Focus, Recompose=ruined shots

Tim Kirkwood

I have had this happen to me. I found a interesting article through our local meetup group. Thought I would share it with you all.


You can take it as a "fart in a tornado" if you want.


Tell me what you guys think. Do you agree? Have you had this happen to you? Do you focus and recompose?

Tim


http://visual-vacations.com/Photography/focus-recompose_sucks.htm



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colourbox

Basic math suggests that the article's right. It never occurred to me, but it makes sense.

The camera manufacturers have a way around this. My Canon has a feature where you can scoot the focus point around the viewfinder. I always thought "I don't need that, I recompose and shoot." Now I see where it would be handy. If the focus point is significantly off axis and depth of field is narrow, this parallax error would become an issue and it could be advisable to maintain the composition while repositioning the focus point. For tricky exposures, it looks like the procedure would be to get the exposure spot, lock exposure, then compose, then position focus point, lock that down, then press the shutter the rest of the way.

Repositioning the focus point around is probably easier on a tripod since it involves quite a bit of button pushing while composing. I never thought I needed that feature when shooting handheld, but based on that article, I will have to reconsider.

wxwax

205 but well worth a repost. Fish and I went around on this. The math is correct, and there are times when focus/recompose can hurt your focus. But it's also true that there are many, many times when it doesn't make a bit of difference.

pathfinder

wxwax wrote:

205 but well worth a repost. Fish and I went around on this. The math is correct, and there are times when focus/recompose can hurt your focus. But it's also true that there are many, many times when it doesn't make a bit of difference.

Canon itself STRONGLY recs against focus and recompose for the reasons stated in the previously listed link. You can find the whole pdf file here
http://www.photoworkshop.com/canon/index.html when you click on the Full Version button. They explain the math just as posted earlier in this thread. Canon recs focusing with an appropriate off-center AF point rather than using the center AF point and recomposing.

It is important to understand that this is MOST important when shooting subjects that are closer than 15 feet and at wide aperatures. Wit telephoto lens focusing at 50 feet, Focus recompose is vastly less in error.

gus

I learnt that very thing doing my pin-holes. Have a flat film paper in & you focal point at the ctr of the paper is shorter than your edges thus i made all my own curved film holders (soaked wood & pressed in a curve until dry) to keep the photo paper the same distance from the pin hole from centre to edge....massive difference in the results.

pathfinder

Humungus wrote:

I learnt that very thing doing my pin-holes. Have a flat film paper in & you focal point at the ctr of the paper is shorter than your edges thus i made all my own curved film holders (soaked wood & pressed in a curve until dry) to keep the photo paper the same distance from the pin hole from centre to edge....massive difference in the results.

Very astute, 'gus. Most people think you want the film plane flat, rather than equidistant from the nodal point of the lens. But with a pinhole, I am sure you are correct.

gus

This is a photo of my 'Big' camera (ive got about a dozen pinhole cameras lying around of all shapes & sizes)

Flat holders at the back & the curved (125mm from memory @ f/400) 5x7

There are slots in the box to allow for diff focal lengths & the apature is just some 'coke' tin or brass shim with a pin hole usually .3mm or .4mm

wxwax

pathfinder wrote:

Canon itself STRONGLY recs against focus and recompose for the reasons stated in the previously listed link. You can find the whole pdf file here
http://www.photoworkshop.com/canon/index.html when you click on the Full Version button. They explain the math just as posted earlier in this thread. Canon recs focusing with an appropriate off-center AF point rather than using the center AF point and recomposing.

It is important to understand that this is MOST important when shooting subjects that are closer than 15 feet and at wide aperatures. Wit telephoto lens focusing at 50 feet, Focus recompose is vastly less in error.

They can recommend all they want. I do it a lot without harm. As you note, there are times when it hurts.

KeithAlanK

Damn.
Thanks for the link.
Now I understand fully why some of my shots have that back-focused look.
I guess I need to lobby the camera makers for curved sensors? Nahh. Bad technique is my fault.

ian408

KeithAlanK wrote:

Damn.
Thanks for the link.
Now I understand fully why some of my shots have that back-focused look.
I guess I need to lobby the camera makers for curved sensors? Nahh. Bad technique is my fault.

This is not back focus. It's incorrect focus.

Sorry, pet peave as many incorrectly believe that because focus is set on
something behind the subject, it's back focus. It's bad focus.

Cheers,
Ian

pathfinder

ian408 wrote:

This is not back focus. It's incorrect focus.

Sorry, pet peave as many incorrectly believe that because focus is set on
something behind the subject, it's back focus. It's bad focus.

Cheers,
Ian

Feeling prickly, aren't we? PUI??

KeithAlanK

ian408 wrote:

This is not back focus. It's incorrect focus.

Sorry, pet peave as many incorrectly believe that because focus is set on
something behind the subject, it's back focus. It's bad focus.

Cheers,
Ian

I realize what the difference is. That's why I said "back-focused LOOK".
And why I said that it was bad technique on my part.
BTW, it's "peeve", if we're going to be like that.

And most of my shots that have this problem are of a train heading towards me at 30+mph, so you can see why back-focus would be my first guess??

ian408

pathfinder wrote:

Feeling prickly, aren't we? PUI??

