D-60 & Sigma 15-30 focus problem

[jwarthman]

Troy,
I don't have the lenses you mention, but I have shot a great deal with the D30, and some with the D60. My technique for focusing sounds much like yours, although I don't generally try to focus at the hyperfocal distance.

When you say:

After focus was established, I flipped the camera on manual so as to not change the focus settings, and then re-composed the pitcure and shot.

Do you mean that you set the lens to manual? If you're simply setting the D60's "mode dial" to "M" (manual), the camera will still try to autofocus when you press the shutter release.

If you are, in fact, setting the lens to the manual focus setting, I'm not sure what's going wrong. You said:

focused about one-third of the way into the scene using the auto focus setting on the lens

Since this, too, resulted in an out of focus image, that suggests your problem has nothing to do with the focus scale on the lens.

Please keep us posted.

Best Regards,

-- Jim

[cwphoto]

I haven't used this lens, but if it's like most current Sigma zooms, the "depth of field" scale on the 15-30mm is a bit of a joke.  It is usually not very accurate, and it is only valid for one focal length setting.

I'm not laughing! Do you know if Canon lenses have similar problems? The EX Sigma series is suppose to be "professional" quality gear. I'm told the DG designation is geared specifically for digital cameras. The 15-30 is a DG lens! I for one am not impressed with what would seem to be rather basic. If we can computer design lenses, what's the problem with a distance scale!


This is where the Canon "DEP" mode comes in handy.

The problem is the depth of field area is very small on the D-60--between the outer two focus squares as seen through the viewfinder.  On my A2 body it works okay, (you can pick the spots here)  but the area measured on a wide angle lens is way to small with the D-60 and not where you need it.  

Well, thanks for the response. I'm not sure where to go from here.

Best,

Troy

[Cliff LeSergent]

Most AF zoom lenses do not have a depth-of-filed scale, since it's not really feasible to incorporate one in a two-ring zoom design.  Sigma is the only manufacturer I'm aware of that puts a scale on their zoom lenses (and promotes it in their marketing hype), but as I mentioned earlier, it is only valid for one focal length setting - you'll have to read the instructions that came with your lens to determine which focal length you can use it with.

As far as Sigma lenses being of "professional" quality, well, that's a purely subjective label.  I guess Canon's L series lenses would be "really professional" quality.

Since you've discovered that the depth-of-field scale on your lens is not reliable, and you are not able to use the camera's "DEP" mode to your satisfaction, there are two more alternatives - you can use the camera's depth-of-field preview button to try and visually judge the correct focus, or you can find a depth-of-field table, and choose the appropriate hyperfocal distance for the aperture and focal length you are using, and manually focus the lens to that distance.

[Ray]

or you can find a depth-of-field table, and choose the appropriate hyperfocal distance for the aperture and focal length you are using, and manually focus the lens to that distance.

In the meantime, you've possibly lost the shot.    

I have the Sigma 15-30mm zoom. I think it's a great lens for the D60. I'd be surprised if the Canon 16-35mm could better it in terms of sharpness and clarity (except with full frame 35mm at the edges). I never bother with the DoF scale. As Erik has suggested, the degree of 'out-of-focusness' that's acceptable is a subjective thing and also depends on the degree of enlargement of the final print. I find the Sigma is still sharp at F11 with the D60 and if you're not enlarging beyond 8x10, F16 is very acceptable.

[cwphoto]

I made an interesting discovery just recently using my Canon D- 60 and the Sigma 15-30 mm lens. I tend to shoot a lot of landscape photography and my normal practice is to tripod mount my camera, and use the hyper focal distance settings on the lens for maximum depth of field. I would typically shoot at a 11 or F-16. At F-16, I would expect sharp focus from about 1.25 ft. to infinity. I also use the self timer and mirror lockup, so this would entirely eliminate any problems due to camera shake or vibrations.

