I have a D300 since 8 months ago (I buyed a used camera from another person with 44000 shots made with it) & it seems I am fighting continuously with his AF. I don't know if the AF is not working the way it should do or i am doing something wrong.
I explain now. I shoot mainly with the AF-S 35mm F1.8 with no flash, no UV filter and in low light (low light could be 1/100 f1.8 iso1600 for a good exposed image). The AF assist lamp is deactivated most of time for not to warn people i am taking pics about them. I know it is low light but i think it is enough. When focus is ok I am very happy with the results. But randomly the focus goes elsewhere. Sometimes closer and sometimes far. It is not much focus shift, but it is enough for a little blurry person and not sharp one. I have made experiments with static objects and static camera in this poor light and from 18 shoots I have had 15 well focused images and 3 not correctly focused ones. It is not much focus shift, but I can see it.
My questions are these:
In the same light and environment conditions, the photographed objects are static and the camera is static. If I shoot a group of pictures (20 for example. And de-focusing manually previously to the shot for the camera to takes focus each time), + all of them must have the focus exactly in the same plane time after time? + the focus accuracy and exactness must be the same each time? + or there is a minimum tolerance-error with the AF module that could be the focus shift i am seeing sometimes?
I buyed this camera mostly because of its known AF accuracy. I don't know if the AF is working badly in my camera (and i have to send for service) or if i am pushing the camera AF to its limits.
Thank you in advance for your help.
update 2013-03-05: Added 3 test pictures & full gallery
Example photos of missed focus.
Focus is on red square: AF-Single mode and one only manual focus point selected by the cursors Middle box is supposed on perfect DOF plane. "Front" and "more front" are closer and more closer boxes. "Back" is a farther box. All boxes are perpendicular to the camera but on different planes. One from another are separated by approx. 2-3mm.
From a series of 18 pictures these are the more extremes.
I think this is ok:
I think this is slightly backfocused:
I this this is slightly front-focused:
The rest of the pictures the focus is between these 2 extremes. Seeing more closer I can see focus slightly varies between shots, not a lot, but some variations. It is not exactly equal. All pictures only converted from RAW to jpg with capturenx2 in 80% quality. Resized to current size by the nikonians "My Gallery" uploader. I hope this will be enough size to see the missfocus. I've just uploaded full series of images to this gallery: https://images.nikonians.org/galleries/showgallery.php/cat/24344 if you want to see them all.
There is no motion on the pictures . I used a remote trigger and the camera and the objects are all static on a table.
The EXIF data from the images is like this (only date and time varies): --------------------------------------- : Camera Manufacturer : NIKON CORPORATION Camera Model : NIKON D300 Orientation : top-left (1) X Resolution : 300 Y Resolution : 300 Resolution unit : Inch Software : Capture NX 2.3.1 W Date modified : 2013:03:05 07:32:51 Artist : White Point : 313/1000 Primary chromaticities : 16/25 YCbCr Coefficients : 299/1000 YCbCr Positioning : centered (1) Reference black white : 0
Exposure time : 1/100 F-Number : 1.8 Exposure program : Manual (1) ISO speed ratings : 1600 EXIF version : 02.30 Date taken : 2013:03:04 21:17:30 Date digitized : 2013:03:04 21:17:30 Components configuration : YCbCr Exposure bias value : 0 Max aperture : F1.7 Metering mode : Multi-segment (5) Light source : Unknown (0) Flash : No flash Focal length : 35 SubSecTime : 50 SubSecTimeOriginal : 50 SubSecTimeDigitized : 50 FlashPix Version : 01.00 Colour space : Uncalibrated EXIF image width : 4288 EXIF image length : 2848 Sensing method : One-chip color area sensor (2) File source : DSC Scene type : A directly photographed image Custom rendered : Normal process (0) Exposure mode : Manual (1) White balance : Auto (0) Digital zoom : 1 Focal length (35mm) : 52 Scene capture type : Portrait (2) Gain control : High gain up (2) Contrast : Normal (0) Saturation : Normal (0) Sharpness : Hard (2) Subject distance range : Unknown (0) : Data version : 0210 ISO : 1600 Image Quality : RAW White balance : AUTO Focus mode : AF-S White Balance Fine Tune : 4294967291 0 ISO setting : 0 1600 Serial Number : 4057881 PictureControlVersion : 0100 PictureControlName : PORTRAIT PictureControlBase : PORTRAIT PictureControlAdjust : Full Control PictureControlQuickAdjust : -1 Sharpness : 6 Contrast : -1 Brightness : Normal Saturation : 1 HueAdjustment : 1 FilterEffect : n/a ToningEffect : n/a ToningSaturation : 127 Picture Control : 0100PORTRAIT Lens type : D G Lens : 35 Flash mode : Did Not Fire Noise Reduction : OFF LensID : 35 35 159 1.8 1.8 Shutter Count : 58612 Lens ID Number : 159 Lens FStops : 7.33 Minimal Focal Length : 35.0 mm Maximum Focal Length : 35.0 mm Max Aperture at Minimal Focal : F1.8 Max Aperture at Maximum Focal : F1.8 MCU Version : 161 : Version ID : 22.214.171.124 : Compression : 6 X Resolution : 300 Y Resolution : 300 Resolution unit : Inch Thumbnail offset : 9960 Thumbnail length : 4166