This is probably a long shot: is there any way to change the aspect ratio of the raytrace preview to match the renderer's?

Of course you can reshape the window itself, but the rendering canvas remains resolutely square. This isn't a problem if you're rendering square images, and with landscape / letterbox images it shows parts of the scene which won't be in the render. Distracting, but liveable-with. However if you're rendering portrait aspect images, the preview doesn't show the top and bottom of your production image, and that is irritating.

It would be nice if there was an INI file somewhere that one could edit, but if there is, I haven't found it. Like I said, it's a long shot, but I may as well ask!

I believe that is a feature that has been asked for but no changes have been made yet.  IIRC, a feature that the development team would like to implement is a live preview with cycles.

As I suspected, thanks. I don't know what technology is behind the raytrace preview but ISTR it predates Superfly, and if it's Firefly related I doubt it will get any further development budget.

the raytraced preview does work with superfly, at least for simple shaders. I didn't try complicated ones. If you're working with firefly, you can use the progressive mode. It's supposed to be the same as the raytraced review and is resizable. It's not automatic like the preview. There's also the option to work with a half or quarter-sized render to see smaller previews without resizing the image

the raytraced preview does work with superfly, at least for simple shaders. I didn't try complicated ones. If you're working with firefly, you can use the progressive mode.

To be fair, the RT preview doesn't always accord with complex Firefly shaders either. There's always something that can only be caught by a full-on test render, but at least the preview helps to eliminate a lot of the early boo-boos.

Thanks for reminding me about progressive mode. If I set render dimensions to 'Match Document Window' it's helpful for a lot of the things I use RT preview for: checking lighting and reflections, and whether there's a forgotten single-sided wall in the way of the camera! I might now use that more often, since the bigger render is useful, it won't wreck my portrait previews, and a lot of the time I think it will be faster than the RT window because I can cancel as soon as the error appears.

The Raytrace Preview does well with complex Superfly shaders, not every shader but well enough to determine how it will render.  You can always render the preview window in the material room, it will give you a smaller image.

You can always render the preview window in the material room, it will give you a smaller image.

Good trick. I have a collection of UI dots with various document window sizes so I can do this in the pose room too.