Focus problems - DPChallenge Forums

Olympus 40-150mm f/2.8 PRO M.Zuiko

02/05/2007 05:09:54 PM · #1

Last weekend I had a big shoot with 2 more students, for the final assignment for our study.

We used a big church as a location, models, everything. We had a great day! The strobes (flashes) didn't work because of the sun shining too fierce at the strobes. They wouldn't communicate, so we had to use reflection screens.

When I got home, I was pretty excited, but after browsing thrue the photos I noticed a lot of them weren't in focus, especially the photos using the big church as a background (the models small on the photo, not closeups)

That was a total bummer!

I mailed with the other students, and the weird part was: they noticed the same!!

I used my Tamron 28-75mm, always thought this was my sweetest lens, never had any problem with it, because I used it in my studio and never on location. The other students used other lenses, don't know which ones that were.

I used a shutterspeed of 1/125, so that probably wasn't the problem.

Why did this happen? Did I miss something? Wasn't this the right lens to use with these kind of shoots?

Brad

Olympus OM-D E-M1

02/05/2007 05:52:24 PM · #2

The why would depend on a lot of things, such as the AF point(s) and f/stop used. AF set to spot, with an f/2.8 - f/4, and maybe it picked up the background rather than the smaller subjects?
Just a thought - hard to say without seeing a particular shot in question.

Olympus 40-150mm f/2.8 PRO M.Zuiko

02/05/2007 05:58:00 PM · #3

hmm I can't really show you one now because I wanna use one for the free study..

we did have to use ± F2.8 because we were inside.

Brad

Olympus OM-D E-M1

02/05/2007 06:06:25 PM · #4

Gotcha'
f/2.8 will yield little dof, as will any lens shot wide open and it may
have been better to bump the ISO up a notch or two and used f/4 - f/8.

f/2.8 and getting all of it in focus, especially if there is any distance between the subjects and the background
is kind of impossible - something will end up OOF, and really depends on how far away you shot from.
The closer you were to the subjects, the more the shallow DOF will be noticeable.

Message edited by author 2007-02-05 18:06:55.

awpollard

Canon EF 100-400mm f/4.5-5.6L IS

02/05/2007 06:20:33 PM · #5

I'm with Brad on this one... The AF Focus points can do some strange things. What Aperture mode did you shot with? Obviously not Auto as you stated you used f/2.8 but P-mode can try to controll the Focus points as well.

On my 20D for two years that I have had it I have used nothing but the center focus point. I will focus on the subject with the center AF and readjust the composition before firing the shot off. When I used all 9 fps I found it to front focus (or somewhere else I didn't want it to) a lot.

Also what Focus Mode? Single Shot AF, AI AF (Artificial Intellegence Auto Focus) or AI Servo Mode... a combination of using all focal points and AI IF or AI Servo can meet with some oof (wrong parts of the shot in focus).

For a scenario that you mentioned, I would use Single Shot AF and Center Point only combination. Depending on the Lighting I might use ISO 400/800 to bring the Shutter up a bit.

The 28-75mm should have worked well for you, I have had some good luck with it indoors at f2.8 with a higher ISO.

Brad

Olympus OM-D E-M1

Olympus 40-150mm f/2.8 PRO M.Zuiko

02/05/2007 06:29:19 PM · #6

I just looked and your 30D has a feature on it same as the 350D called A DEP. This is short for Depth of Field. It permits you to have the camera automatically select the hyperfocal distance and appropriate aperture for that shot, so that the nearest and farthest objects in the scene are both in focus.
Just something to try someday.

02/08/2007 04:50:11 PM · #7

Sorry for the late response.. was kinds busy working on the pics ;)

I always shoot in manual mode, I can't shoot in another way (aperture-thng and shutterspeed-thing). I always thought that the DoF gets shallower when you get closer to the subject. Wrong!

I had to use a higher ISO indeed, but I don't want to go too high because I don't really like noise. The aperture was 2.8 almost the whole shoot, because the light was not good. I think indeed that that was the problem.

I used different focus-points, and usually this works just allright. I'm just not used to work in a very large space (like the church). I always work with AF single shot. Still have to try the AI servo stuff.

Ah well, I got some great shots, it was just a bummer that lots of the shots (not the close-ups) were OOF.

Gonna try these different things soon!

And thanks for the help!

Message edited by author 2007-02-08 16:50:55.

Artifacts

Canon EF 24-105mm f/4.0L IS

02/08/2007 04:58:51 PM · #8

Originally posted by biteme:

... The aperture was 2.8 almost the whole shoot, because the light was not good. I think indeed that that was the problem. ...

Agreed... this is your problem. 2,8 is very shallow and if you combine that with autofocus getting fooled into focusing somewhere dfferent than you want you can get those results.

Depending on composition, you sometimes have to point you camera a different places before you get it to focus where you want and then, while continuing hold down the shutter half-way then recompose and snap the shot.

Tamron SP AF 24-135mm f/3.5-5.6 AD Aspherical IF for Canon

02/08/2007 05:00:48 PM · #9

Originally posted by stdavidson:

Originally posted by biteme:
... The aperture was 2.8 almost the whole shoot, because the light was not good. I think indeed that that was the problem. ...

Agreed... this is your problem. 2,8 is very shallow and if you combine that with autofocus getting fooled into focusing somewhere dfferent than you want you can get those results.

Depending on composition, you sometimes have to point you camera a different places before you get it to focus where you want and then, while continuing hold down the shutter half-way then recompose and snap the shot.

I understand that :)

The fact that we all 3 had the same problem (and all 3 quite a bit of experience in photography) was kinda weird.

The thing is that I always thought that the DoF gets shallower when you get closer to the subject. I was wrong!

nards656

Canon EOS-300D Rebel

02/08/2007 05:05:40 PM · #10

Originally posted by biteme:

The thing is that I always thought that the DoF gets shallower when you get closer to the subject. I was wrong!

It gets shallower as your focal length INCREASES, assuming that the f-stop is set the same. (This is due to the fact that the aperture is physically larger for a longer focal length.) Distance to subject has nothing to do with it. :) Not trying to be overly turdish, just trying to help you understand.

At 2.8, as well, you are pushing the lens to its limit, which steals some of the sharpness anyway. It's not at it's optimal - usually f8 or something close.

Message edited by author 2007-02-08 17:06:40.

02/08/2007 05:06:41 PM · #11

I gotto check on the word increase, brb ;)

Oh, well, I meant the increase of the focal length. And distance.

You know, I've never understood the real technics about photography, the "why is it so that..." etc. I just shoot. technics are something I never understood. So, however you're trying to make me understand, don't bother haha :P

Anyway, I know 2.8 is shallow. But didn't know it would still be that shallow with 28 mm :)

Message edited by author 2007-02-08 17:10:03.

Artifacts