Dodt gradient contrast
Dodt gradient contrast
Thorlabs - Dodt Gradient Contrast for DIY Cerna Systems
Scientifica - A guide to Dodt Gradient Contrast
Leica Microsystems - Simultaneous acquisition of fluorescence and high contrast transmitted light imaging (Dodt Contrast) (Section 8 of the application note.)
Curious if anyone has used this or heard of any DIY attempts?
Scientifica - A guide to Dodt Gradient Contrast
Leica Microsystems - Simultaneous acquisition of fluorescence and high contrast transmitted light imaging (Dodt Contrast) (Section 8 of the application note.)
Curious if anyone has used this or heard of any DIY attempts?
Re: Dodt gradient contrast
It's not so different from oblique illumination. For many in vitro two-photon systems it's pretty standard. Some patching people buy DIC because it costs more, but with DGC there are no prisms in the way of the laser and it's said to be better for thicker slices, which is typically the case for acute brain slices. If you actually compare DIC and DGC the difference isn't as big as the price difference. I've long been wondering why people still regularly buy DIC.
I'm currently tinkering around with an attempt at DGC on my Leitz, but I've little time and the papers that Dodt published aren't that rich in optical information. Thorlabs has some interesting specifics about their DGC system, they use an offset slit and different ones for different NAs. They also run an engineered circular diffuser. I've no idea how much benefit these extras give It's a fairly mysterious technique.
I'm currently tinkering around with an attempt at DGC on my Leitz, but I've little time and the papers that Dodt published aren't that rich in optical information. Thorlabs has some interesting specifics about their DGC system, they use an offset slit and different ones for different NAs. They also run an engineered circular diffuser. I've no idea how much benefit these extras give It's a fairly mysterious technique.
Re: Dodt gradient contrast
I tried it. Turns out my microscope has a small slit that lets me position a thin object between lamp collimator and diffusor. I 3D-printed a quarter annulus (slightly to large diameter) and put it in. It does contrast phase objects like epithelial cells or embedded red blood cells, which are hard to see in brightfield, nicely. The strength of the effect is very similar to oblique illumination but without the intensity gradient in the image, which oblique illumination quickly produces.
Re: Dodt gradient contrast
Interesting, not familiar with Leitz, what model? Would you mind taking a photo showing how the illumination system is arranged and where you put the mask?
I also wonder about the diffuser -- could a mask with varying optical density (like a graduated ND filter) produce equivalent effect as the sharply-defined quarter annulus combined with diffuser? Or is there something more subtle going on with the diffuser? Possibly some subtlety related to this (comparing to oblique):microbear wrote: ↑Wed Dec 16, 2020 10:24 pmThorlabs has some interesting specifics about their DGC system, they use an offset slit and different ones for different NAs. They also run an engineered circular diffuser. I've no idea how much benefit these extras give It's a fairly mysterious technique.
But I don't understand the significance of the mask being earlier in the optical path if it is still conjugate with the condenser/objective apertures...Both methods use a mask to generate an illumination gradient, but in Dodt contrast, the mask occurs much earlier in the optical path.
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Re: Dodt gradient contrast
Or perhaps some thing like DJs radial diffusion mask:
http://bettermicroscopy.blogspot.com/20 ... i.html?m=1
http://bettermicroscopy.blogspot.com/20 ... i.html?m=1
1942 Bausch and Lomb Series T Dynoptic, Custom Illumination
Re: Dodt gradient contrast
interesting, implies that the diffusive character of the tape is important:BramHuntingNematodes wrote: ↑Thu Dec 17, 2020 3:40 amOr perhaps some thing like DJs radial diffusion mask:
http://bettermicroscopy.blogspot.com/20 ... i.html?m=1
But no explanation why diffusivity matters or comparison photos with, for example, a similar mask constructed using transparent neutral density film to give the same pattern of illumination in the objective rear aperture?Matte finish tape, however, apears to be superior to their "Satin finish" variety, which seems to exhibit less desirable diffusion characteristics, at least for this use.
Re: Dodt gradient contrast
I’ve just found this : https://www.scientifica.uk.com/learning ... t-contrast
Not studied it yet ... my Caffeine level needs boosting
MichaelG.
Not studied it yet ... my Caffeine level needs boosting
MichaelG.
Too many 'projects'
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Re: Dodt gradient contrast
That was the second link in the first post. You DO need coffee!MichaelG. wrote: ↑Thu Dec 17, 2020 9:03 amI’ve just found this : https://www.scientifica.uk.com/learning ... t-contrast
Not studied it yet ... my Caffeine level needs boosting
MichaelG.
