100-400 lens questions

[Sheermadness]

I've had my 20D for a few months now and love it. Just bought the Canon 100-400 lens and Canon 2x extender. I had forgotten the autofocus wouldn't work with it. When I was first looking at this lens the camera store only had a Tamron extender in stock and the autofocus worked fine. What's up with that? I saw someone mention something about a tape trick. What is that and will it trick the camera into autofocussing with the Canon extender? And one more question, I'm getting ready to buy a polarizer for this lens. Any opinions on brand preference would be appreciated. Thanks
Meredith

[robertwgross]

The Canon 2x teleconverter will cause a loss of 2 stops. The Tamron teleconverter may have been only 1.4x, so it will cause loss of 1 stop. Also, some non-Canon teleconverters do not pass the lens and teleconverter information completely through to the camera, so the camera might not know what is out there except for the lens.

Some people "fix up" a Canon teleconverter so that it fools the camera intentionally. That might allow you to autofocus at a different level from where the lens, teleconverter, and camera should autofocus. However, if you do that, the camera may autofocus irratically.

---Bob Gross---

[Tom W]

The Canon 2x teleconverter will cause a loss of 2 stops. The Tamron teleconverter may have been only 1.4x, so it will cause loss of 1 stop. Also, some non-Canon teleconverters do not pass the lens and teleconverter information completely through to the camera, so the camera might not know what is out there except for the lens.

Some people "fix up" a Canon teleconverter so that it fools the camera intentionally. That might allow you to autofocus at a different level from where the lens, teleconverter, and camera should autofocus. However, if you do that, the camera may autofocus irratically.

---Bob Gross---

Yes, I tried "fooling" the camera with my 1.4X teleconverter and my 100-400 on my old 10D - focusing on any subject that was less than very-high contrast was erratic. The lens would start to run focus back and forth rapidly. I quit doing it after a couple such episodes. On this lens, its not a good idea.

On your 20D, you may have better luck given that it has a more precise focusing system than the 10D had, but its risky, particularly with a 2X converter where you'll be at f/11 at the long end. That's just too little light to get accurate focusing, which is why Canon limits AF to f/5.6 on most cameras.

[Sheermadness]

Thanks for your responses. Sounds like I better sharpen up my manual focussing skills.
Meredith

[phili1]

I have the 100-400 and 20D and it only manual focuses. The IS works but you have to remember that your dealing with 800mm any movement will effect your shot. I have been practicing with it because I am going to shoot eagles. It must be triopd mounted under 1/1500 of a sec for sharp results.

For flying you want to keep it at 100-400 for best results.

I have the Kenko pro 2X and it gives good results.

[Sheermadness]

Thanks for the info. As a matter of fact I went out yesterday with the intention of shooting eagles but the weather wasn't cooperating. Raining lightly, dense fog and as dark at midday as it usually is late in the afternoon. I did get to watch a few eagles soaring over the Wisconsin River by the dam at Prairie du Sac. I'll go back again and try on a better day. I have really noticed the weight of the lens and know I'm going to have to practice a lot to manage it off tripod even just at 400. My heftiest lens before this was either the 100 macro or the 100-300 USM, neither of which is really heavy. Just to compound the situation, I've also added the battery grip with two batteries to the 20D.
I might get a window mount with a ball head for some shooting. I've wanted one anyone and now I can really justify it. I'm supposed to go deer "hunting" next week so that might be my first real test of this set up.
Meredith

[phili1]

Meredith: The weight at 100-400 is not that bad and I have gotten some good shots hand held, but I find the sharpest is when it is on a tripod, or monopod with the IS on.

Have fun, I go for the eagles next week.

[NILOLIGIST]

I had that lens and tried that lens trick. It worked but then my IS was broke, had to send it to Canon twice to be fixed. Finally, I sold the lens. It is heavy but you will get use to it. IS lenses are not supposed to be used on a tripod. You are suppose to turn IS off when you have the lens on a tripod. Now I have the 70-200 f/2.8L IS it is a great lens. So sharp it will cut you. LOL


Good luck,

NiL