Shutter Speed Priority vs Aperture Priority

I need help! I am having somewhat of a dispute over at another bird photography forum, and I desperately need to hear your opinions, whether it is on my side or not. I've been wrong before, and I could be again, but in this case I'm having great difficulty in understanding the other side of the argument.. This is something that I need the opinions of experts and I consider many members here to be in that category, and even if they are not quite experts yet, if they keep hanging around BFN long enough they will be..
So here is the dispute. It concerns Aperture Priority vs Shutter Speed Priority in taking photographs of birds in flight. My opinion is that Shutter Speed priority is preferred. My reasoning is that because too low a shutter speed will cause a blurred image, the camera must be set up to always shoot a high enough shutter speed. The actually shutter speed required is based on a number a variables, like distance to subject, speed and direction the subject is traveling, etc. In any case, the photographers first job would be to determine the speed necessary to avoid blurring from either camera shake of motion of the subject. . Correct exposure would be achieved by allowing the camera to set the aperture, and using the appropriate ISO. To me, at least, in Aperture Priority there is always a risk that a shutter speed will be too slow, the result would be a blurred image. In birds in flight, especially at a distance, there is no real advantage in a greater depth of field. The whole bird can be in focus at wide aperture. Closer in, depth of field is more important, but how many BIF images are close-ups? Now a group of birds in flight can be shot at a wide aperture if there are in relatively the same focal plane, however this would be helped by a wider aperture.
In SS priority the risk is that the aperture was incorrect, most likely resulting in an underexposed image, or the aperture was insufficient to create a desired depth f field. Now, it is my contention that a blurred image is far worse than an underexposed image, not to say either is great. A blurred image is not salvageable. An under-exposed image might be saved, and since brightening an underexposed image introduces noise, it is possible to use noise reduction software. So what if I need a greater aperture to get greater depth of field, to include a number of birds in flight in an image? I would increase the ISO, and a smaller aperture would result(and of course more noise with the higher ISO). In any case, by using a shutter speed of 1/1600 and SS priority, and using an ISO appropriate for the ambient light conditions I have been fairly successful in BIF images. I could be completely wrong about all of this. I would like to hear how other far more accomplished photographers than I deal with these issues. ~onlybill

William,

Your basic assumption is flawed. The Mode only allows you to pick a preferred value be it the aperture or shutter speed. AS THE SUBJECT FLIES ACROSS VARYING BACKGROUND TONALITIES the meter recommendation will vacillate. The exposure will vary by the same amount regardless of whether you are in Av or Tv mode.

You say "Correct exposure would be achieved by allowing the camera to set the aperture, and using the appropriate ISO" More than likely "correct" exposure will not be obtained in either Av or Tv Mode,

It the light on the subject is constant, the exposure should be the same regardless of the background. Hence, the reason Manual exposure mode is recommended.

All of the following combos allow the same quantity of light to strike the sensor. sunny f/16 ISO 200

1/100 1/200 1/400 1/800 1/1600 1/3200
f/22 f/16 f/11 f/8 f/5.6 f/4

But, each combination will provide a different look to the image. You need only pick the best combination to suit your needs.

Increasing the ISO will allow you to shift the numbers. A higher ISO affords more DOF or faster shutter speed given the quantity of light does not change. sunny f/16 ISO 400

1/100 1/200 1/400 1/800 1/1600 1/3200
f/32 F/22 f/16 f/11 f/8 f/5.6

Tip- if you wish to you maintain the SAME exposure, but use a different f/stop or shutter speed, you need only count the clicks up or down that you turn the INDEX FINGER dial/wheel and go the same amount in the opposite direction with the THUMB dial/wheel. IE... If you go two clicks to the right with your index finger, you need go two clicks to the left with the thumb wheel. If you vary the clicks (one right, two left) you change the exposure.


