Focal length and dragging the shutter

[bulldog413]

I hope this isn't too involved of a question, but appreciate everyone's 2 cents:

I was attempting some shots the other day where I wanted the ambient to be underexposed by several stops, but couldn't get it right. I've done it so many times before, so I was confused. I think problem 1 was that I had the umbrella/light too far away from the subject. But I noticed a difference when I'd switch lenses. Why was this?

Can anyone break down why switching from a 50mm to a 18-135 (canon) would affect the outcome? Even at the diff. focal lengths of the second lens, I would get such different results.

Thanks

[jdepould]

Sample images for the two lenses? Did you have it set to second curtain (rear) sync?

Biggest difference off the bat is maximum aperture.

Very generally, if I'm dragging the shutter with flash:

Moderate aperture (f/5.6-f/8)
Low ISO (100-400)
Shutter anywhere between 1s and 1/30s

[bulldog413]

jd...
here is the flickr link to a test of what I ended up using (not the pic, just the light), then photoshop'd what I needed later.
IMG_7092 | Flickr - Photo Sharing!
my setting for this:
ISO 200, f 5.6 1/200
anything lower that 1/200 was only making things worse.

The umbrella and speedlight were approx. 3-4 feet from subject.

This morning, I was able to get what I wanted, focusing on something on a table. I thought, in the pic, that the darker the room, the lower the speed, but that was never the case. Sometimes, I was baffled because no matter what speed I set at, I would get the same exposure.

[bulldog413]

I added to your response via NEW REPLY... p.s. The other lens... well I threw that pic out

[bulldog413]

so I guess my questions is: will I be able to drag enough to darken out this background and still capture movement? If so, HEEEELP!

[scootermcq]

Originally Posted by bulldog413

so I guess my questions is: will I be able to drag enough to darken out this background and still capture movement? If so, HEEEELP!

Dragging the shutter allows more ambient light in to the image, not less. Shutter speed controls ambient light and aperture controls amount of light allowed in from flash.

The fact that you are at 1/200, which would be around max sync speed should have the room fairly dark. So, either the room was extremely bright, or the flash was lighting up the entire room. You could try snooting the flash so it only hits the dancer and does not bounce off the walls. If you are looking for a softer light, loose the umbrella and get a softbox, even better a softbox with a grid. This will prevent the stray light from bouncing off walls and ceiling and lighting up the whole room.

You could also try stopping down the aperture as well to increase the fall off of the light

[jdepould]

So you don't really want to drag the shutter then? It sounds like you're trying to kill the ambient?

That image looks like you've done that pretty effectively, but because the light is on a similar axis with the camera, it's lighting the room.

If you position the light so that it's perpendicular to the camera (directly to the right of the subject for example), you'll minimize the amount of light hitting the background.

[bulldog413]

Sorry Scott, I thought "dragging the shutter" ref. to going both ways. I kept repeating to myself "Shutter speed controls ambient, Ap. controls flash" sort of like "lefty loosy, rightsy tightsy"...

I believe you are correct about the light bouncing around the room. The ceilings are rather low. I had stopped down as far as I could, but found that the difference between where I wanted and darkness was trickier to get right. I left the softbox and snoot at home (bad photographer). No matter what power I dialed the flash to, I was still getting the same thing. So any back lighting I wanted to set up and any other light I needed to use for the other dancers was just not gonna happen.

Any other advice on how you would have shot this?

Thanks

[bulldog413]

I guess I didn't mean "dragging the shutter" (see reply to Scott).

As far as the position of the light: I did end up moving it too close to the axis, but I was under the impression that where I had it was causing the bounce around the room. I was having trouble with my speedlight so I went with the cheapo portable "studio" (gulp) light/umbrella. The light in the picture is actually pretty close to the dancer.

Any tips on how you would have gone about this shot (besides being in a studio with 12 foot ceilings? settings? lights? I had two other dancers I was going to focus on in the picture, but had to alter my idea due to my light issues.

Thanks for your responses.

[bulldog413]

perhaps a beauty dish?...