The dreaded black hole & window shopping, a theory

[Rusty]

This may be another one of my silly ideas,probably born dead because of my lack of knowledge about the behavior of light and optics
I have no means to test the idea at the moment, but hope somebody will try it out .....
Everybody knows the "black hole " problem when photographing shiny bugs, when the objective is reflected back by the shiny surface of the beetle

Ever tried looking into a shop window when it is brighter outside than inside? all you see is a reflection of the outside world
Even if the shop sells massive microscope objectives and there is one parked just behind the glass, you will never see it
If you cannot see it, you cannot reflect it back to be recorded on the image the guy in the shop is taking of you through this massive objective

So...given that, all we need is a little" shop window" between the bug and objective and a darker environment around the objective ,like the inside of the shop
Like this



Could this be a simple solution to a sticky problem?

[ChrisR]

I daresay Rik will answer you, but in the meantime, where's your illumination?

[Planapo]

That's one cool beetle that is!
I hypothesize he must be feeding exclusively on m&ms.

--Betty

[Rusty]

I daresay Rik will answer you, but in the meantime, where's your illumination?

oops...omitted the illumination , i guess any standard lighting would do as per normal operation
please note that the glass is not to scale , i don't think it has to be very much larger than the tube in case it interferes with illumination
Betty wrote:

That's one cool beetle that is!
I hypothesize he must be feeding exclusively on m&ms. Smile Wink

[Bob^3]

Daniel,

The biggest issue I can see with this concept is that if standard glass sheet were used (say without anti-reflective coating), the amount of light that would bounce off of it toward the subject would be relatively low compared with the light illuminating the subject directly from the source (but this would depend on precisely how the source light was directed at the glass and subject).

One way to enhance the "fill light" effect would be to use a partially silvered mirror for the glass plate (at least in the portion that the lens looks through). This would act like beam splitter and have the effect of a neutral density filter on the lens, which will reduce the amount of light reaching the sensor thus requiring longer exposures.

If you used a large mirror as shown and only the center portion was partially silvered, I think this could work. However, there might be serious problems with flare and ghosting due to light reflecting between the mirror and the lens elements or sensor---tilting the mirror could help with this issue.

This is the concept is what Charles successfully tested a while back using a cube beam splitter in front of the lens. If memory serves, someone also suggested a half sliverd mirror.

[Bob^3]

I hypothesize he must be feeding exclusively on m&ms.

Yes Betty, I vaguely remember reading about a study done on this beetle. Apparently, it originally evolved to feed on a specific bush which produced multi-colored berries and was endemic to just a few acres of land in what is now an industrial park. The hapless beetle was forced to adapt to a new food source when an m&m plant was built directly over its former range!

[Craig Gerard]

Daniel,

Thoughts regarding the characteristics of light are good thoughts.

I expect you would find the book 'Light - Science and Magic' to be a valuable asset. I'm looking at Diagram 6.2 page 131 Third Edition.
http://www.focalpress.com/books/photogr ... 98&sub=114

I like your analogy. It is similar, in some respects, to a one-way mirror.

One-way mirrors are coated with a half-silvered layer,
allowing the mirror to reflect half the light that strikes its surface.

http://science.howstuffworks.com/question421.htm

The 'thin glass disk' in your illustration may cause more problems than initially anticipated (resolution).

..snip.. Charles successfully tested a while back using a cube beam splitter in front of the lens. If memory serves, someone also suggested a half silvered mirror.

I believe the term is 'axial illumination'?

'Tackling the "black hole"'. Basically the light comes in from the side, hits the beamsplitter and a portion of that light falls gently onto the subject.
http://www.photomacrography.net/forum/v ... hp?t=10354

Another link: (using a vertical illuminator and polarisation... see diagram 2.)
http://www.photomacrography.net/forum/v ... hp?t=10176


Craig

[Bob^3]

Bob^3 wrote:
..snip.. Charles successfully tested a while back using a cube beam splitter in front of the lens. If memory serves, someone also suggested a half silvered mirror.

I believe the term is 'axial illumination'

That's it---and thanks for the links. I looked and couldn't find the beam-splitter thread. For some reason, I thought Charles had used a solid glass brightfield splitter, when it actually contained a semi-silvered mirror.

The 'thin glass disk' in your illustration may cause more problems than initially anticipated (resolution).

Yes, but only if it is not of good quality, right?

BTW, a similar "translucent" mirror is rumored to be used in Sony's new 24MP (APS-C sensor?!) model A77 DSLR:

http://www.petapixel.com/2010/10/05/son ... iewfinder/

[ChrisR]

The 'thin glass disk' in your illustration may cause more problems than initially anticipated (resolution).

Yes, but only if it is not of good quality, right?

The obvious glass to use, would seem to me to be a microscopy coverslip. It's thin, and of course many microscope objectives are designed to be used with one in the system. They're also easy to "trim".

See Page from on old Leitz illumination booklet

[Blame]

I am not sure your beetle idea will fly.

Problem 1 is that the sheet of glass looks like invading the beetle's personal space. The idea might not fly but the beetle will!

Problem 2 is more basic. Your window is not stopping the image of your camera being reflected by the beetle. All it does is add a hopefully larger reflection to mask it. You are replacing a dim reflection of the camera with a bright reflection of the beetle. You will get a beetle reflected in a beetle reflected in.... well you get the idea. Just like a hall of mirrors.

Problem 3 is how are you going to get the camera relatively dark? you would need to put the camera in a black box, with a window.

Finally why bother when there is already an easy answer? Use a polarized filter on both lens and a flash. Angle them at 90 degrees. There will be no reflection. The beetle will photograph as if it was not shiny.

[Blame]

Oh, I think I should warn you not to eat the beetle.

It is probably loaded with artificial colors, flavors & preservatives.

[Rusty]

Blame wrote:

Finally why bother when there is already an easy answer? Use a polarized filter on both lens and a flash. Angle them at 90 degrees. There will be no reflection. The beetle will photograph as if it was not shiny.

Darn!.....Think i will go and eat that beetle now !!

[Harold Gough]

Ever tried looking into a shop window when it is brighter outside than inside? all you see is a reflection of the outside world

Exactly the experience I had when I put aside my film camera and borrowed my wife's compact digital camera.

I found out exactly why they call it a "compact": after those little boxes that women carry in their handbags, with a some face powder and a vanity mirror. The digital viewfinder is a vanity mirror, with a camera attached, just as a cell phone is a phone with a camera attached.

Harold

[Craig Gerard]

Here is some more food for thought.

Lieberkühn Reflector

http://www.alanwood.net/photography/oly ... ctors.html


Craig

[Blame]

Craig

A good way of using microscope lighting for macro photography. Could be very easy to setup.

Interesting. but shouldn't it be a new thread?