Magnfying Glass Lens
Posted 15 May 2015 - 08:22 PM
Posted 15 May 2015 - 10:02 PM
A magnifying glass IS a lens. They are usually double convex in shape.
The hand-held type usually don't magnify more than around two times, so the
focal length is probably around five inches.
Infinity focus will be roughly one focal length away from the lens. The closer you get to a
subject, the further you must move the lens away from the film plane or viewing screen to hold sharp focus.
You can fashion a crude barrel out of cardboard and make it slip snugly into another cardboard sleeve
to make a focusing mount.
A simple lens of this type will suffer from a variety of aberrations, which will result in a soft, imperfect image.
If you want to improve its performance, you will have to make a cardboard stop with an opening much smaller
than its full diameter. Do some research on simple optics and you will understand the principles better.
Edited by dan kessler, 15 May 2015 - 10:03 PM.
Posted 16 May 2015 - 07:11 AM
Here you go.
A view out of my office window of a nursery across the road. It doesn't get much charper.
This is without any lens barrel at all.
<a href="http://s5.photobucke...09245.jpg.html"target="_blank"><img src="http://i5.photobucket.com/albums/y180/markrhdunn/DSC09245.jpg~original" border="0" alt=" photo DSC09245.jpg"/></a>
Edited by Mark Dunn, 16 May 2015 - 07:15 AM.
Posted 16 May 2015 - 07:38 PM
In the early days of photography, virtually all lenses were basically just high quality magnifying glasses with a moveable mounting so they could be focussed (usually the accordion-like structure made out of black rubberized cardboard that you see on vintage cameras).
The "focal length" was simply the distance the lens had to be from the film plane to focus at infinity. So a "50mm" lens had to be 50mm (about 2 inches) from the film plane and so on. With layer multi-element lenses this distance could be drastically shortened, making the lenses much more compact, but the convention was retained, meaning a "50mm" multi-element lens would behave optically like a (much larger) 50mm single-element lens.
The front elements out of binoculars are often surprisingly high quality multi-layer lenses. People sometimes use them to get extremely shallow depth of field effects (often to make people look like animated dolls and so on), by making a "camera obscura" type device with a large image area, and then filming just a small part of the image.