I just want to share something that I've used to molt sex little slings without using a microscope. I've had success determining the sex of slings at ~1.5", even had one at ~1" dls.
Ok so here's what I used at first.
I got the lens from a broken dvd-rom, you can also get one from a laser pointer. ;)
I then super glued the lens on a paper clip to act as holder, just be sure to not get glue on the center of the lens.
You can then attach it to the back of your phone with a tape.
Now, preparing the molt is the hard part, to start with, please click here for basic info on sexing tarantulas , this will give you an idea how to open up a molt for sexing. Though, small sized molt would be even more difficult, I personally use tooth picks, not a pair of pins.
You should now be ready to take pictures, in macro, to try to sex your sling! Please note though that your phone should be about an inch or less away from the skin for it to focus. You may device some methods to keep your hands and phone steady so you can get better view and pictures.
Ok, I did find a better and still a cheap way to molt sex a sling, I found a mini 60x LED UV pocket microscope for only $2.78!