What's Better - Phase Contrast or Dark Field for Nutritional Microscopy?
A RECENT QUESTION:
I'm looking into buying a microscope for dark field microscopy for live blood viewing and have found that some people think I should buy a microscope that has a phase contrast turret condenser whereas others think that dark field microscopy can only be done with a microscope having a dedicated dark field condenser (dark field double immersion technique with a Cardiod DF Condenser).
Which do you recommend and why?
As you might recall from class, the turret condenser being driven with a lot of light through our fiberoptic cable does a pretty decent job with darkfield - even using the everyday 40x non-oil objective.
It impresses many long time "darkfield only" folks. With the turret and good optics, you can escape having to use oil everytime you look at a live blood slide, and you have the option of going from phase, to darkfield, to 3D, to brightfield - simply by rotating the turret.
During a session you will be flipping from live to dry and back to live and having to mess with the oil each time gets to be a pain in the butt.
Also, and this is a BIG consideration, when you go to the dry layer you have to take the darkfield condenser off the scope and put on a bright field condenser - and make sure you don't contaminate your dry layer with oil. Then when you are done with viewing the dry layer, you would go back to the live sample and again have to take off the bright field condenser and put the oil dark field back in place. Adjusting dark field is a skill that I have seen lacking in even long time microscope users.
I have seen some microscopy trainers simply take off the dark field condenser and not use a bright field condenser for the dry layer - probably for convenience - but this gives a completely erroneous appearance to the specimen as it requires a condenser to flatten and smooth out the light.
Phase contrast renders very well to a video monitor with its rich grayscale shading while dark field, due to its intense contrast, does not do as well - but through the eyepiece it looks stellar if using the dedicated oil condenser and objective.
Dedicated oil condensers are most used by people that were taught that way and they are familiar and comfortable seeing the blood with that form of lighting.
There are subtle shade differences seen in phase contrast that is completely missed in dark field. Everything that is seen in dark field can be seen in phase contrast (assuming you have high quality phase imaging as on the Biomedx scopes). Due to the intense contrast and white on black of dark field, some things will jump out at you better in dark field then in phase.
My preference is to use the turret everyday over the dark field due to convenience, the shading ability of the phase image, and the ability to have multiple lighting styles.
However, you don't have to decide which one to buy. You can buy both condensers as well as the appropriate oil objectives and use whichever you fancy at any particular time. Or, obtain the turret condenser first - for all the reasons cited above - an add the oil dark field in the future. You are not prevented from using either one on a Biomedx system.
You can see video imaging of all modes of the scope on the Biomedx core website. Just go to the microscope section.
Seeing these videos should dispel the notion that dark field can only be done with a microscope having a dedicated oil darkfield condenser.