testing- Sigma 30/1.4 may be bad

I just got a Sigma 30/1.4 and I notice that it seems soft at 1.4, even in the center. It also makes what seems to be a strange noise when auto-focusing some times. I want to make some conclusive shots of text to test sharpness and accuracy. Depending on how far I place the target sheet from the lens, the text can look sharp to somewhat blurry. At what distance should normal size type (say 12 points or so) appear tack sharp? Put another way, what's the smallest percent of the total image that will look sharp when zoomed in? Say on a Rebel 300, how big does a typewritten page need to appear in the frame to be able to zoom in and see sharp text?

Thanks for any insights.

Look at the lens specifications regarding the minimum focus distance. I don't know the lens, but it should have very decent center sharpness even wide open. As far as the strange noise I can't help. The best way to get help regarding lens issues would be to post a testimage with EXIF information. I'm sure alot of people will be able to help you then! Happy testing.

It may be bad. I purchased the same lens in October. Had to get another copy. I read a couple of posts by folks in this forum that had to do the same. The new copy is much improved and it now meets my expectations. Pretty good lens really... if you get a good copy!

I am getting very good results from mine at wide open. Maybe my standard is lower than yours,,,

olz wrote:
Look at the lens specifications regarding the minimum focus distance. I don't know the lens, but it should have very decent center sharpness even wide open. As far as the strange noise I can't help. The best way to get help regarding lens issues would be to post a testimage with EXIF information. I'm sure alot of people will be able to help you then! Happy testing.

Here are some test images. The large image was taken at six feet with the Sigma 30 EX wide open and a single focus point on the NY State Seal right below the words "Certificate of Authority". These words are 2.5 inches long on the paper.

The small image is a center crop, downsampled just to show the area of detail. I will attach the full area of detail in another post.

HOSTED PHOTO
please log in to view hosted photos in full size.

HOSTED PHOTO
please log in to view hosted photos in full size.

Here's the full size crop.

HOSTED PHOTO
please log in to view hosted photos in full size.

Here's the full crop.

HOSTED PHOTO
please log in to view hosted photos in full size.

Hi again. The images are way to small to conclude anything. If possible, please upload a fulle size image. To be able to say that your lens either focuses in front of or behind your intended "spot" please make a test-setup like this: -->LINK<--. The alternative test will be sufficient to start with.

olz wrote:
Hi again. The images are way to small to conclude anything. If possible, please upload a fulle size image. To be able to say that your lens either focuses in front of or behind your intended "spot" please make a test-setup like this: -->LINK<--. The alternative test will be sufficient to start with.

Thanks , I'll do the real world focus test later this evening. Attached is a center crop of the exact point of focus at full resolution. This was taken at about six feet from the NYS Seal, and the words "Certificate of Authority" are 2.5 inches long. Does this seem to indicate acceptable sharpness at the point of focus, for starters? How sharp and clear should sharp text be at that size and distance?

HOSTED PHOTO
please log in to view hosted photos in full size.