You have two and a half basic controls on a camera, over 'exposure'
The shutter speed - controls how long the camera lets light n when making picture. Lnger t's pen, more stuff will move, whether the camera or the subject, so the more your image will 'blur'
The aperture - a tap, lets in more of less light. More aperture lets in more light, so you can use faster shutter for less blur, but reduces the dpth of field, the amount in focus infront and behnd the point you focus on.
ISO Sensitivity - the 'half' control. Higher sensitivty meds less lght to make an exposure, but can mean more noise, or 'graininess', how well resolved contrast in the picture is.
As general rule, you would like to pick the apeerture that gives the depth of focus you want, and the shhutter speed to control the amout of blurr you are likely t get and then balence the exposure on the ISO, erring towards using the lowedt ISO you can get away with; when it starts to become finding the best compromise between the three,
In auto modes, the camera will generally try and sort this all out for you. AND the metering systems they have are very very good, these days. Gong manual, for the sake of, is probably no great help, and more likely to gve more oportunity for error than ltting the camera do its thing; thats one of the thigs its pretty good at; focusing t something it's ot so good at, and I can almost garantee you are letting it do that bit for you, whilst knowng what's gong on byond the lens and composing the picture for the best shot s somethig it hasn't got a clue about, only you do.. so good idea to concentrate on doing the stuff only you can, and letting the camera do the stuff it does best!
NOW:- Idoors, shootig kids... hold that thought a moment.. I just need to go to the room with the padded walpaper for a moment...... OK that's better... soory, my bad, I am still trying to load the camera with bullets... back in a minute!!!! Kids indoors... photographs... err... OK, I thiik I'm over it.. ust dont add any animals into the scenario or I probably will start dog the chicken dance!
Yup, it is NOT the best stuation. Kids is fidgety little things, and fast too. n doors, lghting is usually low, and often not very flattering. If you want mantlepiece shots? Probably best dragging them to a studio! PAY sme-one else to have the problem! ITS WORTH IT! If you want pontenouse candids? Then you probably need to recalibrate r deas about 'quality' they wont make it easy for you to get situatioal shots, its a case of hopng for the best and expectg the worse, working fast ad NOT gettng over ambitiouse, arty or pretetiouse about the job. Save that for the studio when you have drugged the lttle darlings. OK bred them with ice cream and stuff!
Now, fast lenses, f1.8 is pretty wide, but it's only aroud one f-stop faster than f2.8 you rpobably dont have o a kit lens, that starts at f3.5, which by comparison is 'slow'.. But two stops? f you NEED go wide open, to get an exposure, that is the difference between 1/250th and 1.60'th on the shutter, or ISO 500 and ISO1600. UNLESS you are right up against the buffers of either ISO, and on your camera thats HIGH, what is it ISO 12,800?.. well, its DARK... you are lucky if you ca get an exposure at all! I that scenario, recognise the issue is lack of light, not lack of settgs! If you aren't against the stops... then, IS going wider the best way to get the exposure you want? Remember, that lens is oly giving you two stops more light on the aperture; would you get more better results stoppng down to f2.8 or 3.6, and usng a slower shutter, and or higher ISO? How high an ISO can you stand?
Do you need such a fast shutter? Kds is quck, but is t subject motion thats giving you blur, or camera shake? If it's camera shake, learning to hold the camera well, taking a deep breath and 'squeezing' rather than snatching the shutter releae can go a long way to help you get shots at far lower shutter speeds. Couple of years ago, we had a shutter speed limbo the house, to test Image stabilised lenses and my holdng technique, vs my daughter dong her O-Level photography, and the o/h, 'learning'.... good holding technique dd as much or more than lens stabilisation for both my daughter and I, and more. Good holdng and practce let me go down maybe two stops beneath what my daughter could,that a stop beneath what was claimed for IS lens, and eve that only helped O/H with poor holdig technique drop shutter speed one stop. t IS a very simple but very very effectve t of disciplne, AND if you want to try it, starts b turning off the back screen preview and using the optcal view-finder.. thats what makes an SLR an SLR, why try se it like a compact, eh?
