Could the T3i body be limiting AF with extenders?

I thought I'd ask to see if anybody had any first hand experience or have any insight into something I'm having issues, or perceiving that I'm having issues with.

I'm shooting with a T3i, my first venture into Canon. I'm very happy with it and have felt nothing but positive things learning and improving with this body.

Last year I took the huge plunge into lenses and purchased a 400/2.8 IS V1 used from another forum. I've been amazed at how fast the AF is and how sharp it is. Recently I purchased a EX1.4-VII. I've been using it as much as possible but it seems none of my pictures are really in perfect focus with the extender. I know this lens should be super sharp and fast with the EX1.4, but I'm having trouble.

I've read that anytime you add and extender you almost have to re-learn to shoot with one and it might take quite a bit of practice to get the hang of the extended focal length.

Could the T3i body and its limited focus points have something to do with the inconsistent focusing with the extender added to the 400/2.8? Or is it like all things photography..practice, practice, practice?

Thank you for your time and insight,

Mike

If it were a f4.0 lens being used with the extender, then I would suspect that there is not enough light on the sensor to assists the AF.
Since that is not the case, I would suggest a sample OOF pic and the exif data.
Perhaps if you are using too wide a DOF (IE f8.0) with the extender, then AF can't work well.
I am sure another member will calculate the AF limitation with extender faster than I can.

You *should* be fine with a 1.4x extender on an f2.8 lens, because the T3i can still focus at f5.6... it's only the 5d3 and 1d series that can focus at f8. The extender will make your f2.8 lens an f4 lens - hence there shouldn't be a problem.

There is always slight loss of IQ when you use extenders, but it sounds like you may have another problem... Try and give us as much information as possible... post a pic without the extender, and then one with (with all your exif)... plus what focus point / focus mode you are using, etc.

Heya,

A lot of times, these setups, as good as they are, need calibration to get focus just right.

The T3i doesn't have it's own lens calibration, so you're limited in that sense. A different body would allow you to do lens calibration adjustments for better focus. As it is, to get your lens, extender and T3i focusing better, you may need to have it calibrated. Research this heavily though, it's scary sending in that equipment and expensive.

Very best,

Hi,

The first thing I'd do is clean the lens and teleconverter contacts. Use a clean rag, lightly dampened with a few drops of isorpropyl alcohol (cheap "rubbing" alcohol works fine), to wipe the contacts on the back of the lens and TC, and the corresponding contacts on the TC and inside the front of the camera. Just be careful to keep off all the optics, camera's mirror, etc.

Next, limit yourself to using the center AF point only. That's the only dual axis/cross type point on the T3i. The rest are single axis and not as sensitive. I don't have a T3i, but my 5DII has similar AF array and I use only the center point most of the time. I'll only use the peripheral AF points with stationary subjects in reasonably good light and contrast. Even then, those peripheral points are either horizontal or vertical... so they will need a roughly perpendicular "edge" or pattern to be able to focus well... a vertical edge with a horizontal AF sensor or a horiz. edge with a vertical AF sensor.

Go out and shoot some more tests with the TC and see if things work better. Be sure to use a tripod, 560mm is a lot of lens to try to get a steady shot, especially on a crop sensor camera (and the 18MP cameras are more susceptible to camera shake than earlier, lower resolution models), even with IS.

Also be sure to use IS, even on a tripod and even when shooting sports.

If panning and using a slower shutter speed to deliberately blur down the background, shift the lens' IS into Mode 2. Otherwise, leave it in Mode 1. IS in Mode 2 is designed specifically for panning shots... In that mode IS only corrects movement on one axis, whatever is perpendicular to the panning direction... So if panning horizontally, only the vertical axis is corrected.

With longer lenses it is simply harder to get the lens on target and keep it focused there. Also, shooting wide open depth of field can be really shallow, focus needs to be even more precise. It might help to stop down the lens a little, say to f4 or f5.6, to give yourself a little extra depth of field, which will give a modest allowance for focus errors.

If subjects are moving, you must be in AI Servo mode. This also will work best with the center AF point only.

If not already doing so, you might want to experiment with Back Button Focusing, which is a popular focus technique among users of the big white teles, especially for sports/action shooting.

BTW, I'm assuming you got an EF 1.4X II (mark two)... Not an "EX 1.4X VII" ("mark seven"... doesn't exist, the latest is a "III" or "mark III"). In other words, I'm fairly certain sure you mean "version II", not Roman numeral "VII".