Ladybird (by-product of yet another test)

Images taken in a controlled environment or with a posed subject. All subject types.

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rjlittlefield
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Post by rjlittlefield »

Beatsy wrote:A polariser in the M42 adapter on the camera would be ideal (I think). I'm looking seriously at that.
If you try that, please let us know how well it works out. There is always a concern with reflections causing glare, when a planar filter is mounted close to the sensor. Light bounces off the sensor, then off the filter and back to the sensor.

BTW, this placement is not really ideal from the standpoint of adding aberrations, but it's pretty good because the effective f# is large at that point in the system. As Pau says, putting it in infinite space is ideal from a standpoint of minimizing aberrations.

--Rik

Beatsy
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Post by Beatsy »

I may not be trying that after all Rik. The infinite space location sounds a better plan - as Pau mentioned.

The polariser sheets I found are circular pol (only work in one direction). I also found some stuck to microscope slides which I can cut to size and mount on the back (inside) of a filter thread adapter with spacers (to leave room for Mitties to screw in all the way). The adapter can be unscrewed a quarter turn without becoming too loose - so that gives me pol-angle adjustment at the lens without pushing the objective too far away. Adjustment at the lamps (if needed) is trivial. So I'm on my way.

Thanks both for your suggestions and help.

Pau
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Post by Pau »

Beatsy wrote:The adapter can be unscrewed a quarter turn without becoming too loose - so that gives me pol-angle adjustment at the lens without pushing the objective too far away. Adjustment at the lamps (if needed) is trivial. So I'm on my way.
If you use more than one light source it is not trivial, in fact it's more important that having the analyzer rotatable although it's always better to have all rotatable
Take a look at my setup: http://www.photomacrography.net/forum/v ... hp?p=67184
Pau

Lou Jost
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Post by Lou Jost »

When I have multiple light sources I use a conical lens hood that I made out of a cake decorator tip for the Mitutoyos, with a stiff polarizing sheet attached to the narrow end of the lens hood (the sheet is perpendicular to the lens axis), and a piece of bond paper (for diffusion) on top of it (paper on lens side, polarizer is last in the path of the light). This is lit from above by however many lights I need. All then have exactly the same polarization.

Beatsy
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Post by Beatsy »

Very quick update. Got all the polariser stuff installed. Fully adjustable and working as it should :D

Sadly, the hard, black parts of the ladybird (i.e. most of it) exhibit the same behaviour as your jewelled wasps Rik. That is, they "exhibit" nothing at all under crossed polars - just pitch black :roll:

Overall it looks like crossed polars will help, but not solve all glare issues (hairs and some detailed, glossy surfaces still do funky things). I'll try a different test subject, but it might be a couple of days before I can finish it (other things to do). I'll start a new thread in techniques when I have something to report.

rjlittlefield
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Post by rjlittlefield »

Beatsy wrote:Sadly, the hard, black parts of the ladybird (i.e. most of it) exhibit the same behaviour as your jewelled wasps Rik. That is, they "exhibit" nothing at all under crossed polars - just pitch black
Did you try turning the polarizer on the camera to make the polarizers not perfectly crossed? That should restore some of the specular reflection, hopefully enough to make the legs visible again. Or maybe you need to add some unpolarized diffuse illumination, just so that everything gets lit up to some extent.

BTW, just from your description I would not characterize the behavior as being same as the jewel wasp.

The bizarre thing about the jewel wasp is that they have a lot of reflections that do not look specular -- for example all the stuff that is brilliantly colored despite white illumination -- and yet they still go black under crossed polars.

Your situation with the ladybird sounds like it's just opaque black stuff, where the only thing you ever see is surface reflections, and surface reflections will almost certainly get killed by crossed polars.

The reason I say "almost certainly" is that some textures can give multi-bounce surface reflections that are not blocked by crossed polars. See http://www.photomacrography.net/forum/v ... hp?t=33842 for an artificial setup and explanation.

--Rik

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