Anyone use a Sigma 10-20mm on an IR DSLR?

I know this is a huge longshot, but figured I'd ask.

I have an IR converted 20D, and I'm having a helluva time getting things in focus with my Sigma 10-20mm. The camera is calibrated to the Canon 50mm, which is always great, but I really like the look of the UWA and the IR.

I use manual focus, and then move the focus scale/ring a little towards infinity, but I'm not getting great results. Unfortunately, there is no IR scale on the lens. I've been moderately successful avoiding the hotspot with the lens, which it's known for with IR.

I figured I had two things working inmy favor with this lens on the IR 1) - tremendous DOF and 2) - small focus throw, but I'm only hitting focus about 20% of the time. Anyone have any ideas?

Oh, and the lens focuses fine on my normal 50D. It's just the IR focus difference I can't figure out.

Choose a static scene (at infinity), and focus manually on say 9 points spread from the infinity hard stop to maybe .3m. Then analyze the focus on the photos and decide which focus position was the sharpest for a photo at this focal distance.

When you say

do you mean a scene far away? Like a mountainous landscape? So I guess a focus chart in the mud room wouldn't work.

That's a great idea though. Looks like a project for this weekend.

Choose a distance that you would find useful. If you only shoot at subjects a foot away, design the testing to mach it. If you only shoot landscapes, choose a distance near infinity.

I think I'd have a problem with things at infinity, since typically, the IR focus point is further then the visible light focus point. ie, if the visible light focus point is at 100 ft, the IR focus point may be at 125 ft on the lens, so where do I go from infinity?