yet another focus question - wide angle + wide aperture

[mimi_zhou]

Thanks everyone for their valuable answers to the focusing question i posted a week ago. The DOF calculator is

immensely useful. Here is another problem I am having difficulty wrapping my head around.

 

I photographed two people in front of a church, and had to include the rather large church in the background. I

used a 16-35 mm lens. The couple is about 3 meters away from me,3/4 length in the frame. The church is all the

way like 50-70 meters in the back. I shot at 1/500, f2.8, ISO 100@ 26mm. They were backlit, so I used one point

auto-focus on the couple. I took about 10 shots, all the pictures are again not so sharp. They only appear sort

of clear, a little fuzzy, definitely are not sharp enough to pop. The church in the background does not seem to

be out of focus so much, perhaps due to the size.

 

Does it make sense to shoot at f2.8 with wide angle shots like this? Would it have been better if I shot at f4?

In general, is it much harder to focus a wide angle shot with wide open aperture? I think the answer is yes.

 

What should I do if want to shoot wide to include the scenery yet to have more blurred background than I have

now, but with the subject in sharp focus? The focus dial does not seem to work very well, except for the center

point...

 

Right, I may have problem with my 20D, but everything is sharp most of the time when I shot close up with a 50mm

at f2, auto or manual focus. Problem is with full body and the right amount of DOF.

 

A quick question about the DOF calculator. it says that the near limit of acceptable sharpness is 3.04m, and the

far limit is 5.85m. As far as I understand, it means that subjects from 3.04 to 5.85 m will stay sharp... am I

right?

 

Thanks again for taking your time to answer my beginner questions, very very appreciated.<div></div>

[mimi_zhou]

There is another photo, when viewed at 100%, I can see that the holding hands are in focus as i used center focus. but the girl's face is not sharp, guy's face is out of focus. I am now thinking that shooting at f2.8 is foolish if I want to include two people or include the whole body. But I swear I have seen a lot of photo with great sharpness and excellent DOF plus quite a bit of environment...

 

at f2.8 the background blur sucks in my opinion. again, perhaps should have used a longer lens to achieve more DOF, and step back if I want to include a more surroundings in the shot? if the shooter has to pull back a lot, for example @f2.8, wouldn't he fall out of the distance of acceptable sharpness as well?<div></div>

[wedding-photography-denver]

Shooting at f2.8 is not so bad, but if you want sharp shots, why not stop down to f5.6 for this type of shot, or even f8?

[wedding-photography-denver]

Oh yeah, Canon are not know for accuracy in AF. Especially when they get a bit of use on them.

 

Send your lens and camera to Canon for calibration.

[mimi_zhou]

I wanted to achieve very blurry background and clarity of the main subject without having to PS. It was the goal for this practice.

 

Like this Example, but perhaps with more surroundings:

http://farm3.static.flickr.com/2047/2278369681_9c15c2b52f_o.jpg

 

but i guess,like in image 2, I should have just used a longer lens and go back in order to get the kind of blur I want... am I right? still troubled by the clarity issue, I want to get to the bottom of this f-stop and clarity focus relation before I can blame it all on equipment.

[savagesax]

Regarding the image above - http://farm3.static.flickr.com/2047/2278369681_9c15c2b52f_o.jpg - I believe a different lens was used, not a wide angle, but a lens much longer. My guess is it was above 100mm's at 2.8 to F4, because the DOF is so shallow, maybe even up to a 400mm lens. It's pretty hard to get a wide angle lens to do this type of shot unless it was around F1.2 or so.

 

You are right about your images being a bit soft. It's not movement so you should send the camera and the lens in for adjustment. I'm not sure what Canons pricing would be, maybe try a local repairman first to save some money.

[bangengeman]

Mimi, I think that the lens you are using right now is a bit too wide for the kind of bokeh that you want to achieve. I personally would recommend a 50mm or maybe even an 85mm lens. Be sure to stop down a bit (maybe 2.8-4) if you're doing to focus on 2 (or more) people just to play it safe, but it would definitely help to have a longer lens. Just to be safe, you can get the 50mm 1.8, (it's the cheapest lens in Canon's lineup) and see if it comes close to what you really need.

[picturesque]

On the first picture, are you talking about the apparent lack of bokeh in the background (lack of pop)? Or are the people definitely OOF? If the former, remember that a crop sensor camera is going to have about 1.3 stops more DOF for the same f stop/subject distance/focal length than a full frame camera. So f2.8 has more DOF on the 20D than f2.8 on a 5D. And because using a wide focal length means more DOF to begin with, f2.8 on a wide angle on a 20D isn't going to give you that pop, as in Jessica Claire's image, which, I agree with Bob, probably was shot with a longer focal length.

 

If the people are definitely OOF, that is another thing altogether. Did you do your lens tests?

 

1. f4 would not improve the pop factor. It might have improved the focus factor if your couple was definitely OOF, by extending the DOF range. It is much harder to accurately focus using a wide focal length period, much less with a wide aperture. This was also the case with manual focus lenses. It is just hard to determine correct focus because with wide focal lengths, subjects are generally small. As discussed in your previous thread, the 20D's focus points are larger than marked, so it is difficult not to get 'snagged' onto something else, usually the background, which did NOT happen in this case. And when the focus is unclear (or the camera 'thinks' it is unclear), it will go for the most contrasty thing in the frame, usually the background. You also should know that the 16-35mm is not all that sharp in the corners, particularly at the wider end. That shouldn't have affected the couple's faces in this photo. If the focus was right on, the faces should be sharp.

 

2. To get the extra pop from selective focus, use longer focal lengths with wider apertures and back way up. In good light, the 20D's peripheral focus points are OK. In dim light, I would use the center focus point. Review my suggestions in your last thread. Focusing twice, and then checking the distance scale on the lens, picking good targets, and knowing what situations foil the 20D will get you to the point where you can autofocus with it and be fairly confident.

 

3. The 20D does well with the longer focal lengths and/or large targets.

 

4. The range that the DOF calculator tells you is for 'generally sharp', not pinpoint sharp. Pinpoint sharp is where you put the focus point when the camera has achieved a successful autofocus. I have also heard the theory that with lens formulas being so good these days, modern lenses will show up the 'generally sharp' areas as less sharp more than before, so some people even advocate adjusting DOF tables, which have stood for many years. In DOF master, there is a control where you adjust the sensor to the one you are using, so be sure you've done that.

 

For the second shot, you could have gone way, way back, using a longer focal length, and that would have popped the people against the trees. Is the background in focus and not the people? If so, the focus failed. If the hands are sharp and the background is OOF too, I'd say the woman's face being OOF is possibly motion blur. If she was moving up and down, as seems to be indicated, 1/250th can still show a bit of blur. It is motion across the plane of an image, which shows motion blur more. 35mm on a 20D is actually about 50mm, but even so, the DOF should not be that shallow (the distance between the hands and his face). I would examine that photo more.

 

Incidentally, it is impossible to tell anything from your images--you might post 100% crops of the important areas.

[wedding-photography-denver]

As bob says, that selective focus is achieved with a wide aperture, longer FL. I would swear that it was shot with the 70-200 Canon at F2.8 and from a distance of about 30' to subject.

 

If you want that look, go longer and wider too. 85/1.8 would be great for this IMO.