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05-31-2011, 01:15 AM   #1
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How do you know what aperture to best shoot at?

Title says it all really. I've been going through a phase of shooting with my FA50 at around 2.0-3.5 a lot, mainly shooting people. In fact I'm probably overusing these apertures. I just wondered if people tend to shoot certain subjects at certain apertures or do you just wing it?

05-31-2011, 01:42 AM   #2
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Assuming you have enough light to be able to choose any aperture you like, there could be several reasons to choose various apertures. I'll list a few thing I have worked out. No doubt others have much more experience.

Landscapes are generally shot at smaller apertures for example, something between say F8 and F16. (smaller than F16 can cause other problems) Portraits are usually shot at wider ap's to achieve subject isolation and blur the background out of focus areas.

Whether you chose the maximum aperture of your lens or stop down a little, is a function of what you are trying to achieve. For example a FA501.4 shot wide open will have a depth of field of only a few millimeters at full face portrait range. You could get say, the leading eye in focus and have the tip of the nose and the trailing eye not in focus. Closing down to say F4 would give you a greater DOF and may be enough for the whole face to be sharp.

Taking a group shot at 50mm F1.4 would be just about impossible at F1.4 because only the tip of one persons nose would be in focus at the distance you would need to be back to get the group in the frame of the 50mm. You are therefore forced to stop down the lens to get appropriate DOF and get the whole group in Focus. F8 should be adequate, but of course you only have a fraction of the light collecting properties of a wider aperture, so either the shutter time has to be longer, or the ISO has to increase.

Other properties such as lens softness at wide open apertures come into play as well and most people shoot stopped down a little to find the 'sweet spot' of the lens. Some Pentax camera's even have a function for finding the measured MTF sweet spot of the attached lens, (I don't remember if the K-x has this feature). sometime the 'softness' of the lens is used as a feature in female portraiture. (which woman wants every blemish and wrinkle shown in ultra fine focus?) the softness/blur of a wide open lens can be flattering sometimes.

Last edited by wizofoz; 05-31-2011 at 03:47 PM.
05-31-2011, 02:35 AM   #3
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Generally I'd go with one stop down from wide open to f/16 as a range of apertures to confidently use for good quality.

As for what apertures to apply to which situations, there are lots of variables - most importantly, the desired style of image, the subject to lens distance, the focal length and lighting conditions.

There is no need to 'calculate' the depth of field or aperture to use in portraiture, but an assessment of the combination of those variables gives you an idea of what aperture would be suitable for your portrait. A kind of educated estimate.

The closer the background interacts with the subject, the wider I generally shoot at, whereas a well separated or highly controlled background (such as in a studio) can be shot at f/5.6-8 for maximal subject sharpness since there isn't as much concern about the background distracting the viewer from the subject in the resultant image.

Last edited by Ash; 05-31-2011 at 05:03 PM.
05-31-2011, 02:40 AM   #4
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Your biggest friend is the DOF preview!

Wizofox explains some of it. Try setting yourself a "task". Landscape, portrait still life or whatever. Take a selection of shots and on each one try to shoot them at wide, medium and narrow aperture. Them critically look at the results and try to spot the differences and see what works for you.

When looking at others photos in the gallery etc, check the data.

Kim

05-31-2011, 03:10 AM   #5
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QuoteOriginally posted by Kim C Quote
Your biggest friend is the DOF preview!

Wizofox explains some of it. Try setting yourself a "task". Landscape, portrait still life or whatever. Take a selection of shots and on each one try to shoot them at wide, medium and narrow aperture. Them critically look at the results and try to spot the differences and see what works for you.

When looking at others photos in the gallery etc, check the data.

Kim
Building on this try using different focal length (FL) lenses or zooms, and different distances to the subject.I think (but someone point me in the right direction if I am wrong) The longer the FL and closer the object, then generally the thinner the depth of field. Ie The DA70 can at f/4, 2 metres from the subject will produce a thinner dof than a DA15 at f/4, 2 metres from the subject.
05-31-2011, 04:52 AM   #6
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Lots of good info above. Here is another thing to consider. If you are shooting in Av, the aperture you select determines the shutter speed. Here's a hypothetical case; say you are shooting some flowers, it's breezy, and the flowers are bobbing around a bit (not a whole lot that you can't keep them in the viewfinder, just waving around a bit) You will want to choose an aperture that will give you at the very least 1/160 (and probably faster) shutter speed. Generally speaking I usually shoot between f/5.6 and f/8.0, but shutter speed considerations and DoF issues will frequently make my shoot out of that range.

NaCl(Shutter speed and DoF determine my aperture)H2O
05-31-2011, 07:47 AM   #7
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QuoteOriginally posted by NaClH2O Quote
Lots of good info above. Here is another thing to consider. If you are shooting in Av, the aperture you select determines the shutter speed. Here's a hypothetical case; say you are shooting some flowers, it's breezy, and the flowers are bobbing around a bit (not a whole lot that you can't keep them in the viewfinder, just waving around a bit) You will want to choose an aperture that will give you at the very least 1/160 (and probably faster) shutter speed. Generally speaking I usually shoot between f/5.6 and f/8.0, but shutter speed considerations and DoF issues will frequently make my shoot out of that range.

NaCl(Shutter speed and DoF determine my aperture)H2O
Feeding off of this thought. Sometimes you'll want a slow shutter speed to emphasize movement such as in panning shots, waterfalls, or you just want the subject blurred from motion.

