Evangelos Achillopoulos
Well-known member
I just realized that to post in a thread that has the generic title “Focusing screens” is not most appropriate, because its not understood that the subject of my experiments are for a Fiber Optic ground glass or better focusing screen (its not grounded by either side…).
So I started this thread to post the specific results of my research.
Questions and answers…
Q. What is a Fiber focusing screen?
A. It’s a bucket of very fine (6 microns each) optical fibers perfectly aligned in parallel, compressed in a special process together to form a plate that then its being cut to thin slices that after polishing and coating are forming the fiber focusing screen. The look and feel is like a piece of glass polished in both sides that can be cleaned as a glass lens. The fibers are taking the light from one side and they transfer it to the other, each fiber is like a light pipe that doesn’t spill the light to the adjacent pipes. When you try to see from the other side is totally opaque, so the hot spot effect is not existent and a condenser lens is not needed. To see something it has to be touching the surface of the other side. Also the light allowable entry angle is 180 degrees, so light can enter even on the edges of a very wide lens.
Q. Its sounds as cutting edge technology?
A. Yes, fiber optic screens are used in very special imaging applications, from military imaging to nuclear reactors, that’s why they are subject to strict export regulation rules.
Q. Where is being used in the motion picture industry?
A. Arri and Panavision optical viewfinders are build around fiber optic screens.
Q. What are the potential benefits to 35mm adapters?
A. Due to the special properties that are incorporating, they can transfer an image with minimal loss in quality (contrast, resolution, it preserves original MTF etc.). Actually they transfer from one side to the other an image with no intervention at all, like if it was a clear glass window. That means, it is possible to get the pure image that a lens can formulate in the surface of the fiber screen, without the slightest intervention of the focusing screen, which is typical to all other screens. As it is known a different ground glass has a different bokeh i.e. Fiber screens are eliminating the GSE and in a certain design can eliminate totally the vignetting effect up to F22 in wide angle lenses or with lenses that are having small exit pupil. Also they don’t exhibit flare at all, so you can have a very bright area and no spill to the dark areas, the flare that is visible is solely from the lens characteristics. Moreover in certain conditions they can work without spin or vibration at all.
Q. OK it sounds perfect… what is the bad news?
A. It seems that they are loosing more light than a typical ground glass, about ½ stop more. But this is not final since experiments are still being done. And they costing almost double as a typical branded GG.
Q. Can they benefit spinners as well as vibrating adapters?
A. Yes, except that vibrating can also benefit from the lack of vignetting, spinners can’t due to the spinning of the GG. The trick is that they can work also as static with Brevis 35 i.e.
Bokeh and resolution comparison in a Brevis 35 MP.1 with CFX.
Stopdown test from F1.4 to F16.
http://www.motionfx.gr/Files/Stop_down_Zeiss_50mm_F14_FiberGG.mov
Sample footage
And some HD video
http://www.motionfx.gr/Files/Demo_footage_FiberGG.mov
All shown tests are with Varicam recording in AVC-Intra 100, GG.relay rev2 2/3 B4 mount., Brevis MP.1, Zeiss 50mm F1.4 ZF, graded in Color.
More tests will come in a few days.
If you have more questions please ask.
So I started this thread to post the specific results of my research.
Questions and answers…
Q. What is a Fiber focusing screen?
A. It’s a bucket of very fine (6 microns each) optical fibers perfectly aligned in parallel, compressed in a special process together to form a plate that then its being cut to thin slices that after polishing and coating are forming the fiber focusing screen. The look and feel is like a piece of glass polished in both sides that can be cleaned as a glass lens. The fibers are taking the light from one side and they transfer it to the other, each fiber is like a light pipe that doesn’t spill the light to the adjacent pipes. When you try to see from the other side is totally opaque, so the hot spot effect is not existent and a condenser lens is not needed. To see something it has to be touching the surface of the other side. Also the light allowable entry angle is 180 degrees, so light can enter even on the edges of a very wide lens.
Q. Its sounds as cutting edge technology?
A. Yes, fiber optic screens are used in very special imaging applications, from military imaging to nuclear reactors, that’s why they are subject to strict export regulation rules.
Q. Where is being used in the motion picture industry?
A. Arri and Panavision optical viewfinders are build around fiber optic screens.
Q. What are the potential benefits to 35mm adapters?
A. Due to the special properties that are incorporating, they can transfer an image with minimal loss in quality (contrast, resolution, it preserves original MTF etc.). Actually they transfer from one side to the other an image with no intervention at all, like if it was a clear glass window. That means, it is possible to get the pure image that a lens can formulate in the surface of the fiber screen, without the slightest intervention of the focusing screen, which is typical to all other screens. As it is known a different ground glass has a different bokeh i.e. Fiber screens are eliminating the GSE and in a certain design can eliminate totally the vignetting effect up to F22 in wide angle lenses or with lenses that are having small exit pupil. Also they don’t exhibit flare at all, so you can have a very bright area and no spill to the dark areas, the flare that is visible is solely from the lens characteristics. Moreover in certain conditions they can work without spin or vibration at all.
Q. OK it sounds perfect… what is the bad news?
A. It seems that they are loosing more light than a typical ground glass, about ½ stop more. But this is not final since experiments are still being done. And they costing almost double as a typical branded GG.
Q. Can they benefit spinners as well as vibrating adapters?
A. Yes, except that vibrating can also benefit from the lack of vignetting, spinners can’t due to the spinning of the GG. The trick is that they can work also as static with Brevis 35 i.e.
Bokeh and resolution comparison in a Brevis 35 MP.1 with CFX.
Stopdown test from F1.4 to F16.
http://www.motionfx.gr/Files/Stop_down_Zeiss_50mm_F14_FiberGG.mov
Sample footage
And some HD video
http://www.motionfx.gr/Files/Demo_footage_FiberGG.mov
All shown tests are with Varicam recording in AVC-Intra 100, GG.relay rev2 2/3 B4 mount., Brevis MP.1, Zeiss 50mm F1.4 ZF, graded in Color.
More tests will come in a few days.
If you have more questions please ask.
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