Simplified Variable amplitude contrast (VAC) setup & DIY HMC

Here you can discuss DIY adaptations to the microscope.
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imkap
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Joined: Thu Nov 25, 2021 9:44 pm

Re: Simplified Variable amplitude contrast (VAC) setup & DIY HMC

#31 Post by imkap » Mon Feb 27, 2023 12:18 am

Thanks for sharing, I like the footage. Probably I'll get back to this in some time and try to print (and understand a bit better), now I'm pretty busy.

dolmadis
Posts: 45
Joined: Mon Jan 08, 2018 6:06 pm

Re: Simplified Variable amplitude contrast (VAC) setup & DIY HMC

#32 Post by dolmadis » Mon Feb 27, 2023 7:13 am

Thanks for this very interesting thread.

I would welcome a thingiverse link please.

John

Sansub2
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Joined: Wed Oct 20, 2021 3:34 pm

Re: Simplified Variable amplitude contrast (VAC) setup & DIY HMC

#33 Post by Sansub2 » Mon Feb 27, 2023 11:45 am

Sure. Will post it later today.

ldflan
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Location: Morna Moruna

Re: Simplified Variable amplitude contrast (VAC) setup & DIY HMC

#34 Post by ldflan » Mon Feb 27, 2023 4:22 pm

That's starting to look right! Nice job. The analyzer slit needs to be at the back focal plane of the objective. For low power objectives, your insert is probably at close to the right place - the back of the objective. For higher power objectives the back focal plane seems to be in the barrel - harder to get to. I'd be really interested to see what kind of results you get with a dedicated HMC objective, one where we know the analyzer is properly placed. Should work well.

Sansub2
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Joined: Wed Oct 20, 2021 3:34 pm

Re: Simplified Variable amplitude contrast (VAC) setup & DIY HMC

#35 Post by Sansub2 » Mon Feb 27, 2023 11:44 pm

dolmadis wrote:
Mon Feb 27, 2023 7:13 am
Thanks for this very interesting thread.

I would welcome a thingiverse link please.

John
Hi John,

I recreated my account today and uploaded the files. Looks like I have to wait for 24 hours before I can publish it. Will post the final link around this time tomorrow.

Sansub2
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Re: Simplified Variable amplitude contrast (VAC) setup & DIY HMC

#36 Post by Sansub2 » Mon Feb 27, 2023 11:55 pm

ldflan wrote:
Mon Feb 27, 2023 4:22 pm
That's starting to look right! Nice job. The analyzer slit needs to be at the back focal plane of the objective. For low power objectives, your insert is probably at close to the right place - the back of the objective. For higher power objectives the back focal plane seems to be in the barrel - harder to get to. I'd be really interested to see what kind of results you get with a dedicated HMC objective, one where we know the analyzer is properly placed. Should work well.
Thanks ldflan. I was looking at the image in this link below and tried to follow it. The modulator sits on top of the last lens element as a seperate add on. It is possible that i might have to move a bit up to find the back focal plane. That might be the one causing dark shadow on one side and light creeping on the other side. Given that not much spec information available for HMC, it is going to be trial and error.

I would like to see the full effect of HMC as well. Very few videos in youtube and the following one gives me some idea.
https://youtu.be/ipMbyo4Y4U8


https://www.olympus-lifescience.com/en/ ... -contrast/

Image

ldflan
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Re: Simplified Variable amplitude contrast (VAC) setup & DIY HMC

#37 Post by ldflan » Tue Feb 28, 2023 5:23 am

Sansub2 wrote:
Mon Feb 27, 2023 11:55 pm
The modulator sits on top of the last lens element as a seperate add on. It is possible that i might have to move a bit up to find the back focal plane. That might be the one causing dark shadow on one side and light creeping on the other side. Given that not much spec information available for HMC, it is going to be trial and error.
Yes, the diagram shows the analyzer at the back lens element, but that's not where the back focal plane always is. Like I mentioned before, sometimes it seems to be well down inside the barrel, at least based on where Hoffman placed the analyzer in those objectives...

apochronaut
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Re: Simplified Variable amplitude contrast (VAC) setup & DIY HMC

#38 Post by apochronaut » Tue Feb 28, 2023 3:27 pm

Hoffman's design was derived from the existing concepts and optics geometry surrounding phase and DIC microscopy of the time (1972) and it made perfect sense in the context of purpose building an HMC objective. In retrofitting an objective however, it isn't that difficult to do so on an older straight forward conjugate finite objective such as many were in 1972, where the back focal plane is projected beyond the rear lens element. In 1972, the only infinity corrected objectives were AO and just beginning Reichert. Arthur Shoemaker's 1972 patent of an infinity corrected 100X 1.25 planapo with 14 elements in 8 groups forever altered objective design and since then most well corrected objectives have the back focal plane in advance of the rear most lens group. The rear most lens group exists expressly to confer aberration and directional corrections upon the focused convergent ray bundle. Even if you did remove the rear group of your intended objective, your modulator would need to become part of the shim stack preceding the rear lens cell, not an impossible task but a bit tricky with plastic. It's not the 40X PlanF is it, because I've had one of those apart?

