How do I test Sigma 50mm f/1.4 EX DG HSM Lens ?

[vikas_kohli]

<p>I have bought a new Sigma 50mm f/1.4 EX DG HSM Lens for use with D90.</p

>

<p>Be

ing aware of some of the (maybe older) feedback about focusing issues with the Sigma 1.4 I want to know how

can I definitely test and confirm that the piece I received does not suffer from the focusing.</s

pan></p>

<p>Thanks for your h

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[Matt Laur]

<p>First, go out and just shoot! <br /><br />To be more careful about it, you want to use a tripod, and use your flash for lighting so that you can be sure you're not dealing with any camera movement when you're looking at individual pixels while you test. If you use the lens fairly wide open (say, at f/2), and use your center spot focusing sensor, you should be able to try a shot at an angled piece of paper, and see the expeced very shallow depth of field, with your chosen spot in focus.<br /><br />Remember that your D90's center spot focusing area is actually fairly large, and that can cause you to be a bit imprecise. If you shoot with the lens all the way open at f/1.4, remember that - especially on fairly close subjects - you're going to have very, very little DoF. Even a tiny movement on your part as you're shooting can move the in-focus area of your image. So, be slow and deliberate while you're testing.<br /><br />Have fun, it's a great lens.</p>

[vikas_kohli]

<p>Thanks Matt ! I've read mostly great feedback about the lens and that is what swayed me to buy it against Nikon 50 1.4. But some of the comments about back/front focusing issues caused some agnst for me.</p>

<p>Honestly, I did't even know to check it for sure. So thank you.</p>

<p> </p>

[mike_earussi1]

<p>Having back/front focusing issues with a Sigma lens on a Canon/Nikon body is a very common problem. This is the answer I gave a few days ago on this forum to someone who was having that problem with a 10-20.</p>

<p>"A lot of people use a ruler photographed at a 45 degree angle, but I've tried this and it doesn't really give me the exact amount of front/back focusing, so I now photograph the DVDs in my bookshelf edge on. With the lens wide open I choose one DVD in the center to focus on and then move one next to it 1" in front and then one on the other side 1" behind it and take a picture. This tells me right away whether the lens is front or back focusing (or focusing correctly if the center one is sharpest). So say that I determine it's back focusing, I then vary the distance of the DVD behind the center one and take a series of shots until I see where it's the sharpest. If it's sharpest at 3" behind the center one then I know my lens is back focusing by 3." Admittedly, this is not very technically sophisticated, but it works."</p>

<p>Obviously this should be done on a tripod for best accuracy.</p>

<p>Here's the link if you wish to read the entire discussion:<br>

<a href="../canon-eos-digital-camera-forum/00Vqfi">http://www.photo.net/canon-eos-digital-camera-forum/00Vqfi</a></p>

<p> </p>