Ask Uncle Ronnie

 shutter speeds

Maxim asks Maximum Questions!

1. If I have f/4, f/2.8, f/1.8 lenses, which will be the sharpest at f/4?

2. What is the minimum shutter speed to get sharp pictures on a tripod, for different focal lengths; for example, using a 70-300 mm lens at 70mm or 300mm, or 50mm prime lenses?

3. While taking multiple shots of the same picture, is it better to use the Single shot mode and fire twice/thrice one after the other, or use the Continuous firing mode?

4. Does VR/IS help us under 1/500 second even during day time if I need faster shutter speed at aperture priority mode?

5. What camera parameters does exposure compensation alter?

Is this function equal to raising brightness levels in Photoshop?

6. Are pictures shot at 1/500 sec or more, affected by slight regular hand shaking?

I can ask some more next month, though I think it s enough for now.

Maxim, via E-mail

Sure, Maxim. It s enough for now!

1. Assuming that all the three lenses are of the same focal length, with similar optics, and with the subject at the same distance, the f/1.8 lens should be the sharpest at f/4. This is because the f/1.8 lens would be stopped down a little over 2-stops from its widest opening (which generally defines the optimum aperture). In the case of the f/2.8 lens, it would be 1-stop down

from the widest opening, and in the case of the f/4 lens, the lens would be used wide open.

2. In theory, and assuming that you are using a high performance tripod, and that the subject is not moving at all, all shutter speeds should provide the same sharpness (not considering the extra depth of field that would be achieved with the narrower apertures/ slow shutter speeds, that could make some images appear sharper). In practice however, certain shutter speeds (like 1/15, 1/8, 1/ 4, and 1/2 seconds) tend to cause greater mirror vibrations and hence a slight loss in critical sharpness.

3. You must set the camera to Continuous High firing mode. In a sequence of, say 3 shots, the first could be slightly blurry due to the application of finger pressure on the shutter release button (and thus shaking the camera), and the last shot could also be slightly blurry as a result of releasing the pressure on the shutter release button (which can also cause a slight camera movement). The middle shot is likely to be the sharpest.

4. Sorry, your question is not clear. I am unable to understand what you mean exactly.

5. If you set exposure compensation in Aperture Priority mode, the camera will apply the compensation to the shutter speeds. If you are using Shutter Priority mode, the compensation will be applied to the apertures.

Using  plus compensation , the subject brightness increases compared to what it would have been without the plus compensation. Using  minus compensation  the subject brightness decreases, compared to what it would have been without the minus compensation. The effect is similar to that of raising/lowering the brightness levels in Photoshop.

6. Faster the shutter speed, sharper the picture (sharper at the point of focus). However, when using wide or medium telephoto lenses with stationary subjects, you are unlikely to see a difference in sharpness between, say 1/500 sec and 1/1000 sec. If your subject is moving, then, depending on how fast it is moving, the faster shutter speed will provide a sharper image. Also note that with heavy and long telephoto lenses, one must strive to use the fastest shutter speed possible under the given lighting situation.

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