• Ultraviolet Photography
  •  

a hypothetical filter made out of opalite

16 replies to this topic

#1 Fandyus

    František G.

  • Members
  • 229 posts
  • Location: Czech republic, Northern Bohemia

Posted 16 June 2021 - 20:07

Definition of opalite according to wikipedia: Opalite is a trade name for man-made opalescent glass and various opal and moonstone simulants.

For those of you who know what it looks like off the top of their head, you might remember that it looks quite peculiar. https://media.istock...IPdG2ODmkqeMD8=

That makes me wonder what it would look like if somebody fashioned this into a 2-4mm thick filter. Maybe it's a dumb question since the material is naturally cloudy. But I don't know.

#2 Stefano

    Member

  • Members(+)
  • 2,174 posts
  • Location: Italy

Posted 16 June 2021 - 20:30

Opalite has those colors because of Tyndall scattering, similar to Rayleigh scattering as fas as I know. You could achieve the same effect (more or less) with milk in water, or soap in water, etc.

#3 Fandyus

    František G.

  • Members
  • 229 posts
  • Location: Czech republic, Northern Bohemia

Posted 16 June 2021 - 20:35

Interesting, thanks.

#4 Andrea B.

    Desert Dancer

  • Owner-Administrator
  • 9,115 posts
  • Location: UVP Western Division, Santa Fe, New Mexico

Posted 16 June 2021 - 20:49

One of those things that you'll never know unless you try!!
I suppose if the material is naturally cloudy, then exposures might be long. But that's never stopped us. :grin:

Also the brittleness factor might play a role. Is this material sufficiently hard to permit a surface polish for optical use.
Andrea G. Blum
Often found hanging out with flowers & bees.

#5 Fandyus

    František G.

  • Members
  • 229 posts
  • Location: Czech republic, Northern Bohemia

Posted 16 June 2021 - 20:56

View PostAndrea B., on 16 June 2021 - 20:49, said:

One of those things that you'll never know unless you try!!
I suppose if the material is naturally cloudy, then exposures might be long. But that's never stopped us. :grin:

Also the brittleness factor might play a role. Is this material sufficiently hard to permit a surface polish for optical use.

I'm not sure, but they are sold as decorative beads so I don't assume they're overly brittle, probably something like glass.

#6 dabateman

    Da Bateman

  • Members+G
  • 3,004 posts
  • Location: Maryland

Posted 16 June 2021 - 23:12

Well you could try it.
This one is cheap and should fit between 37mm to 52mm and 52mm to 37mm step rings:
https://www.amazon.c...1B8SKQG18JY1BTG

Its translucent, so that should help. Its 13mm think, so you will need to stack empty 52mm rings to sandwich it. The opening for a 37mm step ring is around 35mm.

Edited by dabateman, 16 June 2021 - 23:15.


#7 Fandyus

    František G.

  • Members
  • 229 posts
  • Location: Czech republic, Northern Bohemia

Posted 17 June 2021 - 17:26

View Postdabateman, on 16 June 2021 - 23:12, said:

Well you could try it.
This one is cheap and should fit between 37mm to 52mm and 52mm to 37mm step rings:
https://www.amazon.c...1B8SKQG18JY1BTG

Its translucent, so that should help. Its 13mm think, so you will need to stack empty 52mm rings to sandwich it. The opening for a 37mm step ring is around 35mm.
Could be interesting but I also don't think it would be sharp at all.

#8 Andy Perrin

    Member

  • Members+G
  • 4,416 posts
  • Location: United States

Posted 17 June 2021 - 18:05

No, it definitely would not be sharp. That's a scattering filter. But you might get some interesting effects anyway.

#9 Stefano

    Member

  • Members(+)
  • 2,174 posts
  • Location: Italy

Posted 17 June 2021 - 18:14

I think it would more or less be equivalent to a “sky” filter. The “Rayleigh haze” we see doesn’t reduce sharpness, it adds light instead. The Moon for example is still sharp in daylight, it simply has less contrast.

