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Why I often mess up with the autofocus?

Published November 10th, 2011

Hello to everybody,



I'm sure that everybody is sometimes annoyed about blurred pictures, especially when you captured a good shot.
But I often mess up with the autofocus and somethimes I realy don't know why.
Especially in in the case of "walk by shots" I know that I have to get a short shutter-time to freeze the motion, so it works sometimes good.
But in any cases when I want to have the background and the person sharp it often happens, that the background is sharp and the person passing by the background is blurred. Or as in this case everything went wrong.
Look at the picture below and you'll get perhaps an imagination what I mean.
I saw this man coming and noticed this sad face made with tapes on the wall and I was sure to get a fantastic shot.
I put quickly the setting of my camera to the exposure time 1/125s and the aperture was 1:10, ISO 200, so this are my exif data of this shot.
In the uploded version I resarpened it as best as I could and it's unfortunately still unusable.
So if you have any tips or advice how I can improve my skills to get better shots with the autofocus I would realy apreciate this.



Best regards and happy shooting to you all, without any autofocus-trouble :-)



Ines

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borge
Børge Indergaard (inactive)  over 2 years ago
0
What focal length are you using? You should try to stay at 1/250 or 1/320, and just crank the ISO up. Using Auto-ISO for street work (where you have no control over the enviroment, subject or rapidly changing light) is also recommended.

My experience with autofocus for street work is that it can be very frustrating at times. I prefer manual focus and pre-focusing / zone-focusing. That way you don't have to worry about focus at all. You'll always know that your shot will be in focus as long as your distance to the subject is at the zone-focused distance.

prgauthier
Paul Gauthier  almost 3 years ago
0
ISO 200 is a bit slow for street, especially on the fly. I'd recommend 400 at least. So, pick an ISO (at least 400, higher in lower light) then set aperture according to the old adage "f/8 and be there". Also, a wider angle lens will give you greater depth of field, which allows you more margin for error -- and, more importantly, allows you to turn that AF off and zone focus. If you're not already familiar with zone focusing, google it. Wider angle lenses also make you get in closer, which is what you want to do when shooting street.

And while Blindman shooting makes some good points, it's not necessary to go Sunny 16. I love Sunny 16, I use Sunny 16 all the time -- but I also shoot meterless, fully manual rangefinders, go figure ;P But the idea of turning off the autofocus, turning off most of the automatic exposures, zone focusing -- kicking it old school even on a new digital SLR -- there's a cetain wisdom in that.

But... out of focus and motion blurred shots are one of the occupational hazards of street photography. It happens to all of us. Just accept and keep shooting.

blindmanshooting
Awesome Account
Blindman shooting  almost 3 years ago
0
JUst enjoyed your blog I have an answer for you. The problem is universal and the roots go back to the masters with Rangefinders in their hot little hands.

the solution is simple. Revert to sunny 16. That's F 16. adjust your ISO from 400 to 1600. this should capture your subject. Also the shutter speed might be 200-250-@f16 . Your image seems to be in open shadow. SO you are safe. If you are at an indoor sports event you would be iso 1600 at 2.8 and your speed would be 500.

Your subject is in my books an easy one of please give it a try. Also looking at your shot you had to be no more than 10 feet from him with a 35mm lens. Photography becomes fun when you learn to shoot inn hyperbolic focus like my last image posted tester day. Behind every man is a strong woman, and behind the iron veil.

If you want to learn this you will have to email me cheers . I'll be glad to help you.

gocandid
John Drossos  almost 3 years ago
0
a true story! I hope that you have already found a solution
InesNjers
Ines Njers  about 3 years ago
0
Hi Gustavo, thanks for your tip. When I shot I switch between aparture mode and shutter mode. My ISO settings are during the day alsways at ISO200, but I will try ISO400 and do some experiments to see how it works. Cheers, Ines
g281
Plus Account
Gustavo Mondragon  about 3 years ago
0
Ines,

One thing that I have found very useful is to set my both the cameras I use for street, Digital and Film, in aperture mode, and ISO 400, and with the marvelous lens you use (I also have one 50mm 1.8) I think that it might help you to minimize this issues.

