focus issues? - DPChallenge Forums

05/08/2005 01:10:15 AM · #1

I locked focus on the eyes, but it's coming out "soft" to me. The nose and other parts are more in focus. Is this an issue with my focusing technique, or should I look more into my lens?

The lens is 24-70 L, shot with 20d body. aperture 2.8 at 70mm, 1/250 sec.

Thanks.

05/08/2005 01:50:00 AM · #2

focusing with 2.8AV can be tricky. If you want to test if your lens is missfocusing... Lay down a ruler, and shoot at the 6 inch mark at approx. a 45 degree angle wide open. you should be able to tell if the lens is focusing farther or nearer or dead on very easily with this test.

05/08/2005 01:53:46 AM · #3

Thansk for the suggestion. I'll try that. Preferred distance from the ruler for this shot?

My suspicion is that my technique is lacking, and I'm too "near" the subject while at 2.8. I also tend to focus lock using the center point and recompose, which I suspect also shifts the distance and in a shallow dof situation, throws the focus off. Any opinion on this?

Canon EF-S 10-22mm f/3.5-4.5 USM

05/08/2005 01:58:13 AM · #4

I think you should be as close as possible for the test as it'll be easier to tell where the focus point hit.

I compose the same way as the 7 focus points on my camera I find fairly limiting and the center is always what I use. I also find that i get a lot of slightly oof shots at 2.8AV as well. I've been trying to blame the camera as it's not as accurate supposedly as yours or a 1 series camera. I'm not sure how much recomposing changes the focus... I can't imagine it would be much if you and your subject remain stationary.

srdanz

Canon EOS-5D Mark IV

05/08/2005 01:59:27 AM · #5

Yes, at fully open aperture, any distance change affects focus drastically. If you are careful when you lock focus and only slightly move your camera parallel to the pane perpendicular to the line betweel the lens and the subject, you should be fine. I've experienced similar out-of-focus photos when I moved too much - any forward or backwards movement will throw you out...
Why not trying with f/4 after you do the ruler test and see if it is still bad..

lemondster

Canon EF 28-135mm f/3.5-5.6 IS USM

05/08/2005 01:59:59 AM · #6

Originally posted by robgo:

i think one thing that you might want to pay attentition to is that if you focus on the closest part of the subject, half of the DOF is infront of the subject; effectively cutting your usable DOF in half.

hope this makes sense

mpemberton

05/08/2005 02:05:31 AM · #7

Originally posted by lemondster:

Originally posted by robgo:
Thansk for the suggestion. I'll try that. Preferred distance from the ruler for this shot?

My suspicion is that my technique is lacking, and I'm too "near" the subject while at 2.8. I also tend to focus lock using the center point and recompose, which I suspect also shifts the distance and in a shallow dof situation, throws the focus off. Any opinion on this?

i think one thing that you might want to pay attentition to is that if you focus on the closest part of the subject, half of the DOF is infront of the subject; effectively cutting your usable DOF in half.

hope this makes sense

Makes a lot of sense, my father, used to talk about hyper focusing. That is focusing in front of the object to use DOF. Anyone else ever heard of this term?

05/08/2005 02:06:44 AM · #8

yes but hyperfocal isn't the same thing as this... that's generally the point at which the most of the entire frame is in focus. Here you're trying to hit the focus on the subject's eyes, changing the focus point and hitting the nose is less desireable.

05/08/2005 02:16:08 AM · #9

Just making sure that it is generally agreed that in the shot I posted in the original post, the eyes are softer than the nose, etc? It's not just my eyes, yes? Thanks again for all the suggestions.

If I were to shoot at f/4 or smaller aperture, and wishing to preserve as much bokeh as possible, longer focal lengths would help? I think this is what my reading so far is telling me, but it'd be nice if someone can advise on this.

Message edited by author 2005-05-08 02:18:00.

05/08/2005 02:17:39 AM · #10

Originally posted by robgo:

Just making sure that it is generally agreed that in the shot I posted in the original post, the eyes are softer than the nose, etc? It's not just my eyes, yes? Thanks again for all the suggestions.

I would have to agree, but a crop might help it be more clear.

Canon EF 17-40mm f/4.0L USM

05/08/2005 02:23:56 AM · #11

Originally posted by kyebosh:

Originally posted by robgo:
Just making sure that it is generally agreed that in the shot I posted in the original post, the eyes are softer than the nose, etc? It's not just my eyes, yes? Thanks again for all the suggestions.

I would have to agree, but a crop might help it be more clear.

100% crop closer to the head. Thanks again.

Message edited by author 2005-05-08 02:42:34.

mpemberton

05/08/2005 02:33:17 AM · #12

Access denied.

You should never serve off your own machine.

Message edited by author 2005-05-08 02:34:38.

dahkota

Canon EOS-7D

05/08/2005 08:18:52 AM · #13

//www.outsight.com/hyperfocal.html

This sight has calculators for DOF, etc.

d

Prof_Fate

05/08/2005 11:28:07 AM · #14

At 5 feet ffrom the subject, the DOF is .16 feet. at 15 feet it is 1.42 feet.
//dofmaster.com/dofjs.html is my source for that info.

.16 feet is 3/4 of an INCH. DOF is less the length of a human nose!