Diffused light.

[richbart]

I took with just a piece of frosted scotch tape on slip over diaphragm with the diaphragm about a quarter the way open. It reduced the chromatic aberration and gave it a little bit of a DIC look.

[DonSchaeffer]

Fantastic! I have to try this.

[richbart]

This is another with field diaphragm closed more. Causes blue color background

[Phill Brown]

Good contrast effect.
Looks like there needs to be polarising going on.
ND filters are often partially polarised.
Somewhere else in the light path could be acting as an analyser, possibly in the camera?
If the condenser isn't aligned some oblique lighting helps to give an impression of 3D and depth.
Whatever the cause it would be good to picture the setup so it is repeatable.
The tape may be under internal tension that isn't easy to replicate.
Definitely an improvement on the aberration caused by clear acrylic.
If the contrast is caused by differential
interference it is DIC at any price?
Always happy to be corrected.

[Phill Brown]

IMG_20220411_081209698~2.jpg (178.5 KiB) Viewed 2480 times

This is using polarised to extinction BF with the 2 inline diffusers from a Nikon Labophot 2 placed over the lower polariser.

IMG_20220411_101625280~2.jpg (75.37 KiB) Viewed 2469 times

This needs some imagination.
Trying to hold a phone while tracking at 400x. Not the image I'm seeing.
Using the film from the window of an envelope with glass diffuser.

IMG_20220411_102406127~2.jpg (94.01 KiB) Viewed 2468 times

[Sansub2]

This is another with field diaphragm closed more. Causes blue color background

I have seen this method used few times before but never able to repeat it. The gentleman who invented this method gets pretty awesome results with very nice colors with blue background as you mentioned. I read his PDF throughly and still was not able to reproduce it.

Can you please show your setup and let us know what patch and what light spectrum are you using to get blue background? Appreciate it.

[richbart]

Just put the cover slip with frosted scotch tape over the condenser. The I put a filter holder on the bottom of my condenser. I start with condenser wide open, and field diaphragm open. Then just start closing them until I get what I want. You have to have your condenser all the way up, but that can sometimes work better slightly lowered. I sometimes do put a layer of linear polarized film on the field condenser. It seems to even out the color. Make sure your sample has all excess water wicked out. I noticed excess water between slide and coverslip can screw up my results.

[Sansub2]

Thanks richbart for the response. Going to try as you mentioned..

[Phill Brown]

Thanks for sharing your images and methods.
There appears to be a DF and oblique patch stop along with the mention of polarization below.
Both images have oblique lighting however it is caused,with the second being partially DF or indirectly BF for want of a more accurate description.
For this to be effective an analyser needs to be present above the subject in the light path.
Under the head may be possible possible.
My Chinascope has room for a 27mm which seems to be the smallest round glass easily available,my Nikon Labophot only has 20mm or so from memory so either mod the part or maybe use plastic type film.
Combinations of circular and linear polarisers give many different effects.
Without the diffused refringent effect of the plastic tape over the condenser lens too little light will pass for subjects that are not refringent or birefringent.
When both polarisers are circular there is a combination that gives an intense blue.
It's definitely worth getting some linear and circular polarising filters and have a play with rotating and tuning them with a light behind, clouds or a bright white painted surface will work.
I paid £8 from eBay for a pair of linear camera filters recently.
Wicking water is really good tip, not found a way to realistically release the subject safe and well, they will need counseling and it's unlikely the story of their experience will be believed anyway.