Making DIC Prisms

Here you can discuss different microscopic techniques and illumination methods, such as Brightfield, Darkfield, Phase Contrast, DIC, Oblique illumination, etc.
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microb
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Making DIC Prisms

#1 Post by microb » Mon Jan 20, 2020 4:49 am

Hi,
I have some CNC setups built, and there are some people I work with here with their own setups to consult. As a goal for 2020 I’d like to expand that to grinding and polishing. So I’d like to polish calcite flat and parallel, and then at opposing angles to make DIC prisms cheaper than used ones available used on ebay.

If someone is interested in researching the specs, let me know. I don’t know the various designs for the different magnifications, versus the adapters with one crystal that Olympus and B&L sold for multiple objectives.
Any info would be appreciated. For now I’ll focus on finish some setups in progress, and slowly by Summer find out adhesives to mount calcite to a lapped metal slab and then disconnect it once polishing is done.

Attached is an example of calcite I can get pretty cheap. These have flaws, but should be good enough to try a few for practice and figure out a workflow before buying higher grade manufactured calcite.

If by the end of the year I can grind, polish and glue a couple dozen for myself that would be great. If someone wants to really jump and research the prism thickness and angles, maybe find patents that might give the specs for Olympus for example, AND if this works, I’d be happy to send them a set of prisms – maybe more if they are giving some away to educational groups. I think someone said they were doing that.

Thanks,
Ted
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microb
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Re: Making DIC Prisms

#2 Post by microb » Mon Jan 20, 2020 5:42 am

Here is a link to patents citing Nomarski's 1960 patent:
https://patents.google.com/patent/US292 ... 2+#citedBy

Wes
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Re: Making DIC Prisms

#3 Post by Wes » Mon Jan 20, 2020 11:20 pm

Great project! I was under the impression that making DIC prisms is extremely difficult hence the astronomical prices. Something along the lines of cutting slabs at an angle of 30 seconds. A lot of prisms have to produced to generate a few that are fit for purpose, these are then binned according to minute angular difference.

Keep us posted, this sounds pretty exciting!

microb
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Re: Making DIC Prisms

#4 Post by microb » Tue Jan 21, 2020 1:15 am

If anyone finds pointers to articles to calculate the theta angle based on something like objective magnification or something else, please send me pointers. Info appreciated.

Tom Jones
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Re: Making DIC Prisms

#5 Post by Tom Jones » Tue Jan 21, 2020 5:27 pm

I've been looking for more or less the same information for some time. I want to assess prism compatibility, both within a manufacturer's system, and between manufacturers, without actually having to do direct, and therefore very expensive, comparisons. For example, will a Zeiss prism system work well enough with an Olympus system to be worth acquiring the necessary parts? How well can I expect a PlanAchromat lens to work with a PlanApochromat prism from the same manufacturer? How about a 60x dry prism with a 60x oil objective, or even with an oiled top condenser lens? Maybe SPlanApos with SPlan or DPlanApo prisms on my BHS, or the reverse. 160mm objectives or prisms with infinity objectives or prisms?

I wanted to know what the shear values are for individual prisms, and how the are related to various objective parameters, and what else they might vary for best compatibility, in order to determine the above. The parts are rare and pricey enough, as you mentioned, that buying them to "try" is a risky and expensive venture.

Beyond the suggestion that the shear value needs to be less than 1/2 the point spread function of the objective, and that small shear values create higher resolution but lower contrast than high shear values, I've found very little that might be useful.

There is a page on the Nikon site (that I cannot find this morning) that lists shear values for some Nikon objectives. I'm afraid I'm not enough of an optical physicist to be able to calculate prism angles from shear values though. That patent information didn't help me either.

I have found one research study where some Olympus prism shear values were measured as the manufacturer wouldn't divulge the information to the researchers. The report is included as Chapter 2, Differential Interference Contrast Microscopy, in "Biomedical Optical Phase microscopy and Nanoscopy", by Nathan T. Shaked, et. al. Elsiever/Academic Press. ISBN is 978-0-120415871-9.

If you find anything useful, please post it!

Tom

Scarodactyl
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Re: Making DIC Prisms

#6 Post by Scarodactyl » Tue Jan 21, 2020 6:55 pm

This is a very interesting project! I will look forward to future updates.

microb
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Re: Making DIC Prisms

#7 Post by microb » Tue Jan 21, 2020 8:52 pm

At first it seems that the angle cutting the calcite and the thickness are not the main factors, as much as the angle of the optical axis one of the two attached halves. So unlike Wollaston prisms, the distance to the interference plane seems to be the main issue. So measuring the distance from that interference plane to the "located at the (effective) objective rear focal plane" is the main calibration to match up to.

How to run light through an objective and a prism to get those distances, I don't know right now. But it seems if you had those numbers, you could raise or lower another manufacturers prism mounts to match up to their objectives.

