Aperture vs. Shutter: Effect on Light

Mnemosyne

I have a question about aperture versus shutter speed in exposing for sunny days.

My 1ds MkII has a 50 ISO option (which I love), but sometimes even that isn't enough.

So my question is, given the choice between closing the aperture or speeding up the shutter speed, do those two affect the light differently (I already know one affects the DOF and the other motion, I'm just refering to the effect on the light)?

Say for example, would the light at 1/250 at f9 look any different than 1/2000 at f 1.4, assuming these are equivalent exposures (I'm sure they're not, I just picked numbers cause I can't do the math right now).

Or do those not have differing results on light, just the amount?

pathfinder

Get a two or three stop ND filter, and you will be able to shoot wider at slower shutter speeds.

As far as I know, stops are stops, whether created by aperture or shutter speed changes, other than the other changes of DOF or motion blur. With film, you had to worry about reciprocity failure, where the ISO of the film actually changed for very long exposures, but with digital this is not really an issue.

Not sure if this answers your question or not, Chris.

eL eSs Vee

Leaving depth of field and motion blur (or freeze) completely out of the picture and speaking strictly in terms of how much light reaches the sensor, start with any f/stop and time. Go one stop smaller for the aperture and one stop slower for the time; for instance:

f/8@1/500
f/11@1/250
f/16@1/125
f/22@1/60

You can use all of these under the same light condtions - over-, under- or properly exposed - and get the same exposure. The reverse, larger f/stop@faster time, is also true. Just change each by the same amount (in these cases, one full stop for each) and if your light is consistent, so will be your exposure.

Mnemosyne

But what about the how the light looks. Like how ISO changes saturation at different levels. Would a smaller aperture have deeper blacks versus faster shutter speed?

And dad, the only filter we're allowed to use for PJ is a UV filter. Anything that alters how the photo actually occurred (such as circular polarizers or ND filters are taboo, according to the people I've asked).

pathfinder

Maybe BD will comment, but I fail to see how using a 3 stop ND filter is different than dropping the ISO from 800 to 100 - 3 stops different speed.

By that line of reasoning you could not use flash either, as that was not intrinsic to the scene.

I am aware of the ethical constraints for PJs, but really I do not fully grok these subtle distinctions, myself.

Mnemosyne

I just go with what I'm told

And I assume the flash is to light a photo otherwise not obtainable. Filters are for more creative effect

Scott_Quier

Mnemosyne wrote:

I just go with what I'm told

And I assume the flash is to light a photo otherwise not obtainable. Filters are for more creative effect

I'm with PF on a couple of the points he's made:

• A stop is a stop. Leaving aside the effect of DOF and/or motion blur, I don't think there's any difference between 1/125 @ f/8 and 1/30 @ f/16.
• RE: the use of filters. CP - OK, I think I can get my head around that as being a problem for PJ. But an ND? There's no difference between using an ND and using a small aperture. They both have an effect on the aperture (assuming the same ISO). Further, a photography is constantly making decisions with respect to choice of aperture vs. shutter speed. Next thing you know, PJs will be restricted to which focal lengths they can use and, even sillier, which individual lenses (EF 50 f/1.2 vs. EF 50 f/14) because one may induce more flare than another and flare wasn't in the scene Maybe I'm missing something?

Qarik

Assuming no flash then a stop is a stop is a stop. The lighting should look exactly the same. There will be of course motion blur if the shutter gets too slow. If you are using a TTL flash then this changes everything.

dkoyanagi

Mnemosyne wrote:

I have a question about aperture versus shutter speed in exposing for sunny days.

My 1ds MkII has a 50 ISO option (which I love), but sometimes even that isn't enough.

So my question is, given the choice between closing the aperture or speeding up the shutter speed, do those two affect the light differently (I already know one affects the DOF and the other motion, I'm just refering to the effect on the light)?

Say for example, would the light at 1/250 at f9 look any different than 1/2000 at f 1.4, assuming these are equivalent exposures (I'm sure they're not, I just picked numbers cause I can't do the math right now).

Or do those not have differing results on light, just the amount?

Smaller aperture may lead to loss of sharpness due to diffraction.

Longer shutter speeds may lead to excessive noise, though this may not be a problem on a 1Ds MkII.

