Dodt Gradient Contrast?

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GaryB
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Dodt Gradient Contrast?

Post by GaryB »

Has anyone used Dodt Gradient Contrast?

I was reading up on the Zeiss Axioimager and they mentioned 'Dodt Gradient Contrast' as part of it. I've never heard of it so I did more looking around and it seems like quite a nice illumination technique. I did a quick rough and ready version of it that's far from the actual thing and no doubt gave vastly inferior results, but it does hint at it's promise so I was wondering if anyone has ever seen/used it. It's a sophisticated variant on oblique lighting.

Here's a rundown of the basics.
http://photos.labwrench.com/equipmentMa ... 5-4769.pdf

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dolmadis
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Post by dolmadis »


GaryB
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Post by GaryB »

Yeah, I saw that.
Thorlabs wants as much for the device as a full second hand DIC microscope. The device itself as I've seen on other sites is a fairly simple setup provided your scope is equipped with external illumination like a Hal lamp. If I had a metal lathe I'd make one. :lol:

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dolmadis
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Post by dolmadis »

What about 3D parts ?

Might interest a member with a printer?

JohnyM
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Post by JohnyM »

This is just a fancy name for classic oblique light. Just decenter your condenser aperture and insert a grad filter into condenser tray.

It's been rediscovered many times in many forms, my guess is that it's easier to sell that way.

One simple, yet effective is Litonotus UFG filter, do exactly the same thing.

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Post by Pau »

JohnyM wrote:This is just a fancy name for classic oblique light. Just decenter your condenser aperture and insert a grad fliter into condenser tray.
Not exactly: Dodt (what this mean?) places the sector stop at the illumination train and a diffuser after it. It isn't clear if it is placed at a conjugated plane of the condenser diaphragm where it would be equivalent to an oblique stop at the condenser.

It seems worth to try with DIY approaches.
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Saul
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Post by Saul »

Pau wrote:...Not exactly: Dodt (what this mean?) places the sector stop at the illumination train and a diffuser after it. It isn't clear if it is placed at a conjugated plane of the condenser diaphragm where it would be equivalent to an oblique stop at the condenser...
Hi Pau, this is little bit different path ...

Image
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Post by Pau »

Saul, yes I saw the Thornlabs scheme, it seems about the same than the Zeiss, the only clear difference is the mirror (irrelevant) and that the collimating lens is not pictured because they include it in the illuminator sold separately

The name comes from Hans-Ulrich Dodt (It's better to search before posting :oops: )
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Saul
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Post by Saul »

Pau wrote:Saul, yes I saw the Thornlabs scheme, it seems about the same than the Zeiss, the only clear difference is the mirror (irrelevant) and that the collimating lens is not pictured because they include it in the illuminator sold separately

The name comes from Hans-Ulrich Dodt (It's better to search before posting :oops: )
Hmmm...correct me if I'm wrong - in the Thornlabs scheme annulus is double diffused immediately after the light source. Zeiss - between lenses (collimator, illuminator, condenser ? )

Image

If it is really after collimator - so in this case I could use it in the base filter on my Labophot base ?
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Pau
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Post by Pau »

Saul, yes, you're right, Zeiss uses lenses and this could allow for more room to place the stop and diffuser, maybe even to use a single sector stop for all NAs (?) while the Thorlabs version just places the system inside the collimated beam and needs different stops for each magnification, this could be easier to replicate.
Of course I ignore if it can be easily DIY adapted to your microscope but I think it could be as you say between the lamp house collimator and the microscope base (some microscopes like my Zeiss has all the collimating optics built in the lamp house while others have all or some of the lenses inside the base... )

This could be the Dodt's original scheme (the same at Zeiss):
http://www.sciencemag.org/site/feature/ ... 2873.xhtml

Here it is explained in more detail: https://www.google.ca/url?sa=t&rct=j&q= ... eX_l5LhTpU

There are commercially available systems. A key part seems to be able to displace the position of the after stop diffuser to regulate contrast

http://www.scientifica.uk.com/learning- ... t-contrast

http://www.luigs-neumann.com/product/dg ... t-contrast

Edit: Science link fixed
Last edited by Pau on Mon May 14, 2018 12:57 pm, edited 1 time in total.
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Saul
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Post by Saul »

Pau, thank you very much for the links, very interesting material, should go through my "hardware" and recent 3d models ...
Saul

JohnyM
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Post by JohnyM »

Pau wrote:
JohnyM wrote:This is just a fancy name for classic oblique light. Just decenter your condenser aperture and insert a grad fliter into condenser tray.
Not exactly: Dodt (what this mean?) places the sector stop at the illumination train and a diffuser after it. It isn't clear if it is placed at a conjugated plane of the condenser diaphragm where it would be equivalent to an oblique stop at the condenser.

It seems worth to try with DIY approaches.
I've seen it first hand. Just check your rear focal plane. It IS just oblique light with more theory behind it than DIC microscopy.
It's just not as directional and contrasty as oblique thanks to diffuser. Technique is VERY old and was described in books like Pluta "Advanced light microscopy"... just like Zeiss own "Plas DIC"... (funny thing is that they actually quoted it in paper and still get the patent).
There is lots of "forgotten knowledge" that manufacturers suddenly rediscover and sell.

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