Mastering Panning Photographing Moving Subjects
Waterfall Digital Photography
How to Capture Motion Blur in Photography

The easiest way to accomplish this though is not by stopping the lens down, but to use the Tv mode to set the shutter speed and let the camera determine the appropriate aperture. Brighter conditions and a slower desired shutter speed will result in stopping down the lens.
05-31-2011, 09:11 AM   #8
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You shoot at whatever aperture gets you the depth of field, shutter speed, and/or overall sharpness you want, in roughly that order of importance. In low light light, shutter speed is usually a more important concern than depth of field (in other words, you settle for whatever depth of field you get in order to get a fast enough shutter speed).

If you don't understand how these factors relate, then I suggest a visit to the local library to check out a basic book on photography - the concepts are universal.

But once you understand the relationships, it's a simple matter of you the photographer deciding what kind of DOF you want and what kind of shutter speed you can accept in order to get that DOF, and then also maybe give a small thought to whether the lens itself might be a little sharper at some apertures (like between around f/4 and f/8 than others) - but still, DOF and shutter speed would normally be more important concerns.

05-31-2011, 09:52 AM - 1 Like   #9
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QuoteOriginally posted by NicoleAu Quote
I just wondered if people tend to shoot certain subjects at certain apertures or do you just wing it?
Depends on what your goals are. If you are merely taking snapshots and aren't overly concerned with the artistic quality of the photo, then winging may be just fine. But if you're seeking to control the look of the photo, then setting the aperture becomes crucially important. Aperture vitally affects depth and field and sharpness. There exist various trade-offs between depth of field, center sharpness, and corner/border sharpness at different aperatures. Depth of field consistently increases as one stops down. Sharpness initially increases as one stops down, reaches its highest point at around f4 or f5.6, and then begins decreasing. Border to border sharpness follows a different path. Wide open, most lens are moderately sharp toward the center but soft toward the corners. Corner/border sharpness usually improves until f8, after which it gradually worsens.

Now depending on what your goals are for your image determines your optimal focal length. For portraits, you want to shoot wide or close to wide open, because the narrow depth of field lets you isolate subject. There's a bit of a tradeoff between wide open and close to wide open. Wide open will allow you to get the most isolation (with a real fast lens, the background may be entirely blurred out), but your subject won't be tack sharp. Stopped down to f2.8, your subject will be sharper, but your background won't be as blurred out and you'll therefore have less dramatic isolation. So you have to choose what is most important to you: isolation or tack sharpness. BTW, there's really no reason to shoot a portrait at f8, unless you want to include the background (e.g., a portrait with the Grand Canyon as a backdrop).

Landscape photography, on the other hand, usually has different aims. With landscapes, border to border sharpness is often desires, so f8 becomes an optimal aperture in landscape work.

In macro photography, where depth of field, even stopped down, becomes exceedingly narrow, the optimal f-stop may be f16.
05-31-2011, 02:53 PM   #10
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When using a focal length of 100mm at f4 and then another shot with a focal length of 50mm at f4 with the subject filling the frame the same amount, which one would have less depth of field?
05-31-2011, 05:06 PM   #11
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QuoteOriginally posted by mhaws Quote
When using a focal length of 100mm at f4 and then another shot with a focal length of 50mm at f4 with the subject filling the frame the same amount, which one would have less depth of field?
They would be essentially very similar AFAIK, since the difference in focal length is cancelled out by the change in subject-to-lens distance. To know precisely, the exact subject-to-lens distances need to be obtained for both captures.
05-31-2011, 05:28 PM   #12
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QuoteOriginally posted by mhaws Quote
When using a focal length of 100mm at f4 and then another shot with a focal length of 50mm at f4 with the subject filling the frame the same amount, which one would have less depth of field?
About the same DOF but twice the background blurring for the 100mm.

Last edited by twitch; 05-31-2011 at 05:37 PM.
05-31-2011, 05:44 PM   #13
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Thanks for all the answers, it certainly has given me a lot of food for thought, thank you. I had been wondering if I was overusing the larger apertures too much in my photography as I love DoF. I love to isolate a subject from the background, especially in portraiture.

I tend to even use the larger apertures when I'm shooting against a white sheet that I use for a background in my sunroom, as it helps to make the wrinkles disappear lol. One day I may invest in a proper background if I get enough space.
06-01-2011, 05:32 PM   #14
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I pick apertures based on the depth of field that I want (I'm certain you are familiar with that term).. That is, if I want it shallow, I'll open the iris. If I want it deep, I'll close the iris. I'll let the exposure mode I'm using dictate exactly how I handle everything else but again, it's a matter of what I want the photo to look like. Using it too much? Are you getting the photos you want? If not, rethink and adjust.

06-01-2011, 09:36 PM   #15
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All the above is good advice. Another bit of wisdom from Ye Goode Olde Days of photojournalism is: f/8 and be there! Which means, set the aperture for fairly deep DOF (f/11 would be appropriate for dLSRs) and be ready to shoot whatever happens around you. On sunny streets, I'll use a manual 21mm lens with the aperture at f/11, prefocused to 2m, and everything from 1m to infinity is in focus. Point and shoot, eh?

At the other extreme, hair-thin DOF is artistically appealing. Super-fast lenses are expensive; the effect can be faked by using short macro tubes or cheap close-up adapters. But maybe only serious photographers appreciate such thin DOF. Leaf through some illustrated magazines. Note how many pictures have thin vs thick DOF. View photos in a gallery and make the same comparison. Draw your own conclusions.

There is a rough division: Thin DOF is for art. Thick DOF is for sales.
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