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Jewel Beetle
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mjkzz



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PostPosted: Sat Sep 15, 2018 8:40 pm    Post subject: Reply with quote

I think overall, the smaller the opening for the lens (requiring smaller lens), the larger the globe, the less impact the black hole will have on overall image. So this might be another good experiment -- I will get a larger, possibly a globe of 300mm in diameter and a longer working distance lens. I will definitely try this when I come back in mid Oct.
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mawyatt



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PostPosted: Sun Sep 16, 2018 5:28 am    Post subject: Reply with quote

The bottom chip image I posted was from a very uniform lighting setup about ~5 years ago I recall. It's consist of a small light tent (~30cm) sitting inside a larger light tent surrounded by multiple diffused strobes. The lens poked thru a small slit in the smaller tent. All was done to try and achieve as uniform a lighting as possible, since these tiny solder balls are like spherical mirrors and will show any light variation as well as the lens and it's surroundings as you can see from the image. The strobes illuminating the face of the small tent where the lens (Mitty) poked thru was adjusted to make that source of light equal to the other sources inside the small tent. I used a light meter as best I could to try and get things uniform inside the small tent.

I just envisioned being small and standing where the chip subject would be and looking around and thinking of what I would "see", this gave me a better understanding of what was going on.

Never been able to subdue the solder ball lens reflection well, and even thought of using a "one way mirror" or partially reflective glass, so subject doesn't "see" the lens. Wonder if anyone has tried anything like this before??

The subject surface has a lot to do with this effect and how it influences the final image, chips without solder balls don't require the illumination effort.

You've got your lighting dome setup & lenses working well for these beetle images, what do you & Beats use for the LED lights? I've replaced the strobe modeling lamps with LED bulbs which work OK, but only have 18W...so not that bright.
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rjlittlefield
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PostPosted: Sun Sep 16, 2018 7:14 am    Post subject: Reply with quote

mjkzz wrote:
I think overall, the smaller the opening for the lens (requiring smaller lens), the larger the globe, the less impact the black hole will have on overall image. So this might be another good experiment -- I will get a larger, possibly a globe of 300mm in diameter and a longer working distance lens. I will definitely try this when I come back in mid Oct.

The absolute size of the globe should not matter much, as long as it is large compared to the subject.

What you want is a hole that is just big enough for the lens to see through.

If the working distance of the lens is larger than the globe radius, then consider making a conical lens hood that tapers down toward the hole, to block stray light from entering the lens.

An example is shown at http://www.photomacrography.net/forum/viewtopic.php?t=424, panel #1, lower left corner.

Note, BTW, that this approach does not require a small lens, because the lens does not need to fit inside the hole in the globe.

--Rik
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Lou Jost



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PostPosted: Sun Sep 16, 2018 7:20 am    Post subject: Reply with quote

Mike, epi illumination should completely eliminate those black spots. Likewise the arrangement I suggested here:
http://www.photomacrography.net/forum/viewtopic.php?t=30024&start=15
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rjlittlefield
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PostPosted: Sun Sep 16, 2018 7:28 am    Post subject: Reply with quote

mawyatt wrote:
using a "one way mirror" or partially reflective glass, so subject doesn't "see" the lens. Wonder if anyone has tried anything like this before??

There is a standard trick for axial illumination, that involves shooting through a slanted partial reflector. See for example http://www.photomacrography.net/forum/viewtopic.php?t=15820 . This method works OK at low magnification (small NA), but it has the drawback that image quality rapidly degrades due to aberrations as the aperture gets wider. Light rays on different sides of the aperture go through different amounts of glass. The wider the aperture, the greater the differences.

The problem with aberrations is less when the reflector is perpendicular to the line of sight, but even then the reflector introduces spherical aberration. With a microscope objective, this is the same as wrong cover slip thickness.

I expect that a partially silvered pellicle would work OK, but those are expensive and fragile. I am not aware of anybody in this forum trying the pellicle approach.

--Rik
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Lou Jost



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PostPosted: Sun Sep 16, 2018 7:31 am    Post subject: Reply with quote

Mike, note that the mirror solution that I suggested in the link above does not cause any aberrations (if the surface quality of the mirror is high enough) and does not require a pellicle mirror.

That said, on eBay I did stumble onto a pellicle mirror that was included in an optical comparator for epi lighting, and the whole thing was very very cheap. I'll test it someday when I have time...
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mjkzz



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PostPosted: Sun Sep 16, 2018 4:16 pm    Post subject: Reply with quote

rjlittlefield wrote:
mjkzz wrote:
I think overall, the smaller the opening for the lens (requiring smaller lens), the larger the globe, the less impact the black hole will have on overall image. So this might be another good experiment -- I will get a larger, possibly a globe of 300mm in diameter and a longer working distance lens. I will definitely try this when I come back in mid Oct.

The absolute size of the globe should not matter much, as long as it is large compared to the subject.

What you want is a hole that is just big enough for the lens to see through.

If the working distance of the lens is larger than the globe radius, then consider making a conical lens hood that tapers down toward the hole, to block stray light from entering the lens.

An example is shown at http://www.photomacrography.net/forum/viewtopic.php?t=424, panel #1, lower left corner.

Note, BTW, that this approach does not require a small lens, because the lens does not need to fit inside the hole in the globe.

--Rik


Right, absolute size does not matter, but to optimize it, seeking smaller hole and larger/longer WD, so the angle of cone formed by the yellow circle is smaller.

