Nikon D3100 Viewfinder is blurry?

Hi, so I got a nikon d3100 and for the longest time I have only been using the lcd screen when taking pictures because the viewfinder is just blurry.
I know there's a knob next to the viewfinder, but it doesn't really help as far sharpness. It looks really blurry and is really unusable as far as taking pics. The glass seems to be clean so I don't know if its just not aligned or something.

Please let me know if there's anything I can do to fix this problem within settings or any other way.

The knob next to the viewfinder is called the Diopter adjustment control. First, focus on something. Then, while looking through the viewfinder, move it one direction until it stops, and then back all the way. At some point the subject should become clear. If it doesn't, and all the glass is clean, it could be the mirror in the camera, which means taking/sending it to a repair shop. But first, try adjusting the diopter - remember to autofocus on some subject first.

I would have suggested giving that small circle a twist next to the view finder, but you have already tried that. Perhaps it has had a bit of a knock somewhere, causing the view finder to be blurry. I would take it in to a local camera store and ask, or send it to Nikon and see if they can do something for it.

Guess you know about the diopter adjustment that is discussed on page 22 in your manual. It could be that your eyesight is bad enough where the diopter adjustment doesn't have enough range to compensate for your eyesight. Unfortunately, the D3100, and the other low-end Nikon DSLRs, have a pretty limited diopter correction. When you move up to the D7100, and better bodies, the diopter adjustment range is wider.

You can get eyepiece correction lenses that extend the correction range. See page 176 in your manual.

If the dioptre correction isn't working at all then it's broken and needs repair. If it's working but doesn't improve the image sufficiently then it suggests that the focussing screen has become dislodged. You may be able to re-seat that yourself, but it can be a bit fiddly and you risk getting dust, grease and fingerprints all over it.

Note that you might be able to buy a good used d3100 body for less than the cost of repairs to yours after you've allowed for the resale value of your existing body.

If you use prescription glasses, wear it when adjusting the diopter and wear it whenever you use the camera.

If it really is blurry beyond reason, have it checked at the store you bought it from.