Len/camera front focussing?

DB_SamX

DB_SamX

DB_SamX

Soldato
Joined
17 Feb 2006
Posts
8,962
Location
Winchester
My third thread asking help in as many days!

Since I bought my D90 is Jan, yesterday was the first time I used it with my 50mm and wide open (wider than f/2.8). Over the course of the day, I noticed that my focus (auto but using various AF points by hand) was rather off when shooting at f/2.8 and wider. Examples below. Now, I've had my 50mm for over a year, so unless it's gone wrong, I am thinking it is the camera. When I went to Marwell in Jan and shot at f/2.8 and f/4 with my Sigma 50-150 and borrowed 70-200, I didn't notice anything obviously wrong, but then, these aren't as wide, so any focussing issues wouldn't be as obvious?

Few basic exmaples, jpegs off the camera directly:

dsc0137z.jpg

Focussed on head, focus seems a good foot in front; is that even possible? f/2.8

dsc0131v.jpg

Same again, focus very much on grass in front. f2.8

dsc0152a.jpg

Focussed on top raisin, not too bad but possibly in front again by a cm or more. f/4

Will need to do some focus tests using an online template and check with my lenses this week, but any tips or advice from anyone, who's come across the same issue? Is it a costly fix if I need to have the camera+lens calibrated and would it be free under warranty? Is it possible for only certain focus points (11 total on the D90) be off?
 
Last edited:
Any chances of some higher res ones? Big ol' pictures makes is nice and easy for all of us to tell if its front or back focussing :D
 
The first two definitely look like something has gone wrong! This could be down to user error, you said that you were using manual focus point, do you reckon there was any chance that you accidently left it on a lower focus point rather than the centre one? You should be able to find a front/back focussing chart online some where that will be able to make it crystal clear if there are any issues going on.

I don't know if the D90 has a micro adjustment feature, if not will have to be off to Nikon for a calibration of some sort!
 
Oh dear; that's one thorough test! I don't think I have the choice though, so will go through them this week. Thank you for the link.

I'm hoping it's user error but wider than f/2.8 and it's quite consistent across my photos taken over a whole day, but I doubt it. Photos where the subject was at a distance turned out ok due to the larger dof though.
 
Yeah its pretty in depth but its worth it. To be fair maybe the easiest way may be to just use a lined sheet of paper.. set it to centre focus point.. stick on a tripod and on auto focus and shoot wide open... quick and dirty way to see :)
 
Canons seem to be prone to front focus on wide aperture lenses, not really seen much on Nikons. I have a 550d (also no micro adjust) and that front focused on my 50mm f1.8. An interesting trick to try is using the live view to focus, its much slower but it uses contrast AF not phase detect. I found that this gives me much better repeatable results when shooting wide apertures. There is also a theory that on such lenses spherical aberration in the center of the lens throws the focusing off but as spherical aberration is less prevalent the further from the center of the lens you go, choosing to focus on one of the off center AF points should also give you better results. Of course all this doesn't help if you just want your lens to work as it should. So, you can send your camera and lens to Nikon with a covering letter and example photo and people say they will calibrate it for you. I ended up taking my lens back to Jessops and tried all the lenses they had in stock until I found one that was acceptable (not sure I made myself very popular that day :o)
 
Last edited:
forget that focus chart it can show you issues that you dont actually have.

to quote hoppyuk over on TP:

For focus testing, the cerial box works well. Just don't shoot at artificially close distance (like the chart you linked to - tests like that should really be banned ). While the shallow DoF helps you see shifts more easily, very few lenses are perfect at all focal lengths and all focusing distances and at close range you are pushing right to the edge of the tolerance envelope, and possibly beyond it.

The danger is that you see a slight error, correct it with micro-adjust, which then puts the AF out at normal range. Say 25x focal length, but no closer than 2m as a rule of thumb.
Click to expand...

the cerial box method..

http://www.talkphotography.co.uk/forums/showpost.php?p=3427473&postcount=14
 
You must log in or register to reply here.
Back
Top Bottom