Focus issues shooting Canon 24 f/1.4 lens wide open

[ray .]

What are the mechanical reasons that could cause focus problems shooting a fast lens wide open

on a 5D body? I just returned a 24mm L (version 1) Canon EF lens, concerned that the lens might not be

perfect with focusing when shooting at f/1.4. There seemed to be problems at times, and I'm not sure if it was with

both AF and manual focus, and/or only at certain distances. I know it wasn't a case of motion blur, but unfortunately while I had the lens I didn't have time to fully test it.

 

Thanks in advance...

[kou_lee]

<p>Mechanical reasons would be a malfunctioning lens. But it can also depend on the subject that you are shooting. From the T2i owners manual (the camera I own):</p>

<p>-Very low-contrast subjects<br>

-Subjects in very low light<br>

-Extremely backlit or reflective subjects<br>

-Near and far subjects covered by an AF point<br>

-Repetitive patterns</p>

[alan_bryant1]

<p>I'm thinking the razor-thin depth of field is the most likely culprit. I use this lens on a 5D quite often and wide open the DOF is very narrow. Also, if you're pixel-peeping, the lens is somewhat soft at f/1.4 even when it is focused right. It is usable for many purposes though.</p>

<p>Post a sample?</p>

[William Michael]

<p>Dunno what you term "sharp" but the 24 is a little soft at the edges wide open. Also were you using a filter - that is a killer at the edges IMO.<br>

Here is the 24 on a 5D under great pressure to perform: in low light - broad light - soft light - areas of little contrast, yet a wide EV range:

<p>It is difficult to comment much more, without an image from you.</p>

<br>

BTW DoF is about 30ft when focused at 25ft at F1/4.<br>

 

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WW<br>

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<a href="../photodb/folder?folder_id=958772"></a></p>

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<a href="../photodb/folder?folder_id=958772">http://www.photo.net/photodb/folder?folder_id=958772</a></p>

[alan_bryant1]

<p>Maybe it is 30 feet @ 25 feet, but I never use this lens with subjects 25 feet away. Typical shot of mine - probably about 4 feet away - this was at f/1.6 -</p>

<p>http://img.photobucket.com/albums/v490/alanpix/IMG_3753M.jpg</p>

<p>The near eye is sharp, distant eye OOF</p>

<p>http://img.photobucket.com/albums/v490/alanpix/IMG_3753MCrop.jpg</p>

[craigd]

<p>You can expect some degree of spherical aberration (cloudy halos) when shooting an f/1.4 lens at f/1.4. Are you sure that's not the issue?</p>

[daniel flather]

<p>This is the 35/1.4 @ 1/250 f1.4, iso 200. Different lens, but sharp in the centre @ 1.4.</p><div></div>

[William Michael]

<p>Yes, that is the point I was making, Alan.<br /><br />Ray writes: "There seemed<em><strong> to be problems at times</strong></em>, and I'm not sure if it was with both AF and manual focus, <em><strong>and/or only at certain distances</strong></em>."<br /><br />I was pressing the point to identify: what distances? - do you remember? <br /><br />Yes - if at a close SD, then DoF should be a consideration. <br /><br />As even at F/3.2 at and SD at about 3ft 6 inches, there is not much room for focus error as there is only about 9 inches / 12 inches DoF, and certainly at the limit of Focus and Recompose: <a href="../photo/9567749">http://www.photo.net/photo/9567749</a><br /><br />WW<br /><br /></p>

[ray .]

Indeed, there are a few at close distance that have focus problems. After examining them it seems the

thin DOF could be the issue. But since I didn't have time to do stringent tests on a used lens, I decided

to return it for now. I'll try to post an example tomorrow if possible.