Olympus NeoSplan 80 / 0.75 Ulwd

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Adalbert
Posts: 1062
Joined: Mon Nov 30, 2015 1:09 pm

Olympus NeoSplan 80 / 0.75 Ulwd

Post by Adalbert »

Hello everybody,
Does anybody know how to use this lens for the focus-stacking?
I would like to illuminate the subject from the side and have to avoid the scattered light (taking the pictures against the light).
BTW, WD=4.1mm
BR, ADi

ChrisR
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Location: Near London, UK

Post by ChrisR »

(Can you clarify what you want to do?
"Illuminate from the side" and "take pictures against the light" are different things.)

4mm is tight, but doable, imo. The lens metalwork becomes significant. You need a subject which isn't too shiny.

If you illuminate from the objective side, (solid subject, no back-light) you'll find you have to illuminate very evenly. Unless you illuminate through the lens, your lighting can only be from a triangular section ring, because the glass of the high NA lens and its surrounding metal, gets in the way. The ring sits on the plane of the subject.
If you illuminate predominantly from one side ( I mean for instance "the left" when looking down the microscope) you're only illuminating from a very small part of the solid angle which µ-man, laying on the surface of your subject, sees in his hemispherical sky.
High NA objectives necessarily have a lot of glass occupying the vertical sky, short WD objectives tend to have larger proportion of metalwork adding to what you might call the "dark angle". All you can do is fill the rest with light.

Then, much depends on how Diffuse the Reflection is, from the subject surface. This https://en.wikipedia.org/wiki/Diffuse_reflection illustrates.
If the reflections are specular, you will have horrible problems.
It will appear as though all the little shiny µ-men have hand-held bright smoky fireworks, pointing them up, and away from the incoming light. As you focus up and down you'll be able to sharpen a patch of atmosphere with the bright smoke for that height.
It's in part an effect of using a very small part of the glass of the lens, where all that light is directed. It's a very small effective aperture, so it's heavily diffraction blurred.
Irregular surfaces will show firework plumes squirming around and interacting, as you focus up and down. They occupy different parts of the out-of-focus sub-cones which relate to each individual firework. Those cones aren't in the same relative positions as the features are on the surface, so the light sources in your viewfinder, do move about. In a stack, they of course constuct a three dimensional volume of unwanted light source, sharp enough to record. :evil: :evil: :evil:
I worked out a way to remove it, but there isn't enough room in the margin, to explain.
:twisted:

About all you can do, is light from as large an angle of sky as possible.
One method which I have found works, to the extent that the geometry allows, is this.
Uses:-
- Ring flash,
- Table-Tennis Ball. Optional - you could try a paper tube
- expanded polystyrene cereal bowl, base removed
- 52m to( M42f + 52m) adapter (rafcamera) which allow height adjustment by M42 tubes for the ringflash when fixed to a 52mm thread "tube" lens
- Blue is Blu-tak, not really necessary but works for me.
- Green (shown only one side) is a ring cut from white plastic strip, sprung in place, in case I need to avoid reflections from the subject plane, going into the lens (where the TT ball isn't being used )

A Yongnuo ring-flash is running at minimum (1/128) output. One side can be turned off, which makes surprisingly little difference to evenness, if the Table Tennis ball (etc) is used. The light-sources on the right flash are just about bright enough to focus.

Image

Typical bowl:
Image
Chris R

Adalbert
Posts: 1062
Joined: Mon Nov 30, 2015 1:09 pm

Post by Adalbert »

Hello Chris,

Many thanks for your answer!
”Illuminate from the side" and "take pictures against the light" are different things”
Yes, I want to illuminate the object from the side and I want to minimize any reflexion.
I don’t want to take the photographs against the light and I don’t want to illuminate through the lens.

So, I will try to implement the solution, you have recommended.

Till now, I have experimented with the flocked light trap from Protostar:
Image
red: lens
yellow: light
green: diffuser
blue: gap slit
orange: flash ( 4 * YN660 )
black: light absorber


BR, ADi

Adalbert
Posts: 1062
Joined: Mon Nov 30, 2015 1:09 pm

Post by Adalbert »

Hello everyone,

So, I had to saw the silver ring and to fill the hole with the rubber-joint:
Image
That enables a better illumination.

The second problem is CA.
I have tried to remove the CA by LR during the conversion from RAW into TIFF.
- Noise reduction->color 100
- Lens correction->manually->defringe (purple & green)

e.g.
Image

BR, ADi

Adalbert
Posts: 1062
Joined: Mon Nov 30, 2015 1:09 pm

Post by Adalbert »

Added gum ring
Last edited by Adalbert on Tue Jan 28, 2020 1:09 pm, edited 2 times in total.

Lou Jost
Posts: 4338
Joined: Fri Sep 04, 2015 7:03 am
Location: Ecuador
Contact:

Post by Lou Jost »

Chris, wouldn't it be better to turn the cereal bowl upside down?

Adalbert, very brave of you to saw the objective. How did you know it was safe to saw where you did? Did you make a lower cut for observation of the guts of the objective first?

Adalbert
Posts: 1062
Joined: Mon Nov 30, 2015 1:09 pm

Post by Adalbert »

Hello Lou,

It was easy, I only had to saw the cylinder 1:

Image

BR, ADi

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