(http://olympus.magnet.fsu.edu/primer/ja ... index.html)

microb
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Re: Making DIC Prisms

#8 Post by microb » Tue Jan 21, 2020 9:13 pm

Thanks. I ordered a copy of the book. But if you dig up your copy anytime soon, I'd be curious what the scale of some of the numbers were just to get an idea. The distance to the interference plane is supposed to be shorter for prisms aimed into a condenser versus objective.

viktor j nilsson
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Re: Making DIC Prisms

#9 Post by viktor j nilsson » Fri Jan 24, 2020 8:12 am

No need to búy it, you can read the chapter here:

https://www.researchgate.net/publicatio ... microscopy

viktor j nilsson
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Re: Making DIC Prisms

#10 Post by viktor j nilsson » Fri Jan 24, 2020 8:40 am

Re: shear angles and focal planes, we had a nice discussion about this over at photomacrography.net, see especially the posts by abednego:

https://www.photomacrography.net/forum/ ... highlight=

My own attempts to do Diy DIC with my set of Nikon Epi DIC prisms is slowly moving forward. I have a set of four prisms: a 5x, a 20x and two 10.40.100x prisms.

I've identified the location of the interference band for each prism. Since I have the prisms and some of the objectives they were intended for, and the nosepiece in which they were supposed to be held, I only need to know the location of each objectives' rear focal plane to know the location of the interference band (plus minus 0.1 mm or so with my simple setup).

To locate the rear focal plane, I used the method described by Paolo Possi here: https://www.researchgate.net/post/Is_th ... ctive_lens
I.e., I shone a laser pointer through the front of each objective and measured the diameter of the projected image at different distances, and interpolated the positition where the diameter would be 0.

From my measurements, the distance from the shoulder to the rear focal plane is
-1.36 mm for the Nikon M plan 10x DIC
-1.14 mm for the Nikon M plan 40x DIC
-4.06 mm for the Nikon M plan 20x DIC

The 10x,40x and 100x objectives uses the same prism (labelled 10.40.100x), but the 20x and 5x objectives have separate prisms.
This should give you and indication that Nikon feels that a mismatch of around 0.2mm between the interference band and the rear focal plane to be tolerable (i.e. 10x vs. 40x), whereas a o mismatch of around 3mm (20x objective) to be too severe as to require its own prism.

If someone here has a NIkon M Plan 5x objective, I would be very happy he they could use this method to locate the rear focal plane in relation to the shoulder of the objective. (I have the 5x prism, but not the objective).
Last edited by viktor j nilsson on Mon Jan 27, 2020 8:40 am, edited 1 time in total.

viktor j nilsson
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Re: Making DIC Prisms

#11 Post by viktor j nilsson » Fri Jan 24, 2020 8:42 am

Another thing. In abednego's post above, note the formula:
Image
where:
fc: condenser focal length
alphaQ: condenser prism wedge angle
fob: objective focal length
alpha: objective prism wedge angle


One aspect that I haven't seen discussed much in relation to DIY DIC is the condenser focal lenght. It seems to me that slightly mismatched prism combinations could be tweaked to work better by altering the focal length of the condenser. Of course, this is what we do when we change top lenses on the condenser. But this only gives you a limited number of combinations. One thing I am going to experiment with next is to introduce various diopter lenses before the condenser to alter its focal length. I'll report the results in due time.


I'm very intrigued by your idea to make your own prisms. I very much look forward to hearing how it goes and learn from it along the way.
Last edited by viktor j nilsson on Mon Jan 27, 2020 8:40 am, edited 1 time in total.

Wes
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Re: Making DIC Prisms

#12 Post by Wes » Sun Jan 26, 2020 1:13 pm

Out of interest have you also considered making quartz wedge compensators? Add it to a 3d printed DIN 6x20mm holder and you have my money ;)

microb
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Re: Making DIC Prisms

#13 Post by microb » Mon Jan 27, 2020 12:26 am

So the DIN 6x20 is a standard for compensator optics. Mentioned a was down on this web page (https://www.mccrone.com/mm/senarmont-co ... tions-0-1/). I'm curious about more details though if anyone has any. Thanks.

I'll have tested a lapping polishing machine in the next couple months. So I'll try on cheap calcite at first and then can try the much more expensive synthetic quartz.

abednego1995
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Re: Making DIC Prisms

#14 Post by abednego1995 » Mon Jan 27, 2020 2:30 am

Viktor, thank you for the Paolo Pozzi reference. I had some difficulty in determining objective BFPs on my bench so this method is excellent.

BR,
John

viktor j nilsson
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Re: Making DIC Prisms

#15 Post by viktor j nilsson » Tue Jan 28, 2020 8:11 am

abednego1995 wrote:
Mon Jan 27, 2020 2:30 am
Viktor, thank you for the Paolo Pozzi reference. I had some difficulty in determining objective BFPs on my bench so this method is excellent.

BR,
John
Glad I could give something back, your input has been exceedingly helpful to me.

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