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rjlittlefield
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Joined: 01 Aug 2006
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Location: Richland, Washington State, USA
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 Posted: Thu Feb 09, 2017 12:45 am Post subject: |
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| ChrisR wrote: | I think the color at 20º should match what you get at
(original wavelength)/cos 20º = 282nm . |
That's what I thought too. But the calculator disagrees. In fact the calculator's shift has the opposite sign. Increasing the angle causes the calculator's spectrum to shift right, while increasing the maximum film thickness causes it to shift left. I'm very confused. 
The paper at https://www.osapublishing.org/viewmedia.cfm?id=79472 supposedly explains how the calculator models the physics of the film reflection, but I haven't read it in enough detail to resolve my confusion.
In any case, here's an animation of the chip as photographed with two angles of light:
Each of the two frames of this animation was a single camera exposure, shot with a 20X objective, using a non-diffused Jansjö lamp.
Despite the obvious change in apparent geometry, nothing physically changed between the two exposures except for the angle of the light.
The difference in aspect ratio between the two frames is entirely due to the "utilized aperture" effect. Physically the slide is at a fixed angle, tilted about 22 degrees with respect to the objective. In one frame the light is positioned above the slide, so that the reflection enters roughly the center of the objective. In the other frame, the light is positioned at a much lower angle, so that the reflection barely enters the edge of the objective. Effectively, the slide is being viewed at a lot lower angle in the second case, and the difference in aspect ratio is just perspective foreshortening corresponding to the different virtual viewing angle.
In both cases, the narrow angle of the illumination greatly stops down the objective, resulting in greatly increased DOF and correspondingly reduced resolution for focused detail.
--Rik |
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ChrisR
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| Posted: Thu Feb 09, 2017 4:46 am Post subject: |
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Nice demo. I expect those who haven't witnessed the effect on geometry, wouldn't believe it..
If I'm understandng the colour shift change at all, it isn't as simple thought because of the light spectrum. Different frequencies having different behaviours in the dielectric. What comes out is rather like a Michel-Levy chart.
I'd wondered how they came about... 
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mjkzz
Joined: 01 Jul 2015
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Location: California/Shenzhen
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mjkzz
Joined: 01 Jul 2015
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Location: California/Shenzhen
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| Posted: Thu Feb 09, 2017 7:12 am Post subject: |
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on second thought, maybe it is not virtual view angle, it is the real but equivalent thing -- for a super smooth surface where things are measured in nm, if we use the light source as reference (instead of the lens) and look at the light path, ie, line of sight entering the lens . . .
So even though the angle between the lens and subject does not change, the angle of light beam entering the lens change due to super smooth surface, by line of sight, effectively, it is equivalent of changing the angle between lens and subject surface as if the position of light source is fixed.
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ChrisR
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| Posted: Thu Feb 09, 2017 8:09 am Post subject: |
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Fan, you need page 6 of Rik's article about the No-Parallax Point.
Try it with paper with a pencil-diameter hole over a camera lens. It's surprising. 
Much the same happens if the light from the subject only hits one part of the lens. It's just like having a small aperture over the lens.
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Adalbert
Joined: 30 Nov 2015
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| Posted: Sat Feb 18, 2017 5:39 am Post subject: |
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Hello everyone,
I have just taken a photograph of the BWO-test illuminated by two LEDs.
( CANON EOS M3 + CANON EF 70-200L + NIKON LU Plan 10x / 0.30 )
Some areas have been illuminated OK but some not softly enough (too many reflections).
Maybe should I change the alignment?
BR, ADi
Last edited by Adalbert on Sun Feb 19, 2017 5:09 am; edited 3 times in total |
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ChrisR
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| Posted: Sat Feb 18, 2017 6:11 am Post subject: |
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How does it look at 100%?
(I've been thinking ... crossed polars  )
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Chris R |
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Lou Jost
Joined: 04 Sep 2015
Posts: 3841
Location: Ecuador
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| Posted: Sat Feb 18, 2017 6:56 am Post subject: |
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"Nice demo. I expect those who haven't witnessed the effect on geometry, wouldn't believe it.. "
Yes, this is one of the most interesting and counter-intuitive things I've yet seen on this forum! And that's saying a lot.
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Lou Jost
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ChrisR
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| Posted: Sat Feb 18, 2017 7:51 am Post subject: |
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You've presumably seen it with those inter-lens apertures you make?
Put one in front of a large diameter lens with everything fixed, while you live-view. Move aperture back and forth on centre, then round and round.
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Chris R |
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Adalbert
Joined: 30 Nov 2015
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| Posted: Sat Feb 18, 2017 11:19 am Post subject: |
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Hi Chris,
Do you mean polarizing filters on the LEDs ?
| Quote: | | ”inter-lens apertures” |
I am using a tele as a tube lens.
So, I only can change the aperture of this tele. But the changing from 4 to 5.6 causes vignetting on my camera 
What kind of the inter-lens aperture do you mean?
BR, ADi |
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rjlittlefield
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Location: Richland, Washington State, USA
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| Posted: Sat Feb 18, 2017 12:07 pm Post subject: |
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| Adalbert wrote: | | ChrisR wrote: | | ”inter-lens apertures” |
What kind of the inter-lens aperture do you mean? |
I'm pretty sure that ChrisR was replying to Lou Jost, who is fond of using added apertures (search "Waterhouse stops") between the lenses in a combo. The experiment ChrisR suggests is to make such an aperture small, position it between lens and subject, and move it around laterally while observing the image in live view. The result may be shocking: as you move just the aperture, the appearance of the scene changes just as if you were moving the lens -- even though the lens and camera are actually staying in one place! The explanation is provided in the link that ChrisR gave, to my paper about "Theory of the No-Parallax Point..."
--Rik |
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Lou Jost
Joined: 04 Sep 2015
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Location: Ecuador
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| Posted: Sat Feb 18, 2017 1:00 pm Post subject: |
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ChrisR, I never have moved those apertures around, since they are sandwiched between lenses. I will try that!
And Rik, thanks for explaining this in the link and paper.
Adalbert, you are less likely to get vignetting if you put an aperture between your objective and tube lens, rather than using the aperture of the tube lens. Hence my fondness for paper apertures between lenses.
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ChrisR
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| Posted: Sat Feb 18, 2017 2:11 pm Post subject: |
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Rik, thanks for the straightening.
Lou prepare to be amazed
Adi:
| Quote: | Hi Chris,
Quote:
”crossed polars”
Do you mean polarizing filters on the LEDs ? |
No, I mean one on the light source, the other on the camera.
For a simple metal mirror you would get extinction if the polarizers were fully crossed.
It isn't exactly a simple mirror, so I expect the edges at least, would show.
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Chris R |
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Adalbert
Joined: 30 Nov 2015
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Adalbert
Joined: 30 Nov 2015
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| Posted: Sat Feb 18, 2017 2:58 pm Post subject: |
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Hi Chris,
I only have used crossed polarizing filters for the taking of the photographs of the crystals up to now.
BR, ADi |
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