dark field is overrated for microbiology
it is used for seeing spirochetes - but the data tells us that spirochetes are just not present in sufficient numbers in the blood of chronic disease patients to see them ( one exception is the acute phase of TBRF - but that's not a typical case for people with CFS who have been sick for years).
for example PCR tests can detect 1 spirochete in 0.5ml of blood - and yet PCR tests of confirmed positive patients are negative 50% of the time - therefore spirochetes are v rare in the blood ( they live mainly in tissues)
BTW 0.5ml of blood is enough blood for 20 sides
it will take you a week to look at 20 slides properly and your chances of seeing a single spirochete in 20 slides are near zero
darkfield can be used to look at spirochetes in culture where the numbers are much higher - but culturing spirochetes is difficult - and its only one of dozen or so potentially interesting pathogens
by the way - there is a huge amount of rubbish posted on the internet by people who earnestly claim they can "see" spirochetes all over the place in blood samples. in 99% of cases these are artefacts moving under Brownian motion being misidentified as spirochetes. artefacts are a common issue in microscopy.
fluorescence microscopy is a whole other topic - really only used in the research setting - needs super expensive kit and has limited applications - ask yourself what is the benefit and can you even buy the fluorescent dyes, filters, prisms, or fluorescent tagged antibodies etc used
simple bright field is the most useful place to start
you need a decent compound biological microscope with abbe condenser, 10x, 40x and 100x (oil) objectives and 10x Eyepieces ( this is pretty much the standard configuration )
aim to spend around £300+ to get something suitable - amazon has offering from Swift etc that fit this
used microscopes can be cheaper -perhaps even ultimately better - but most used ones will need some form of refurbishment - which is its own can of worms
a camera attachment with at least 5mp is useful to document your findings - consult others for input etc - an iphone can be adapted to do this
be aware - its a learning curve - the instrument itself is the relatively easy bit - the learning how to stain and use the instrument the next relatively easy bit - most of the effort is in training yourself to identify what you are looking at accurately.
you can get a scope next day - look at a sample that afternoon and exclaim you see stuff moving so you must be infected - but this has zero real world value as everything moves at this scale and you will have no clue what you are looking at.
have a look at my thread here where i documented my own journey with microscopy if you need further input
https://www.healingwell.com/community/default.aspx?f=30&m=4268122&g=4268131#m4268131
the thread takes a while to get going as you can see my own learning curve - initially i thought perhaps i was looking at Babesia - later as my knowledge increased i was able to definitively identify it as Bartonella