I hear "oh, my image is back focused. I wonder why that is" a lot these
days. Almost like an excuse for a poorly focused shot

No PUI.

Ian

ian408

KeithAlanK wrote:

And most of my shots that have this problem are of a train heading towards me at 30+mph, so you can see why back-focus would be my first guess??

Hmm. Slow shutter

KeithAlanK

ian408 wrote:

Hmm. Slow shutter

Yes, us stupid newbies get everything wrong, don't we
Must make you feel very superior.
Thanks for the help.

wxwax

KeithAlanK wrote:

Yes, us stupid newbies get everything wrong, don't we
Must make you feel very superior.
Thanks for the help.

Nah, ian's just expressing his pet peeve. He's the last one to act superior. See, this is what folks who don't like smilies fail to appreciate - unless one goes out of one's way to use very delicate language, intent/emotion can quickly be misconstrued on the internet. So let's eee, the correct smilies would be:
:uhoh and :bluduh and :poke and :hang and and

ian408

KeithAlanK wrote:

Yes, us stupid newbies get everything wrong, don't we
Must make you feel very superior.
Thanks for the help.

To satisfy your curiosity, no. It doesn't make me feel superior. Waxy's
right. From your side, you can't "hear" the tonality. And because of that,
you probably miss the humor in the post.

But if you know the difference between back focus and poorly focused,
you're obviously neither stupid or a noob.

Ian

pathfinder

wxwax wrote:

Nah, ian's just expressing his pet peeve. He's the last one to act superior. See, this is what folks who don't like smilies fail to appreciate - unless one goes out of one's way to use very delicate language, intent/emotion can quickly be misconstrued on the internet. So let's eee, the correct smilies would be:
:uhoh and :bluduh and :poke and :hang and and

That is exactly why I included 2 ( count'em 2) , following my post to Ian about PUI. So as NOT to be misunderstood. I'm sure Ian understood that it was a joke too.

My solution to poorly focused, back focused, or just plain blurred images is to deep six them in the circular file cabinet.

Steve Cavigliano

KeithAlanK wrote:

Yes, us stupid newbies get everything wrong, don't we
Must make you feel very superior.
Thanks for the help.

Awwwww Keith, don't be like that

As Sid and PF mention, that's why most of us use lots of smilies. So people can tell when we're just kidding

Ian was just joking here. If you frequent any other Canon forums on the web, you'd understand better where he was coming from. A day doesn't pass without at least one "My lens/camera back-focuses" thread being posted. In many cases it's not back-focusing issues at all but instead, as Ian points out, just BAD focus issues.

That you bring up this point about FLR, shows that you are neither stupid, nor a newbie


Steve

Tim Kirkwood

Never thought I would start something here with this thread:D



Glad to see that you guys took interest. It was a bit new to me. I knew of the problems that can be present with focus, recompose and when I came across that article with the math and some illistrations then it kinda all came together for me.


I agree that its not going to happen everytime you do it.


Tim

tmlphoto

wxwax wrote:

They can recommend all they want. I do it a lot without harm. As you note, there are times when it hurts.

I agree with Sid. I do it all the time, especially if I'm not in a controlled studio situation and it almost always gives a sharply focused image. In the studio I will move the focus point around, but still do some slight recomposing, as I like to focus right on the eyes and then recompose. My center point stays active 95% of the time. I think its more of a theoretical problem than an actual one in most cases.

pathfinder

tmlphoto wrote:

I agree with Sid. I do it all the time, especially if I'm not in a controlled studio situation and it almost always gives a sharply focused image. In the studio I will move the focus point around, but still do some slight recomposing, as I like to focus right on the eyes and then recompose. My center point stays active 95% of the time. I think its more of a theoretical problem than an actual one in most cases.

I used Focus Recompose a lot with the 10D, because I felt the peripheral AF points didn't work very well unless the light was pretty bright - like outdoor sunlight. Shooting available light indoors I used the center AF point and recompose, but if you take the time to read the pdf link I gave on the canon website, they are VERY specific to avoid Focus lock and recompose, because it WILL give inferior focusing results on images shot within 10 or 15 feet or less - the closer the worse the effect. Large aperatures are also more affected, which is precisely aperature I was using for indoor available light. Once I switched to avoiding FLR, I find my images are sharper. The 1series cameras and the 20D are superior to the 10D in their peripheral AF point sensitivity too.


But I still do it occasionally too, so don't take offense at this post, ok??

Higgmeister

Focus and recompose works in many instances

Tim Kirkwood wrote:

I have had this happen to me. I found a interesting article through our local meetup group. Thought I would share it with you all.


You can take it as a "fart in a tornado" if you want.


Tell me what you guys think. Do you agree? Have you had this happen to you? Do you focus and recompose?

Tim


http://visual-vacations.com/Photography/focus-recompose_sucks.htm



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Hi Tim,
You asked. The math is correct, but the result is going to depend on the focal length, distance and aperture. I used the link above for the numbers and this link (DOF Site calculator) for the numbers below. As you can see, even from 6 ft away and using a 50mm at f4, the eyes would still be in critical focus. The assumption here is that this sites math is correct.

Just my .02,
Chris

ridetwistyroads

wxwax wrote:

205 but well worth a repost....

wrong forum sid.....