lucagiuliani
luca giuliani  about 3 years ago
0
Hi Ines,
another hipotesis: may be 1. 1/125 sometime may be not enought for walking people and 2. the wall behind the man hasn't focus problem but micro-moved problem during shot. Just an hipotesis.
bye
Luca
InesNjers
Ines Njers  about 3 years ago
0
Hi Luca, thanks a lot for your comment. And yes, you're right.
Meanwhile I know that 1/125 is not alsways enough for walk by shots. It's amazing how many I learned about photogrpahy and it's technique the last year with the help of photographers like you and wich I met on 500px and google+. I realy appreciate this.
bye
Ines
HansvandenBosch
Hans van den Bosch  over 3 years ago
0
Well, autofocus is always difficult in these situations. The errors may give some nice surprises, like this one. That the focus is on the wall makes the picture more interesting and gives some ideas to experiment further.
InesNjers
Ines Njers  over 3 years ago
0
Hallo Daniel,

erst mal vielen Dank für deine ausführliche Antwort/Hilfe.

Ich hab in der Tat noch fast nichts über das DOF gelesen oder gehört, außer dass ich schon mal Kommentare unter ein Bilde bekommen habe in dem es hieß: "Nice DOF" und ich dacht mir nur hä? :-)

Aber so wie du das erklärst macht es Sinn. Das DOF wäre dann so etwas wie die Brennweite/Abstand vom Motiv zum Objektiv?

Ich habe das Foto auf nem Bürgersteig geschossen und bin so weit nach hinten gelaufen, wie ich dachte dass es passen könnte dass der Mann dieses getapte Gesicht passiert.
Wie du siehst kam er von rechts und ich drehte mich ein wenig frontal zu ihm und fokussierte auf ihn, was mir in dem Fall nicht mehr gelang, weil er schon auf dem Fokus (DOF) raus war, bzw. ich zu nah und vielleicht auch noch zu spät abgedrückt habe.
Das hieße, dass ich gewisse Abstände zum Motiv beachten müsste, oder?
Ich werde gleich mal nach diesem DOF Kalkulator googeln und mich damit auseinandersetzen.

Vielen Dank noch mal und ein schönes Wochenende wünsch ich dir.

Liebe Grüße
Ines

danZ
Daniel Zuellig  over 3 years ago
0
Ich versuch mal zu erklären wie ich denke wie das mit dem Fokus ist.

Es gibt drei verschiedene Arten von Unschärfe:
- Total daneben fokussiert.
- Verwackelung durch zittrige Hände, hastiges Atmen usw.
- Bewegungsunschärfe

Eins beachten wir mal nicht.
Zwei wird durch kurze Verschlusszeiten oder allfällige VR und was weiss ich was für Gadgets minimiert.
Bei Nummer Drei kommt das sogenannte DOF (Depth Of Field) zum Zuge.
Dieses DOF ist abhängig von: Brennweite, Blende, Diameter of confusion und Distanz auf welche Du fokussierst.

Nehmen wir an, Du fokussierst auf jemanden in 1.5m Distanz mit 50mm Brennweite und Blende 5.6, hast du ein DOF von nur mal 19.6cm. Bei Blende 2.8 ein DOF von 9.8cm.
Stell Dir also vor, jemand läuft auf Dich zu. Je nach Blende und Distanz, ist die Nase noch scharf, das Ohr aber nicht mehr.
Wenn Du also auf das Auge fokussierst, kann es je nach Verschlusszeit schnell passieren, dass die Person schon aus dem DOF raus ist und unscharf ist.
Das kannst Du verhindern indem die Person rechtwinklig zum Objektiv läuft (also nicht auf Dich zu oder von Dir weg) oder indem Du eine kleine Blende wählst (11 oder 16) und die Verschlusszeit trotzdem kurz ist.
Im Web gibts jene 'DOF calculator' womit Du mal rumspielen kannst und siehst was passiert. Wenn Du keinen findest, melde Dich und ich schick Dir einen.

Ich hoffe das macht alles irgendwie wenigstens ein bisschen Sinn :)
Sonst frag ungeniert nach.

Unscharfe Bilder haben manchmal auch ihren Reiz :))

Cheers