I have a telephoto lens and I wanted to stitch together several pictures of the Baltimore-Washington International airfield. Taking the pictures was just fine, although I hadn't learned how to set the exposure settings yet (see my post on this), and need to do it again on a clear day. What I didn't realize was that there's essentially no 'barrel distortion' with narrow-angle shots.
I found that it's hard for Hugin to figure out the angle of your shots when there's no barrel distortion. It misbehaves if you try to use the same procedure as you would for wide angle panoramas, and gives you completely insane average errors and if you try a preview--it won't be pretty. There are two things you need to do: tell it your horizontal field of view angle, and don't allow barrel distortion optimization. Only use "Positions and View (y,p,r,v)", and check that the barrel distortion stays close to 0.000 for now. This means that your panorama is essentially flat.
I was taking my panorama shots in portrait mode, which meant that my horizontal angle was 75% (the inverse of the aspect ratio 4/3) of the angle in landscape mode. That angle was about 8.10 degrees, and so the angle for each shot was 6.08 degrees. I got my focal length from the EXIF data, 224 mm, but the angle is most important.
Before final optimiztion and stitching, you may want to change the barrel distortion to something between 0.0034 and 0.006. This will add perspective to the panorama. Make sure you still don't run the optimizer for barrel distortion.
