Start your conversion on an image with an important subject in focus. Head to the Lens Corrections panel, choose the Profile tab, and check the box to Enable Lens Profile Corrections. It's especially useful to get rid of vignetting before stacking. Make the usual adjustments to exposure, contrast, and white balance. Then synchronize. Choose your adjusted image from the column of thumbnails on the left, click the Select All button, then click Synchronize. Use the pulldown menu to choose Synchronize: Everything, and click OK. Finally, output TIFFs via Save Images.