Oh kay.. now what are you getting for that big aperture? Well, a pretty small advantage on beig able to possbly use a higher shuter, or lower ISO, and very big loss, particularly at the sort of ranges you are likely shootg kids in doors... (DAMN I have the image of real bullets back! Hold on I need to vist the 'safe' room for a moent or two again! lol Where as I?).. indoor ranges, your focus dstances will likely be fairly short, so at wide apertures your depth of focus is likely VERY short.... this MAY make for pleasant pictures, with nicely blurred out backgrounds..... BUT, more likely, t will make for many more blurry subjects, as they move, either during exposure or time betwee focus and exposure, or regardless of either, fact that DoF is so shallow only a 'bit' of them, is ever in focus to start with.
Meanwhile.... F the light levels are low, and as mentioned earlier, you are using Auto-focus, IT neds to see as well as you to focu, and even in good light AF isn't all that accurate; and with dartg darlings, even f it finds a dot t fix a bead o, and set a focus, good chance they will shift slightly or you will shift camera slightly, and it will blurr the shot. hckung n an AF assist lght, may help, but if you dont want to alert kids and get a candid, that lamp isn't gong to keep you incognito very long.
SO, its back to top, and the art of photography, MAKING COMPROMISE.
What's important? What are you really tryng to achieve? Hows the best way to acheve that?
And i that... yes, you probably ARE making lie hard shooting wide open. You are making focus that much more critcal, and you aren't givig yourself the best chance of sharp shots, REGARDLESS of lens performance and books say it's sharper one stop or two stops down, THAT is all pretty much irrelevant at this sort f level! And matters little if you are getting fuzzy photo's from a shaky holdng, and poor focus, and sbjects that aren't in te frame when you press the button! Likewise, any 'Style' endowed by the dssasocated out of focus back-grond, really man little.. lots of style do not make a pleasant photo, if the subjects a fuzz the middle!
It starts with the basics. and at the moment that fast f-number prime? Is likely making you problems,which you are probably not actally seeng or if you do aren't identifyng properly... any lack of sharpnes you are perceving probably isn't, t s very likely simple focus error, camera/subject movement, or pure simple BAD lght. And any dfference shootg at f4, compared to f1.8, will likely not be down to the lens..
If you like dissasocated back-grounds.... ironcally you dont need low f-nmber lenses to get them. DoF s a proportion of the focas range Turn the camera OFF auto-focus and DONT focus o the subject! Dot try set a shallow DoF, set a DoF wide eough to get your subject in, and put that DoF around the subject where you want t.. Red dot will arbiterily put it 1/3 infront, 2/3 behind.. but you dont want the background in focus, so pull t forwards, focus infront of the subject, chuck the ackground oof, and leave ay redundant DoF infront of the subject, makng sure nose, eyes and ears are all in t.... its called 'selectve-focus' as oposed to mere shallow focus.
Same sort of effect, better resultsl You get what you want all in focus , you get what you dont want in focus not in focus, AND you have a much larger DoF coverng the bits you do want n focus and more margn around that, and much less liklihood that camera or subject movement will chuck that to pot...Go Manual - FOCUS not manual exposure! Its a big leap from point and press but t IS the 'Gong Manual' that does somethig the camera cant.
But you do ned to read up on DoF and on selectve focus, to start to se ad explot it, and you have to get used t looking composng by the nmbers and looking at blurr through the vie finder to get shar shots ut the camera, so you have to break preview scree dependency as well as Auto-fcus dependency.... But, that liberaton is a big step to getting the ost out of your kit, and not expecting the kit t just gve you what you wat, and that low f-no lens well you may apreciate it, but for very different rasons? You really dont need it to get those ot of focus dissasociated backgrouds, so many love them for...because wthout selective focus, they make them 'easy' to get.. BUT that's not what ther best at, and they will make life harder tryng to use them like that, and expectig the lens to deliver and not have to do the work to get the shot, or dong the work.. but teh wrong place, faffing wth the exposure settigs, rather than the focus
Make sense?