Originally posted by hydriv Excuse my naivety but I have to ask. Assuming that I am shooting outdoors on a nice sunny, cloudless day, would I not have the sun to my back? Or at least mostly to my back and one side? IF so, then what would be the position of the reflector? Take me serious. I ask these questions because I don't know the answers. Do you have a style of reflector in mind that you feel would best suit my needs? If the day was totally calm, could such a reflector be mounted on a tripod? I agree that a helper would be best because I could direct him/her while looking at the screen.
Bright sunny days can sometimes be the most challenging.
Reflectors are great in bright light because the hard shadows created by the sun get softened and you can get more detail in areas that might otherwise be lost. If you have the sun coming in over your left shoulder, your reflector would be to the right of the subject, and angled in to fill in light on the subject. You should see it quite clearly through the viewfinder when the light hits. As another post mentioned, they can also be used to shade your subject when the light is too strong. These are perfect for portraits and you are really taking a portrait of a tractor, so the same theory fits. Try a couple shots with & without and you'll see the difference.
As for type, your subject is large so you need a fairly large surface to reflect from which is why a white sheet or piece of silky material may work. The small round reflectors sold in the camera shops probably wouldn't be enough. I like the idea in the previous post of a windshield heat reflector...I'll have to try that. There is a different quality between silver & white though, so some more experimentation for you there. You can build an inexpensive frame out of pvc pipe from the hardware store and tape/clamp the sheet/reflector to it (don't glue the pieces together, just friction-fit so you can break it down for transport). If you put a couple Tee's on it with extra supports, it can be free standing so no assistant required.
In all I would say practice a lot and expect your later pictures to be better than the earlier ones.
Here's a shortcut to the type of thing I'm picturing but you would hold it horizontally to match your subject (and maybe even larger than this one):
http://subdoc.com/marc/diy/lightrpanel/bin/images/full/20070825_PICT8776.jpg