Underexposed when using Flash within 2-3ft, indoors, with Phototix Odin

LilyJack

Okay. So trying out off camera flash. Not an expert but I understand (I think) some basic stuff.
I was finding this when while using the SB-600 to set up for something else last week and finding it happening again with Phototix Odin triggers with Phototix Flash (new toys today so just getting familiar with them). So here goes:

Flash set up within 2-3 feet of subject, using my 50mm, ISO 400 (although I know I want 200), speed at 1000 (doesn't matter in regards to flash but does with ambient which I don't want any of and I have high speed sync set), f3.2 (and had down to 2.0) and it doesn't render bright. Batteries are fully charged. In the first instance, I was using a white background and so I assume the histogram should be heavy on the right, showing blown highlights. It's not. Using TTL so is it trying to meter to gray?...OK tried this with new Phototix system. In this instance, it's not a white background but a midtone piece of fabric. Still, histogram is heavy on the left and when I bring it into PS, the images are totally underexposed. I've checked to make sure exposure compensations and flash compensations aren't set. It just seems wrong that I’m not completely blowing out highlights (the entire white background) at the above settings. Histogram is all the way on the left and barely hitting the middle. To get correct histogram/exposure, I have to turn compensation up to +3.

So, speed doesn't effect flash but just for S&Giggles, I change the shutter speed. Things are looking better and it's not the ambient light. I swear because the white balance looks is, well, balanced for flash.
I then set the Odin transmitter to M instead of TTL and bring it to 1/1. Looks even better but still not getting any pure whites so it's slightly underexposed. Shouldn't TTL work?

Does that feel right to you? How am I not blowing subject way out? I feel there's got to be a setting wrong on camera but I can't figure it out. I'll be really embarrassed if it's something simple but gotta ask at this point.

Thanks for your help,
Take care, Kate

kdog

TTL is horrible when you're using a white background. It will indeed meter the flash to set the background gray, not white. That's why you're getting things underexposed. I don't know what color your other background is. If it's black then I would expect that your flash would overexpose any subjects in front of it. It gets even worse. Simply zooming into your subject will affect your exposure with TTL because the ratio of background color to subject changes and flash system will try to compensate. You will pull your hair out trying to get consistent exposures. The moral of the story is always use manual flash in a studio environment where the distance from your subjects to lights is stable. Trying to second guess TTL and playing with FEC is way more difficult than simply setting your flash power once and setting your camera to that.

I don't know how Odin high-speed triggering works, but I would remove it as a variable as well. Set your camera on manual, with your shutterspeed at your synch speed (1/300s typically on Nikon I believe). If you're worried about shutting out ambient light, use a lower ISO and stop your lens down instead of shooting at larger apertures which aren't really conducive to studio shooting anyway.

CameraCharlie

Camera meters will indeed affect indicated exposures. The reason being meters don't know what the desired exposure effect is. Meters are generally calibrated for 18% gray, thus will turn both black or white to graytones. To comphensate you'll need to add (for white) or subtract (for black) some exposure, that is either adjust shutter speed, or aperture change (not always practical). With todays electronics its a simple matter to dial in exposure comphensation, while in the "film" era the common practice was adjust the ISO setting on camera. A simple test of this theory is shoot some sky containing bright white fluffy clouds in manual mode so your camera cant provide any exposure adjustment. Meter on a bright white cloud and shoot at the metered exposure, then take a few subsequent shots increasing exposure, either by opening the aperture, choosing slower shutter speeds, or increasing ISO setting. I find generally increasing 1 to 2 stops gives me proper "white" exposure, while decreasing a like amount gives "black" blacks.

Using flash will add some variables however.
Keep in mind the inverse square law, doubling flash to subject distance results in the subject recieving 1/4 the light. So with a flash 3 feet from a subject, and the background an additional 3 feet away, or 6 feet from the flash, the background will only recieve 1/4 the light.
Basic solutions are add a flash to light the BG. exposure for white, can be set to equal camera exposure or overexpose the background forcing a brilliant white. For a dark BG, the opposite will be true, flag the light(s) with black cardstock to eliminate stray light from hitting the background. Remember to seperate subject and background as much as possible, which not only helps prevent stray light on the BG, but helps eliminate unwanted flash shadows from being seen on the background. (lighting angles have alot of effect here also.)

A simple exercise to help demonstrate using only a few pieces of white matte board,helps understand basic lighting principals and can be done anywhere. Prop up a white matte board vertically on the dining room table, then with a small object, say a tennis ball, or small vase as a subject, light it with a continuous light, moving the light back and forth to increase/decrease light to subject distance, and do the same varying subject to background distance and observe both the light intensity on the background as well as how hard, or sharp the shadows are when varying the light to subject distance. Use different light sources of varying sizes and observe that effect also.
Lastly keep in mind the larger the light source, the softer the shadows, as will be seen in the demonstration.

pathfinder

The beauty of a mid-tone grey back ground in the studio, is that it can be white or black ( or anything in between or even colored ) depending on how you structure your lighting - if it is far enough from your subject to light it separately from the subjects lighting. This requires manual flash or studio lights not auto ETTL or whatever though.

Gary752

As was mentioned earlier, you need to lower your ISO to around 200, and then set your SS to your sync speed, usually around 200 or lower. Then set the F-stop to something like F8, and take a shot without the flash. That frame should be totally black. If not raise the F-stop higher till the frame is black. Once you have the cameras set, turn on your off camera flash in Manual and set it to get a proper exposure for your subject. as far as the background going grey, either move your subject closer to the backdrop, or add a second flash to light the backdrop.

If you truely want to learn studio/flash lighting, check out some of the workshops on Creative Live. The ones I highly recommend are Scott Robert Lim (Crezy Stupid Light), and Tony Corbell. They cover the basics and give a few advanced tips as well. Scott Robert Lim's workshop covers manual off camera flash, a little theory, and his technique to getting
close on the first shot. Tony Corbell's workshop goes into more detail on the theory, then shows different lighting setups. Tony also gives a tip on how you can calibrate the Sekonic light meters that have dual ISO buttons.

Hope this helps.

GaryB