Alex Elias 
, Apr 28, 2009; 04:16 a.m.
I know this might sound like a stupid question, but here it goes. The main reason I got this lens is to shoot my kids indoors with available light. I'm using a D40 if that makes a difference.
Today I took a few pictures at f1.4 and I can see how nice is to have such a fast lens. In the other hand at f1.4 the DOF is so narrow (next to none existing) that unless I'm not understanding something it renders the lens unusable for what I intended it the most. I could not get any sharp image of the eyes, every one was out of focus. I tried auto focus as single and servo to see if this would help since my one year old is not much of a posing guy.I know I must be missing something since many people favor and use lenses this fast on various focal distances such as the 24mm, 28mm, 35mm, 85mm and so on.
One other thing. I also looked at the 30mm f1.4 from Sigma and as much as the focal length is very appealing specially for a crop sensor I had second thoughts about getting a Sigma (not trying to be a snob) I did not do any research about the IQ of it and also I don't don't about compativility issued with future Canon bodies I might get. For the long haul would you buy this 30mm sigma or stick with a Canon? and I do realise they are not the same focal lenght.
Thanks for your feed back
Regards,
Alex
Ilia Varlachkine , Apr 28, 2009; 04:31 a.m.
Alex,
I use this lens more than any other for making portraits of my doughter. She's only slightly over a year old and is very fast and unpredictable in her movements. After several initial tests I've discovered that at f/1.4 the camera must be nearly parallel to _both_ eyes for them to be in focus, else DOF is so small that focusing on one eye makes the other noticible less sharp. I've setled on f/2.0 as sufficient to blur the background and still keep eyes sharp. Focusing only on the eyes by choosing AF point that would require least movement for recomposing. Shooting mostly in single-shot AF.
Alex Elias , Apr 28, 2009; 04:41 a.m.
Here is one raw image not corrected at all at 100% crop as an example. ISO 200, speed 125, flash 580EX diffused and this was not even at f1.4 it was at f1.8. If you noticed the focus was done mainy in the shirt/ear and also there is that magenta purplelish cast on his eye.
I know I got the active AF point right on his eye. Not saying he did not move while I was shooting but how do you guys shooting weddings and things like it deal with this?
Thanks again
Alex
100% crop
Paul Marbs , Apr 28, 2009; 06:08 a.m.
To start with I would try to see if you can a sharp image of say your wife's eye in good light at f/1.4.
To shoot pictures of your kids with this lens wide open is really very difficult especially if you are close enough to a small child to fill the frame. The kids must be very still when trying to shoot close shots like this. When I had my 10D (cropped sensor) I had to use this lens at f/4 to ensure eyes were sharp for close ups. As you already know the DoF is so very shallow wide open.
My advice would be to try to use this lens in good light (it contradicts a little your reasons for buying the lens), make sure the subject is not moving, lock your exposure and keep dabbing the AF in AI servo until the moment is right then fire off a burst of shots.
These were shot at f/4 on a 10D with 50mm f/1.4
http://photo.net/photodb/photo?photo_id=3759542
http://photo.net/photodb/photo?photo_id=3460375
and this one (yes I know I keep posting it but it shows the shallow DoF) at f/1.4 on a 5D..
Harry Baker 
, Apr 28, 2009; 06:36 a.m.
I just got the Sigma 50mm f1.4. This is wide open with autofocus on her left eye using centre focus point only
Elliot Bernstein 
, Apr 28, 2009; 06:46 a.m.
You need to determine whether there is a focus problem (back focus) or if the issue is user error. Assuming the lens is functioning correctly, moving farther away from your subject will increase DOF. You can also stop the lens down a bit for the closer shots to increase DOF without affecting the exposure too much.
Leszek Scholz , Apr 28, 2009; 07:54 a.m.
Shoot from a tripod with cable release, static subject - then you will know if the lens is OK. If there is a sharpness problem - check for bac/front focusing. If there is none - the lens may be a dud. But most likely you will find out that you need to practise with this settings in order to get usable images. And this includes focusing/camera shake/subject moving etc.
Stephen O'Sullivan , Apr 28, 2009; 08:09 a.m.
I discovered that for kids when running around, a flash is much much better than opening up the aperture so wide. I've learned to use a diffuser and bounce the light so it doesn't cast shadows and it looks very natural, while having the aperture at 2.8 or 4, to keep the entire face in focus.
The 1.4 is ok under very controlled circumstances, when you're going for the artsy look, but it's difficult as you've found out, to get any shots of quality.
SOS
Kasper Hettinga , Apr 28, 2009; 08:14 a.m.
I'm using the sigma 30mm f/1.4 and a zuiko (manual) 50mm f/1.4 a lot for playing kids. I have accepted that quite a few photos are to some extent out-of-focus due to the tiny DOF. But as I like making indoor available-light photos, I'm OK with it.
On the other hand, raising ISO 1-2 steps, and closing the aperture 1-2 stops helps quite a bit to increase DOF.
I do love my (Haoda) manual focussing screen: it allows my eyes to confirm focus for both AF and manual lenses, which is really nice for wide aperture lenses.
Larry Cooper , Apr 28, 2009; 09:26 a.m.
I think you are trying to use the lens for pictures it is not suited to capturing. No lens at f1.4 is going to be very effective on moving subjects, and that includes moving subjects that are just sitting and talking. The DOF is just too shallow to control effectively unless you are very careful. Careful and kid photography are not very compatible.
You will just have to accept a large number of pictures where the focus plane is not where you want it if you use it much. I agree with Stephen that you would probably be better off to get a really good flash unit and learn to bounce and diffuse it. You could use a zoom at a smaller aperture and likely get a lot more "keepers" with the flexible framing of the zoom and the deeper DOF of the smaller aperture.
Otherwise, all you can do is stop it down to get better DOF, and raise the ISO to get your shutter speed up to something useful. It's that, or get the kids to be very quiet and still. Good luck.
