On Jun 18, 2012, at 12:22 PM, Igor Roshchin wrote: > > Larry, sorry... that can be easily looked up in the PDML archives, > (that's how I am reading the list anyway), - as Godfrey posted only one > response. > > Here it is: > http://www.a-p-s.org.au/pdfs/articles/macro.pdf > As I wrote, - the interesting thing is the formalism for exposure > at high magnifications (p13 of the PDF, p.12 of the paper).
I had known about the effect of losing light at higher magnification. I had seen it mentioned and realized that it made sense that as you are using less and less of the image field and you are exposing the sensor (film) with less light. The mention of diffraction is also interesting because it effectively describes diffraction as a ratio of edge to area, which is something that I've always suspected. Specifically: Non-imaging forming rays are those that are not affected by the optics, but rather, are bent by diffraction as they pass near a knife-edge (the aperture).There will always be a percentage of diffracted rays. The compromise is to keep the image forming rays at a high percentage and the diffracted rays at a much lower percentage. In high magnification photography, this is a challenge. This makes me wonder if there were some way to design an aperture so that there was no knife edge. Perhaps a curved coating of sapphire on the edge of the blade so that it became progressively more opaque over the distance of several wavelengths of light. -- Larry Colen [email protected] sent from i4est -- PDML Pentax-Discuss Mail List [email protected] http://pdml.net/mailman/listinfo/pdml_pdml.net to UNSUBSCRIBE from the PDML, please visit the link directly above and follow the directions.
