My TC seems to be front focusing - any ideas?

Make sure that, if you are hand-holding the rig, that you have shutter speeds that are fast enough to limit blur due to camera/lens motion. If you are at the edge to begin with, you will have to divide your shutter speed times by the 1.4. In other words, if you are hand-holding using 1/200 without the extender, you may need to use roughly 1/280 with the 1.4x extender to have the same effect on the image.

For purposes of testing the camera's ability to focus, you should really be using a very sturdy tripod to eliminate the variable of camera/lens motion.

Which is exactly why I want to go back and try reshooting. I am guessing a handful of images poorly represent what's happening and I didn't use a tripod, and Tv's were definitely below 1/250 in a lot of cases - the sun was setting fast.

Tomorrow I am going to (really this time!) get out during lunch and try out the lens with a tripod. I think the posts and signs in the park allow me to see the degree to which the lens mis-focuses, if it does. But as a real world test, I am happy with the 200mm and sorta happy with the TC and no filter...

Thanks SkipD for the advice.

godzakka wrote in post #3174705
Well...

It seems to help in some shots, but I hastily took my shots today and not anywhere near as scientific as Lester would've liked. I will post them to my site here: http://picasaweb.googl​e.com/ztross/TestShots​2

And try again tomorrow, but with better shots. The first set are 200mm, filter, no TC. The second set are 200mm, filter, w/TC. The last set is 200mm, no filter, w/TC. Again, probably not much use in posting them, but you are welcome to look at them and if need be I will put up full crops later.

I am not quite sure where you focus point is centred, but some with a sign and trees behind the AF looks like it has locked on the sign in one case and the trees in another.

This is part of the problem with real world lens testing, you don't know for sure where the AF is placing the plane of sharp focus even if it working ideally.

Another is when people compare wide apertures on a 3D subject, difference in curvature of field and the above uncertainty of the position of plane of focus make a mockery of the value of comparisons; but that is another story.

Really the best think to start with is a plane target with a high contrast pattern on it, no ambiguity there. Easy to set-up by using the old hack's method of blue-tacking some newsprint on a wall. If you don't have enough room or want to test at longer distances find a large brick wall or building and set the camera up square and level to that.

Again make sure you use a sturdy tripod with mirror lockup and timer or cable release, if outside make sure your subject is solid enough to not move in the wind.

I am going to do this brick wall test tomorrow morning, since I've failed to have time for any real scientific study so far. But everytime I take the lens out in the "real world" I am disappointed with the results.

I took the lens/TC combo out for a walk-around at the local lake today, and basically everything is not as sharp as I'd like, which I think has more to do with my Tv setting of f/5.6 than focusing issues. I did remove the filter beforehand. All shots were on a 10D, 70-200 f/4L w/1.4x TC mk1, no filter on lens, ISO100, f/5.6, high Tv's (in most cases, but I am not counting the low Tv's), One-Shot AF, center-point only, refocused each time between shots, evaluative metering.

A lot of close signs I took shots of were perfectly in focus, super sharp and contrasty, while from farther distances they were totally (on multiple refocused shots) OOF or blurry. I will post images up at picasaweb.google.com/z​tross if you want to see them and comment.

Tomorrow I am going to be shooting some games for a friend and I will try it out with f/8 on my 1D. If I still can't get nice shots, I don't know what I will do.

godzakka wrote in post #3192246
I am going to do this brick wall test tomorrow morning, since I've failed to have time for any real scientific study so far. But everytime I take the lens out in the "real world" I am disappointed with the results.

I took the lens/TC combo out for a walk-around at the local lake today, and basically everything is not as sharp as I'd like, which I think has more to do with my Tv setting of f/5.6 than focusing issues. I did remove the filter beforehand. All shots were on a 10D, 70-200 f/4L w/1.4x TC mk1, no filter on lens, ISO100, f/5.6, high Tv's (in most cases, but I am not counting the low Tv's), One-Shot AF, center-point only, refocused each time between shots, evaluative metering.

A lot of close signs I took shots of were perfectly in focus, super sharp and contrasty, while from farther distances they were totally (on multiple refocused shots) OOF or blurry. I will post images up at picasaweb.google.com/z​tross if you want to see them and comment.

Tomorrow I am going to be shooting some games for a friend and I will try it out with f/8 on my 1D. If I still can't get nice shots, I don't know what I will do.

At least it sounds as if you have eliminated the filter as the source of the problem.

Good luck with your shooting, let us know how it goes.

Ok, here's what I finally got to doing:

All pictures were with center point focus only, evaluative metering, using tripod, MLU, 2 second timer, refocused between each shot...no shake evident, 5 shots for each setting, posted at picasaweb.google.com/z​tross under Brick Test Shots

At the 200mm end of my 70-200 f/4L
1. with a TC, filter at f/5.6, 25'
2. with TC, filter, f/8, 25'
3. with TC, no filter, f/5.6, 25'
4. with TC, no filter, f/8, 25'
5. no TC, filter, f/4, 25'
6. no TC, no filter, f/4, 25'
7-12. Repeat 1-6 but at 75-100'

At 25' were all pretty good. Without the TC the shots were noticeably sharper even wide open. At f/8, the shots are noticeably sharper than f/5.6 with the TC. Filter didn't appear to make a difference here.

At 100', the filter still didn't appear to make a differnce, or at least not much of one, and the weird thing was, it appeared to slow down my shutter speed by about 20%. I had been getting Tv's of 1/800 with a filter and 1/1000 without at f/4. Same thing happened at differnt Av's and with or without the TC attached...interesting​...

Anyways, at f/5.6 vs f/8, obviously stopping down helped. The filter didn't seem to affect the focal plane. I am planning on heading out while there's still light and trying from further away. At f/4 (no TC) vs with TC, it's still sharper wide open.

My conclusions: filter has little to no affect at close distances. I usually shoot outdoors soccer/frisbee games with the TC on (anywhere between 25' and 300' plus, so I am going to need to get further away and see if that affects anything. TC degrades image (duh!) but by stopping down 1 stop it helps A LOT! That's all I can say for now.