Glenn Kroeger
15-Oct-2000, 14:37
Although I understand theoretical (simple) optics, I need some info on practical optics.
I understand that wide angle formula's, like biogon derived optics, use pupillar y expansion to achieve better off axis illumination. My question is can this tec hnique beat the 1-cos^4 law, and if so, there must be some expense in distortion .
I have an old Rodenstock catalog, dated 4/89, that shows the illumination of a 7 5mm f/4.5 Grandagon-N. This graph shows illumination at f/11 and f/16 exceeding the 1-cos^4 law at off axis positions for about the outer 2/3 of the image circl e.
A current Rodenstock data sheet on Grandagons shows illumination for the same le ns as becoming asymptotic to the 1-cos^4 law, but not exceeding it across the im age circle.
The only apparent difference between the graphs is that the latter is at 1:30 wh ere the former is at 1:infinity magnification.
I don't think Rodenstock have change the lens, and certainly they wouldn't chang e it to reduce off-axis illumination.
So is the first graph simply in error, and lenses can't beat the 1-cos^4 law, ev en with this optical "trick"?
I understand that wide angle formula's, like biogon derived optics, use pupillar y expansion to achieve better off axis illumination. My question is can this tec hnique beat the 1-cos^4 law, and if so, there must be some expense in distortion .
I have an old Rodenstock catalog, dated 4/89, that shows the illumination of a 7 5mm f/4.5 Grandagon-N. This graph shows illumination at f/11 and f/16 exceeding the 1-cos^4 law at off axis positions for about the outer 2/3 of the image circl e.
A current Rodenstock data sheet on Grandagons shows illumination for the same le ns as becoming asymptotic to the 1-cos^4 law, but not exceeding it across the im age circle.
The only apparent difference between the graphs is that the latter is at 1:30 wh ere the former is at 1:infinity magnification.
I don't think Rodenstock have change the lens, and certainly they wouldn't chang e it to reduce off-axis illumination.
So is the first graph simply in error, and lenses can't beat the 1-cos^4 law, ev en with this optical "trick"?