The image you shared has shallow depth of field, causing part of the image to be softer focused... actually slightly out of focus. There is a plane of sharpness running through the middle of the image, with gradual fall off in sharpness both closer to you and farther from your camera position. Without knowing the focal length and lens aperture being used, it's difficult to suggest a very precise solution, so the following are generalizations.
Use a smaller lens aperture to increase depth of field. It also will help if you zoom to as short lens focal length as possible (though too short will cause distortions, so watch out for that). Try to use f/11 aperture. That will probably be as good as you'll be able to get. Larger apertures are smaller numbers... f/8, f/5.6, f/4 are progressively larger, leading to shallower depth of field. Now your lens can be set to even smaller apertures... f/16 and even f/22. However with those an optical effect called "diffraction" starts to occur in images, which robs them of fine detail. Still, you might try f/16 to see if it's okay for your purposes.
Because of that small lens aperture... and because you also should try to keep the ISO to 100, 200 or maybe 400 at most for optimal image quality... you will need to make a longer exposure by using a slow shutter speed. And for that a tripod is necessary. Be sure it's a sturdy one and well situated. For example, a tripod on a wooden floor with people walking by or even traffic in a nearby street can have enough movement to blur images a little when using longer shutter speeds.
Try to not touch the camera during the exposure. Use a remote release to trip the shutter. Or set the self timer to the short delay, so that any movement from pressing the shutter release is stopped by the time the shutter actually fires.
I do not know if your T3i has this feature, but "Mirror Lockup" (MLU) is another thing used during longer exposures, to reduce chance of internal camera vibrations spoiling the image. There may be a setting in the menu where you can enable this. However, even if your camera can't do MLU, you can probably get the same effect by using Live View. That also lifts the mirror up out of the way, so that it's not "slapping around" inside the camera during longer exposures.
There have been 5 or 6 different Canon EF-S 18-55mm lenses and at least 2 or 3 different Canon EF-S 55-250mm. Most of them are pretty good and able to focus fairly closely... However image quality may be less good with earlier versions. Also, if you have a filter on the lens you might try some shots without it. Sometimes filters do more harm than good. (Only buy high quality, multi-coated filters.)
Autofocus may not be the way to go, shooting these types of images. That leaves it too much up to chance where the camera and lens will focus. With camera on a tripod, switch to manual focus, use Live View and magnify the image on the rear LCD for precise manual focusing (but remember to return the rear screen to normal magnification for composition... this is only magnifying what you're seeing on the LCD screen, not actually "zooming" the image itself).
The ideal lens for this type of photograph is a "tilt shift". I use Canon's TS-E 45mm for tabletop studio work. It's a manual focus lens, but the tilt mechanism allows me to control the plane of focus rendered by the depth of field, so that it "lays" over the subject (depending upon how it's adjusted, it can "increase" or "decrease" depth of field). Today that lens is no longer made, but Canon offers a TS-E 50mm that's closer focusing. They also offer a TS-E 24mm lens that would work well for this purpose on a T3i (APS-C format) camera. However, tilt shift lenses are quite expensive. So unless you do a lot of this type of photography and can justify the expense, you might need to look elsewhere. EDIT: I did a quick search at MPB.com and found they have a TS-E 45mm like mine, used but rated in "good" condition with no optical problems, for $529. That's a pretty good price! A brand new TS-E 50mm sells for $2199!
Canon TS-E 45mm f/2.8 Tilt Shift lens review at The-Digital-Picture website
Macro lenses are another possible approach, designed specifically for close up work and among the sharpest lenses available. For tabletop shots like you're doing, you would want a relatively short focal length.. so I would suggest the Canon EF-S 35mm f/2.8 IS STM Macro, older Canon EF 50mm f/2.5 "Compact Macro" or EF-S 60mm f/2.8 USM Macro. All these lenses have been discontinued, I believe. So you would need to shop used or Canon USA refurbished (the 35mm and 60mm are out of stock there right now, the 50mm is an older model that will only be available used from other sources). DO NOT buy the Canon MP-E 65mm lens for this purpose. That's a special, ultra-high magnification lens... It's a truly great lens, but all it does is high to ultra-high magnification. Even at it's very lowest setting It is way too high magnification for your purposes.
Canon EF-S 35mm f/2.8 IS STM Macro lens review at The-Digital-Picture website
Canon EF 50mm f/2.5 Compact Macro review at The-Digital-Picture website
Canon EF-S 60mm f/2.8 USM Macro lens review at The-Digital-Picture website
Macro lenses do not offer the control over the plane of focus that tilt-shift lenses do. Macro lenses do typically offer ultra small apertures for increased depth of field... f/22 is common and some can do f/32 or even f/45. However, remember that diffraction is an issue at these tiny apertures.
Another approach to achieve more depth of field without need to use tiny lens apertures is called "Focus Stacking". This is done by taking a series of images with each focused slightly differently.... then assembled in post-processing by stitching the sharp part from each to make up a single image with "impossible" depth of field sharpness from near to far. This technique is made easier by putting the camera on a "focusing rail" on a tripod to take the images and using a specialized software like Helicon Focus to assemble the images. With this rig you simply take a series of shots, moving the camera incrementally between each shot. Below is a link to the Helicon Focus website where you can see some examples. Their software is some of the best. There are numerous sources of focusing rails, some of which are relatively inexpensive (try everyone's favorite online auction or Amazon).
Helicon Focus website.
I hope this helps and gives you some ideas.
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Alan Myers
San Jose, Calif., USA
"Walk softly and carry a big lens."
GEAR: 5DII, 7DII (x2), 7D(x2) some other cameras, various lenses & accessories
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