h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

Entry: Brief History of Optical Lenses - A2805725
Author: radioactiveBIGAL1 - on a different planet - U723247

This is a "Brief History" as it is intended to support another of my Guide entries on Cameras obscura. In that entry I tried to argue that glass lenses would have been available in medieval times to make a camera obscura capable of producing the image on the Shroud of Turin.

Hello, I skimmed over this Entry. Nice so far, I will have a closer look later on.

There are a couple of Entries you might want to link to, IMO:

A666128 (History of optical science)
A397316 (Telescopes)
A712612 (History of optical Microscopy)
A627266 (Photographic Lenses)
A724989 (Microscope Objective Lenses)
A603677 (Adaptive Optics and Laser Stars)

HELL

I'll look at those

Hallo Hell,

I've had a quick look at the references you sent me. I hadn't picked them up before because, although I searched h2g2 for 'lenses', it told me there were no entries. (I had a discussion with someone else yesterday, who experiences the same problem.

I feel that your entries are for much more recent developments than I wanted to cover. Thus, the point of my article was to support a contention that glass lenses could have been available in the 15th Century; to put into a camera obscura to make the image on the Turin Shroud. To make it a cohesive argument, I decided I had to say s'thing about the development of lenses to the present day, but it really focussed (pardon the unintentional pun)on 'materials' rather than optical properties and mathematics. However, there might be something in your 'History of Optical Microscopes' and 'Telescopes' that I can refer to. I'll have a closer look shortly.

In fact, thinking about it, I think I definitely need to make mention of Leeuwenhoek, Hooke and Galilieo

Oh, I was just pointing out the links. I think I understood what your Entry is aiming at. I did not mean to cause the impression that your Entry is overlapping with the other ones, or that your Entry is redundant. I was just pointing out some links in the case there's something in there for you. Keep on writing, you're doing a fine job.

HELL

PS: I *will* have a closer look later on, maybe I'll come up with some suggestions, that could add to your Entry. But then again, it looks pretty complete already.

Hi Hell, Don't worry, I didn't get any false impressions at all. I was very grateful for your comments and I still think that I should say more about (or at least link to)the very important 17thC developments that led to telescopes and optical microscopy.

Hi there,

I think this article is now as complete as I need it to be for the reasons given above.BIGAL

Great entry - short but highly informative.

The only suggestion I can make is of dispensing with the subheader at the top that says 'history', because you have already established in the title that this a history.

Well done.

Done that. In retrospect, can't undersrtand why I had that sub-header there anywayBIGAL

Aspheric lenses - perhaps you are referring to moulded lenses? Ground lenses are invariably spherical because they are so simple to make. The most amazing thing about optics is that if you take two flat discs of hard material and rub them together by hand, using the right method, with some abrasive, you naturally form a nearly perfect spherical surface. In mass production, dozens of lens blanks can be placed on an approximately spherically shaped tool, ground against a matching tool, and each lens will come out with the same spherical surface, because any part of that surface has the same uniform curvature everywhere.

Spherical aberration can be minimized by designs with convex and concave lenses of differing refractive indexes, and also for specific arrangements of spherical lens pairs. Chromatic aberration is minimized using a positive and negative lens of glasses with different dispersions. These lenses fortunately usually also have good correction for spherical aberration. An aspheric lens has no correction for chromatic aberration and has the same or worse off-axis aberrations as a spherical lens. This is why spherical lenses are so common.

So maybe the part about aspherics should come out in hindsight.

I just noticed that the edited guide entry A724989 incorrectly uses the term 'aspheric lens' to mean one that has spherical abberation corrected. Aspheric lenses have non-spherical surfaces. This entry contains several other misleading statements as well.

Hi BigAl

Fascinating and informative

I had a few questions when I read through, and on re-reading found a few typos.

You note that Aristophanes and Senecus mentioned lenses, but not where or in what context. It may not even be relevant, but seems incomplete.

You also note that Roger Bacon is associated with the manufacture of true glass lenses but not how, other than a speculation that he *may* have invented spectacles.

What is 'crown glass'?

This seems a bit run-on >>Prior to the mid-18th Century only crown glass was available, but by 1758, flint glass, which was denser and disperses light into a specrum more strongly, started to become available, enabling the spectacle-maker, John Dolland (1706-1761) to manufacture small 'achromatic' telescopes.<<
Maybe removing some of the commas will fix (I'm usually guilty of this as well, I put commas wherever my brain pauses whether they belong there or not ); try the ones after 1758, 2nd available and spectacle-maker. Also you've used two tenses in your description of flint glass - was denser and disperses - maybe should be 'is denser and disperses...'

Also there's a word missing here >>and only the efforts of a Swiss glass-maker, Pierre Guinand (1748-1824) did a significant improvement occur.<<
Maybe add 'through' after only, or change 'did a significant improvement occur' to 'resulted in significant improvement'.

Are you still planning on adding something about Galilieo?

Shaping up nicely

Thanks for those comments Dr Miloso and Milso. I'll have a think on those points. I agree with the sentence length; it needs a bit of sleeping on to get this right.

I thought about saying s'thing about different types of glaas, but I thought I might write another Guide article on different kinds of glasses.

I had decided not to say anthing about Galileo because I think he just combined didfferent lenses to make telescopes; he didn't develop lenses per se. But perhaps I should say s'thing like "enabled Galileo to...."

BIGAL

For a minute there I was wondering when I became a doctor...

There's no need to add Galilieo if it adds nothing to your entry. I only asked because you said earlier in this thread that you would. If, upon digging, you find that he's not integral to your subject, the entry is fine without.

for that; obviously I meant Dr Memory and Miloso.

Just trying to write s'thing sensible about 'classical times - it's amazing how these projects grow!BIGAL

I think I've addressed most of the points now. I've left the bit in about aspheric lenses, at least for the time being, because it provides the link to spectacles and telescopes which I think is important to mention, even if its a bit of an 'aside'. Also, most sources that I read seems to talk of 'aspheric lenses which I now interpret as meaning they have a 'wavy' surface (and so, I suppose, have to be moulded?). I orginally thought 'aspheric' meant that the surfaces of the lens, whilst being smooth, did not formn the arc of a sphere (i.e. are elliptical)
Hmm, I think there is still the tiniest bit of confusuion in my article, because the sentence contains 'aspheric' and 'elliptical' in the same sentence. You can tell I'm not an optics specialist!
BIGAL

Looking good

In the paragraph about Descartes I spotted 'skilful', should be skillful.

There are still a couple of extra commas in there, maybe you can read through and pause wherever you see a comma to see if they all sound right to you

I think I''ve sorted the comma problem now, so this article is now completeBIGAL

Hi BigAl

Nice entry. I'd suggest a footnote would be helpful after the first mention of burning glass to explain what such a thing is (eg "A burning-glass is a large convex lens which can focus the sun's rays on a small area and so ignite materials." http://encyclopedia.thefreedictionary.com/Burning-glass) "Burning Mirrors" with the same purpose are also known.

typo: specrum > spectrum (just after flint glass mentioned)

In Ancient Lenses be consistent with AD and BC. I believe h2g2 guidelines are to use these abbreviations without full-stops.

Pimmsaloonie