Bruce Weinstein wrote:.

Can someone explain the differences(aperture, SS etc) when focusingon an object zoomed out and when zoomed in..

In principle the focussing should not change whether the lens is zoomed out or zoomed, assuming that the focus point doesn't move. In practice I sometimes find that I can focus more accurately if I zoom in, and I then zoom out again to recompose the shot..

However, with most camera settings, half pressing the shutter to focus lock also locks the exposure, and I suspect that this is what your question is about..

The camera will calculate the exposure based on what light is falling on the sensor, which is pretty much the area covered by the viewfinder/LCD. If you zoom in, this area will change and, if there are areas of light and dark in the scene, the exposure may change as well..

For example, if the main subject is quite dark against a light background and the exposure mode is set to evaluate the light from the whole image area (e.g. average or evaluative exposure mode), then the overall image will be correctly exposed but main subject will tend to be underexposed..

If you zoom is so that only the main subject is visible in the viewfinder, the camera will set the exposure for the main subject only. If you then zoom out again before taking the shot, the main subject will be correctly exposed but the background will be much too bright or blown out. You may or may not prefer this..

Note that you can get the same effect without zooming in by using a spot metering mode and putting the focus point on the main subject. The camera will then only evaluate a small area of the image around the focus point, i.e. the main subject.Chris R..

One additional point, in addition to Chris's detailed reply above..

You can get the same exposure lots of different ways: 1/1000 sec at f/4 for example lets in the same amount of light as 1/60 sec at f/16. IN the first case the shutter is open for a short time but the aperture in the lens is large. In the second case the shutter is open for much longer (about 16 times longer) and the aperture in the lens is much smaller (the hole only has 1/16 of the area)..

If you are 'zoomed in', i.e. a more telephoto setting of your lens, camera shake is more likely because as you magnify the image tiny tremors in your hands are also amplified. Your camera will know this if it is in fully automatic mode. So if the zoom lens is at a telephoto setting, the camera may bias the exposure more towards faster shutter speed / wider aperture to prevent camera shake, so you may have a different ocmbination of shutter speed and aperture compared to what the camera would choose if you zoomed out..

Best wishesMike..

You need additional support for camera(tripod), when using powerful zoom. Can you imagine what damage could be done to image detail by slight hand shake if your camera is using full 12x zoom for example? As result you get bad focus, that is actually motion blur...http://www.stan-pustylnik.smugmug.com..

Stan_P wrote:.

You need additional support for camera(tripod), when using powerfulzoom. Can you imagine what damage could be done to image detail byslight hand shake if your camera is using full 12x zoom for example?As result you get bad focus, that is actually motion blur....

How "powerful" the zoom is doesn't matter. How telephoto the lens is does. With a long focal length the angle of view exaggerates any lateral or rotational camera shake..

Brian A...

Hugowolf wrote:.

Stan_P wrote:.

You need additional support for camera(tripod), when using powerfulzoom. Can you imagine what damage could be done to image detail byslight hand shake if your camera is using full 12x zoom for example?As result you get bad focus, that is actually motion blur....

How "powerful" the zoom is doesn't matter. How telephoto the lens isdoes. With a long focal length the angle of view exaggerates anylateral or rotational camera shake..

This is a good point here.......12x means nothing unless you know the focal length of the lens involved. Consider a lowly 2x zoom, say the Pentax 12-24mm versus an even more lowly 1.5x zoom, say the SMCP-K 400-600mm or perhaps the Nikon 1200-1700mm zoom. Zoomed out to the full 2x range on the 12-24mm you can safely shoot at around 1/30th of a sec with no problem.....zoomed out the the full 1.5x range on 400-600mm, you'll need at least 1/1000th of a sec shutter speed or better, where as with the Nikon zoomed out to a full 1.5x, you'd need a heavy tripod since the lens weighs 4 pounds and you'd need a shutter speed of at least 1/2000th of a sec for a steady shot handheld.......

Zoom ratios such as 1.5x, 2x, 12x, etc, are really meaningless and more of a marketing ploy. Just keep in mind if you are handholding a lens, you need a shutter speed of roughly 1/focal length (35mm eqiv) sec to prevent camera shake...better still, since the digital sensor in much smaller than 35mm film, I've heard it suggested to use 1/2*focal length..

JohnPentax *ist-D, K100D, Fuji F20/31fd, Oly Stylushttp://www.pbase.com/jglover..