Re: Dodt gradient contrast
I needed coffee just to focus on the web page Looks like interesting, but like Hans I'm struggling to see the difference from a gradient NDF (or one laser printed on acetate).BramHuntingNematodes wrote: ↑Thu Dec 17, 2020 3:40 amhttp://bettermicroscopy.blogspot.com/20 ... i.html?m=1
Re: Dodt gradient contrast
.viktor j nilsson wrote: ↑Thu Dec 17, 2020 10:12 amThat was the second link in the first post. You DO need coffee!MichaelG. wrote: ↑Thu Dec 17, 2020 9:03 amI’ve just found this : https://www.scientifica.uk.com/learning ... t-contrast
Not studied it yet ... my Caffeine level needs boosting
MichaelG.
My apologies
MichaelG.
.
Edit: Clever chap, Herr Dodt
https://www.researchgate.net/profile/Hans-Ulrich_Dodt
Too many 'projects'
Re: Dodt gradient contrast
After endless search in his papers and not finding anything of value, I checked for patents. E voila, there it is, with all detail.
DE000019514358C2
At https://depatisnet.dpma.de/ the fulltext and figures are available.
DE000019514358C2
At https://depatisnet.dpma.de/ the fulltext and figures are available.
Re: Dodt gradient contrast
The Leica app note and Scientifica page both mention the diffuser position being adjustable axially, so perhaps sharp mask plus movable diffuser is just a way to control the strength of gradient, but for any particular setting, equivalent to a gradient NDF? However on the Thorlabs module, no indication that the position is adjustable, but they still use a diffuser. (And a pretty fancy one, too...)
Re: Dodt gradient contrast
Nice find, thanks, do you read German? (I do not, although my name may give the impression otherwise...) Will try machine translation later.
Re: Dodt gradient contrast
Do not know which translator you use. Here are two, providing both as depending on what is being translated either one or the other seems to be a bit better on the day.
https://translate.google.com/
https://www.deepl.com/translate
Zeiss Standard WL (somewhat fashion challenged) & Wild M8
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Re: Dodt gradient contrast
Yes, I'm a german scientist. I think they filed a US patent as well and google also has a translation. The condensed version of it is:
The tube is fully self contained and inserted into a part of the illumination path were the light source is focused to infinity, basically directly after the collimator of the lamp house. The tube contains to symmetrical lenses of equal focal length, with the focus in the middle. The disk is positioned in the fourier plane although in the drawing it's slightly offset from the focal point. Behind the disk is a diffuser that can be shifted forth and back to control the strength of the effect.
Now I know where to position these two things!
Thorlabs seems to use a different system, interestingly! At least based on what they show on the website, their system is no Dodt contrast. They replaced the two lenses with their engineered diffuser, if I understand it correctly. The engineered diffuser is not the Dodt diffuser but a second one before the annulus. After the annulus it seems they have a traditional diffuser.
The tube is fully self contained and inserted into a part of the illumination path were the light source is focused to infinity, basically directly after the collimator of the lamp house. The tube contains to symmetrical lenses of equal focal length, with the focus in the middle. The disk is positioned in the fourier plane although in the drawing it's slightly offset from the focal point. Behind the disk is a diffuser that can be shifted forth and back to control the strength of the effect.
Now I know where to position these two things!
Thorlabs seems to use a different system, interestingly! At least based on what they show on the website, their system is no Dodt contrast. They replaced the two lenses with their engineered diffuser, if I understand it correctly. The engineered diffuser is not the Dodt diffuser but a second one before the annulus. After the annulus it seems they have a traditional diffuser.
Re: Dodt gradient contrast
Thank you for the summary.
Does it say which direction this goes? I would guess, the effect is strongest with the diffuser close to the mask, and weakens as the distance is increased?
Re: Dodt gradient contrast
Thanks for the inspiring posts. I just tried a DIY Dodt method on my Amscope 120. I have been testing oblique illumination by placing a sharp edge over the light source to get axial illumination. It gives a nice 3D shadow effect across the center of the field but illumination is uneven (one side dark and one side light). By placing a diffusing disk in the filter holder below the condenser, this gradation is smoothed out. The diffusion disk was made from a 32 mm circle cut from a transparent food container which was then covered in one layer of translucent scotch tape. Having the edge stop and the diffusion disk separated by a few centimeters makes all the difference (cf. an earlier post where the scotch tape and edge stop were combined in one radial filter: #5 Post by BramHuntingNematodes » Wed Dec 16, 2020 8:40 pm http://bettermicroscopy.blogspot.com/20 ... i.html?m=1 ).
Re: Dodt gradient contrast
What you're doing there is actually almost the same as Dodt contrast. You aperture is in a fourier plane and you use a diffuser to get a smooth gradient. Now switch to a quarter circle plate and you get the additional advantage of having a gradient in two orthogonal directions, not just one!
