Question re:Apeture priority

[qwerty]

I am trying to get off of program mode and for now apeture seems the easiest for me to use. As I understand things, apeture priority means you set the F-stop and the camera sets the shutter speed based on it's metering. If this is the case then isn't all you are really changing is the depth of field? Ok I admit I have more gear than knowlege.

[mkothare]

You are right in a way. You use aperture priority when the most important thing to you is to decide on the depth of field you want in the picture. You may want shallow depth of field for portraits in bright light or great depth of field for some architectural shot. The camera then determines the shutter speed so that you obtain a correctly exposed picture.

Conversely if shutter speed was important (fast speed to freeze motion like sports or slow speed to blur motion like moving water) - you use shutter priority and let the camera set the aperture.

You balance the two as in some cases both may be relevant.

[Gabby498]

Judy, to a degree you are correct. As long as you are relying on the camera’s meter the results, exposure wise, should be the same either in Program or in Aperture.

But rather than think of it as “changing” depth of field, think of it as “controlling” depth of field. In Aperture mode you are able to set your aperture to match the situation. If you need maximum DOF you use a small aperture (high f/number). If you wish to emphasis a certain element in your composition by using shallow DOF you select a large aperture (small f/number). True you have changed DOF but you have changed it with the ability to control it.

The same thing works when you go to Shutter Speed mode. You then will have control of the amount of sharpness or blur in your photograph by selecting the shutter speed appropriate to your subject or to your creative intent.

In Program mode, you will get the very same exposure as long as you meter the very same area but you give up your control of DOF and sharpness to the camera. That is not a bad thing, as you will frequently hear on the forums. It is not bad, it is just different. In better than fifty percent of the cases Program most likely will work equally well and provide additional convenience.

The trick is to learn to judge the situation, to know when you are actually going to receive benefit form going to Aperture or Shutter Speed mode and to judge the situations where giving up that control is not going to matter. There is no one mode that is superior or inferior to any other, and that includes Program mode. They all have their purpose. You have a wonderfully sophisticated piece of equipment, so to not take advantage of that by arbitrarily not using a specific mode is simply to limit yourself.

[qwerty]

Thanks for the information. Yesterday I found an exposure chart that lit a candle in my understanding and that is where the question came from. Seeing how ISO, apeture and shutter speed work together for the same exposure value in a chart really helped.

[humminboid]

Qwerty:

Think of exposure as a hotdog. The whole 'dog represents proper average exposure, with the middle as the mythical "perfect" exposure, with shutter speed and f/stop balancing equally on either side. Let's say the metered exposure is F/8 at 1/125 sec. And the DOF includes a biker babe, where age, overeating and gravity have won the battle, wearing Daisy Duke shorts, sporting a large butterfly tattoo centered on her navel.

Now, say you, "I don't want to include that!" If you wait ,the "moment "will be forever gone.

Soooo... to blur the unwanted object, you quickly open up your lens (open up= larger diaphragm aperture, smaller number, lets more light in.) to f/3.5 or 2.8, but, to achieve proper exposure, you have compensate by increasing your shutter speed, so the exposure is again balanced, with the same amount of light striking the sensor, and falling within the hotdog.

Again, "proper" exposure, but controlled to eliminate Madame Butterfly, or at least, make her less...ummm...obtrusive.

A combination of any shutter speed and f/stop anywhere along the hotdog will produce a properly exposed photograph.

I hope this helps some. Photography is a magical pastime, but does require some skull sweat, at least at first. Now, go take some pictures!

[qwerty]

Thanks Humminboid,
That was quite the visual but it does make the point.

[BillMellett]

Ha! Awesome explanation!

[toverman]

Get used to the priority modes a little and then try manual mode. A great thing about that is ultimate control, and once you've had a lot of experience about how certain colors react to light and other things, you'll begin over- or under-exposing images on purpose to get what you want, in connection with stop-motion/depth of field control.