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Feb
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Posted by digitalcameras
February 13, 2008 |
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Christian wants to know why the images that he produces from his Canon Rebel XT with a 50mm 1.4 are not as sharp as the images that I get out of my Canon 20D. Is it the camera? Is it the lens? Or perhaps it’s technique, post processing, or the clean air here in San Francisco. Actually, all of those items could be contributing factors. Let’s go through each of them one by one.
- I don’t think it’s the camera itself. My 20D isn’t really any more capable than the rebel XT. As a matter of fact, if you check out the resolution tests at dpreview.com, you’ll see that the two cameras are identical in terms of resolution and thus, should be able to produce equally sharp images, all else being equal.
- It could be the lens. Some examples of the Canon 50mm at 1.4 have proven to be a bit soft, especially when used wide open. Also, the narrow depth of field would make it difficult to keep more of the image in focus. It could also be that the lens and camera combo are either front or back focusing. You can test it by taking a picture of a ruler at a 45 degree angle (one side closer, one side farther away) at 1.4 and seeing if the focus sweet spot is precisely on the number you expect it to be on. Put the ruler and the camera on a table and use the timer to eliminate any user variables.
- It could be post processing. I shoot entirely in RAW and post process after the fact although I tend to have a gentle hand in sharpening. If you’re shooting jpg, verify that you’re using the largest resolution setting with the lowest compression available.
- There are a number of points on technique that could help.
- Use as fast a shutter speed as you can to reduce motion blur of both your subject and your hand.
- Try bracing yourself against a wall or table. Also, pay close attention to if you move the camera when you depress the shutter release.
- As a general rule, keep the shutter speed at 1/focal length at minimum.
- Stop down the lens to 4.0 or 5.6 to increase your depth of field.
- Use higher ISO to get faster shutter speeds at a given aperture. Keep in mind that this will likely increase the “noise” that shows up in your image. ISO 400 is as high as I would go with the Rebel. Go higher if you must but understand the tradeoffs.
- Use a tripod if you can. This will eliminate hand shake but won’t do anything about your subjects moving of course.
- Use prime lenses vs zooms. Typically, prime lenses are sharper than zooms.
- Improve your lighting situation by opening curtain or turning on lights. You can also move yourself so your subject is more front lit than back lit. All this is in the name of increasing your shutter speed.
- Take a few shots of the same scene in continuous shooting mode. Sometimes, you will find that the second shot will be sharper than your first because your finger isn’t moving down on the shutter release. Also, more images to choose from increase your chance of getting one where your subject isn’t moving.
- Take out a second mortgage and buy one of those new fangled DSLR’s with super low noise at high ISO. The new Canon 1DIII and 1DsIII and the new Nikon D3 in particular produce amazingly clean images at high ISO. Actually, even the “lesser” Canon 5D and 40D as well as the Nikon D300 will produce very clean images compared to the previous generation of DSLRs. (Ok, this isn’t really technique, but it will certainly give you a better chance at getting a sharper image.)
One other side comment that is particularly relevant given how many people blog today is to make sure you’re comparing pictures on your computer using the original jpg file and not the ones you’ve posted to something like blogger. The reason is that pictures once posted to blogger get compressed to hell to save on their bandwidth. One alternative to pursue is to use Flickr to host your images and copy and paste the code from them. It’s super easy to use and they don’t compress your images nearly as much. If you have questions as to how it’s done, let me know and it will be it’s own entry here!
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