I just bought my Sigma Lens 30mm f1.4, i just realised that it has minor focusing problem. With apperture open wide (that's f1.4) and my subject distance is around 2 feets 6 inches, i focus at one point but the result is the sharp image is slightly at the back of my focus point (my original focus point is blur). I dont know whether this is front focus problem or back focus. I use Sony Alpha A100 DSLR. Please help me.
Re: Front/Back Focus Problem at Sigma 30mm F1.4 Lens
I recommend that you print this test chart: http://www.photo.net/learn/focustest/scale45.jpg
Just print it on an ordinary paper, then put it on a table, and take a picture at it from a 45 degree angle, using the center focusing point only, aimed at the thicker line in the middle. The numers are centimeters. Take the test picture at f/1.4. Make sure you have good light so you get a fast shutter time. If you have a tripod, mount the camera on the tripod prior to taking the test picture.
Then examine the picture in your computer, zoomed to 100%. Now it should be clear wheter you got back- or front focus, and how large the problem is.
Unfortunately, there is no way for you to adjust the camera and lens combination yourself, you will have to send/bring the camera to an autorized camera workshop. This is covered by the warranty.
Hope this helps!
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Hi, not sure if you still have this issue. I have just decided to look into it again, as I had a lot of focus problems with my Sigma 70-200mm HSM lens. Since there is no Sigma support here in Beijing, I took a look - and fixed it.
Here is what I did: On the front of the lens barrel is the rubberised focus ring. This can be removed (gently ply it away from the barrel by sticking a flat bit (or plastic letter opener) between the barrel and the rubber grip. It will come not entirely loose, so you need to work your way around the lens. Keep doing that until you moved it about half way forward. At this point two fixing screws become accessible on the barrel below.
In my case, one of the screws had come loose and that blocked the focus ring from turning, as the screw was blocking rotation in the access hole on the barrel.
Hope this helps others. Simple to fix, if you know how.
How new is the lens? In or out of warranty? If out or warranty most likely solution is to find a Sigma authorized repair shop because your description sounds like the auto-focus motor gear has failed. If in warranty, check out Sigmaphoto.com for repair sites and also download the SIGMA_SERVICE_REQUEST.PDF. I've only had to deal with Sigma once on warranty matter and they were very helpful, provided UPS authorization for shipping on their nickel.
Set either the camera or lens (or both) to manual focus. Most Nikon cameras have the focus selector switch on the front, under the lens release button.
Look through the viewfinder and turn the focus ring until the image (or at least the subject) appears sharp. A green light will light up when the camera thinks the subject under the currently selected focus sensor is sharp.
Did it ever work on this camera?
I have seen some Sigma lenses that are auto focus on canon film cameras but then when put on the digital they dont work right. If you have used it on this camera then make sure the lens is clean.sometimes dirt on the front wil make it try focusing on the dirt. Next try focusing in manual focus to make sure the focus is working. Then take the lens off and then put it back on and make sure it clicks into place.
Let me know if none of those things work. also make sure to try focus on something close and somthing far away.
I would send it into sigma. They are in NY,
They are really quick about checking things out and I have neverhad them charge me to look at a lens and tell me whats up. aot of times they will just fix it while it there is it looks like something is worn out from normal use.
its a great lens. Some would say its a slower focus. than the Canon brand and you do get what you pay for but its hard to spend as much on canon lenses as they want. :)