symptoms of damaged lens


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x33133x

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Jun 18, 2009
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#1
hi guys,

need some advice.

is it possible for a lens to be damaged e.g. @ f/1.8 but working fine @ f/20?
 

Octarine

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#2
is it possible for a lens to be damaged e.g. @ f/1.8 but working fine @ f/20?
Please describe your symptoms more in detail. Lens type, brand, camera etc.; what have you tried so far, how and when did the problem occur?
My first guess: your aperture got stuck :dunno:
 

x33133x

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Jun 18, 2009
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#3
canon 50d on a canon 50mm 1.4.

put it on a stand ISO 100. at f22. picture is sharp but on f1.4 the picture is blur.

do give your input even if you think there is possibly a user (me) problem. :)
 

catchlights

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#4
two possibility, front/back focusing issue, or Depth of field too thin than you can't focus it properly.

to check/confirm, Google focusing test chart, download the chart and follow the instruction to do testing on your lens.
 

i2d2roger

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Jun 19, 2009
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#5
what is front/back focusing issue, or Depth of field too thin?
 

Octarine

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#6
Is the focus point (red dot) directly at the subject that is supposed to be in focus? Are you using single AF point or let the camera decide which one to take?
 

Octarine

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#7
what is front/back focusing issue, or Depth of field too thin?
Front / back focus: although the camera focuses and confirms that focus is obtained on a certain object the lens optically focuses either at a point closer to the camera (front) or at a point further behind (back) the actual focused object.
Understanding Depth of Field - pay attention how aperture affects DOF, then read again the description of TS.
Lastly: there is a search function upper right hand and there is Google.
 

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x33133x

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Jun 18, 2009
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#8
so Front / back focus is an issue with the lens?
 

Linnl71

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#9
so Front / back focus is an issue with the lens?
Could be due to your camera's AF function or if your lens has AF capability could be due to your lens as well... I think so :bsmilie:
 

Octarine

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#10
so Front / back focus is an issue with the lens?
Yes, usually it's an issue about the lens. The camera measures and determines how much the focus ring of the lens has to move according the current blur image and the position of the focus element as reported by the lens. The respective focus command is given to the lens. If the lens is not at the correct focus position after executing the command then it's either an issue of focus motor not working properly or the position of the focus element does not match what the lens is reporting.
Some bodies have micro adjustment capabilities where the body can "learn" how much the lens is off (to back or front) and the focus command is adjusted accordingly. The other option is lens calibrating which is done at the respective service centers for the lens.
 

x33133x

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Jun 18, 2009
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#11
Octarine thanks for the explanation, so am i right to say that this happens only for AF mode? if i switch it to manual it should not be a problem right?

can another possibility be that at 1.4 due to bokeh, the clear focus point is too small to be noticed and hence the rest of the picture looks blurred?
 

Octarine

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#12
Octarine thanks for the explanation, so am i right to say that this happens only for AF mode? if i switch it to manual it should not be a problem right?
Yes. Then your eye has the full control.

can another possibility be that at 1.4 due to bokeh, the clear focus point is too small to be noticed and hence the rest of the picture looks blurred?
This is what catchlights mentioned: Depth of Field is too thin. Check the link that I posted earlier, use the calculator, enter your data (focal length, aperture, distance, 1.6x crop) and you can see how the results changes when you change from f/1.4 to f/22.
 

gazkw

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Jan 12, 2009
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#13
whats the performance at f2, f2.8, f4 and f8?

f1.4 the dof can be too thin to be conclusive and that lens people normally stop up to f2 to get more usable images (perhaps f1.8 onwards). f1.4 can be a bit hard to use.
 

calebk

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#14
Why don't you just post sample images. Right now we're just guessing what the problem is based on your vague description.
 

x33133x

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Jun 18, 2009
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#15
here are the shots i took

this is the shot taken with EF 50mm 1.4 at f1.4


this is the shot taken with EF 50mm 1.4 at f22


i also used a FD 50mm 1.4 with adaptor and it seems sharper


EFS 18-200 at F5, the fastest available at the same focal distance seems even sharper than the EF



please comment what is wrong. photographer included. :)
 

IamJeFfy

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Apr 15, 2002
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#16
i don't think there is anything wrong with your lens.

judging from the shot you shot wide open at f/1.4, the sharpness on the right side of the photo looks reasonably sharp.

the center to left portion is slightly soft due to the shallow DOF.

shoot at f/2 or f/2.8 it should get better...
 

wave125s

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Apr 27, 2009
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#17
Hi, from all those lens test reviews I've read, there is no problem.
Most lens are 'soft' (blur) when you use their max aperture. Unless it's those super expensive one.
Therefore those cheap lens, even though they may have f2.8 constant for all focal length, using the max aperture will be blur. Maybe those lens review might be helpful before you commit to buying lens.
 

limwhow

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Jun 9, 2009
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#18
Hi x33133x,

If you really do study the shots closely, you would indeed find the shot taken at f/1.4 to be soft.
Of course by taken a full frontal shot of the newspaper page, it's hard to tell. It may be good to take the page from an angle and tell yourself which character you are auto-focusing at, and examine that particular character closely to see if it is sharp at the character itself, or the character in front or behind it.
This problem plagued me for a while before Canon Service Centre checked and determined my 50mm f/1.4 to have a front focusing problem. Ever since the calibration, the focus point has no problem.
I would suggest you bring it back to CSC for a check esp if your lens is still under warranty. Otherwise you will never have peace of mind.
My opinion.
 

eosandy

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Sep 14, 2008
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#20
Need more info on yr setup... flash used?

The 1.4 is renowned to be soft @ 1.4...

CSC service center for calibration is ultimately the advice you will get, together with yr cam body.
 

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