/7650/metamorfozaprismelorfor.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.imageshack.us/img29/1992/lentila1testrlunetajpg.jpg
Airy disc, crop100%, unprocessed: http://img809.imageshack.us/img809/1469/steaartificiala241md28m.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.imageshack.us/img585/8504/lenochelarid32mmf1320mm.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.imageshack.us/img809/7715/imagine003redjpg.jpg
Biconvex (my lens): http://img171.imageshack.us/img171/6779/imagine010cr100l2455pxr.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.imageshack.us/img687/4930/lentilad60mmf5400mmjpg.jpg
The 18 feet long refractor (in provisional form): http://img717.imageshack.us/img717/243/lunetasimpletd60mmjpg.jpg
Moon, afocal set-up: http://img109.imageshack.us/img109/9518/luna4imglunetad60mmjpg.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.imageshack.us/img13/2961/img5348cr.jpg
Ronchi tests using a distant terrestrial light source, wire thickness=0.11mm, inside-focus:
http://img689.imageshack.us/img689/5992/testerlentiled40f2400mm.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.imageshack.us/img267/2444/obtinereadiscurilorjpg.jpg
http://img196.imageshack.us/img196/1158/etapedeslefuirejpg.jpg
http://img585.imageshack.us/img585/8164/sdvurijpg.jpg
http://img534.imageshack.us/img534/5558/transparentalafinalulsl.jpg
http://img534.imageshack.us/img534/3710/polisareajpg.jpg
http://img407.imageshack.us/img407/3364/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