What I discovered was literally hundreds of images that were out of focus from a November trip to Zion national park. Determined to get at the root of the problem I conducted a simple test to see what I could discover about the problem. I set up the camera, again on a tripod, and focused about one-third of the way into the scene using the auto focus setting on the lens. After focus was established, I flipped the camera on manual so as to not change the focus settings, and then re-composed the pitcure and shot. The aperture setting used was F-11.

I then repeated the test using the lenses hyper focal distance, which I would expect to give me a similar if not identical results to the above procedure. What I found was rather surprising to me. Focus was much closer than one-third of the way into the image, so that the bulk of the image was out of focus. That is to say very near objects in the foreground appear sharp on both of the tests but anything from one-third of the way into the scene out to infinity was considerably softer or less sharp than when I auto focused one-third of the way into the scene.

Clearly there is a problem when using the distance scale on the lens. Is it possible that since the Sigma was designed for a full frame 35 mm that when the lens is used on the D-60 (smaller imaging area) that the depth of field scale is no longer accurate? I'm thinking that there's something more to it than this as the images are so far out of focus that something else seems to be going on. Need less to say, I'm rather bummed as I have hundreds of images that are totally useless due to this problem.

It anyone else has the same combination of camera and lens, I would appreciate you trying this test yourself and let me know the results. So far, I have not confirmed this problem on anything but the 15-30, but I also have the 28-70 Sigma as well, and intend to run a similar test on this lens to see if it is an isolated problem or not.
Cheers,

Troy

[Cliff LeSergent]

I haven't used this lens, but if it's like most current Sigma zooms, the "depth of field" scale on the 15-30mm is a bit of a joke.  It is usually not very accurate, and it is only valid for one focal length setting.

For example, if the scale was intended for the 15mm focal length setting, and you were shooting at, say, 28mm, your hyperfocal distance would be off by quite a bit.

This is where the Canon "DEP" mode comes in handy.

[Erik M]

You do realize that you can only have one plane of focus? Only one plane is in focus in any photo, say one third or half way into the photo (or wherever you focus), and the rest is out of focus. Normally the out of focus sections only look out of focus when enlarged (or looked at at 100% magnification in Photoshop). To minimize this you stop down a good deal to decrease the circle of confusion. The smaller the circle of confusion the larger you can make your enlargement before the out of focus sections become apparent.

I was rather shocked to learn this a few years ago myself. If you want to learn more, I can give you a url to the Hasselblad site, where they have an article about this topic.

I usually focus visually on the horizon (or those distant mountains) when I do landscapes then stop down to f11-16 for my medium format wide angle photos. This seems to work for me. Your mileage may vary.

[Cliff LeSergent]

Try this link for a depth-of-field calculator:

www.dudak.baka.com/dofcalc.html

[cwphoto]

<<Most AF zoom lenses do not have a depth-of-filed scale, since it's not really feasible to incorporate one in a two-ring zoom design.  Sigma is the only manufacturer I'm aware of that puts a scale on their zoom lenses (and promotes it in their marketing hype), but as I mentioned earlier, it is only valid for one focal length setting - you'll have to read the instructions that came with your lens to determine which focal length you can use it with.>>

No mention of this in the Sigma docs or possible errors in distance scale.

<<Since you've discovered that the depth-of-field scale on your lens is not reliable, and you are not able to use the camera's "DEP" mode to your satisfaction, there are two more alternatives - you can use the camera's depth-of-field preview button to try and visually judge the correct focus, or you can find a depth-of-field table, and choose the appropriate hyperfocal distance for the aperture and focal length you are using, and manually focus the lens to that distance.>>

With a Distance scale that is not accurate! Sounds like a catch 22 to me! Autofocusing 1/3 of the way into the image and switching the lens to manual after focus I suspect is the best approach.

<<As far as Sigma lenses being of "professional" quality, well, that's a purely subjective label.  I guess Canon's L series lenses would be "really professional" quality.>>

Sounds like another thread. Overall, I think Sigma's EX series repersents a good optic for the price. They certainly are not "L" lenses though, and you'll get no debate from me.

Thanks!

Troy