[LargeFormat] Old vs New Glass (was Re: Rapax shutter CLA)

[Les Newcomer]

Clive Warren wrote:
> 
  The 12" Commercial Ektar sitting here is used for some portraiture
> - but not for the female of the species, it's just too truthful :-)


 Yeah I made the mistake early on of doing some available light
portraits, unfortunately there was a whole lot of light available so I
used my f2.8 7.5" aero ektar. <shudder>  Talk about brutally honest!

> Tell me more about zone plates!

At the other end of the spectrum is the zone plate.  From  "pinhole
Photographery Rediscovering a Historic Technique":

A zone plate diffract light, consequently zone plates are closely
related to pinhole photography. Zone plate render soft-focus imgagery,
yet they are not like soft-focus lens imagery. The beauty within a zone
plate image is the recognizable halo or glow that surrounds any strong
contrast edge. this glow occurs becuase light rays are considerably bent
when hitting the edges of the opaque ring within the zone plate*.
Foliage such as green leaves under certain lighting conditions may
resemble infrared imagery.

a zone plate is made of concentric rings about a clear aperture. (think
tiny target) The entire plate (hole) is usually less the 1/8" dia and
made of tech pan or lith film backed by a brass shim.

The images are etherial, ghostly (with people) and quite different than
what is usually stived for in photography.

There are other sites about zone plate that get more technical, but this
one is a start. I have a couple a 240mm and a 190mm. Most people use
them with medium format, thus the picky ness about knowing what focal
length you need. 

Exposure is about 1/7 of a pinhole.   My plates are around f90, and they
do need to be focused, so  spend a summer with these and that Series V
Protar will feel like a Speedic when you get back.

http://www.pinholeresource.com/products.html#zoneplates
http://www.xmission.com/~ralcon/zonequ.html (this one looks painful)
http://www.movingpixel.com/zpgen.html
http://www.pinhole.com/discussion/2000/msg00134.html
http://web.bham.ac.uk/ceu716/mid-term/node13.html
http://dau.ing.univaq.it/~laser/Research/Basopt/Pinhol/Pinhol.htm

Zone plates get used in holography and electron imaging, so a search on
the web will end up with a lot of 'noise' hits
> 

> 
> All the best,
>                  Clive   http://www.f32.net
>                          Large Format Travel and Stock Photography
> 
> _______________________________________________
> LargeFormat mailing list
> LargeFormat@f32.net
> http://www.pairlist.net/mailman/listinfo/largeformat