It doesn't matter where the modulator is located though, as long as it's location is matched by the slit location relative to the condenser. A similar principle is used in locating the phase annulus outside the objective in some phase systems, such as Reichert did also around 1972 and for all contrast systems.
If you locate the slit at the entrance pupil of the condenser you can locate the modulator at the conjugate location of the objective, which will be somewhere above the objective.
Last edited by apochronaut on Tue Feb 28, 2023 4:22 pm, edited 1 time in total.

ldflan
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Re: Simplified Variable amplitude contrast (VAC) setup & DIY HMC

#39 Post by ldflan » Tue Feb 28, 2023 3:42 pm

What's a "moderator?"
If your history is correct, why do HMC objectives built on short barrel 160TL Olympus objectives have the gradient stip inside the lens assembly, deep in the barrel? Clearly your recitation is not fully correct.

apochronaut
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Re: Simplified Variable amplitude contrast (VAC) setup & DIY HMC

#40 Post by apochronaut » Tue Feb 28, 2023 4:21 pm

Of course many HMC objectives have the modulator inside, obviously as more objectives utilized a rectfying back lens group. Not necessarily the case at the beginning though, nor in diagramatic representations, which no doubt harken back to a simplified view.
Those diagrams give a false impression of the actual design in a modern objective , always making the back focal plane look accessible.

Sansub2
Posts: 101
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Re: Simplified Variable amplitude contrast (VAC) setup & DIY HMC

#41 Post by Sansub2 » Tue Feb 28, 2023 5:37 pm

apochronaut wrote:
Tue Feb 28, 2023 3:27 pm


It doesn't matter where the modulator is located though, as long as it's location is matched by the slit location relative to the condenser. A similar principle is used in locating the phase annulus outside the objective in some phase systems, such as Reichert did also around 1972 and for all contrast systems.
If you locate the slit at the entrance pupil of the condenser you can locate the modulator at the conjugate location of the objective, which will be somewhere above the objective.
Thanks Phil, really appreciate the info and your knowledge as always. Your above paragraph gives me hope :). I did put the objective insert few mm above the last lens elements and it seems to work better(getting much more even illumination)

At the end of the day, even though it may not look like exact replica of the purpose built HMC, if the output is close and get good results, that is what I am aiming for. Based on the results I got, it is getting close. The output is much better and cleaner than the normal oblique. The details are clear. It is bit of work initially though. I wish I had test diatoms to compare. Cheek cell is my go to now :mrgreen: and I can make plenty.

Sansub2
Posts: 101
Joined: Wed Oct 20, 2021 3:34 pm

Re: Simplified Variable amplitude contrast (VAC) setup & DIY HMC

#42 Post by Sansub2 » Wed Mar 01, 2023 12:07 am

dolmadis wrote:
Mon Feb 27, 2023 7:13 am
Thanks for this very interesting thread.

I would welcome a thingiverse link please.

John
Please see whether you can access this link

https://www.thingiverse.com/thing:5881647

dolmadis
Posts: 45
Joined: Mon Jan 08, 2018 6:06 pm

Re: Simplified Variable amplitude contrast (VAC) setup & DIY HMC

#43 Post by dolmadis » Wed Mar 01, 2023 4:05 pm

Sansub2 wrote:
Wed Mar 01, 2023 12:07 am
dolmadis wrote:
Mon Feb 27, 2023 7:13 am
Thanks for this very interesting thread.

I would welcome a thingiverse link please.

John
Please see whether you can access this link

https://www.thingiverse.com/thing:5881647
Yes, i was able to DL.

John

rmb
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Joined: Fri Dec 01, 2017 5:38 pm
Location: scotland near Edinburgh

Re: Simplified Variable amplitude contrast (VAC) setup & DIY HMC

#44 Post by rmb » Sat Sep 09, 2023 6:45 pm

Interesting but.
Firstly the centre of each vac stop need to be a different sizes for each objective. This depends on your objectives and their NAs. Greater NA bigger the central stop. Try something less than 10mm for lower powers first. A 40x objective might need near to a 19mm central stop which is very difficult to fit into a condenser
The stop has to be centred and focussed in the back focal plane of the objective as you would with a phase condenser stop(indeed a phase condenser makes the best device for vac because you can centre the stops and they are in the right place)
The condenser iris should be fully open at all times to get the full benefit of the illumination and to uee the full NA of the ob.
When the central piece of polariser is correctly orientated on the 3/4 segment beneath it should be completely black or as near as the polariser film allows. This central spot also needs to be precisely in the centre of the piece it is stuck to.
Use a circular camera polariser innthe light well and turn that to see what happend. If you are putting the stop in the filter holder of you condenser try racking it up slightly yo bringbthe stop into focus. Some condensers just dont work
Vac is not dic but the illumination effect is equally profound and arguably with grater resolution. and it works well with thicker specimens. It takes a bit of fiddling to get sizes and centring set up properly

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