HMC / Phase Contrast comparison

[Radazz]

As requested, Here is a comparison between Hoffman Modulation Contrast and Phase Contrast.
I chose a Pleurosigma from and antique slide in my collection.
Had a heck of a time finding the same one on two different microscopes. These were shot with two different cameras.

IX70 HMC 20x 8 shot stack Canon EOS 7D


BX40 Phase Contrast 20x 7 shot stack 14MP digital microscope camera


Enjoy,
Radazz

[Hobbyst46]

Thanks for posting this comparison! amazing result! the HMC did well, the phase not so well. Probably the stacking affects the result? may I ask, do you see the same trend in single images?

[viktor j nilsson]

Agreed, the HMC one looks good, the phase one not so much. Would it be possible to shoot them using the same eyepiece and camera? Difficult to say to what extent these differences are due to the camera. I'd guess quite a lot. I'd expect the phase to look better, honestly.

[desertrat]

Great images!

Does a phase ring in an objective reduce its resolution somewhat? I think I remember reading about this. Also, do the two objectives have the same N.A.?

[apochronaut]

HMC is somewhat similar to using a slit lamp, a technique that was used over 100 years ago. It produces a kind of oblique illumination which shows up relief, primarily when the slit aperture is offset.

Straight on phase doesn't but, if the phase condenser is offset and the iris used as well to produce an oblique illumination, all the while maintaining annuli centering, phase can be coaxed to produce a considerable amount of relief as well. I have seen phase images that get pretty close to DIC.

love these comparisons. nicely done Radazz.

[Radazz]

Agreed, the HMC one looks good, the phase one not so much. Would it be possible to shoot them using the same eyepiece and camera? Difficult to say to what extent these differences are due to the camera. I'd guess quite a lot. I'd expect the phase to look better, honestly.

Might be possible for a microscope that has both phase and HMC.

Now this is a phase contrast image made on a Nikon Labophot-2 phase contrast and the Canon EOS 7D


Stuck with this camera on the BX40. No way to use the Canon camera.


This camera mount is the best one I’ve ever used with a DSLR. The 50 pound microscope damps out most of the mirror vibration

Radazz

[Hobbyst46]

Still, by reference to the top photos,

Does a phase ring in an objective reduce its resolution somewhat? I think I remember reading about this. Also, do the two objectives have the same N.A.?

IMHO, the resolution of the HMC (top image in the post) and phase image (second image) is about the same, judging from the striata in the top half of of the longest diatom (Gyrosigma ?). There is a strong CA in the phase image, and this effect, I believe, would appear in the single images as well. This CA may be cause the less appealing PC stack vs the HMC stack.

The third image is very attractive, and much less CA, owing to different optics and or illumination. Is it the same type of phase (negative/positive) as in the second image?

[ImperatorRex]

Radazz, thanks for the comparison. Is the comparison what contrast methode makes the better resolution?
Not sure if a stacked image is really the preference to compare in that case.

Some thoughts and assumptions:

Question on the numberic aperture of the Objective. The 20x objective maybe has a n.A of 0.40?

To me the diatome shown on your fotos look like Gyrosigma, I have this diatome on a test plate. So it is probabely not Pleurosigma. For Gyrosigma I found the below description:

"The Gyrosigma balticum has a relatively rough structure, about 11-16 transverse and longitudinal stripes per 10µm. A objective with n.A. of 0.45 shall resolve the structure."

I tested the Gyrosigma balticum with an 16x/0,40 Objective and neither bright field nor phase contrast did resolve the structure. With oblique illumination the structure was at least partly visible - similiar as you have shown on HMC, but of coarse with less contrast. DIC seems to begin to resolve both, transverse and longitudinal stripes, but I am not sure if I would be able to document such with a foto. The ocular often shows a bit more details

[Radazz]

Did I say NO Way?


I couldn't find exactly the same diatom, but had to test this.
Just a single shot concentrating on the texture.
BX40 40x phase contrast


Definitely the camera.
There will be better.
Radazz

[ImperatorRex]

Looks great Radazz.
It also confirms that with a n.A of 0,65 (typical n.A. for a 40x Achro) it is possible to resolve the structure of Gyrosigma balticum.

[viktor j nilsson]

Did I say NO Way?

I couldn't find exactly the same diatom, but had to test this.
Just a single shot concentrating on the texture.
BX40 40x phase contrast

Definitely the camera.
There will be better.
Radazz

Thanks! Love these comparisons. Great job finding out a way to set up the 7D on the BX40. Looks like time well spent, the results looks very promising. Do you think you will use this setup, or is the inconvenience of moving the camera too great? The

In due time, I hope to be able to compare DIY Hoffman with Nikon 40x 0.55 HMC LWD vs. Nikon CF N Plan 40x 0.70 Ph3 on the same scope.
My expectation is that they will be good att different things. Phase NA 0.7 should clearly outresolve HMC 0.55, but the HMC should be cleaner and more pleasing to the eye. Your 40x Phase image certainly has that restless background.

How do you find the colors to be with your HMC setup? I keep seeing HMC described as "greyscale", but I am wondering what would happen if you combine the HMC effect with some color gradient like litonotus GUF filter.

[Radazz]

Obviously I couldn’t tell you the difference between pleurasigma and girosigma, and like amoeba, I am going to stop trying to identify them. Wouldn’t want to put misinformation on the internet

So far, it looks to me that, just like phase, if the subject has pigment you will see color, but I see more refractive colors with HMC if I accidentally use the wrong slit in the condenser.
Birfringent materials don’t really react without an extra analyzer, but the combination of POL and HMC is much like POL and oblique, and can make the image look like raku pottery glaze.
Radazz

[Hobbyst46]

One small note: IMO, and as far as the cleaned diatom resembles glass, it is not birefringent. Its colors in micrography photos arise from refraction/diffraction, and are visible irrespective of polarization of the illuminating light.