[Sini]

Coucou les amis,


Si vous n'avez rien à faire ou que votre matos vous procure des cheveux blancs à cause d'un autofocus capricieux, je vous propose de partager une méthode que je viens de découvrir au hasard du surf

la méthode DotTune est en fait assez logique, la technique consiste à trouver la map (diode verte fixe) et ensuite vérifier l'étendue de la plage de tolérance et d'en déterminer le juste milieu,
je le faisais en shootant une mire mais cette méthode est tout aussi bonne je crois et évite la série de shoot inutiles

voici le lien de la vidéo
http://www.youtube.com/watch?v=7zE50jCUPhM&feature=player_embedded   c'est gratuit

A+

[domenge]

merci Sini
la meme methode mais "ecrite" in  english" par Fred Miranda son auteur    avec mise a dispo de son calculateur de midle range AF http://www.fredmiranda.com/forum/topic/1187638

J'essaie avec mon lenscal à 50 fois la focale min  et à la plus grande ouverture sur D7000 ET SIGMA 17 70 qui souffre de BF

Procedure    
1. Enter Live View and establish critical focus on a high-contrast subject. For cameras    
with poor LV clarity (D800/E), you may want to take a photograph and evaluate it on    
. the computer to confirm critical focus. I recommend the focus chart here   
2. Leave the body and lens set to AF and configure your body for back-button    
focusing if not already configured so. This is necessary to disable AF engagement for    
shutter half-presses, which you'll be using in steps 3 and 4. To configure back-button    
focusing, set the "AF Activation" option to "AF-ON only". For the D4/D800 this is    
option a4, the D3/D3s/D700 it's option a5, and for D600 it's option f4 and D7000    
option f5 (for D600/D7000 the AE-L/AF-L button will serve as the AF-ON button). Do    
not set the body or lens to MF as an alternative to back-button focusing; doing so will    
increase the confirmed focus range and make DotTune inaccurate.    
3. Look through the viewfinder to see if the camera thinks the subject is in focus.    
You'll need to half-press the shutter while doing this to keep the metering/rangefinder    
from going to sleep. If you see the green arrow pointing to the left, then the    
camera+lens is back-focusing, so you need to decrease the value of AF tune    
(negative adjustment). If you see the green arrow pointing to the right, then the    
camera+lens is front-focusing, so you need to increase the value of AF tune (positive    
adjustment).    
4. Repeat step 3 until you get a green-dot from the rangefinder.    
5. Depending on focal length and subject distance there will be a range of AF tune    
values which produce green-dot confirmation. For example on my D800 w/50G f/1.4    
@ 5' subject distance, I get the green dot from -6 to -14. Conceptually the optimal AF    
tune value should be the value that's the middle of the range, which in the above    
case is -10. So you'll want to establish the range of green-dot values by progressively    
increasing the AF tune values until the camera stops showing the green-dot (it'll    
alternate between the green dot and an arrow when it's at the margin of the    
range)...and repeat that procedure in the opposite direction to find the other end of    
the range. Use the midpoint of that range as your final AF tune value.    
Notes    
When establishing the precise range of green-dot AF tune values you may need to    
examine the rangefinder for several seconds. I've found that for the extreme margins    
of the AF tune range the camera may take a few seconds to flicker the arrow/green-    
dot.    
http://www.fredmiranda.com/forum/topic/1187638/0 03/03/   

[OldyNikon]

Merci Sini, merci Domenge, je vais prendre mon pied pour faire le test, et prendre mon pied en le faisant  


[EDIT 8h plus tard : test super facile (1mn pour paramétrer l'AF, et c'est l'occasion d'utiliser un bank "custom", 1mn pour faire la map et vérifier), diode verte allumée => ni front, ni back focus. Je recommence demain avec d'autres optiques)