Focus Problems

Hi All

First of all my wedding shoot went well on Saturday. I will post some images in a few days.

Yesterday I did a photo shot and noticed a focus problem on many of the pictures. I set my camera (K10D) on a tripod used the 18-55mm lens and used F5.6 at various lengths.

I used the select focus point with the dial so when I looked through the viewfiender I could select the exact point I wanted the red dot to focus in this case it was the face. The subject was about 2 feet in front some hedging (bush) but I noticed although I was exact with the red dot in the viewfinder on the face it seems the hedge to the left or right of the face seems more sharply focused ????

Any ideas

Cheers Pete

Set the focus point to centre only, focus/lock and then recompose. Much easier.

On a tripod, use manual focus, much easier.

Hi Pete
Good to see you're back - must be all that PS work you've been up to

I've never had a lot of luck with the red dots on the K10D due to the problems you describe. I also find it quicker and easier to use MF.

Did you have SR turned off?

Thanks Roger/John

Think I may have left the SR on

MF is ok but it kind of defeats the point. If I am doing quick work like a wedding I would like to rely on AF is this a common problem with DSLRs ?? is it the lens or camera ??

I enjoy manual but dont trust my own Focusing 100%

Also why does leaving the SR on make a difference when using a tripod ??

John said Im trying to get my head around this one will have try it. Trouble when you have got irretable folk wanting you to get on with things its kind of difficult while your messing about manual.

Oh well at least I know it aint the Camera (was worried a bit)

The SR systems allows for natural shaking from the hands and is always trying to adjust for it. As there is no shake on a tripod it gets confused and can give odd effects.

The manual (and a lot of stuff on this forum) says turn it off when using a tripod.

I'm sure Matt will be able to give the technical details if you need them.

Well use the green hexagon in the viewfinder to confirm that you're focused. Then you have the best of both worlds.

Do you think cycling through the focus points to get to the one you want is slower than manual focusing?

By the way, you are aware, aren't you, that the red dot doesn't tell you it's in focus. It only tells you which focus point it's using. It's the green hexagon at the bottom that confirms the focus. They often do appear at the same time, but it's only the green hexagon that's reliable, by all accounts.

Maybe it would be helpful in the longer term not to always assume first that it is.

Without looking at an example and knowing the shutter speed used I couldn't comment any more.
Possible explanations:
a) The person moved (especially forward or backward)
b) It's equally in focus but the face has less contrast
c) It mis-focused because there wasn't enough contrast in the area you selected (e.g. a cheek)
d) You didn't stop down enough (it's normally the otherway round - the edges softer) to hit the lens sweet spot.

AFAIK, turning SR off when on a tripod is required when the exposure is longer. For normal shots (ie when a tripod wasn't really necessary) I haven't found SR makes a difference at all. Once you get slower than about 1/2s the SR starts introducing errors and makes the image worse.

Matt

Probably not a left or right focus issue but adjustment of focus point. Not sure of the exact terms, but the depth at which the focus point is located may be a bit off.
My K10D seems to focus at the back end of the focus range.
In other words, you know how when you focus, there is a range of acceptable focus that extends with 2/3 of this range behind the point of focus and 1/3 the range is in front of the point of focus...
Well, the point that my K10D signals is in focus is at the back end of this range. So that point and some amount of the subject forward is acceptably sharp.

I know I need to get it fixed, but cannot do without my little friend for 8 weeks.


Perhaps you have a similar issue?

Try this... take a sheet of news print or a page in a book. Hold it about 45 degrees angle so that the first line is close to the lens and the last line is far away. This will allow you to get some form of measurement to the extent of your DOF -- before and after your focus point.
Open the aperture and get in close to get a good amount of blur going.
Focus on a line in the middle. You should see a couple of lines in focus and blurring as the text comes closer and as text goes further away from the focal point.
Take a photo and check on the computer.

For me, the line I focus on is sharp. Several lines closer to the camera are sharp. The line immediately past the focus point is starting to blur.
This makes some shots difficult when DOF is critical. Argh!

Thanks Matt I tended to focus on the centre of the face from about 6 feet away. I will PM you some examples

Cheers Pete

Pete, promise me you'll never pull that manual out in front of a client again.
memorize it, type a note or two, and tape said note to back of a grey card.
Don't make a client, or anybody else watching (possible future clients) worry about whether or not you're getting the job done!
focus on the eye (closest to the lens) then recompose, bearing in mind that you'll generally get sharpnes 1/3(of your available dof) in front of your point of focus, and 2/3 behind. How much dof depends on your aperture, use the smallest aperture possible when you need more, widest aperture possible when you need less.
There's an old saying: "F8 and be there" can't go too far wrong with that.

I think Pete meant that manual in the term manual focus instead of the book?


I could be wrong but that's how i read it?

yep you're right.......that dyslexia thing......I read "messing about with the manual"!!!!
my mind sometimes fills in the blanks on the fly, when I'm reading things, and having letter reversals....when one part of my brain causes a word or two come up scrambled, another part of my brain adds words that make sense, to complete the sentence.

Pete I'm sure they'll be happy with thier images. I suspect you'll try to improve each and everytime, so hhere's a decent book, you might lioke:
Digital Wedding Photography
capturing beautiful memories
Glen Johnson

publisher: Wiley

Cheers Don

I'll have a look for it on the internet

Pete

I used to use this a lot but someone pointed me to

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

Not sure it should make too big a difference on most subjects with smaller appertures but I hadnt considered it until then. Also I find the ability to manually override the autofocus on the new DA lenses very convenient with this.