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View Full Version : Would an ISO change help this situation?



toriaj
05-23-2006, 07:01 PM
I tried to take a picture of my dad with a baby. He was bouncing the baby a little, trying to calm her. We were in the kitchen at night, and the lights were all on. The picture was always blurry. I put my D50 in shutter priority (since he was moving, I thought that would help) but at different shutter speeds, the picture either turned out black or blurry. Nothing in the middle. I didn't want to use the flash, or ask him to stop moving.

Later I thought of ISO -- would adjusting ISO help to take a successful picture under these conditions? I've never messed with ISO, I've always just kept it on the auto settings. What ISO number would you recommend? Or is this situation just never going to work?

kgosden
05-23-2006, 07:37 PM
Raising the ISO would certainly help the situation. ISO is the same as it was in film; higher values are 'faster' and require less total exposure. But just as in film higher ISO tends to be lesser quality overall. In film this was generally lower color depth and grain. In digital it is still reduced color depth and now noise in place of grain.

With all that stated most DSLR's can produce fine images at ISO of 400-800. Assuming your Nikon was set for ISO 100 or similar you would be able to increase your shutter speed by a factor of 4 without changing your aperture. Will this solve your problem? Can't tell from here since we don't know what your actual test images and exposure settings were.

toriaj
05-23-2006, 09:04 PM
Okay, thanks! That helps a lot. I also read the "Shutter Speed" thread, and it sounds like I should

1) Have a wide aperture (a low number, such as 5.6.)
2) Have a fast shutter speed (is 1/1000 reasonable to start with?)
3) Then adjust ISO so the picture isn't black. Start at low numbers, then work up to high numbers. The lower the number, the higher the quality.

Does that sound right?

Norm in Fujino
05-24-2006, 02:13 AM
Okay, thanks! That helps a lot. I also read the "Shutter Speed" thread, and it sounds like I should

1) Have a wide aperture (a low number, such as 5.6.)
2) Have a fast shutter speed (is 1/1000 reasonable to start with?)
3) Then adjust ISO so the picture isn't black. Start at low numbers, then work up to high numbers. The lower the number, the higher the quality.

Does that sound right?

Not entirely. You didn't mention what length lens you were using, but assuming it was in the "normal" range, I would try this under "ordinary" household incandescent light:

1. Set White Balance to 2700-3000 (or your camera's incandescent setting)
2. Set ISO to 800
3. Set camera to shutter priority, and select 1/60 second to start.
4. Look at the subject and half-press the shutter button. Do you get adequate exposure? (a light should come on or something indicated in the viewfinder display to let you know whether the camera is getting enough light).

5. Under these conditions, if your lens has a maximum fstop of (for example) 3.5, but the viewfinder display says that the aperture will stop down to f8 (for example), you have more light than you need, and you can (if you wish) either a) reduce ISO to 400 (or 200), or increase the shutter speed to 1/100 or 1/200 (which path you choose depends mainly on how much the subject is moving; if it's moving around a lot, choose a higher shutter speed; if your father is holding the baby asleep, choose a lower ISO (for less noise).

6. On the other hand, if under these same conditions the camera tells you it isn't getting enough light (red light flashes in the viewfinder or whatever), then you must either lower the shutter speed (1/30 or lower) or increase the ISO (1600). Remember that at 1/30second you're pressing the envelope for stable pictures handheld with a "normal" lens. It may work if you have very stable hands, but it'll work better with a tripod.

Basically, all these adjustments are reciprocal and can be used to adjust the amount of light getting to the sensor, but aside from adjusting the amount of light reaching the sensor, they each have different side-effects:

1. Raising the shutter speed helps stop motion but decreases light to the sensor; lowering it gives more light to the sensor, but leads to danger of blurring (due to camera shake or subject movement).

2. Lowering the fstop value to a smaller number (e.g., f8 ->f5.6) makes the aperture larger and provides more light to the sensor, but decreases the depth of field (how much of the depth of the subject is in focus). Raising the fstop value to a larger number (e.g., f5.6 -> f8) makes the aperture smaller and decreases the light to the sensor, but it gives a deeper depth of field (sometimes you want this, sometimes not).

3. Raising the ISO increases the sensor sensitivity, allowing you to use higher shutter speeds and smaller fstops--or shoot under very low-light conditions, but it does this by raising the sensor gain, which results in increased noise in the shot.

toriaj
05-24-2006, 09:20 PM
Norm, thanks for sharing your expertise with me. I'll need to study your reply for a while ... but I know it will help a lot. Thank you.