#10 Andy Perrin

    Member

  • Members+G
  • 4,416 posts
  • Location: United States

Posted 17 June 2021 - 20:21

Stefano, I think it's more like the situation with frosted glass, which definitely does reduce sharpness? I don't know, I haven't seen one of those stones in person, but certainly lots of rocks with small bubbles and things in it will substantially blur the image.

Edited by Andy Perrin, 17 June 2021 - 20:22.


#11 Stefano

    Member

  • Members(+)
  • 2,174 posts
  • Location: Italy

Posted 17 June 2021 - 20:53

Aerogel is blue because of Rayleigh scattering but judging from the images you can see online it doesn't blur images.

I think an important parameter is the refractive index. Both air and Aerogel have a very small one, while opalite probably has a glass-like one. This means that if it isn't flat it will distort the image.

Frosted glass scatters light because it isn't smooth. This works because of the difference in the refractive indexes between it and air. I think it isn't quite the same phenomenon.

#12 Andy Perrin

    Member

  • Members+G
  • 4,416 posts
  • Location: United States

Posted 17 June 2021 - 21:13

What does aerogel have to do with anything? We were not discussing it?

If the scattering in Opalite is due to bubbles it will have the same issues as frosted glass. Doesn't matter if it's a rough surface or an inclusion. However, it will matter how big the bubbles are relative to the light wavelength. Smaller bubbles than the wavelength will probably not blur things much, but if they are similar sized then it may.

Another way to say that is, how sure are you that this is Raleigh scattering and not Mie/Tyndall? (Tyndall is the large bubble limit, Raleigh is the small bubble limit, and Mie is the general theory which includes both Raleigh and Tyndall for spherical inclusions.)

Edited by Andy Perrin, 17 June 2021 - 21:20.


#13 Stefano

    Member

  • Members(+)
  • 2,174 posts
  • Location: Italy

Posted 17 June 2021 - 21:17

View PostAndy Perrin, on 17 June 2021 - 21:13, said:

What does aerogel have to do with anything? We were not discussing it?
It resembles opalite in that it produces Rayleigh scattering (Tyndall in opalite, but they are similar). They are not the same material though, so probably we can't compare them.

#14 Andy Perrin

    Member

  • Members+G
  • 4,416 posts
  • Location: United States

Posted 17 June 2021 - 21:50

That's what I'm trying to tell you -- Tyndall and Raleigh are not that similar. They don't behave the same way. They are opposites. One is for scattering by objects much larger than the wavelength and the other by objects much smaller.
--
ETA: Thinking about it, the blur is mostly coming from when you have multiple scattering (vs. single scattering). If the light changes directions multiple times, it diffuses, which makes the blur. So the density of scattering centers actually is the most important thing here, even more than Raleigh vs. Tyndall.

Edited by Andy Perrin, 17 June 2021 - 22:06.


#15 Fandyus

    František G.

  • Members
  • 229 posts
  • Location: Czech republic, Northern Bohemia

Posted 18 June 2021 - 23:31

It's nice that my comment has sparked a discussion, but what I really was referring to when I said the image most likely wouldn't be sharp was the refraction that the opalite would cause, acting like a lens of it's own.

#16 Andy Perrin

    Member

  • Members+G
  • 4,416 posts
  • Location: United States

Posted 19 June 2021 - 02:15

Fandyus, just polish it flat. Then it won't behave like a lens.

#17 Fandyus

    František G.

  • Members
  • 229 posts
  • Location: Czech republic, Northern Bohemia

Posted 22 June 2021 - 22:41

View PostAndy Perrin, on 19 June 2021 - 02:15, said:

Fandyus, just polish it flat. Then it won't behave like a lens.
Would be nice but I'm not sure I have the tools for that to be honest. I was actually thinking I could ask Cadmium if I could pay him to fashion a piece of opalite into a filter, since I suspect he might have the right tools.