Major Problem Need Help - DPChallenge Forums

10/08/2005 10:34:51 PM · #1

I need an indept explanation or tutorial on using a Nikon sb-600 in combination with the matrix metering system on the nikon d70. Exspecially for indoor use. One photo will come out with text book perfect exposue and the next will be completly blown out. I have no idea why this happens. Also how does the way the flash is pointed effect the exposure? I find if I poit the flash at the ceiling when I shoot the exsposure is better than pointed directly at the subject. But then somtimes if I point the flash straight up, the photo is badly unerexposed. I really need some help with this. I can't seem to figure out what I am doing wrong.

Please help.

Travis

Nikon AF Nikkor 50mm f/1.8D

10/08/2005 11:05:17 PM · #2

Does this have anything to do with the area that I am focusing on?

David.C

10/09/2005 01:30:11 AM · #3

With matrix metering mode the camera makes it's best guess at the 'correct' exposure for the scene. It does this by sampling the light levels at various parts of the image and performs calculations on them to arrive at a set of exposure settings. So to answer the last question first -- it depends; if the calculations it performs are weighted for or against what is in focus, it might make a difference.
Experimentation would be your best bet, but without knowing exactly how the metering mode is calculating the exposure you can expect the results to continue to vary. Center-weighted or spot metering give you more control, with spot metering giving the greatest degree of control.

The camera knows you are using the flash, and adjusts the exposure based on what it knows of the strength of the light the flash will produce. There seems to be two factors at work here; one is bouncing the light off the ceiling and the other the cameras idea of how strong the light is. The light bounced off the ceiling will probably be much more diffuse than if aimed straight at the subject, so the lighting 'looks' better. However, by bouncing the light off the ceiling, you are also reducing the strength of the light -- both by adding distance the light has to travel and by reflection. There are two things to keep in mind when doing this; first, doubling the distance the light has to travel will half it's strength and second, the darker the color of the ceiling the less light will be reflected. The end result is the same, the camera is setting exposure values for more light than is reaching the subject making the image underexposed.

To correct this I would use a flash bias -- estimating the loss of light and adjusting the strength of the flash to compensate for the amount of light lost. I am, of course, assuming your camera has something similar to the flash bias mine has -- it may not, but if it doesn't I would think your flash would have a way to do set it.

David

Bear_Music

Samsung Galaxy S24 Ultra

Sony 24-70mm F4 Vario-Tessar T* FE OSS

10/09/2005 01:53:17 AM · #4

I'm not up to speed on using these units with modern SLR cameras, so I don't have an answer.

One thing, though; the light diminishes with the square of the distance traveled, so doubling the distance between source and subject will require more than twice the exposure.

With flash, this doesn't mean much close-in (there's not a lot of difference between a flash at two feet and four feet) but it's significant at longer working distances. With dimmer lights the difference is pronounced; ever try to read by candlelight? 6 inches away may be readable, 12 inches away unreadable. On flash bounced off ceilings, there's a BIG difference between an 8 foot ceiling and a 12 foot ceiling as far as how much light reaches the subject.

Robt.

faidoi

Pentax K10D

Pentax DA 18-55mm f/3.5-5.6 AF

10/09/2005 01:55:58 AM · #5

You may want to try a STO-FEN Omni-bounce for that non flash look.

Nikon AF Zoom-Nikkor 70-200mm f/2.8 VR DG IF-ED

10/09/2005 10:06:18 AM · #6

I am also having problems with the backgrond turnin out extremly dark. Is there anyway to get them as bright as the subject when indoors in low light situations?

Pedro

Nikon D200

10/09/2005 10:12:52 AM · #7

Originally posted by Travis99:

I am also having problems with the backgrond turnin out extremly dark. Is there anyway to get them as bright as the subject when indoors in low light situations?

