Where do you put the focus point???

Hey guys!

Just trying to learn some more here by your advise. I spent christmas day at Las Vegas with my family. Now when im trying to take some photo during night time, I was trying to capture the ambient light of buildings and such. I had a lot of keeper (for me at least). Now when I take pics during that time, I usually take like 2 or 3 just to make sure i nail the focus. The thing im trying to learn is, when your subject is almost the same size of the focus point, or half the body is covered by focus point, where do you put it? Im asking because when I convert in DPP, I can see where the focus point was, but sometimes, it grabs its focus from the building across the street. Pics was like that thats why I took 2-3 pics of the same shot.

I was putting the focus point on the face, where the top of the box would lay approx. on the hair or eyebrow, but its dark to 100% accurate all the time. Do I put the top of the focus point on the chest area? Lower? Im just wondering "WHAT DO YOU GUYS DO", when such occasion arise from your shooting.

Thanks a lot and happy new year to everyone.

Oh by the way, I was using single focus, not spot single, as I have read here that single focus grabs focus faster than spot single focus in low light. If im also wrong in this, please let me know.

The focus points may very well grab focus of something halfway into the next focus point, if there's good contrast there.
Even the spot AF point is slightly larger than the point as it's indicated in the viewfinder.

The fact that spot AF may be less sensitive in low light is simply that it's smaller. The less area the AF point has available for evaluation, the less the chance there there's a high contrast within the point's domain.
And in low light, it's high contrast that's needed, for the AF point to be able to determine anything at all.

In a situation like what you describe, try aiming the AF point at whatever works, lock focus there and then re-compose. If that doesn't matter, another option is to focus where it makes sense to you, see if the camera did acquire focus on the correct place and if not, adjust focus manually whilst you keep the focusing button pressed, to keep focus locked.

This doesn't work if you have a simple kit lens or something like that, since they don't allow for full-time manual adjustment of the focus. In such a case, you have to switch the lens to MF and focus manually. If it's difficult to see the focus in the viewfinder, then this is one of the cases where live view can be of good help.

Thanks for the reply. I considered that, but since its night time, shooting, everything I see in the VF is dark colored, other than the background lights and all.

One example is when locked focus on my wifes face, since its dark behind her, the focus locked on the building behind her which I guess is more contrasty than her face at that time, the thing that bothered me is, the building which it decided to focus on, was across the street.

I rarely do focus recompose since I just move my focus point to whichever I think has more contrast, in this situation I was out with the whole family so I was kinda taking landscape'ish type of shot since the family was spread apart, thats why the subject that i try to focus on, lets say my wife or my brother, was just as big as the focus point itself.

btw I was using my 17-55 the whole time. didnt even occured to me to adjust focus manually. i dont think i could have done any better, but it should have been worth to try it.

You have a 580ex2. Slap on the flash... if you don't want to use flash.. you can disable it and should be able to just use the focus-assist of the flash unit.

But when there's a severe lack of contrast... the camera is pretty much SOL'd. (At least for Canon DSLRs. I believe most Nikon have focus assist.)

At that distance it isn't really going to matter.

The 7D has a nice focus screen. You can actually see focus pretty well on it to be able to double check what the autofocus has done. Using the focus assist light from the external flash is a great idea if your subject is close enough. Using the flash often looks good to light the people when you have exposed for the background. If your wife and brother had contrasting clothes, get them to stand side by side to make a high contrast vertical line for the autofocus then move them where you like once focus is achieved.

Actually you don't need to focus on the subject. You can focus on anything that is the same distance.

Another suggestion would be to have AF only work from the AF-ON button and not from the shutter release so that once the focus is correct, it won't try again if you have taken your finger off of the shutter button. This way autofocus only runs when you ask it to and you can manually focus without the autofocus changing it unless you want it to.

Julian, I was already using the flash. I guess that kind of situation is kinda extreme for me to ask too much of the camera. Would you happen to know the range of the focus assist for the 580, and if it works if i have the focus point anywhere other than center point. I thought I have seen that info here somewhere, just didnt bother reading it thoroughly since I didnt expect to be in those kind of situation. I guess now I know better.

Im at work so I cant post any samples, but here is my info if it would help.

I probably have 7 subjects, all adults, in front of me, lined up sided by side so they were going pretty wide.
AF - on
IS - on
I was probably 5 feet from them.
I have the lens at 17mm
ISO 800
F5.6
SS is variable but its ranging from 1/30 - 1/60
FEC is -1 (only because the flash is directly pointing at them)

Is these setting optimal? I now you cant really tell without the photo, but put in the prospect of general night landscape shooting. Keep mind this is Vegas, so there was a lot of lights of different kinds and color. I will try to upload pics tonight. Thanks guys.

edit: macroimage I already had the focus setup to af-on at the back.

Those settings sound about optimal. Some people don't stand very still so at 1/30, you might find that there is a sharp image from the flash with some blur around it if they moved.

It is hard to see to manual focus at 17mm, especially in low light. You could double check it by looking at the distance scale to see if it looks reasonable. According to the 580ex II manual page 49, the range for the AF assist light is 2-32.8' for the center point, 2-16.4' for the periphery points and it is compatible with lenses 28mm and longer so it should just be OK with your 17mm lens.

Motion blur I would accept, but focus to be 30ft behind subject to come out sharp and my intentional target to be blurred? When clearly the focus point is covering a persons body or half a body. Also, for the range of the AF assist, is it only 28mm and longer? So anything under 28mm is what, reduced ranged or no help at all? Thanks for all the replies so far. Whew! I guess im lucky its not user error but just somewhat kinda extreme situation.

Well, with the situation you described... at 5-7' from the camera, the focus assist lamp should have been able to help you pick up the faces. At the same time, if the camera was still struggling to acquire focus on someone's face, I would have just asked someone to take out their cellphone and illuminated it and hold it up around their neck/face area so I can spot-focus and then switch over to MF so that focus is locked and recompose.

I'm not sure if your settings would have been optimal for the lights, but I suppose w/o a sample photo, it's hard to critique. I would have kept it at f/2.8 or f/3.2, instead of f/5.6. That would then allow more of the background to bleed in at ISO800.

I was just thinking about that too. The only reason I chose 5.6 was that since the nice buildings and light were across the street, I didnt want it blurred out due to wide fstop.

Here is the screen shot of the focus points, I dont know if you cant tell much, but this is just to show where the focus was. I will upload same pics converted with dpp + 100% crop.

HOSTED PHOTO
please log in to view hosted photos in full size.

here is the converted file. whew! I forgot how small 150kb is! It was a challenge getting a 100% crop without going over the POTN limits.

Im requesting some advise on how I could have done this any better. Obviously, I did it this was, because it was all I know. Lol.

This was just 1 out of the many that was like this, but like I said in my first post, I did multiple shots. I took this shot maybe like 3 times. 2 out 3 for keeper is not bad, I think. But if I can enhance my skill some with the help from you guys. Maybe I can have 100% rate as far as hitting focus goes. Might not be a keeper, but at least I know im hitting focus. lol. Thanks a lot guys.

HOSTED PHOTO
please log in to view hosted photos in full size.

HOSTED PHOTO
please log in to view hosted photos in full size.

Weird. Maybe its me. Even though the focus point is on the girl, my eyes see the focus somewhere behind the group. Anyone else?