Diatom 640X Oblique Illumination

[mrsonchus]

olie images en éclairage oblique.
To achieve beautiful oblique lighting, you have to play more or less with the cardboard or plastic cover to have more or less the sought after effect.
Because depending on the nature of the object, the plastic cover will not be adjusted in the same way.
The one I use the most and Mathias's arrow.

Must agree, the most useful I find are the set of Mathias-arrow cardboard cutouts that I made about 5 years ago after reading of them for the first time when perusing articles by the late Walter Dioni.
These simple cardboard 'arrows' or pointed-oblongs as they (mine at least) are, have consistently given me better results for oblique than any 3D-printed sets, as varied and at first-look useful as they (the 3D-printed sets) appear to be.
Walter Dioni demonstrates Mathias arrow...

Images to follow.....

My tatty set of MAs,


In use,


A rather tatty 2-week old temporary slide of a Geranium's anther and some pollen-grains. Dehydrated with alcohol then covered with PVA-glue and coverslip - apologies for the horrid mount but the only one to hand that was thick enough to show the effect...
Pollen-grains with a little surface texture from MA,




These are druses - flower-shaped bunches of (probably) Calcium-oxalate crystals within a large proportion of the cells of the Geranium it seems,


Brightfield of trichomes, little visibility of intra-cellular detail,


Quite a bit more structure's visible, including nucleus, with a simple MA in use,


MA is visible - dried mountant with polarisation and MA,


More druses, MA with polariser and full lamda retarder-plate slotted-in - getting a little surreal...


Some of the glandular trichomes that, when their terminal 'flasks' of essential-oil' are ruptured, give us that distinctive Geranium smell! Polarised with full-lambda and MA.


A few more...


A handy little device made from cardboard!

[tgss]

For some reason or other I can't see your images John. Am I the only one so affected?
Tom W.

[mrsonchus]

Oops - fixing this now!

Should be fine now!

[Hobbyst46]

Not just fine - Charming !
Which objective, mrsonchus ?

[mrsonchus]

Here's an example of background-correction with Photoshop. Simply take image as usual (with it's uneven backgroun, in this case as a result of using a Mathias arrow) them move slide to an area (still with coverslip) that's blank and take an image of this, the uneven background to be corrected).
Open both images in Photoshop.
Next 'duplicate layer' of the background image, with destination to be the full image also just opened - which will now have the uneven background on top of it's original (full image) background layer, obscuring the image altogether - don't panic!.
Invert the uneven background (i.e. swap the light & darks over).
Change the blending-method of the layer to 'colour-dodge' with the original image layer.
Corrected!
If it's too bright or dark, altering the brightness of the (inverted) uneven background layer will alter the brightness of the final image.
When you have it just right, 'flatten image' to produce the final result jpg, with the uneven background corrected!

Here's an example....


Really easy to do! A link to my G-Photos of this excursion...

[mrsonchus]

Not just fine - Charming !
Which objective, mrsonchus ?

Hi hobby' - erm, a mixture....
I was messing-about and experimenting but I know the largest mag is the 60x dry 0.90 UPlanApo with the coverslip correction-collar (so useful for 'non-std' slides such as this) I think set to 0.12mm. Then there are 40x 0.65 PlanC N images and some from my shiny-new (used of course) 20x 0.70 UPlanApo objective - the reason for my recent (still for sale) listing of the now usurped 20x 0.40 PlanC N on e-bay - less 10% for forum-members!

Here's the new baby - (beside the for-sale 20x....) looking at this image makes me feel a little guilty....

20x for sale and its replacement.jpeg (140.81 KiB) Viewed 3825 times

[tgss]

Thank you mrsonchus
These are quite a bit more informative than the previous "No Entry" signs Very nice to see the technique so well used on botanical samples, rather than the usual pond life studies.
Tom W.

[janvangastel]

Very nice technique. Alas, I don't have photoshop. Tried with PaintshopPro, but didn't work.

EDIT: maybe I found it.....will try tomorrow.

[rudnicki]

I know Mathias' arrow, but I think my method is more versatile. It requires a lot of light and I made a 13W "Kohler fixed" illuminator with an old condenser. Most 80-100 ISO photos are good. Here is what I can do with this material. In some photos the water bear is seen from below.

[75RR]

.
Very nice!

Perhaps you can walk us through your method. Is it a type of Circular Oblique Lighting (COL)?
.

[rudnicki]

The condenser on the photo is the P51 condenser from the Polish biolar PZO microscope. It has a movable diaphragm. I place my filter in the slit above the diaphragm. The condenser mat filter is not used.
You have to find a semi-opaque plastic sheet, mat on one side. You can see its density in the photo. It allows you to read printed text without problems.
We make a set of filters with 12-16 mm patches cut from black electrician's tape. I most often use the 14 and 16mm patches. With blue scotch patches we get a nice blue background with a 20x objective.
The condenser must be raised as far as possible.
You need a strong illuminator. I made a "fixed Kohler" illuminator with an old condenser and a 13W led to photograph live protists.



I presume it works because the patch is flush with the plastic backing, above the diaphragm, but I haven't tested other solutions. I made a VAC-2 filter with polarizing foil for screens and it seems to work too.







The position of the filter between the condenser and the diaphragm may be decisive. It remains to be verified. In any case, it would be fun if it only worked with the biolar PZO.
Various effects are obtained by pushing the patch more or less under the condenser. We get photos between high key and low key, but also a whole range of photos in grey, and the DF.
The low key photos are in black and white. This works best with a 20x objective, but with a little practice you get good results with a 40x objective. My trino head has a magnification factor of 1.5X and my 20x is actually a 30x. This is enough to photograph life in a drop of water. From what I've read, oblique lighting increases the NA of the lenses. I often do stacks of 5 to 15 photos, but we get good results with single photos.

[Rapidray]

Great water bear photo’s!