Im doing my first couple shoot on Sunday and I'm comfortable enough with the process but I have only done singles before. Its an outdoor shoot and I would like to blur the background but obviously keep both sets of eyes in focus. Any thoughts on what Aperture I should be looking at with my 50mm 1.8 or the 17-50 2.8 ?
If you can keep both faces on the same "plane of focus" you can play with very shallow DOF and it can turn out GREAT! Trouble is ... it's very easy to have one or the other move out of range.
What aperture works best? Wow, there's no way to answer that. It depends on focal length, distance to subject, and how much DOF you need to keep both sets of eyes in focus.
I'm almost always using either the 24-70 f/2.8 or 70-200 f/2.8 lens and most often shooting around f/4.0. But I vary it depending on my needs.
I filled the frame with a lightbulb today at f/2.8, and the little bar that normally holds the shade over the bulb was OOF, maybe 2 inches from the focal point.
Pictures of my niece had her eyes sharp but the back of her scalp blurred, also at f/2.8.
So I'd suggest starting at least at f/4 and checking the first few shots. Or search online for a DOF calculator.
One note: the lens doesn't matter, only the magnification (how big the subject is in the frame, controlled by focal length and distance) and aperture. So if the subject's the same size in the frame, you're at 50 mm on the 17-50, and you're using the same aperture, either lens will give you the same DOF.
thanks for the tips guys, its at the beach at dawn so the background runs to infinity, but there will be beach stairs shots etc, so I guess I'll start at the f4 as you have suggested and go from there.
Take a look at this photo (yes, even after many weddings, many engagement pictures, it's still easy to make a mistake):
This was shot at 200mm at f/4.0. Notice that the girl's eyes are in focus and ultra sharp? The guy, however, is outside the DOF and has blurred eyes. Clearly I made a mistake shooting at f/4 without their eyes being on the same plane.
And yet ... here's another shot of the two of them, this one 100mm at f/2.8, and it is clear that both sets of eyes are perfectly in focus:
As a rule of thumb, one-third in front and two-thirds behind. As levyj413 mentioned, you can download a depth of field guide from the internet - I have found this site useful.
with a 18-50 or a 50mm, DOF should be more forgiving. As long as both faces are close enough, that you focus on a point that is more or less in the middle of the range, f/4.0 should be ok.
anything below is getting more risky, esp. if for example you focus on the eye of the person further away from you.
You haven't said what camera body you're using. As an example, on a 400D with a 50mm at f/1.8 with the subject focused at 10 feet, the sharp focus range goes from 9.61 feet to 10.4 feet (DOF = 0.81 feet). Keep in mind that some lenses/bodies will front or back focus and move the DOF around. Practice side-on on a fence to get a feel for it.