Re: Dodt gradient contrast
Thanks, had not tried DeepL before but it seems to be doing a better job than Google.
The last paragraph of section 2 translates:
So I guess that answers the question of whether there is anything more subtle going on with the diffuser vs. just being a convenient way to adjust the strength of the gradient.Finally, the gradient can be created by vapor deposition of gradient reflective or absorptive layers on glass platelets, where the transmission at each point of the glass plate must imitate the effect of the combination of ring diaphragm and diffuser described above. Finally, this gradient can also be realized by liquid crystal devices (LC-SLM). This has the advantage that the gradient can be arbitrarily can be adjusted by computer. This would also allow the realization of several concentric rings, which in combination with phase-shifting components to over-resolution (Toraldo apertures).
In the Thorlabs diagram it is not clear how the mask is positioned relative to an image of the light source. However it does show the mask being in a region where the field stop is collimated, which I think is not necessarily inconsistent with it being in a Fourier plane conjugate to the objective rear aperture as in Dodt contrast.microbear wrote: ↑Thu Dec 17, 2020 8:08 pmThorlabs seems to use a different system, interestingly! At least based on what they show on the website, their system is no Dodt contrast. They replaced the two lenses with their engineered diffuser, if I understand it correctly. The engineered diffuser is not the Dodt diffuser but a second one before the annulus. After the annulus it seems they have a traditional diffuser.
Re: Dodt gradient contrast
Speaking of needing coffee... just realized Chris was referring the "radial diffusion mask" but I responded about the diffuser in the Dodt system. There are more blog posts following the one Bram linked but no further discussion of the diffusivity of the tape that I saw, and the later posts stop calling it "radial diffusion mask", just "radial 3D mask", so maybe they changed their mind. However diffusivity issue aside it does seem like the mask would give illumination similar to Dodt, just not as smooth a gradient.hans wrote: ↑Thu Dec 17, 2020 5:35 pmThe Leica app note and Scientifica page both mention the diffuser position being adjustable axially, so perhaps sharp mask plus movable diffuser is just a way to control the strength of gradient, but for any particular setting, equivalent to a gradient NDF? However on the Thorlabs module, no indication that the position is adjustable, but they still use a diffuser. (And a pretty fancy one, too...)
Re: Dodt gradient contrast
This would be convenient for experimentation, but it appears reputable brands like 3M and HP are no longer available or very expensive, and I mostly see generic stuff with mixed reviews that I'm not sure I would want to put through my laser printer. Anyone have recommendations for decent quality transparency film that is safe for laser printers?
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Re: Dodt gradient contrast
Big run on that stuff to make covid masks I thought
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Re: Dodt gradient contrast
Ah, that would explain it. I was thinking even the generic stuff seemed pretty expensive, but I don't remember how much it used to cost back when people actually used it on overhead projectors.
Re: Dodt gradient contrast
Thinking about it a bit more, if the mask/diffuser were placed just below the condenser as is more common the diffuser would also be blurring the image of the field stop. So perhaps the motivation to add the additional pair of relay lenses and place it earlier is to avoid interfering with the imaging of the field stop?
Re: Dodt gradient contrast
For convenience ... This page is in English, and includes citations, etc.
https://patents.google.com/patent/DE19514358C2/en
MichaelG.
Too many 'projects'
Re: Dodt gradient contrast
Google's translation has quite a few strange phrasings. I was getting somewhat less confusing results pasting the OCRed text from Espacenet into DeepL that 75RR mentioned. I never found any US patents.MichaelG. wrote: ↑Tue Dec 22, 2020 10:51 amFor convenience ... This page is in English, and includes citations, etc.
https://patents.google.com/patent/DE19514358C2/en
Re: Dodt gradient contrast
.hans wrote: ↑Tue Dec 22, 2020 7:25 pmGoogle's translation has quite a few strange phrasings. I was getting somewhat less confusing results pasting the OCRed text from Espacenet into DeepL that 75RR mentioned. I never found any US patents.MichaelG. wrote: ↑Tue Dec 22, 2020 10:51 amFor convenience ... This page is in English, and includes citations, etc.
https://patents.google.com/patent/DE19514358C2/en
Noted, and agreed ... I am a big fan of DeepL
The main reason I linked that page was for all the other references.
MichaelG.
Too many 'projects'
Re: Dodt gradient contrast
In case "circular oblique", "radial diffusion", etc. sounded too dull, we now have "curved, tapered lightsaber" illumination courtesy of Google translate:
As shown in FIG. 3, the increased contrast is clarified by the fact that the object, such as brain sections, is no longer illuminated with a full light cone ( 9 ), but only with a curved, tapered lightsaber ( 10 ).