why can't you focus when zooming all the way in?

[ph0toe]

using a zoom lens and zoom all the way to the maximum focal length say 105mm. why it won't focus in the viewfinder? but it will focus when i turn the zoom down to say 70 or 24mm?

 

[480sparky]

What lens?

 

[ph0toe]

standard 24-105 canon L 1 series

 

[480sparky]

Are you close to the minimum focus? Perhaps when you zoom out, the camera's focus module can find enough contrast to focus, but at 105mm there isn't enough contrast.

 

[Dacaur]

That should not be the case. There may be a problem with your lense or camera.

 

[Destin]

Are you close to the minimum focus? Perhaps when you zoom out, the camera's focus module can find enough contrast to focus, but at 105mm there isn't enough contrast.

This.

Try putting the focus point over a high contrast area of the image. Also, at longer focal lengths your depth of field becomes thinner. This means that your camera may hunt for focus more, and if it’s already on a low contrast area then the this may just make it too hard to find focus.

Its always possible that there’s a problem with your camera or lens, but that would be hard for us to diagnose without being able to examine it.

 

[Original katomi]

Have you tried using manual focus just to see if/that the lens will focus
Eg rule out a least one fault
Ok back just been looking at some reviews to remind myself.
The mfd minimal focus distance is .45m
You will have to look to see that you are not shifting the auto manual focus selector as you zoom,
Finally for now
There were some flare problems on some of those lenses that canon repaired model dependent.
Personally for the cost of a phone call/e mail I would find the serial number of the lens and contact canon explaining the problem or if bought from a dealer /camera shop
go back to them
Info source should you want to look up is
The digital picture dot com
Look for the review of the lens
Just looked at canon home uk,
There was a problem with some of their early lens
I am looking at the software manuals section the info on Effected lenses is there
Hope this helps

 

[wfooshee]

Isn't the minimum focus distance different at different focal lengths? That's actually something I would expect, and have seen myself. Short focus length and fairly close, with good focus, when I try to zoom in I'd be unable to focus.

How close a subject are you trying to shoot?

 

[480sparky]

If it changes based on focal length, then it should be in the specs.... just like variable-aperture zooms.

 

[Solarflare]

It should always focus, unless you are too close and thus the lens is simply physically unable to focus.

All zoom lenses I own have the same minimum focus distance, no matter what focal length you choose, but maybe that lens you have there is different ? After all, I dont have many zoom lenses and I havent used any of those I have in years by now.

 

[Original katomi]

Have you spoken to canon to see if your lens was one of the ones affected.
Otherwise, take a tape and measure the distance that you are trying to focus at.
Avg male stride is 3/4 of a meter which is about the min focusing distance for that lens.

If you have one put a steel tape rule out with the camera on a tripod, with the end of the tape at the focal plane and take pics of the tape getting closer till it will not focus
I can’t see if you replied did you try manually focusing the lens?
Re specs, they can be found at canon home uk or your equivalent

 

[petrochemist]

It should always focus, unless you are too close and thus the lens is simply physically unable to focus.

All zoom lenses I own have the same minimum focus distance, no matter what focal length you choose, but maybe that lens you have there is different ? After all, I dont have many zoom lenses and I havent used any of those I have in years by now.

I DO have many zooms (over 80).
Its pretty rare to find a zoom that does change MFD with focal length. I'm fairly sure the only ones of mine that do are those with jury rigged adapters (projector lenses etc). If adding extension of a macro supplementary MFD will be highly focal length dependent but this is not normal operation.

 

[wfooshee]

My 70-300G ED VR does make me move back a couple of inches for minimum focus distance at 300 compared to 70. That said, I believe the distance from the front element to the subject is the same. Sensor to subject distance is different, I have to back up just a bit, and while I didn't measure, the difference is very close to the length change of the lens barrel.

So in this case, I would say the minimum focus distance is different, measured from the sensor plane. Lens-to-subject, probably the same distance.

 

[Dacaur]

Generaly MFD is measured from the sensor, and at whatever zoom allows the minimum focus distance.
Whether the MFD changes with zoom depends on the lense design. Many do change, but many do not.

 

[ph0toe]

what you mean minimum focal? isn't 24mm the minimum? and i experimented with a few different angles, like moving a few feet away as oppose to close