An orange or gold hologram always seems brighter than a green or red one because your eye is more sensitive to yellows and oranges
Actually, green seems brighter. It's green light that the eye is most sensitive to. That's one reason that a green laser pointer at 5mW seems so much brighter than the same power of red.
http://hyperphysics.phy-astr.gsu.edu/hb ... right.html
http://www.ndt-ed.org/EducationResource ... sponse.htm
In search of a Brighter Denisyuk...
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Dinesh
In search of a Brighter Denisyuk...
Notice that photopic peaks at around 550 and scotopic peaks at 500. 550 is a sort of orange/yellow-y green and 500 is deep green. However, when you look a a hologram in a dark room, are you using your photopic or scotopic sensors. I've had this argument many times in the past because it's important for some kind of HOE's. MIL specs on some kind of HOEs specify scotopic and photopic efficencies. My feling is that the scotopic sensors take over under low ambient light, but when you hit the hologram with the reconstruction beam, there's always glare from the front surface and noise from the hologram. I think this makes it impossible not to see with scotopic sensors. Some have agreed with me and some have not. What if you're making a hologram of a night-time scene and viewing it in a dark room? Would you then use scotopic vision?
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Dinesh
In search of a Brighter Denisyuk...
Wouldn't a lot of the light be scattered off the back of the object?
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JohnFP
In search of a Brighter Denisyuk...
OK, I cannot resist. If you want a brighter Denisyuk shoot in DCG!!!!
Hahaha!
Hahaha!
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Jeffrey Murray
In search of a Brighter Denisyuk...
Get some BB plates, give them a lot more exposure than usual. and see this RATIO tip from Vidar from below: http://www.network54.com/Forum/message? ... 1084300676 I would use more smaller mirrors to get more light on the object. Remember 1:1 ratio is the goal. Jeff
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Michael Harrison
In search of a Brighter Denisyuk...
What if you're making a hologram of a night-time scene and viewing it in a dark room? Would you then use scotopic vision?
As I understand it, ambient light levels aren't important when determining if you're using photopic or scotopic vision.
It's the amount of light entering the eye.
If the room is dimly lit or dark, you'll be using scotopic when looking at most of it but if you're looking at something in the center of the room that is brightly lit (say with a green laser), I'd expect the cones to take over and their green sensitivity to assert.
If you had two holograms in this darkened room and one were lit with a 5mW green laser and the other with a 5mW red laser I'd expect the green to look brighter because the amount of light entering the eye is still high enough to activate the cones.
If you dialed down the power on each laser you'd get to a point where the rods took over and the red hologram would appear brighter.
It would be an interesting demonstration of photopic and scotopic vision, but who looks at holograms this way?
As I understand it, ambient light levels aren't important when determining if you're using photopic or scotopic vision.
It's the amount of light entering the eye.
If the room is dimly lit or dark, you'll be using scotopic when looking at most of it but if you're looking at something in the center of the room that is brightly lit (say with a green laser), I'd expect the cones to take over and their green sensitivity to assert.
If you had two holograms in this darkened room and one were lit with a 5mW green laser and the other with a 5mW red laser I'd expect the green to look brighter because the amount of light entering the eye is still high enough to activate the cones.
If you dialed down the power on each laser you'd get to a point where the rods took over and the red hologram would appear brighter.
It would be an interesting demonstration of photopic and scotopic vision, but who looks at holograms this way?
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Dinesh
In search of a Brighter Denisyuk...
"As I understand it, ambient light levels aren't important when determining if you're using photopic or scotopic vision.
It's the amount of light entering the eye."
True, to an extent. The trouble is that these curves are designed for radiometrics and not photometric, they were never intended for laser light. I agree it's just the light from the hologram, but the hologram would have to be super-clean and the medium itself, glass plastic what-have-you, would have to have no surface scatter or glare at all. Any noise or glare would constitute ambient light and, since it's coherent, would appear pretty bright to your eye since even a small amount of laser light swamps the retina. Compare a 12mW Christmas tree bulb to a 12mW HeNe lase with both reflecting off a white surface. As I say, the comparison is a little unfair since one is photometric and one is radiometric.
"...but who looks at holograms this way?"
People in art galleries? If anyone remember the wandering holography show that I saw at Pier 39, San Fransisco ca 1986 will remmeber an awfully dark room. I believe you were supposed to think you were in an"art" gallery.
It's the amount of light entering the eye."
True, to an extent. The trouble is that these curves are designed for radiometrics and not photometric, they were never intended for laser light. I agree it's just the light from the hologram, but the hologram would have to be super-clean and the medium itself, glass plastic what-have-you, would have to have no surface scatter or glare at all. Any noise or glare would constitute ambient light and, since it's coherent, would appear pretty bright to your eye since even a small amount of laser light swamps the retina. Compare a 12mW Christmas tree bulb to a 12mW HeNe lase with both reflecting off a white surface. As I say, the comparison is a little unfair since one is photometric and one is radiometric.
"...but who looks at holograms this way?"
People in art galleries? If anyone remember the wandering holography show that I saw at Pier 39, San Fransisco ca 1986 will remmeber an awfully dark room. I believe you were supposed to think you were in an"art" gallery.
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Tom B.
In search of a Brighter Denisyuk...
I'm thinking of a frosted glass or translucent object, so I expect most of the back light would get through to light up the object, which might also serve as a diffuse light source for other objects in the scene... Before I further embarass myself, I'd better try it and see if it works at all Will have to rummage aroung for a fast concave mirror and a translucent object...
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JohnFP
In search of a Brighter Denisyuk...
Tom, it will work. In my Vodka bottle I found that very thing. It is a frosted glass bottle. In every one of my first four holograms of it with the mirror, and white card the object was brighter then with out the mirror. Why? The mirror did not reflect light directly back to the object but back down to the white card. Also, because I used sides to the encasing the object was in a box, a box with a mirrored top at 45 degress, a white bottom and two black sides. The additional ambient light caused more light to be reflected on the bottle and thus a brighter object.
I would be willing to bet that if you can get just another 5% additional lighting to your object you will see a significant brightness increase. Just make sure you do not reflect back and hit the plate directly from the object side.
I would be willing to bet that if you can get just another 5% additional lighting to your object you will see a significant brightness increase. Just make sure you do not reflect back and hit the plate directly from the object side.