Is my lens not working correctly?

rwalsh81

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As I'm still fairly new this is definitely a noob question. I recently purchased a used canon macro lens specifically the Canon EF 50mm f/2.5 Compact Macro Lens. When I try to take a picture using auto focus the lens just keeps on zooming in and out on me. So far I've only been able to use it while doing manual focus. Is it supposed to do that or did I get a lemon?
 
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I think macro lenses have difficulty with auto focus. The reason is the the DOF is very thin, so depending on factors such as the camera's focusing engine, DOF, your subject, etc., auto focus will be a problem. Just use manual focus for macro.
 
This lens has a 9" minimum focus distance. So if you are within 9" of your subject then the lens will not be able to lock in focus but continue trying.
 
This lens has a 9" minimum focus distance. So if you are within 9" of your subject then the lens will not be able to lock in focus but continue trying.

Ok, but if that's the case how can I focus in manually if I'm within the 9"? Like I said I'm a noob.
 
This lens has a 9" minimum focus distance. So if you are within 9" of your subject then the lens will not be able to lock in focus but continue trying.

Ok, but if that's the case how can I focus in manually if I'm within the 9"? Like I said I'm a noob.

Do you have enough light?
 
This lens has a 9" minimum focus distance. So if you are within 9" of your subject then the lens will not be able to lock in focus but continue trying.

Ok, but if that's the case how can I focus in manually if I'm within the 9"? Like I said I'm a noob.

Do you have enough light?

I believe so, when I get the manual focus up close I can clearly see the subject. Plus the shots have either been outside or at my desk at work which has tremendous lighting.
 
Have you tried a non-macro shot and it still doesn't auto focus?
 
Have you tried a non-macro shot and it still doesn't auto focus?

With that lens I thought it was just macro. My other lenses auto focus with no problem.


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Have you tried a non-macro shot and it still doesn't auto focus?

With that lens I thought it was just macro. My other lenses auto focus with no problem.


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It can be used like any other lens. Go outside and take a picture of your car or anything really and see if it auto focuses properly.
 
Have you tried a non-macro shot and it still doesn't auto focus?

With that lens I thought it was just macro. My other lenses auto focus with no problem.


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It can be used like any other lens. Go outside and take a picture of your car or anything really and see if it auto focuses properly.

Thanks I'll take a look when I get home. Didn't bring the camera with me today.


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Ok, but if that's the case how can I focus in manually if I'm within the 9"?
From the list:
  • Closest focusing distance: 0.8 feet
Which is 9.6 inches. I presume you already know this, and are not trying to get closer.

Things to try:

Choose a different subject. Sometimes the edge/contrast of the subject is marginal for AF.

Have a small flashlight available to shine light from a slightly different angle onto your subject. (same reason as above)

Use a tripod. Your natural body movement may be enough to prevent the AF from locking on.

If none of those help your lens AF, then just resign yourself to focusing manually for macros.
 
Have you tried a non-macro shot and it still doesn't auto focus?

With that lens I thought it was just macro. My other lenses auto focus with no problem.


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Nearly all macro lenses focus right out to infinity. The only exception I can think of is the Canon MP65E which is a very specialist lens.
AF is not good for macro, where having the focus on slightly the wrong part can make the important bit seriously out of focus. Your lens should easily focus on things a few feet away in good light. If it can't then somethings wrong - unless the switch is just set to MF :).
 
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A few thoughts

1) Macro lenses often have a limiter-switch on them. This lets you limit the focus range that the lens will move through to either its long or close distances. This is so that when you're shooting normal distance subjects you can cut out the long range of close focusing distances. You don't need them and they are often quite fine on a macro lens; so cutting them out means you can focus quicker (there's less range to hunt through).
If this limited switch is enabled for long distance and you try to focus close the lens can't achieve focus. On some the limiter affects manual focus as well and on others it doesn't.

2) When you focus closer on most macro lenses the aperture of the lens reduces. This isn't reported to the user (barring on Nikon lenses which do); but it means that the AF sensors are getting less light than if you were focusing at normal distances. Furthermore what is bright to our eyes can be very dim for a camera; indoors at night under normal indoor lighting is often bright enough for our eyes; but the camera will find it far more challenging. Thus a lack of light could be a factor.

3) AF at macro distances is hard because at those distances your natural body motions back and forth are very large shifts to the lens and its focal plane. As a result the lens and camera has to work extra hard and this can defeat many situations. It's why most macro photography is done with manual focus.
Thus far Canon has attempted to improve on this with a hybrid IS system in their newest 100mm f2.8 macro and their newer camera bodies.

5) The lens you have achieves half-life-size which means that a subject reflected on the sensor by the lens is half the size it is in reality. This is half of what a normal "true" macro lens gets. As a result your lens shouldn't be having as much hunting problem as a normal macro at its closest focusing distance (though its still a challenge). As its sounds like macro is new to you chances are that its still operator error/inexperience playing a part here more than anything else.
 
Cool thanks for the advice.
 

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