Charles P Loc: Southern Central NY State

Yes Sally, it makes a lot of sense that there is probably something wrong with that lens. After I posted, I went back and looked at the link that Linda posted to your horse pictures. And they are very nice indeed! They were taken with a much longer lens, and there is certainly no camera shake there. And you're right, even wide open the Sigma should have been in better focus than it was.

E.L.. Shapiro Loc: Ottawa, Ontario Canada

Before taking any equipment on an important vacation shoot or making uninformed decisions about buying other lenses, it pays off to do some basic testing to determine if any lack of sharpness, acutance or resolution is due to some deficit in your technique or an actual defect or shortcoming in the equipment.

You don't need laboratory or "optical bench" equipment to perform some practical tests. Good troubleshooting starts with a process of elimination by first negating some of the common causes of poor sharpness or blur such as camera shake, mirror slap, autofocus errors and othere basic issues that can sometimes occur- it even happens to experienced photographers when the are engrossed in artistic matters and may forget some of the basic precautions. Make certain that your AF setting is appropriate for the work you are doing.

Set you camera up about 10 or 15 away from and parallel to a brick wall. Make sure the wall is evenly lighted. The lines on a brick wall can be used to detect certain distortions or lens aberrations and the texture can make a good test target for fine detail. I also advise affixing some pages with fine print at the edges, corners and center of your field of view. Make certain the camera is secured to a firm tripod. Use a slower ISO setting to eliminate (max. 200) the possibility of noise. Make exposures at a full range of apertures compensating with the shutter speed for correct exposure. When slower speeds are required, lock up the mirror and use a remote release or cable.

Focus carefully in both auto and manual modes. When focusing manually, bring the image into sharp focus, then go beyond that point and go back to the sharpest point. Use a slate, paste up notes or record the Exif data. With zoom lenses, perform the test a various focal lengths.

Then observe the results. By close examination of the images at high degrees of magnification, especially observing the sharpness of the small print, you will see if your focusing mechanisms are accurate. You will see of there is any significant fall off of sharpness at the edges and get some idea when an if any significant diffraction occurs at smaller apertures and when it kicks in.

Many lenses exhibit their best optical performance, as to sharpness at about 2 stops down from the maximum aperture. Do not confuse this with depth of field which increases as the lens is stopped down.

There are many othere causes of poor accutane or lack of sharpness such as poor quality filters, dirty, dusty or smudged lenses or filters and uclan sensors so make certain that everything is clean and remove any filters for theses tests. You can make comparisons with the filters in place as well. Sometimes lens flare and the resulting loss of contrast tends to give images a mushy look that can be mistaken for a lack of sharpness. Use a good lens shade.

If you do everything in a methodical and precise manner and there is a significant deficit in sharpness, this may indicate the the system or part thereof may be harboring a defect or is in need of replacement or repair. At least, you will get to know the attributes and limitations your lenses.

This s a basic controlled test. Trying to determine any of this under field conditions- just shooting random shots of scenery, is like a cat chasing its own tail- very frustrating!

If all the mechanics are working acceptably, then you need to concentrate on your technique as to holding the camera steadily, using a tripod, monopod, grip or improvised support system when possible, avoiding mirror slap, external vibration and errors in focusing technique.

Longer telephoto and longer zoom setting require faster shutter speeds, especially in hand held situations. One rule of thumb is to use the focal length number as the minimum shutter speed- a 200mm focal length needs at least a t 1/200 sec. shutter speed in a hand held scenario. Wit longer or heavier lenses, find the center of gravity of the rig so as to gain a balance. On lightweight gear, take time to insure that you gave a firm grip, good access to the shutter release and and avoid "poking" it- depress it gently. Lock in focus when required so it won't drift at the last second. Sometimes, with the convenience of more compact and lighter weigh equipment, we can get a bit sloppy with our camera handling like holding the camera in one hand and not steadying it as we are used to with bulkier gear.

You may want to read up on or research depth of field techniques utilizing hyperfocal distances. It's important in scenic and landscape work to know exactly where in the scene to focus on in order to obtain sharpness in all the "layers" of the composition- foreground, middleground and background.

A day set aside for testing can preclude long term of disappointment in lost images of unrepeatable scenes. I routinely perform theses kinds of tests even on newly acquired gear or when equipment is returned from service or repair. I don't want to discover bugs after or during an assignment.

I hope this helps.

ggab Loc: ?

I certainly understand. DPP will show you which focus point(s), if any, the camera considers in focus. It is an effective troubleshooting tool. If none of the focus points show as red, then the camera didn't consider any point of the picture in focus. I would then look to other avenues such as technique, lens etc. I saw some of the pictures you took with your L lens, clearly, based on those pictures your technique is good.
Have you taken pictures of more clearly defined images? If so, are they bad as well?

amfoto1 Loc: San Jose, Calif. USA

I don't find any info on that older Sigma 18-35mm lens, so am not sure about it. All three of your sample images are showing a variety of problems.... soft focus from near to far, aberrations, flare.

Do you have a "protection" filter on the lens? If so, take it off and try some shots at f/5.6 to f/8... maybe f/11 at the smallest. I've seen filters cause problems. (Note: if yours is the original 100-400L with the push/pull zoom, avoid filters on it, too... that particular lens "goes soft" even when good quality filters are fitted... it's excellent without a filter and its lens hood does a fine job protecting the lens anyway.)

If those efforts don't sharpen things up, ditch the lens for something better. Especially for landscape shots, you need lots of fine detail and sharpness throughout.

Canon EF-S 15-85mm IS USM and EF-S 17-55mm f/2.8 IS USM are two top quality options, but both are rather pricey... right now about $800 each, new... could be less refurbished or used.

EF-S 18-135mm IS USM is a pretty decent lens too for a bit less, but still not exactly cheap at around $600 new. There's an STM version of that lens for around $400, too... slower focusing, but otherwise largely the same.

EF-S 18-55mm IS STM is an inexpensive "kit" lens sold with many of the lower cost Canon cameras.... Costs about $250 new and would give better image quality that what I'm seeing in you images... but is rather plasticky.

None of these are L-series lenses...by definition, no EF-S "crop only" lens will ever qualify to be L-series... even if the lens has top quality and performance... Canon defines L-series that they must fit and work on all Canon cameras past, present and future... and EF-S lenses are only usable on APS-C crop cameras.

But because they aren't L-series like your 100-400mm, the above lenses don't come with a lens hood. I do recommend buying one, though... and using it. Good protection for the lens and can improve images.

There's a "gap' between some of the above lenses and your 100-400mm shortest focal length. Honestly, I wouldn't worry too much about that. 55 to 100, and especially 85 to 100mm isn't a big deal. But if it really bugs you, it's an excuse to pick up another lens sometimes... such as a 60mm or 90mm macro lens!

Sally D

Thanks for looking.

Sally D

You’ve made a great effort to help me and I sincerely appreciate it. The idea of comprehensive testing of the lens in a controlled situation is something I have never done. I’m leaning toward purchasing a new lens but even if I go that route I plan on testing it as you described.

Sally D

User ID

I must be losing it. I never noticed any mention of
"f/1.8" .... and I somehow must have just imagined
the mention that this is an "older" sigma lens.

Time to recalibrate my meds ......

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