What kind of microscope should be used to view biological structures (such as spores) roughly 5 µm in length?

Question

I would like to be able to identify genera of fungi based on the shape, size, and colour of spores. So the requirements are:

• Must be able to view a 5 micrometre object clearly with reasonable resolution
• Must be true colour
• Must facilitate the measurement of an object within reasonable accuracy (500 nanometres would be nice)
• Should be inexpensive (\$100-\$400) ^{fingers crossed}
• Bonus: Be able to take photos

What type of microscope do I need? What magnification/resolution? Is there a good rule of thumb relating size of object with magnification?

How do I find and purchase a decent microscope after defining my requirements? Any tips?

Blue light is ~450 nm, so does that mean I will not get very good resolution?

(For the sake of context: I have absolutely no formal experience in biology, but I have recently taken an amateur interest in mycology and might enrol in an undergraduate course as part of my degree at some point.)

Answer 1

I think you have a good question, but if you want to get a good understanding of the issues you raise with it, then you really ought to consider spending some time reading this optical microscope primer. In my opinion, you need not bother with taking an undergraduate course at a physical university. As an intro to biology (which is not really necessary if all you want to do is look at small things in a microscope and understand what you're seeing), you might want to consider enrolling in this free class, but if all you want to do is look at small things and have a basic understanding of what you're seeing, I think all you need to do is read the primer.

If it was me, I'd read at least some of the primer before investing the money in a microscope. Otherwise you're just taking a blind leap of faith from someone's (perhaps biased) suggestion.

Answer 2

I agree with Kevin F, if I was you, I'd take a bit of training before buying something or even trying. Biology teachers or staff from the university are usually happy to provide you with a microscope to test something, so just ask. If you want a resolution that high, there are a lot of adjustments to do, commonly referred to as "Köhler illumination", because otherwise you won't get a nice picture.

To answer your question, you can basically forget microscopes at that price range for this resolution, let alone the ability to take photos. You would have to spend >$1000 to get something good enough. As in photography, this is largely due to the lenses. I don't have much experience with fungi, but you might want to have a phase contrast microscope to be able to see the specimens properly. You can buy microscopes with have a port for a DSLR camera, with which I've made good experiences.

For a 5 µm object, you could use a $60 \times$ lens (which, together with a $10 \times$ ocular makes a magnification of $600\times$), or even a $100 \times$ lens, when you want to resolve surface structures, but no idea, if the latter really works with your specimens, so you'd have to test that before buying.

So: First, get a bit of formal training, as suggested by Kevin F. Then, try it yourself without buying, and try it with your own specimens! Then, save money and buy. :-)