Focusing Issues

[extremelyloud]

If anyone could provide me with some answers, that would be much appreciated!
So my problem is as follows:
I was trying to do some close-up shots with my Canon Rebel Xt DSLR and when I zoomed in really close on the images after taking them, the objects seemed somewhat out of focus. This kept happening every time I tried. This is a relatively new camera for me, so maybe I just don't know what to do correctly to get my image in perfect focus. As for details, I was using a 50mm 1.8f lens, trying both auto focus and manual focus. Any idea what my problem might be? Let me know if more clarification and/or information is needed. Thanks!

 

[Forkie]

Are you getting too close to your subject? I think the minimum focussing distance on the 50mm 1.8 is about 50cm.

 

[Big Mike]

The minimum focus distance of that lens, is 45cm (1.5 feet). So if you are closer than that, you won't be able to focus.

Also, when you get very close (especially if you're using a wide aperture), you DOF can get very thin.

Depth of field at F1.8 while focused at two feet away...
Near limit 1.98 ft
Far limit 2.02 ft
Total 0.03 ft

So in other words, at those settings, only a tiny sliver of distance will actually be in focus...so even if you have focused accurately, you likely won't have enough Depth of Field (DOF) to encompass what ever you are shooting.

 

[extremelyloud]

Thanks, that information is very helpful! How/where does one find out about the focusing distance of lenses? Sorry for the ignorant questions.

 

[Forkie]

You're questions aren't ignorant at all!

It's almost always in the specifications on the website you find it on, sometimes on the box and always in the manual.

There's some formulae HERE for working it out if you're so inclined. I'm not, but you might be!

 

[Big Mike]

Thanks, that information is very helpful! How/where does one find out about the focusing distance of lenses? Sorry for the ignorant questions.

Yes, it should be in your lens's manual...but I just when right to the Canon website and looked it up.
Canon U.S.A. : Consumer & Home Office : EF Lens Lineup

Then I used a DOF calculator to give you the details in my example.
Online Depth of Field Calculator

 

[rachard1583]

The 50-60mmmacros are good for repro and close-up work, but their working distance is too low in the true macro range.

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