Yes, the paper hood actually is a bit "conical" -- the front is smaller than its base. I was surprised that it did not cause any vignetting, so I will make the front smaller till it starts causing vignetting.
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mjkzz



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PostPosted: Sun Sep 16, 2018 4:51 pm    Post subject: Reply with quote

rjlittlefield wrote:
mawyatt wrote:
using a "one way mirror" or partially reflective glass, so subject doesn't "see" the lens. Wonder if anyone has tried anything like this before??

There is a standard trick for axial illumination, that involves shooting through a slanted partial reflector. See for example http://www.photomacrography.net/forum/viewtopic.php?t=15820 . This method works OK at low magnification (small NA), but it has the drawback that image quality rapidly degrades due to aberrations as the aperture gets wider. Light rays on different sides of the aperture go through different amounts of glass. The wider the aperture, the greater the differences.

The problem with aberrations is less when the reflector is perpendicular to the line of sight, but even then the reflector introduces spherical aberration. With a microscope objective, this is the same as wrong cover slip thickness.

I expect that a partially silvered pellicle would work OK, but those are expensive and fragile. I am not aware of anybody in this forum trying the pellicle approach.

--Rik


Pellicle? Now you guys are confusing me . . . I will google around and see what that does and learn. Thanks
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Lou Jost



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PostPosted: Sun Sep 16, 2018 5:24 pm    Post subject: Reply with quote

Here's an example of an optical comparator with a pellicle mirror that might be in good condition:
https://www.ebay.com/itm/New-Mitutoyo-100X-P-Hexanon-Lens-Optical-Comparator-P-Zoom-Projection-Lens/263903816805?_trkparms=aid%3D555017%26algo%3DPL.CASSINI%26ao%3D1%26asc%3D20160706104836%26meid%3Dd43ee945b35a416f8e6b4c8bdba0879e%26pid%3D100642%26rk%3D1%26rkt%3D1%26%26itm%3D263903816805&_trksid=p2045573.c100642.m3226

Here's another cheaper one (I don't know why one port is at an angle):
https://www.ebay.com/itm/NIKON-OPTICAL-COMPARATOR-LENS-100X-Dp-No-44222/322244545025?hash=item4b07458a01:g:DlIAAOSwFV9XxGGU

The idea here is to remove the pellicle mirror segment and put it in the infinity space between objective and lens.
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mjkzz



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PostPosted: Sun Sep 16, 2018 6:12 pm    Post subject: Reply with quote

Lou Jost wrote:
Here's an example of an optical comparator with a pellicle mirror that might be in good condition:
https://www.ebay.com/itm/New-Mitutoyo-100X-P-Hexanon-Lens-Optical-Comparator-P-Zoom-Projection-Lens/263903816805?_trkparms=aid%3D555017%26algo%3DPL.CASSINI%26ao%3D1%26asc%3D20160706104836%26meid%3Dd43ee945b35a416f8e6b4c8bdba0879e%26pid%3D100642%26rk%3D1%26rkt%3D1%26%26itm%3D263903816805&_trksid=p2045573.c100642.m3226

Here's another cheaper one (I don't know why one port is at an angle):
https://www.ebay.com/itm/NIKON-OPTICAL-COMPARATOR-LENS-100X-Dp-No-44222/322244545025?hash=item4b07458a01:g:DlIAAOSwFV9XxGGU

The idea here is to remove the pellicle mirror segment and put it in the infinity space between objective and lens.


OK, how would it reduce or eliminate the "black hole" if the pellicle mirror (which essentially a half mirror?) is in the infinity space? The only way I see is to light it through the objective/lens, but isn't that the so called coaxial illumination? Or maybe the pellicle mirror is better in those items on eBay?

Thanks, I will keep learning from you guys.
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Lou Jost



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PostPosted: Sun Sep 16, 2018 6:20 pm    Post subject: Reply with quote

Yes, the light comes through the side port of that assembly and goes through the lens.

My other suggestion (see above) uses a front-surface half-silvered mirror, sending light that does not go through the lens.
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mjkzz



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PostPosted: Sun Sep 16, 2018 7:00 pm    Post subject: Reply with quote

Thanks Lou.
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Lou Jost



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PostPosted: Sun Sep 16, 2018 7:04 pm    Post subject: Reply with quote

I've never actually done it, but it should work.
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rjlittlefield
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PostPosted: Sun Sep 16, 2018 7:32 pm    Post subject: Reply with quote

The simplest thing I can imagine is to put a partially-silvered mirror (either glass or pellicle) right over the hole in the globe, with the lens on the outside, masked against stray light from the globe. Then the subject, looking toward the lens, will see the "black hole" replaced by a reflection of itself and its immediate surroundings. That won't be as bright as the inner surface of the globe, but it should be a lot brighter than black.

I'm pretty sure that people have mused about combining through-the-lens illumination with around-the-lens illumination. In theory that avoids the black hole but replaces it with a dark ring around the aperture. In practice, I don't know how much improvement can be made.

--Rik
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rjlittlefield
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PostPosted: Sun Sep 16, 2018 7:41 pm    Post subject: Reply with quote

To be clear, when I say "pellicle" I'm talking about a very thin film. Typically they're made of nitrocellulose and are only a few microns thick. See for example https://www.thorlabs.com/newgrouppage9.cfm?objectgroup_id=898 and https://www.edmundoptics.com/f/Pellicle-Beamsplitters/12443/ .

My guess is that those instruments linked by Lou do not have pellicle beamsplitters, but instead just thin glass or maybe even prisms. Placed behind the objective, there is no need for the thinness of a pellicle, and glass would be a lot more robust.

--Rik
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