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How do you choose your aperture value?


eolaystwyth

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Hi. I'm quite new to digital photography. I wanted to ask you guys how do you choose the aperture setting for any distance, be it landscape or a close subject. I've read about the 'exposure triangle' and how a larger or smaller aperture affects either or both ISO sensitivity and shutter speed. I'm also aware of how a different aperture value can provide deeper/shallower depth of field. Still, I'm curious as to what are the variables other photographers take into consideration, in order to choose a particular F-number, either for landscape, medium or close distance. Thanks!
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I don't think there is a set answer, it all depends on the circumstances, I'm afraid. As you have realised, the aperture affects more than the exposure, and of course the shutter speed is important to avoid camera shake, except when using a tripod. What you could try doing is setting up a situation (or preferably several), and changing the aperture for each shot, then when you look on your monitor it should be apparent which gives the most pleasing result each time - and of course the exposure info is encoded in the EXIF file for reference.
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I select my aperture based on the depth of field I want in the photo.

 

This could be directly, observing the changes in the viewfinder, most likely with a still subject such as a landscape, macro or a posed portrait.

 

Or it could be based on experience, for more fluid shooting situations, I know that f4 (for example) will give me the depth of field I need, so I'll just 'set and forget' altering it only for specific shots where I want a different result. Street and social (parties, weddings) would be good examples of this.

 

Or the aperture could be determined by the need to use hyperfocal focusing techniques.

 

Or I could be shooting in very low light, so it needs to be wide open.

 

With modern cameras, I rarely find myself needing to stop down in bright light to avoid running out of shutter speeds.

 

 

So I think my answer is 'experience', combined with taking the time to fine tune things when possible.

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Depth of field mainly. However, backgrounds can be blurred to varying degrees with different aperture openings. A controlled blurring of a background may be more important than depth of field in some shots, like outdoor portraits for example. The depth of field may only need to be 2 feet, so the aperture will be wide open enough to blur the background sufficiently for the subject to stand out against it.
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Generally I'm less concerned with depth of field and more concerned with best overall performance. To that end, whenever I get a new lens, or camera with a fixed lens, I test it out with a sacrificial roll (or in the case of a lens, I put it on a m4/3 digital body for the initial test). I look for things like color fidelity, overall sharpness both in the center of the frame and at the edges as well, vignetting, and various types of distortion...with the primary goal of determining the optimal aperture for most work. I know the axiom that many lenses are optimized for about 2 stops from wide open, but there are often reasons why that axiom doesn't hold true for a particular lens. My general conclusion from over 60 years of shooting film (and digital since the 1990s) is that f/5.6-8 works well in many cases across the spectrum, but may not produce the most artistic result. I've tagged all of my lenses in a database (although I've also memorized most of the results) for reference in particular circumstances - where I want to achieve specific results. It may be OCD behavior, but if I haven't used a particular lens for a year or so, it is a good quick refresher.
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My guiding principle is "first, get the picture".

 

In my lifetime as a photographer, the highest color slide film ISO (then ASA) was 32, then 100, then 200, then 400, then 500 (the infamous GAF 500). That was when the compromises implicit in fast lenses were accepted as part of the cost of getting that picture.

 

Some time ago someone here refused to accept the idea that f/1.2 and even f/1.0 lenses were bought to cram all the photons onto the film possible. But that was why we used those lenses. Shallow depth of field and "bokeh" were hardly even thought of at that time.

 

Nowadays we can pump up ISO on the camera to hundreds of thousands, and the compromises (now noise, not graininess) are still acceptable to those of us who like to shoot in "available darkness". One of Ansel Adams' "basic books" was even on "Available Light Photography".

 

This sort of compromise seems no longer popular, and many people just won't take a picture that is noisy at all. To each their own, I guess.

 

As for minimum aperture, there the problem is diffraction; but sometimes (again) the compromises in sharpness

are acceptable to those of us who want some semblance of depth of field. I do recognize that 'stacking' is a preferred alternative, but it is not always an option in what used to be called "candid photography".

 

For maximum sharpness, most lenses will be at their best stopped down a few stops from maximum--on many lenses that will be between f/5.6 and f/8.

 

By the way, f/8 to 11 at 125th of a second was daylight standard for Kodachrome in the middle years.

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and how a larger or smaller aperture affects either or both ISO sensitivity and shutter speed.

 

Aperture has no effect on the ISO unless you have 'ISO Auto' selected in the camera menu.