Note- It is the Meter Pattern - Evaluative/Matrix, Center-weighted, Spot that recommends the exposure.
The Auto Modes - Av, Tv Program allows you to choose a one preferred variable, while the camera selects the other variable according to the Meter Pattern in use. In Manual Mode it is no different...you select and set, based upon your need, one preferred variable (f/stop or shutter speed) into the camera , and then manually set the other variable..

Determining the "correct exposure" is another issue altogether.

Best,

Chas

I think BiIl's argument is basically:

"If in any instance a certain shutter speed is required to freeze the motion in order not to result in a blurred image, then why not set the shutter speed first, then set the aperture and ISO accordingly?"

To simplify the discussion, I assume the camera does give the correct exposure.

I used to use primarily shutter-priority mode with auto ISO for the reason as Bill stated. Now I use mostly manual mode and aperture-priority mode with no auto ISO. This is for no reason but to practice using other exposure modes. And I find myself keeping an eye on the shutter speed time and again.

From my limited experiences, I've noticed most people use aperture-priority as the auto-mode. Some do use shutter priority when shutting fast subjects (and it makes sense to me). At this point, I personally don't see why it has to be aperture-priority mode over shutter-speed priority mode. In fact, when I used shutter-priority mode with auto ISO, I noticed that all the time the chose the largest priority. If one is to shoot with the largest aperture unless there's a reason to do otherwise, and if the camera could give me clean image even at high ISO's, then I don't see anything wrong with using shutter priority mode with auto ISO.

My 2 cents.

Desmond,

Yes, this will surely work.

"If one is to shoot with the largest aperture unless there's a reason to do otherwise, and if the camera could give me clean image even at high ISO's, then I don't see anything wrong with using shutter priority mode with auto ISO. "

If the camera is not able to figure the correct exposure it becomes moot.
If you strive for consistency in your flight imagrey....the Auto modes will prove detrimental.

Best,

Chas

Hi William! Chas and Desmond both make good points. I use either manual exposure or aperture priority for my bird photography. No matter which mode you use to do your photography, you're always well advised to know your camera settings. For birds in flight, you do need plenty of shutter speed to stop the action. In aperture priority, if you shoot wide open, you will get the fastest shutter speed the camera is capable of for the given lighting conditions. If you pay attention to your camera settings, it's easy to get plenty of shutter speed and control your DOF in either aperture priority or shutter priority. It is somewhat of an oversimplification to focus only on shutter speed in flight photography. We do care about DOF.

With regard to the following statement: "In SS priority the risk is that the aperture was incorrect, most likely resulting in an underexposed image, or the aperture was insufficient to create a desired depth f field," you will in fact get an identical exposure in either shutter priority or aperture priority. Shutter priority gives preference to shutter speed and uses aperture to create a proper exposure, and aperture priority does the opposite. Both modes will give an identical exposure although the effect that you get can differ substantially between the two modes. Chas explains this concept quite nicely above.

If I'm shooting birds in flight with aperture priority, this is how I approach a given photographic situation. I select the aperture I want (usually f/7.1 or f/8). I check to see what shutter speed I'm getting at that aperture. If it's not fast enough, I bump my ISO, or possibly use a larger aperture.

Manual mode makes more sense for BIF, particularly when dealing with varied BGs. You set your aperture, shutter speed, and ISO for the bird, and the bird will be well-exposed regardless of the BG that it's flying in front of.

In summary, you can use whichever mode you want to do bird photography as long as you are continuously aware of your camera settings, making changes as necessary to accomplish your photographic goal.

Thank you very much. You wouldn't believe how much I appreciate everyones explanation, especially Doug's. You have explained it quite well, and although I was hearing bits and pieces of what you have said, since it was from different sources, I failed to bring it all together into a coherent line of thought. About the ISO, I never let the camera determine it for me, and choose it ahead of time depending on the lighting conditions. When all is said and done, considering the f-stop and shutter speed of many images I've taken, the vast majority are at full aperture when using SS priority. Thus these would be identical to if I had been manual mode the whole time, chose full aperture and the shutter speed. Thanks again for clarifying this for me!