aperture settings

[ron moore]

hello everyone
as you all probably know i am quite new to photography and i have been trying out different settings in AV mode on my camera. can anyone explain what the difference is when i set the camera to 60 at 5.6 and when i set the camera to 90 at 6.7 or when i set the camera to 125 at 8.0.
When i look at the pictures taken with these settings i cannot see any real difference.
What settings do i need to take a reasonable sharp picture.

regards ron moore

[rbarry]

There are numerous "methods" of capturing an image using the different settings within your camera body and lens. You should be aware that there are also many combinations of settings that could give you the same over-all exposure, but make huge differences to the outcome of your captured image.
It depends what the subject matter of your image is, whether it conveys movement and how sharp you want the subject in relation to the background. You may want to purposefully under or over expose an image for effect or combine more thean one image in post processing.

The example settings you give above are not that far apart to make an obvious difference, but it still depends on the subject matter; portrait, landscape, action etc.

Will follow up later when I have more time unless others respond with better advice than I can give.

Rick.

[amk1977]

Hi Ron,

As Rick rightly says, there are a number of different combinations of aperture, shutter speed and ISO combinations that will result in a properly exposed image. Imagine it like a mathematical formula, where x (aperture)+y (shutter speed)+z (ISO) = 1, where 1 is the correctly exposed photograph. x,y and z can all have different values BUT (and its a big but), the differing values of x, y and z affect the look of the photo.

Take photographing a subject that has movement, like a waterfall or fountain for example. If you had the camera in shutter priority and select a shutter speed of 1/10 sec. The camera chooses the appropriate shutter speed at the current ISO setting to get the correct exposure. The resulting image will have blurred water due to the slow shutter speed. Now take the same photo at 1/1000 sec. The resulting image will have freeze framed the action. Same scene, same exposure, totally different look.

With the aperture, that too has a huge impact on a photograph. I'm guessing you are using a lens that is somewhere in the region of f/4-5.6 as its widest apertures (I'm memory serves you had the Tamron 18-270mm??). The aperture controls two things essentially. That is the depth of field and sharpness. The lower the f/ number the wider the aperture, the shallower the depth of field and the softer the resulting image. You probably won't see a huge difference from f/5.6 to f/8 unless you pixel peep. What you should see is that the image becomes sharper as you head from f/5.6 to f/8 and that objects in the background (and foreground if you are focused further into the image) come more into view.

Its when you have fast glass, like f/1.4 to f/2.8 that you really notice the difference that the aperture has to an image. At those wide apertures, you can isolate your subject in the scene and create nice blurry backgrounds. The 50mm f/1.8 is great for this. Wide open your depth of field is so shallow that if you had the eyes in focus, the ears would be beginning to blur. In fact, the DOF is so shallow at that aperture, that if the person isn't facing you directly, that one eye can be in focus, the other out. Take the same lens and stop it down to f/22 and the photograph will pretty much be in detail all the way into the distance.

Generally a lens achieves optimum sharpness a few stops down from its widest aperture. Beyond that and you start venturing into the realms of diffraction and although you increase the depth of field, you do lose detail. For kit lenses which are usually between f/3.5 and f/5.6, the sharpest aperture is f/8-f/11. For something like my Nikkor 50mm f/1.8D, optimum sharpness is f/3.2 if I remember correctly. However, just because that is the sharpest aperture, it doesn't mean its the best option for all scenarios. The DOF is still very shallow at f/3.2 and so if I was shooting a couple standing next to one another, I may need to stop the lens down a lot further to increase the depth of field and get them both in focus. An additional issue created by doing this is the loss of light by closing the aperture down, which means either reducing my shutter speed (may result in blur from camera shake or movement by the subjects) or upping my ISO. The higher the ISO, the more noise creeps into the image and loss of detail.

Also, sharpness also has a lot to do with you. Camera shake at slowish shutter speeds is going to result in less than sharp images. The same applies to your subject. For instance I have a Tamron SP 90 macro lens. Blisteringly sharp lens. If a bug moves whilst I'm shooting it and it travels beyond the focus plane or the shutter speed is relatively low due to available light, then my image is not going to be nice and sharp.

I guess the point I am trying to make is don't focus so much (no pun intended) on your lens. Sharpness has a lot more to do with the photographer and subject, that your glass itself. You can also increase the sharpness of an image later in post processing. Pay more heed to your composition, like subject placement in the frame, depth of field, etc. That will serve you much better than optimum sharpness.

I hope my long winded post proves useful to you and I apologize if I have covered areas you are already familiar with.

AK

[silversnapper1]

Originally Posted by amk1977

Hi Ron,

Take photographing a subject that has movement, like a waterfall or fountain for example. If you had the camera in shutter priority and select a shutter speed of 1/10 sec. The camera chooses the appropriate shutter speed at the current ISO setting to get the correct exposure. The resulting image will have blurred water due to the slow shutter speed. Now take the same photo at 1/1000 sec. The resulting image will have freeze framed the action. Same scene, same exposure, totally different look.


AK

Excellent way to put it and sorry to interject but shouldn't that be aperture?

Easily lost in a long train of thought when you are trying to explain something like this.

Also, if you changed the shutter speed to 1/1000 you would notice a change in aperture to compensate and balance the equation out.

[amk1977]

Well spotted Steve! Got my A and S all muddled there lol.

Just to clarify Ron, Shutter priority, you choose the shutter speed you want, the camera selects an appropriate aperture for you. Aperture priority, you choose your f-stop, camera selects shutter speed for you to get a correctly exposed image.

Double check that for me Steve, in case I made another error lol.

[silversnapper1]

Originally Posted by amk1977

Well spotted Steve! Got my A and S all muddled there lol.

Just to clarify Ron, Shutter priority, you choose the shutter speed you want, the camera selects an appropriate aperture for you. Aperture priority, you choose your f-stop, camera selects shutter speed for you to get a correctly exposed image.

Double check that for me Steve, in case I made another error lol.

That's the way I get it.

I call it the eternal triangle - ISO, Shutter speed and Aperture.

[amk1977]

Originally Posted by silversnapper1

That's the way I get it.

I call it the eternal triangle

I am so tempted to make an ex-girlfriend joke out of that... but I shall refrain.

[silversnapper1]

Originally Posted by amk1977

I am so tempted to make an ex-girlfriend joke out of that... but I shall refrain.

That's the infernal triangle isn't it?

[ron moore]

thanks to all of you for all that information, i will have to read a few times before i can take
it all in.


regards ron moore

[Manamarak]

Hi mate,

Aperture and depth of field is pretty hard to grasp, but here are a few links to help.

http://en.wikibooks.org/wiki/Basic_Photography
http://www.illustratedphotography.com/basic-photography
http://www.wikihow.com/Categoryigital-Photography