The short answer is 'not really' if you're only using one flash unit. Like Bear said, the light from direct flash falls off really fast, so if the background you're trying to light is any distance away from your subject, it will be pretty dark. One method i've used to cheat this is to use a lower power flash and bump the ISO to 400 or 800. then you're at least getting some of the ambient light in the background, and are less reliant on the flash to light your subject.

Of course this method adds some noise, but them're the tradeoffs...

eschelar

Canon EOS-7D

Canon EF-S 17-55mm f/2.8 IS USM

10/09/2005 10:43:51 AM · #8

I am assuming that when you say you are shooting indoors, that does not mean that you are shooting in a studio, but are shooting a number of different indoor locations with different variables such as ceiling heights and colours.

Like Pedro and Bear said. When you are viewing a picture where the background is say 12 feet away and the subject is 10 feet away, this isn't going to be a huge issue, but bring the subject to 6 feet away, and that background is going to be around 4 times less bright - that's about 3 stops. This is why flash is often used to turn a background really black in macro photography. If your camera has a 6-7 stop dynamic range, and you can get the foreground to be lit nicely in the midtones, but your background is 3 stops lower, your background is going to be within 1-2 stops of the darkest things your camera can possibly record.

Want to see the difference of 3 stops? Take a simple picture and then use your manual settings to deliberately underexpose 3 stops.

If you use a diffuser, you are going to reduce the amount of light actually hitting your front and center subject, simultaneously spreading the light all over the rest of the picture. This will bring the rest of your picture up in illumination AND lower the amount of light hitting your subject. You will usually need to play a bit with flash exposure compensation to get this working out well.

The best thing to do is to find a setup that you know works AND that you know HOW it works. Make an artificial subject, maybe some wood with some clothes wrapped around it and a Mask or something. Set your camera at something very stable and useable, maybe F5.6, 1/80 and shoot different flash variations without letting your camera change anything. Keep your white balance and ISO exactly the same. Hook your flash up manually and shoot at different distances. Observe your background and foreground lighting. Find a distance from subject that you like and that could reasonably suit most of the pictures you take. Once you can take a few shots and control your lighting and shadows from your flash, change one thing like turning the lights off or switching from fluorescent light to tungsten or something really challenging like candlelight.

Once you have established a comfort level using a particular setup in different levels of light, start to play with the positioning of your subject in relation to other objects such as walls and other random objects in the foreground (If you are shooting with kids, they have a way of showing up in odd places in photos). Shoot all of this with bare flashes. Then add a few different kinds of diffusion. Use tissue, handkerchiefs, white paper, off-white paper (like you might find on a wedding invitation (?)) and whatever it is that you use to clean your camera with that is always in the bag with you. You never know when you might need to know how your camera performs without your diffuser.

Then, using some kind of diffuser like the OmniBounce or Lightsphere II, do the whole thing over again.

You should be able to get a comfort level within a couple hundred shots and an hour and a half.

Some people shoot off-camera flash only. I like experimenting with on-camera and off-camera slave.

One guy told me that the best pro's usually have just a few basic configurations that they like to shoot and choose which one based on the circumstance. They then just eyeball a few key distances and compose.

If you are going to shoot a lot of attempts to make something work in a static situation, sure, experiment with ceiling bounce. If you are going to be on the move and working with a little outdoors and in dance halls and churches and people's homes and offices and whatnot.... you have to know your flash really intimately.

soup

Canon EOS-30D

Canon EF 17-40mm f/4.0L USM

10/09/2005 10:58:17 AM · #9

on the rebel aperture priority/shutter priority will use the matrix metering. manual mode uses center weighted average metering. not sure how the d70 works.

i could be wrong here, but if the aperture setting is changed - say you're shooting in shutter priority, the exposure will also change. this seems to be the case even in ETTL mode on the flash. i would think the flash would give an even exposure at varying apertures because of ETTL, but have found that isn't the case with my rebel and 550ex. so in order to eliminate the matrix metering - i shoot in manual mode, at 1/200th and adjust the aperture or the flash exposure compensation to get proper exposure.

Message edited by author 2005-10-09 10:59:54.