Problem with my 50mm 1.8 prime lens - HELP

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McNyat

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Ciaran
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Hi everyone, I have touched on this one before a while back but wasn't sure if the problem was with me. I have read some items about 'back focusing lens' and am experiencing this when using auto focus. The last time round I tested by using manual focus and shooting down a tape measure etc which seemed to point to user error (my fault in other words).

However, now with alot more experience and having used a 17-55 2.8 I can now say that the lens focuses slightly closer than it should when using auto focus. The pic below should show this problem clearly where the eyes are soft and the focus is on the front of the hat. I want to get the type of shallow DOFshot where the eyes are in focus and the focus drops off v quickly.


emma_test.JPG



I have read that lens' can be callibrated along with a camera. Where can I get this done, and is it expensive. Also I have just bought a second hand 7D with the above mentioned 17-55 2.8. I have read that the 7D can be slightly tweaked in the settings menu. Does this change for all lens' or can it be done for each individual lens. If I was getting the 50mm 1.8 callibrated would I need to have both cameras and all my lens' done together?

Help me please
 
In the shot you have posted, it may well be that the lens isn't front focusing, but just picked the front of the hat to focus on.

The only way to truly test if a lens is front/back focusing is to do test shots in a controlled way.
 
post a 100% crop of the focus point.. posting somehting that small is pretty useless to be honest..

canon dont calibrate lens and camera together.. sigma do.. canon will calibrate camera and will calibrate lens.. but they dont calibrate lens to camera..

hth :)
 
I will take a few more test shots as mentioned. The focus point on the pic above was on one of the eyes. What I have asked is how/where can I get the callibration of this lens checked out?
 
i would concur with those who have suggested that you need to perform more tests in a controlled environment.

there are a few things that can cause this problem in a portrait such as this that i can think of: -you moved, the subject moved, the focus point focused in the wrong place and the lens front/back focuses. 3 of the 4 of those things are not the fault of the lens or the camera.

it also has to be said that the 50 1.8 doesn't have the most consistent, accurate autofocus either and the 17-55 is going to be much, much better in that regard.

but looking at that photo above, and whilst i'm am not sure what focus point you actually used and where it was placed but assuming for a moment it was placed over the right eye, it's very likely that the focus point actually just picked up on the front of the hat.

also, on my camera, there are focus points which seem to perform much better than others at wide apertures, i know which ones they are and i don't use them unless i'm stopped down a bit.
 
Hmmm this is interesting, I use my 50mm F1.8 all the time and I've suffered loads from this and always put it down to me, camera shake, slow shutter speed, the subject moving etc but perhaps its not always that, perhaps something does need a tweak or I need to re-evaluate how I'm using it.

I also saw a similar thing today with my 35mm F2 prime, which is very much in the same vein as the 50mm, plastic bodied budget canon lens. Snapped some stuff which to me was bang on focus looking through the view finder, and looked fine on the camera, but get it on the big screen and its just out. Which is a bit gutting as I bumped into Ronnie Wood from The Stones and snapped him quickly with some guys I know who were recording in the same studio. obviously didnt have a lot of time and just feel the camera let me down.
 
cuthbert said:
i would concur with those who have suggested that you need to perform more tests in a controlled environment.

there are a few things that can cause this problem in a portrait such as this that i can think of: -you moved, the subject moved, the focus point focused in the wrong place and the lens front/back focuses. 3 of the 4 of those things are not the fault of the lens or the camera.

it also has to be said that the 50 1.8 doesn't have the most consistent, accurate autofocus either and the 17-55 is going to be much, much better in that regard.

but looking at that photo above, and whilst i'm am not sure what focus point you actually used and where it was placed but assuming for a moment it was placed over the right eye, it's very likely that the focus point actually just picked up on the front of the hat.

also, on my camera, there are focus points which seem to perform much better than others at wide apertures, i know which ones they are and i don't use them unless i'm stopped down a bit.
Click to expand...

I have since noticed the same thing as mentioned here. Can I get this rectified by Jessops (where I bought the camera) or Cannon? Has anyone had this done or got any other suggestions?
 
Try another test but make sure it's in "spot focus" instead of just the normal focus point. I had some similar problems with my 50 1.8 but with a bit of micro adjustment and spot focussing it was bang on over 95% of the time (apart from the user fault ones where I'd moved or the subject moved etc.) I don't have a 7D any more as I sold it to get a 5D3 so I can't point you to the manual page. If you have to get it calibrated I think you'd have to send it into Canon and you'd be best off sending the lens in first as I think it would be cheaper than getting the body done.
 
Thanks Stuart,

I can work with the 7d with regards to the micro adjustment, but thw main problem is when it is on my 550d. Anyone have any idea what having this fixed might cost?
 
McNyat said:
Thanks Stuart,

I can work with the 7d with regards to the micro adjustment, but thw main problem is when it is on my 550d. Anyone have any idea what having this fixed might cost?
Click to expand...

Probably about the same as buying another lens second hand that doesn't have the issue.
 
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