I finally got my D5100 yesterday!!!

   

   

   

if you use lightroom only then you have to mask it very careful and slow with your brush tool and also play with other sliders too

in photoshop there is a auto mask feature that can easy select the hill only, leaving the sky untouch then you can do your adjustment on the hill only and not affect the sky

for other software i dont know la, i use lightroom to do it only

Because the depth of field of f/1.8 is so shallow

Plus the sensor is more easy n accurate focusing on the centre focus point rather other focus point.try using the cntre focus point

move to your focus point.. try not to focus (lock) and recompose

I learnt this from some of the sifu, sometimes when it is hard to focus, it's because we're to relying on the focus point rather than the techniques.

Some of the techniques he taught me is, you can choose the any of the focus point, but make sure the focus point is on contrasting colours. For eyes, you could lock the focus on between the iris and the white area of the eye. See if it works.

either you moved or your subject moved.. or both

I seem to have this problem as well, especially when the subject is not very close. Not sure its because of shake or skill problem

If the subject not big enough, the camera may backfocus. Not big enough means, the focus point around same size as the subject, OR it could be you focus on something not enough contrast or which the camera unable to differentiate, it may focus on something else.
Hard to explain, you have to experiment yourself, and see carefully whether it's really focus correctly, you can re-focus to double confirm. For far away, subject, sometimes you can focus on the shirt, rather than the face. Sometimes you focus on the face, the focus went focus on the background.

To better understand your situation, best if you have the sample photo and highlight where is your focus point.
EDIT: If you did focus re-compose, do mention it as well.
If you're using Focus Re-compose in high aperture especially, then it's most likely the problem.

G lens will always have the widest open aperture when it is mounted, the F number that you see in your LCD is applied when you click the shutter button

so focus at 1.8 and 2.2 makes no different, since you're in event, i assume it is indoor, there are limitation on the lens AF, if not enough light it wont be able to focus well, sometime even in ballroom also will have trouble focusing

and you cant focus and recompose with f1.8, you have to compose then focus and when you focus cannot focus on single color subject, let's say your AF points is at the person's cheek then the lens might have trouble focusing, try focus between eyelid and eye ball, that way you have the color for the lens to focus

Small subject, if you focus the face, you may notice it's likely to focus somewhere else, either the background or something which not inside the focus point. After you taken the photo, zoom in and find where it focus, sometimes is totally not within the focus point, which can be really weird.

Even the face is well lit, but if the camera unable to differentiate or able to catch it, it will focus something else that is easier. It not like how our eyes see, not sure how to explain, but you can experiment on how the camera focus can easily lock on something fast and accurately, while something else, it just didn't really focus well or you can see it hesitates, OR, you try to release and half press again to re-focus, you may notice the focus plane may have changed. For contrasty and easy to lock on, you may notice there is no such issue, it just locks on easily and accurately.

It's annoying especially if you need to take large group photo in events or say wedding, and the focus went to the back or somewhere else. In such case, you can try take 2 photos, one which focus on the face, and another focus on the shirt, or something that the camera can focus and lock on easily and accurately. You may try compare the results.

i usually shoot 1~2 stops below the max aperture as a general rule.. to get max sharpness...

a non moving subject n a stable tripod helps too... 

normally there is no need for that... you only do that on canons.... well those that i used anyways.. modern bodies should have pretty decent AF.. what body are you using again ?

A bit hard to see the bokeh since there's glass at the back
Sorry about that, thought you were referring to the background bokeh
Are you referring to the out of focus on the teddy bear?
But hell that is one fine-looking gurl   

What focus mode are you on? Single, AF-C or AF-A? The way I see, there's quite a few more contrasting lines in the background that would distract the camera AF (just like how [PF T.J.] is distracted with the lenglui instead of looking at the bokeh !  ).

lol, Have to enlarge the photo alot only can see its out of focus la bro
I think its an okay shot, just that the window bars are not that pleasant~
Keep it up yo~ 

cosplay?

got facebook page?

i also shoot cosplay in event

that looks like back focus.. check out the hair on her shoulder... either that or you move or she moved.

Looking at the distance, I think you're too close so it cannot focus.
This might be cheap workaround, but get back a little, then crop it if you want that close picture.
Nice shot, love it!

Took a look at it in original size and given the circumstances, I think you did good. 
Becareful. Dangerous nowadays with cosplay.

it is more like a personal mindset problem instead of whole ACG community. 

if i use nikon D3s (or any full alloy body) whack people heads and i active here then can i say Nikon users are all psyco? 

Can really see clearly cause on mobile, hehe

The original size seems small, did you crop or you resize smaller to 2048?
Seems the backlight is bright, is the pic originally underexpose? Under this condition, bright background and subject is dark, the autofocus may have accuracy problem too.
How near/far is the subject, as in the focus point is around size of her eyes or you're further behind that the autofocus point is around the size of her head?

Wooooh, nice clicks