#1  
Old 26-11-2010, 10:10 PM
hotspur's Avatar
hotspur (Chris)
Registered User

hotspur is offline
 
Join Date: Apr 2009
Location: south east QLD,Australia
Posts: 2,867
Back Focus issue with70-200 2.8?

How does one go about looking at if there is aback focus issue with a lens,and then getting it looked at?

I have a 70-200 F2.8 canon,and its a very fine piece of glass,I am happy with images,but around 10% or a little less,seem to have back focus.I have noticed when using its not as good as focusing as say my 400 L or my (17-55 F 2.8 which is the best I have ever had for focusing).

Recently I took some images at my son's year ten formal,my work friend asked if I could take some of his daughter,I took some in the hall,some were quite good,I then took some of the girl outside against a tree,but all 6 or 7 images were like the three posted,focus on the tree,I aimed at her eye.

The ones inside hall,pic 4 look ok,the only major difference,I had soft box on flash out side.

Any thoughts,about how I could think about this issue,most likey operator error-99% of lens issues are 98% user error.But the 17-55 F2.8 almost out guns the 70-200,this should not be so.

Images are as is out of camera.
Attached Thumbnails
Click for full-size image (tiana 1.jpg)
197.5 KB27 views
Click for full-size image (tiana 2.jpg)
200.4 KB24 views
Click for full-size image (tiana 3.jpg)
193.7 KB27 views
Click for full-size image (Tiana 4.JPG)
196.9 KB27 views
Reply With Quote
  #2  
Old 26-11-2010, 10:42 PM
dugnsuz's Avatar
dugnsuz (Doug)
Registered User

dugnsuz is offline
 
Join Date: Aug 2005
Location: Hahndorf, South Australia
Posts: 4,261
Hi Chris - Which AF mode are you using with the Camera/Lens?

I ask, as from the shots it looks like the focus is 'centered' on the foliage rather than the girl's face.

I found that going from the multiple point AF mode to the single central AF point sorted out my focus issues as the DSLR didn't pick a point outwith the centre of the image.

When I bought my 300mm f4L I couldn't get a really sharp shot until I switched AF modes - then problem solvered!

Doug

ps..that's probably too simple, but it's all I got!!

Last edited by dugnsuz; 27-11-2010 at 12:32 PM. Reason: punctuation!!!!
Reply With Quote
  #3  
Old 27-11-2010, 01:34 AM
Octane's Avatar
Octane (Humayun)
IIS Member #671

Octane is offline
 
Join Date: Dec 2005
Location: Canberra
Posts: 11,159
Doug,

Simple, but, spot on.

If the lens had a backfocus issue, it would typically show up in each image.

Judging by the sharpness in the final image, I'd say you just need to switch your AF point to the central focus point (typically the strongest performing point) and use the focus and recompose technique. Be careful when using shallow depths of field as the focus and recompose technique may not work for gross movements.

H
Reply With Quote
  #4  
Old 27-11-2010, 11:57 AM
acropolite's Avatar
acropolite (Phil)
Registered User

acropolite is offline
 
Join Date: Feb 2005
Location: Launceston Tasmania
Posts: 9,019
Chris even if the lens has a back focus issue, the 50D allows lens focus calibration. There are several sites with instructions on how to calibrate your lenses to the 50d body, you can calibrate individual lenses and the camera will recognise and apply the calibration when the lens is changed, do a google search.

Last edited by acropolite; 27-11-2010 at 03:21 PM.
Reply With Quote
  #5  
Old 27-11-2010, 01:38 PM
DavidTrap's Avatar
DavidTrap (David)
Really just a beginner

DavidTrap is offline
 
Join Date: Jun 2009
Location: Brisbane
Posts: 3,032
I was talking to my father in law - he had a focus issue with his Nikon D300. They could "electronically" adjust the focus - but only in the workshop.

Nonetheless, I tend to agree with earlier posters, I think your autofocus might be picking the wrong target. Have a play again with your lens and watch which focus point it is using. My camera isn't flash enough to have the face recognition stuff, but I prefer to use the central focus point and recompose.

DT
Reply With Quote
  #6  
Old 27-11-2010, 03:27 PM
hotspur's Avatar
hotspur (Chris)
Registered User

hotspur is offline
 
Join Date: Apr 2009
Location: south east QLD,Australia
Posts: 2,867
re focus

Thanks for your thoughts chaps.I always select the focus point.in these 3 images,I selected the right focus point and used the camera vertically.I was using the 450d,so suspect the Humayan is right-the centre focus point is the strongest one,also being a entry level SLR it may not have very strong focus points apart from centre.

I may have selected the wrong point,as I was heading to car to put gear away.so slightly rushed.

Here is another image this time from 50d and 17-55 lens it has had some slight adjustment in P.S.

Cheers Chris
Attached Thumbnails
Click for full-size image (4106 photo shop.jpg)
191.2 KB16 views
Reply With Quote
Reply

Bookmarks

Thread Tools
Rate This Thread
Rate This Thread:

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump


All times are GMT +10. The time is now 08:22 PM.

Powered by vBulletin Version 3.8.7 | Copyright ©2000 - 2024, Jelsoft Enterprises Ltd.
Advertisement
Testar
Advertisement
Bintel
Advertisement