Open Photography Forums  
HOME FORUMS NEWS FAQ SEARCH

Go Back   Open Photography Forums > Photography Discussions > Medical-Forensic-Scientific-Legal-etc

Reply
 
Thread Tools Display Modes
  #1  
Old October 30th, 2010, 09:53 AM
Doug Kerr Doug Kerr is offline
Senior Member
 
Join Date: May 2006
Location: Alamogordo, New Mexico, USA
Posts: 8,321
Default Vision correction and some associated instruments - three new techncial articles

After photographic lenses, the lenses with which most of us here are most likely to be interested are vision correction (eyeglass) lenses. It is a fascinating field, with its own language and tools.

I will shortly publish on my technical information site, The Pumpkin, a trio of technical articles relating to this field. They are now available directly, via the links below (they will be indexed on The Pumpkin presently).

The first in the series, "Principles of Eyeglass Prescriptions", is available here:

http://dougkerr.net/Pumpkin/articles...scriptions.pdf

It describes the way in which the optical parameters of an eyeglass lens are specified in a "prescription". Included is a discussion of the fact that two different classes of prescribing daycare professionals, ophthalmologists and optometrists, use different conventions for this.

The article begins with background on such related issues as lens focal length and power, the focusing of the human eye, and deficiencies in that, and how those deficiencies are mitigated by corrective lenses.

The next article, "The Refractor/Phoropter—An Important Tool in Vision Correction", is available here:

http://dougkerr.net/Pumpkin/articles/Refractor.pdf

It discusses the refractor (often called phoropter, although Phoropter is actually a tradename of one manufacturer), the mask-like instrument with many dials used to determine the optimum prescription for corrective lenses for an individual.

As with the first article, we being with a review of important background principles (I wanted each article to stand on its own). Then the principle, and mode of operation, of the refractor are described.

The third article, "The Focimeter—Measuring Eyeglass Lenses", is available here:

http://dougkerr.net/Pumpkin/articles/Focimeter.pdf

The focimeter (often called a lensometer or vertometer, although Lensometer and Vertometer are tradenames of two manufacturers) is the microscope-looking instrument used to ascertain the optical parameters ("prescription") of eyeglass lenses or (as required in the making of eyeglasses) of partially-completed lenses. One interesting recent casus belli is described in the footnote on page 1 of the article.

Again, this article begins with essentially the same background material mentioned above.

Then, the basic nature of the instrument is described, following by an discussion of its operation and use. Its optical innards, and some basic theory of their functioning, are explained in an appendix.

All three articles are laced with historical and societal curiosities. A great deal of both technical and historical research (both some months ago and over the last two weeks) went into the project, and I'm pooped.

But the bravest service was by Carla, my ace copyeditor, who had to find all the lost prepositions, disagreements in number, and mismatched parentheses that peppered this magnum opus in manuscript. But she said there was a lovely poetry in some of the technical terms and phrases.

Best regards,

Doug
Reply With Quote
  #2  
Old November 2nd, 2010, 07:02 AM
Doug Kerr Doug Kerr is offline
Senior Member
 
Join Date: May 2006
Location: Alamogordo, New Mexico, USA
Posts: 8,321
Default

The third article in the series announced above, "The Focimeter—Measuring Eyeglass Lenses", has just been reissued, extensively expanded and revised, This new issue includes much additional detail on the internal working of the instrument, and a new appendix describes some of the technical and commercial history of the instrument and gives photographs of some additional models.

The article is available at the same URL as before:

http://dougkerr.net/Pumpkin/articles/Focimeter.pdf

Best regards,

Doug
Reply With Quote
  #3  
Old November 12th, 2010, 10:44 AM
Doug Kerr Doug Kerr is offline
Senior Member
 
Join Date: May 2006
Location: Alamogordo, New Mexico, USA
Posts: 8,321
Default

The three technical articles in the field of corrective lenses and the associated instruments have all now been substantially enlarged and updates. In addition, a fourth article, on an important technical concept in this field, the vertex power of a lens, has been added.

These new or updated articles are all published today (2010.11.12) in honor of the 11:5 (11 years, 5 months) anniversary of my wedding to Carla. I think she will regard the "finishing" of this project as a worthy gift.

The four articles are described here:

Lenses for vision correction are specified (in a "prescription") using a specialized optical notation. This notation is explained in the article, "Principles of Eyeglass Prescriptions", available directly here:

http://dougkerr.net/Pumpkin/articles...scriptions.pdf

In the area of vision correction lenses, the major optical property of the lens is its power, which however is specified in a different way than in most optical engineering work. This system of notation, and the rationale for its use, are explained in the article, "The Vertex Power of Ophthalmic Lenses", available directly here:

http://dougkerr.net/Pumpkin/articles/Vertex_Power.pdf

The specifications ("prescription") for corrective lenses are most often determined by the prescriber (an ophthalmologist or optometrist) using an instrument called a refractor (often, "phoropter", although "Phoropter" is a trademark). This fascinating instrument is described in the article "The Refractor/Phoropter—An Important Tool in Vision Correction", available directly here:

http://dougkerr.net/Pumpkin/articles/Refractor.pdf

The optical parameters of a completed eyeglass lens, or of a partially completed lens "blank", are often determined with an instrument called a focimeter (often "Lensometer" or "Vertometer", both trademarks). This fascinating instrument is described in the article, "The Focimeter—Measuring Eyeglass Lenses", available directly here:

http://dougkerr.net/Pumpkin/articles/Focimeter.pdf

I hope some of you may find these extensively-illustrated articles of interest.

Best regards,

Doug
Reply With Quote
  #4  
Old November 12th, 2010, 11:03 AM
Doug Kerr Doug Kerr is offline
Senior Member
 
Join Date: May 2006
Location: Alamogordo, New Mexico, USA
Posts: 8,321
Default

For those who missed it in its first appearance, here is Carla observing through our Bausch & Lomb "Model 70" Vertometer (a focimeter):


Douglas A. Kerr:
Carla Kerr at the B&L "Model 70" Vertometer, vintage 1963

Her attire and pose were meant to follow a classical 1921 American Optical Company advertising photo.

Best regards,

Doug
Reply With Quote
Reply

Bookmarks

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are Off
[IMG] code is On
HTML code is Off

Forum Jump


All times are GMT -7. The time now is 05:37 PM.


Posting images or text grants license to OPF, yet © of such remain with its creator. Still, all assembled discussion © 2006-2017 Asher Kelman (all rights reserved) Posts with new theme or unusual image might be moved/copied to a new thread!