Sigma 30mm f1.4 AF Test

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Hornet-Wing

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Hi Guys, I have been lurking around many forums deciding on my next lens. I ended up choosing the Sigma 30mm lens as on my 550D (cropped sensor) it would give me the nice "nifty fifty" focal length. It's also a quick and good enough lens for shooting mountain bikers. However, I have been scared by the reviews and "Quality Issues" threads. So 1st thing I have done is to do a focus test. I am not 100% sure what constitutes as fault in AF. I can see a bit of front-focus. Is my lens a "bad" copy?

Thanks for reading! :thumbs:


IMG_6476 by Hornet-Wing, on Flickr
 
focus charts are notoriously ridiculous - better would be to use it in the real world.

if you insist on a test line up some batteries or memory cards (CF cards stand up nicely) so that they make a diagonal line - make sure horizontal space between each card and about 5mm depth.

focus on the middle card (centre point only) and see which one is sharpest
 
Yep agree shootsomething real and make yourasdumptions from that, I did the same with my new 50 f1.4 testing with charts was inconclusive so I did some wide open tests on people the dog etc and it's fine maybe a tad soft at 1.4 but as soon as you get to 1.7-2 it's razorish
 
Don't use that test target. It's the bane of every lens manufacturers' service department. It's flawed, and very prone to user error. The target must be flat, square to the camera, and shot at a sensible distance.

AF accuracy is a bit of a compromise and is rarely 100% cock-on at all distances and focal lengths. If you optimise it for an artificially close distance, it will probably be out at normal range.

There are lots of threads on how to do it properly (search against my user name) but unless you have a good reason to check the AF accuracy, it's not a bad idea to leave it alone.
 
You want to use it to take photos of mountain bikers, so you test it with a photograph of a piece of paper? :thinking:

Get out and use it, it's a crackin' lens! Mine is rarely off the front of the camera. :thumbs:
 
Thank you very much all! Ill have a look into more testing ideas tonight.

Ill also take it with me to the Downhill race this weekend and see who it preforms in real life.
 
If you must check the lens using a focus test chart, make sure that you are using a tripod. The depth of focus @ 1.4 is tiny and slightest movement could make the lens look as if its at fault when it's not!
 
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