I have a EF 24-105 f/4, have been doing great outdoor, but lately taking more pictures indoor wand the constraint of f/4 starts giving problem in stopping the motion. Tried ISO setting etc.

Am thinking now to either (1) get the expensive 24-70 f/2.8 L II USM or (2) just get the 580EX II Speedlite, or (3) a cheaper f/2.8 f/1.8 lens... Which one is a better and more sustainable option?

first of all, what kind of shutter speed you need? and does the place allow flash? how's the lighting? there's a few way to get fast enough shutter speed, but you need to tell more about it.

If the place allow flash, then go for the flash, cheapest and quickest solution. and mind you, f2.8 only gives you 1 stop of faster shutter speed compared to f4, so getting something f1.8 will be better, but you can't zoom with that. and are you using FF or crop body?

Thanks. So far It's for places that allows flash, e.g indoor birthday party and kids events. And thanks for reminding me that I might end up in a no flash allowed situation.

My worry is to buy another lens and end up
still getting a speedlite eventually.. I quite like my current 24-105, though on crop body. May be I shall get the 17-55 f2.8 and a speedlite, since I am using
crop body? Or speedlite alone will do?

This post has been edited by jugo178: Dec 25 2013, 12:38 PM

Getting a flash for dimly lit lighting situations is a no brainer unless your intention wasn't for portraiture, that is just capturing the ambience and essence of the environment.

P/S, if f/4 isn't enough, f/2.8 won't offer that much of a improvement also, it's just 1 stop of light, is that enough for you? I'd go with a f/1.4 lens if you don't mind a prime and with that, I can shoot at higher shutter speed and at lower ISOs ( I hope you aren't shooting like ISO3200 or higher)

Thanks for the advice! Speedlite will be my solution. never want to do ISO 3200 or higher.

If the kids are about the same distance from you, using flash is fine.
But if one, say Tom, is 2m from you, and another, say Jerry, is 4m from you, flash isn't a good choice.
In that case, if Tom is properly exposed, Jerry will be underexposed; if Jerry is properly exposed, Tom will be overexposed.

take a flash, learn to use it remotely with bounce and diffusing. If you are close enough, DIY a ring light.

and something about flash that you need to remember, even getting a speedlite wont gives you good picture instantly. Yes, you can get clear picture now, well exposed too, but it will turns out plain and not appealing if you didn't control it nicely, direct flash gives you bad result most of the time.

Also, let's say you are shooting in a really dark environment and the roof is not white (canceling you the option to bounce), then flash will be really hard to control to get nice pictures. I encountered this kind of situation while shooting a concert yesterday, end up bumping up my ISO to 3200 instead of using flash because without ambient light, people won't know what's happening other than knowing who is the person in the picture.