On 30 Dez., 22:49, Calvin McDonald <[email protected]> wrote: > One last question. Back on the thought that something very unusual is > wrong.... What would happen if the focal length of a zoom lens were to > change just a bit between a pair of otherwise identical exposure-stacked > images? I ask because I did shoot these images with a zoom lens, a Nikkor > 18-200mm VR-II. I shoot all my panos with this lens, with it zoom-locked > at 18mm. It was definitely locked at 18mm when I took the images in > question but I've noticed that even when it's locked the zoom barrel can > still move a little. This is probably a long-shot, but what if the focal > length got bumped slightly between the two sets of stacked images. Could > that account for the trouble I'm having? I'm having a hard time believing > this could because I've never had this problem before in the 100+ other > panos I've done with this same lens.
Reading your more detailed description, I actually had the same idea. The pattern of CP misalignment looks like it might have been the result of a slight change in focal length between the first and second series. Luckily this is easy to correct. Yut just have to assign a 'new lens' to the second set (go to the camera and lens tab, select the images from the second series, and assign a new lens to them), so that the optimizer can detect a different field of view (fov) for the second set. And you do have to tell the optimizer to optimize for fov, as well, for at least one of the sets, but doing it for both shouldn't do much harm, either. Then, if you can see in the camera and lens tab that two different values for fov have been established, this would be the likely cause for your problem, and with a bit of luck you'll have a much better fit now. You can take this method further. After all there is always a chance that such small shifts in focus occur during a series, not only between series, when they are, of course, more likely. In the camera and lens tab, you'll notice that there is also a checkbox next to the fov field which allows you to 'link' the fov, or unlink it. If you unlink the fov for a given lens (or all of them, it's a per-lens parameter) you allow the optimizer to establish a different fov for each individual shot. If the images are well-connected with CPs the optimizer usually comes up with useful values, whereas with too few CPS, the added degree of freedom may prove to much, resulting in wrong estimates. No harm playing with this, though - after all we have the undo functionality now :) I do lots of handheld landscapes, and sometimes unlinking the fov and hence the gain of an additional degree of freedom can help compensate for the small misplacements of the NPP in handheld series. If I optimize such series, I often get fov variations of a couple of degrees within the series, even though my source images certainly are all done with the same fov with my fisheye lens, and sometimes I can compensate better for the unavoidable mistakes in handheld series using this 'cheat'. With your series done on a tripod, you have good chances of getting everything right in the end. Hugin, used knowledgeably, excels at positioning and warping images (short of the morph-to-fit, which hugin's standard toolset doesn't use), but it sometimes takes a fair degree of fiddling about with various parameters before you get there. Happy New Year. Kay -- You received this message because you are subscribed to the Google Groups "Hugin and other free panoramic software" group. A list of frequently asked questions is available at: http://wiki.panotools.org/Hugin_FAQ To post to this group, send email to [email protected] To unsubscribe from this group, send email to [email protected] For more options, visit this group at http://groups.google.com/group/hugin-ptx
