Wow, wow, wow! That's how I felt when I figured out how to do the Blind Hem on my Janome 521. I needed to hem up some pants for father-in-law and didn't want to do them by hand.
It's a machine alternative to the catch-stitch I believe but don't quote me on that.
There's a super cool tutorial on Hoppo Bumpo about how to do it. I've just added some of my own pictures here to show you the process I went through. There's varied fabrics featured as I ended up doing three pairs of pants.
Above: This is my blind hem foot (G). The edge of the white part needs to stay aligned with the fold so your needle just catches this line when sewing. See my lovely bamboo stick pointing to the folded edge! You will be working on the wrong side of your pant leg.
^ To begin what I did was overlock the raw-cut edge of the pair of pants I was hemming.
I folded it to the length of what I wanted it to end up to be, pressed that and pinned a line about an inch from the folded edge. This line will be the catch-stitch of your hemming foot. I advise to pin horizontally so that when you fold the pins under you end up with a flat line.
^Next I flipped the hem so the pins are now on the inside of the pants.
^ You then need to pin this side by removing the inside horizontal pins and placing them on the other side with the fold.
^ Now place your folded edge under your foot to begin sewing. Make sure you have the correct settings for your blind hemming stitch and that the white guideline stays in line with your fold otherwise you end up with open parts of your hem.
When you are done you can see your row of stitching. The pointed part of the stitch is where your needle has caught the fabric, thereby keeping it in place!
When you wear your pants it's not really that obvious, especially if you have matching coloured thread! It's so much faster than doing it by hand but I would just use it on pants rather than skirts which may need more invisible stitching.
I hope this helped you. Let me know if anything confused you. I advise to practise on a scrap piece of fabric. For me, it was really fun and I'm so glad I decided to read my manual and try something new!
Have a great weekend.