 

The primary effect of aperture is to alter the depth of field. A large aperture (small F number), like f/2, will give you a shallow depth-of-field - that is, the amount of distance where things are in acceptable 'sharp' focus. Conversely, a small aperture (big F number), like f/16, will give you a lot more distance between where things get blurry.

 

So, if you want 'everything' in focus, you choose a big f-number, and if you want to throw the background out of focus, you choose a small f-number.

 

The beauty of a digital camera is that you can try these things for free! And immediately see the effect.

 

So go point your camera at something about 3 or 4 feet (1 metre) away. Like a book on a table, and with a cluttered background behind it. Best to do this outdoors and in sunshine, so that your camera has plenty of light to work with.

 

Set your camera on A mode - that's Aperture Priority mode, not Automatic, and set Auto ISO as well.

 

Choose the smallest f-number that your lens allows and take a shot or two focussed on the book.

 

Now choose the biggest f-number and repeat the shots above.

 

If you look at the background beyond the book, you should see a clear difference in how sharp or blurred the background (and foreground) are rendered.

That's depth-of-field and how it can be controlled through the aperture.

 

Middling apertures, like f/5.6 and f/8, will give a moderate depth-of-field. Neither 'all in focus' nor 'blurry background', but somewhere in between.

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Gracias rodeo joe, JDMvW, conrad, BeBu, SCL and everyone for your responses! I can see that the scope of this subject is quite wide and that my best bet is getting out there and shoot in order to get the knowledge! It's interesting to see that many of you have been quite active before the advent of digital cameras. My only experience's been with digital point-and-shoot cameras, and it's only recently that I made the jump from jpeg to RAW. Thanks again!
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Gracias rodeo joe, JDMvW, conrad, BeBu, SCL and everyone for your responses! I can see that the scope of this subject is quite wide and that my best bet is getting out there and shoot in order to get the knowledge! It's interesting to see that many of you have been quite active before the advent of digital cameras. My only experience's been with digital point-and-shoot cameras, and it's only recently that I made the jump from jpeg to RAW. Thanks again!

I agree, get out and shoot lots is the best way to learn.

 

You can see from the responses that there are no hard and fast rules. Some like to get the best quality out of their lenses, so avoid using low f numbers, others love the out of focus backgrounds of low f numbers, and put up with the (very slightly) reduced quality. That last sentence in itself is a generality, because some lenses work great at low f numbers (wide open) especially modern ones. As a novice, I wouldn’t worry about any reduced image quality when using your lenses at maximum ‘openness’, there are so many other factors involved in you getting a good picture. As Joe and Tony have suggested, shoot lots, and use the screen to see what difference it makes when you change aperture. If you like it, that’s all that counts.

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To amplify Rodeo Joe and others: If I have a static object I (try to) use a tripod. I then run a series of shots, aperture priority, from lowest f stop to f8 or 11. If the lighting is constant, and the wind not too hard I then have a choice as to which depth of field I like best. Oh, in this case I have auto iso turned off to use base iso since noise is lowest, and on a tripod a long exposure is ok (wind not a factor).
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  • 3 weeks later...

Here's the thing to remember . . . Through a "normal" range of values, the shutter speed has no effect on the image. Aperture on the other will have a number of different effects on the image, mostly surrounding the idea of depth of field.

 

Most lenses are not as sharp at their maximum aperture and most suffer from diffraction issues at their minimum aperture. Most are sharpest at one or two stops closed from max. Most lenses shouldn't be used at f16 or smaller. So, for the most part, for consumer lenses most images will look best at f5.6 to f11. In fact, in many cases, you really will not see much difference in this range if you are shooting in natural light.

 

So . . . When do you vary from these apertures?

 

When shooting with flash, there are number of advantages to shooting with larger apertures. First, you flash will not use as much power. This will allow it to recycle faster and will usually improve the balance between the available light and flash.

 

When you need an extremely large DoF, you should stop down further. Just remember that at some point, a smaller aperture will result in an overall softer image.

 

When shooting portraits, I usually go for very large apertures. In my wedding work, I have a stable of fast lenses, 30, 50 and 85f1.4, 135f1.8 and an 80-200f2.8. I often shoot these wide open but there are times when I am close enough that DoF is too shallow and I stop down to about f4. But, remember this is a set of extremely well designed, heavy, expensive lenses. It took me years to build this kit and people actually pay me to use them.

 

So . . . To answer your question in a more complete but maybe less useful way . . . I decide what aperture to use based on how I want the picture to look.

 

You don't say what gear you are working with or what you are trying to accomplish. A little more information about your goals, will help us provide more specific information.

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