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GaryB
Joined: 29 Jul 2016
Posts: 521
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 Posted: Mon May 14, 2018 12:37 am Post subject: Dodt Gradient Contrast? |
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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/equipmentManuals/12205-4769.pdf |
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dolmadis
Joined: 07 Dec 2011
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Location: UK
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GaryB
Joined: 29 Jul 2016
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| Posted: Mon May 14, 2018 1:04 am Post subject: |
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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.  |
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dolmadis
Joined: 07 Dec 2011
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Location: UK
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| Posted: Mon May 14, 2018 1:14 am Post subject: |
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What about 3D parts ?
Might interest a member with a printer? |
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JohnyM
Joined: 24 Dec 2013
Posts: 461
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| Posted: Mon May 14, 2018 3:54 am Post subject: |
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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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Pau
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Joined: 20 Jan 2010
Posts: 4751
Location: Valencia, Spain
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| Posted: Mon May 14, 2018 7:42 am Post subject: |
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| 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
Joined: 31 Jan 2011
Posts: 1376
Location: Naperville, IL USA
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| Posted: Mon May 14, 2018 9:36 am Post subject: |
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| 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 ...
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Saul
Studio, horizontal and field setups |
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Pau
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| Posted: Mon May 14, 2018 10:01 am Post subject: |
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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  )
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Saul
Joined: 31 Jan 2011
Posts: 1376
Location: Naperville, IL USA
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| Posted: Mon May 14, 2018 10:21 am Post subject: |
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| 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 ) |
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 ? )
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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Saul
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Pau
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Saul
Joined: 31 Jan 2011
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Location: Naperville, IL USA
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| Posted: Mon May 14, 2018 11:46 am Post subject: |
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Pau, thank you very much for the links, very interesting material, should go through my "hardware" and recent 3d models ...
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Saul
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JohnyM
Joined: 24 Dec 2013
Posts: 461
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| Posted: Mon May 14, 2018 2:13 pm Post subject: |
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| 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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