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Old Jun 14, 2008, 4:10 AM   #1
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Had my 40D for a few weeks now (what a great camera) & have got some questions-

1. Why does the file size increase when you move to using a higher ISO setting?

2. Should you always use Image Stabalisation (I have the 17-85 IS Lens)? What are the Pros & cons?

3. Have noticed that some of my results are slightly 'softer' than I would like so I've increase the sharpness from setting 3 to 4 (for the standard picture style). Will this degrade the overal quality in any way?

Thanks
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Old Jun 14, 2008, 9:25 AM   #2
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sxxu08 wrote:
Quote:
Had my 40D for a few weeks now (what a great camera) & have got some questions-

1. Why does the file size increase when you move to using a higher ISO setting?
Because of noise in the image (the grain you see). The jpeg compression algorithms see this noise as detail (and the more detail in an image, the larger the file sizes shooting jpeg).

Quote:
2. Should you always use Image Stabalisation (I have the 17-85 IS Lens)? What are the Pros & cons?
I'll let the Canon users more familiar with that lens answer the question. With most stabilization systems, you'll probably want to turn off stablization using a tripod. With Canon lenses, you've also got optical elements moving if you have stabilization turned on. Depending on the lens, that might reduce quality from user impressions I've seen about some lenses. But, without controlled condfitions testing (same subjects, same lighting, same camera settings, etc.), I wouldn't put a lot of faith in what you read about the potential for lower quality with it turned on.

Quote:
3. Have noticed that some of my results are slightly 'softer' than I would like so I've increase the sharpness from setting 3 to 4 (for the standard picture style). Will this degrade the overal quality in any way?
It can. Sharpening is mostly an optical illusion. It works by increasing contrast at edge transitions. This can destroy real detail, and give an overprocessed look to photos if you have too much sharpening. You're better off leaving it turned down in camera. Then, use an image editor to sharpen a photo as desired for the viewing and print size you need.

I'd probably post an example of an image you consider to be soft. It may be something you're doing wrong (using an aperture too wide for the desired depth of field, not focusing on the portion of the image you want to be sharpest, using shutter speeds too slow for the conditions, etc.). Or, it may just be your expectations of quality for a given viewing size (keep in mind that if you look at an image at 100% size on screen, you're looking at a much larger size than you'd normally use for prints or web viewing).

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Old Jun 14, 2008, 9:27 AM   #3
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Here are some answers:

1. File size increases because of the digital noise that increases along with ISO increases. That noise equates to more data.

2. There's really no reason to turn IS off for 95% of your shots with that particular lens. Realize it will not always engage anyway - only when the camera detects movement after you've pre-focused.

3. Softness can be caused by a number of things. But in general DSLRcameras apply a lot less in camera sharpening than digicams. How much in-camera sharpening to apply is a personal preference. The reason DSLRcameras default to less sharpening is because sharpening can always be applied in post processing on the computer. But it can't be removed. There can be times when heavy sharpening can look bad - but an increase from 3 to 4 isn't really going to result in that. That being said, learning good post processing techniques can improve about 95% of the photos you take.
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Old Jun 17, 2008, 4:18 PM   #4
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Just to say thank you both for taking the time to answer my questions.
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