Microscopes for use with NA
The following features have been found to provide the necessary functionality for incubating NA.
1. Compound microscopes are preferred by most users.
- So, for NA ova, the compound works great, as everyone knows. However, both the dissecting scope and the USB scope completely failed… I’ve tested several (USB scopes) with poor results.
- Most of the digital microscopes, including USB microscopes, that have been tested so far have had problems, including poor optics and camera quality, and a lack of bottom illumination, although the Carson MM-840 eFlex appears to be an exception to this. See the details, below.
2. Binocular microscopes are more comfortable to use, especially for long scoping sessions, but monocular ones are cheaper, and the user can always wear an eye patch to save having to hold their free eye closed!
- I bought a cheap monocular through Ali Express which was fine, but was then given an old surplus university Olympus binocular which is much more comfortable to use. 
3. A moveable mechanical stage makes it much easier to scan slides to locate larvae, and for egg counting.
- I found the mechanical stage (an extra $20) important for an accurate larva count.
- I cannot imagine trying to count larvae on a fixed stage. 
4. A good lighting system. Either halogen or LED is preferable. A mirror lighting system may not be adequate. A good iris and concentrator system may also help, plus a rheostat for dimming the light.
- A light underneath is important, although I also use a desk lamp. 
5. Magnification of at least 40x - 100x. 40x (i.e., a 4x objective lens combined with a 10x ocular lens) has been found to be adequate by most growers of NA for counting hookworm larvae and eggs, although others say they need 100x for egg counting and larva identification.
- At 20x to 40x, L3s are easy to recognize. For eggs, you need a compound scope with 60x to 100x power. 
Some NA growers even prefer 200x, and one has expressed appreciation for a scope offering 2000x magnification, e.g., the 40X to 2000X Trinocular LED Compound Microscope with Siedentopf Head.
- I have found myself using 40x, 100x, and 400x every single time. I could see the larvae just fine with only 40x, but I enjoy looking much closer. And having the 400x - 2000x (oil) I can look at other much smaller things living in samples that I am working with. 
- I am very happy that I went with the 40-200x AmScope! The trinocular with 5mp camera makes photography so easy, as well as allowing other people to watch what I'm working on on my computer. The movable stage allows me to methodically look through the slides - I can't imagine having to manual move the slide with my hands. And I have found myself using 40x, 100x, and 400x every single time. I could see the larvae just fine with only 40x, but I enjoy looking much closer. And having the 400x - 2000x (oil) I can look at other much smaller things living in samples that I am working with. 
- OMAX 40X-2000X Lab LED Binocular Microscope with Double Layer Mechanical Stage.
- I’m totally happy with this one It's great for incubation. 
- I use an AmScope (M158C-2L) that I got for $80 from amazon. It does 40x (which I use most), 100x, and one higher power that I never use. It's monocular & doesn't have a moveable stage, but works fine for what I need & didn't break my budget. 
- I get excellent images with it, and the price is right, but it does have its problems: I'm having to replace the failing illumination switch and power jack, and its very poor "parcentricity" can't be fixed, I guess. 
- … my AmScopes are great quality; you can also find the same scopes rebranded as OMAX. 
- I used (this) last week for counting NA. It was quite cheap to buy, and I wanted something easy on the eye. I could use it without needing my reading glasses. It was quite easy to use, and you can take photos and video. Basically, it was just fine to use for counting the worms but I would have liked a little more magnification so I could have seen them up close. I wouldn't have been able to use it for counting eggs. I found it a little wobbly - it needed to be set up and then not touched, just move the slide. Another issue was that the worms all had shadows because of the white base. So what looked like two worms moving in exact unison was just one worm with a shadow! 
And a comment from someone who used a Standard Compound Microscope for the first time after previously having only used a USB Digital Microscope.
Dissecting microscopes are ideal for working with HDC, but are generally not considered suitable for use by hookworm incubators. However, one hookworm grower who has longterm professional experience with microscopes does prefer to use a dissecting scope when working with NA. He uses this one which has a 4x objective and 10x oculars.
See the section below ("Microscopes for use with HDC") for more examples of dissecting microscopes.
Some microscopes have a dark-field option, perhaps in the form of an alternative lens assembly. This may not be as useful to hookworm incubators as a standard transmitted light microscope,  but might possibly make the grainy stuff inside L3 larvae more visible by visually separating materials that have different refractive indices. 
"Trinocular" microscopes with built-in photo port
Whilst by no means essential, the option to securely attach a camera to the microscope head has been appreciated by some NA growers.
Microscopes for use with HDC
- OMAX 20X-40X Dual LED 3D Stereo Dissecting Microscope with Multi-Power (Batteries and AC Adapter) and All Metal Frame + Premium Quality Glass Optics.
- AmScope SE306R-P-LED Stereo Dissecting Microscope This is a rebranded version of the OMAX scope above. Identical, but cheaper.
Useful short YouTube video with commentary.