xkaes
22-Jun-2017, 18:39
I wanted to test the possible/probable light fall-off of my Mamiya Sekor-C 37mm Fisheye f4.5 lens. Since I know there is lots of light fall-off on super-wide-angle lenses, I decided to put it to the test.
And while I was at it, I decided I might as well throw in my other wide-angle lenses, and determine possible issues with them, as well. Here is the list of suspects -- I mean, subjects:
Mamiya Sekor-C Fisheye 37mm f4.5
Schneider-Kreuznach Super Angulon XL 47mm f5.6
Fujinon SWD 75mm f5.6
Fujinon CM-W 105mm f5.6
Fujinon NW 125mm f5.6
Fujinon NW 150mm f5.6
The test gear is an evenly illuminated white wall, a Minolta Autometer II with a Minolta Booster II with a ground glass adapter.
All lenses were tested on a TOKO NIKKI II 4x5 camera with a fresnel and Beattie Intenscreen -- focused at infinity. Here is a photo of the gear:
166393
Clockwise from the lower left are:
Schneider-Kreuznach Super Angulon XL 47mm f5.6
Fujinon SWD 75mm f5.6
Fujinon CM-W 105mm f5.6
Mamiya Sekor-C Fisheye 37mm f4.5
Fujinon NW 150mm f5.6
Fujinon NW 125mm f5.6
The base meter setting was using the 150mm lens at f5.6 with the Booster II adjusted to create an EV rating on the Autometer II of ZERO. As this lens has the largest image circle, I would expect it to show the least amount of light fall-off -- from center to corner -- on the 4x5 image.
The following table summarizes the results. They are, surprisingly, exactly what they should be. All of the lenses showed exactly the same EV reading in the center at f5.6. And all of the lenses showed exactly a three stop drop in the EV reading in the center at f16.
166394
The corner readings are a little more complicated. I would expect light fall-off due to the lens, but also due to the screen. The amount due to the lens should be reduced as the aperture is stopped down. With the 150mm lens, there is a one stop difference from the center to the corner at f5.6. At f16, the expected three EV reduction adds up to an EV change of four stops from the base. I think it is safe to assume that the camera viewing screens are the cause of a one stop drop from center to corner. Anything above one stop is due to the lens.
The 125mm and 105mm lenses each show an additional 1 EV drop in corner illumination at f5.6 -- which is completely gone by f16. This is what I would expect.
The 75mm shows different results. At f5.6, there is only a two EV drop, and an additional 1/2 EV drop on the corners. I attribute the first change to the lens having a different optical design, while the second change can be explained by its wider field of view. The 47mm lenses shows similar, but slightly more significant results.
The big surprise, and what started all this, is that I did not see ANY light fall-off in the fisheye lens -- either wide open or stopped down!
And while I was at it, I decided I might as well throw in my other wide-angle lenses, and determine possible issues with them, as well. Here is the list of suspects -- I mean, subjects:
Mamiya Sekor-C Fisheye 37mm f4.5
Schneider-Kreuznach Super Angulon XL 47mm f5.6
Fujinon SWD 75mm f5.6
Fujinon CM-W 105mm f5.6
Fujinon NW 125mm f5.6
Fujinon NW 150mm f5.6
The test gear is an evenly illuminated white wall, a Minolta Autometer II with a Minolta Booster II with a ground glass adapter.
All lenses were tested on a TOKO NIKKI II 4x5 camera with a fresnel and Beattie Intenscreen -- focused at infinity. Here is a photo of the gear:
166393
Clockwise from the lower left are:
Schneider-Kreuznach Super Angulon XL 47mm f5.6
Fujinon SWD 75mm f5.6
Fujinon CM-W 105mm f5.6
Mamiya Sekor-C Fisheye 37mm f4.5
Fujinon NW 150mm f5.6
Fujinon NW 125mm f5.6
The base meter setting was using the 150mm lens at f5.6 with the Booster II adjusted to create an EV rating on the Autometer II of ZERO. As this lens has the largest image circle, I would expect it to show the least amount of light fall-off -- from center to corner -- on the 4x5 image.
The following table summarizes the results. They are, surprisingly, exactly what they should be. All of the lenses showed exactly the same EV reading in the center at f5.6. And all of the lenses showed exactly a three stop drop in the EV reading in the center at f16.
166394
The corner readings are a little more complicated. I would expect light fall-off due to the lens, but also due to the screen. The amount due to the lens should be reduced as the aperture is stopped down. With the 150mm lens, there is a one stop difference from the center to the corner at f5.6. At f16, the expected three EV reduction adds up to an EV change of four stops from the base. I think it is safe to assume that the camera viewing screens are the cause of a one stop drop from center to corner. Anything above one stop is due to the lens.
The 125mm and 105mm lenses each show an additional 1 EV drop in corner illumination at f5.6 -- which is completely gone by f16. This is what I would expect.
The 75mm shows different results. At f5.6, there is only a two EV drop, and an additional 1/2 EV drop on the corners. I attribute the first change to the lens having a different optical design, while the second change can be explained by its wider field of view. The 47mm lenses shows similar, but slightly more significant results.
The big surprise, and what started all this, is that I did not see ANY light fall-off in the fisheye lens -- either wide open or stopped down!