Tim Kamppinen

Perhaps there is some confusion here between a ND filter and a Graduated ND filter? The graduated filter would be used to darken the sky while maintaining a good exposure for the ground as in landscape photography. I still don't see the big deal, but I guess it does alter the scene somewhat unlike a normal ND filter.

Nikolai

As it's been already said by many, the amount light is the same. Whether you open the tap fully, or just leave it trickling, eventually you will fill the cup, and that's about it.

The sideeffects, however, are different, and that's what we all consider when choosing the proper combo and that what you may call the "quality" of light.

• Shutter Speed:
  - motion blur/freeze
  - amount of ambient light vs flash (the latter is unaffected until you reach XSync speed)
  - amount of noise due to the sensor heating over the long exposures
• Aperture
  - DOF
  - bokeh quality
  - amount of both flash and ambient
  - edge effects (like sunstars, CA, etc)
  - image sharpness (all lenses have a sweet spot where they are the sharpest)
  - image degradation due to the diffraction at high f values
• ISO
  - slight color shifting (while engineers try to maintain linear response of the censor, it never is perfectly linear; effect can be negligible for the most applications, though)
  - amount of noise due to the censor imperfectness during the high ISO exposures
• ND
  - possible color shift due to the fact the glass tint may not be ideal gray (very much like ISO)
  - as *any* filter (i.e. anything put into the light path), it introduces an extra intrasystem reflection, thus theoretically diminishing the dynamic range and possibly introducing glare and ghosting. For good ones the effects are minimal.

HTH

Blackwood

DOF aside...

Given diffraction, I find it hard to imagine that light passing through one size/shaped aperture will be exactly the same as light passing through another.

However, I doubt that any differences are easy to resolve by looking at an image.

ziggy53

High ISO settings will impact dynamic range and color fidelity. Aperture settings and shutter speeds should have no visible effects on color, contrast, hue, etc., except that "optimal" apertures will impact micro-contrast which is directly related to sharpness.

I suspect that Tim is correct that there is some confusion relating to graduated ND versus ND filters. ND filters do not generally affect scene tonality, similar to basic exposure settings, and should be allowed in photojournalism. Graduated ND might be considered a "manipulation" of the image and so it may not be allowed (similar to HDR). The use of an extreme ND filter to alter the time perspective might be a cause for concern. In that case an explanation of the image might be in order as either part of the article relating to the image, or at least the word "illustration" used to describe the image.

Polarizing filters, including circular polarizers, are probably a point of contention in that they can affect scene tonality, compared to human vision at least, but I believe they are in fairly common use for particular circumstances (so maybe a caption/article explanation might be in order.)

Here is, I believe, a very good synopsis of the ethics involved:

http://www.articlesbase.com/visual-art-articles/photojournalism-good-practice-guidelines-1039730.html

Here is a pertinent article from the NY Times:

http://www.nytimes.com/2009/06/22/business/media/22askthetimes.html?_r=1&pagewanted=9
http://www.nytimes.com/2009/06/22/business/media/22askthetimes.html?_r=1&pagewanted=10

Ethical guidelines from other sources:

The Washington Post
Photographs are trusted by our readers to be an accurate recording of an event. Alteration of photographs in a way so as to mislead, confuse or otherwise misrepresent the accuracy of those events is strictly prohibited.

The Kansas City Star
It's the Star's policy that any content alteration of news photographs is unacceptable. We do not concoct news photographs and try to pass them off as reality...Photojournalists should not set-up, re-create, direct, or otherwise intrude on the reality of an event. Direction is allowed for situations such as portraits, fashion, studio work, and photo illustration and should be obvious to the viewer.

The National Press Photographers Association
Photojournalists operate as trustees of the public. Our primary role is to report visually on the significant events and on the varied viewpoints in our common world. Our primary goal is the faithful and comprehensive depiction of the subject at hand. As photojournalists, we have the responsibility to document society and to preserve its history through images.

Stan Grossfeld, Pulitzer Prize-winning photographer, Boston Globe
Burning is really to redirect the eye to the center of the image, not to eliminate content. You have to be true to the reader about what you witnessed.

jogle

Mnemosyne wrote:

But what about the how the light looks. Like how ISO changes saturation at different levels. Would a smaller aperture have deeper blacks versus faster shutter speed?

Not really.

The different ISO's have different levels of noise because they are amplifying the signal that comes out of the sensor. you could argue that is is changing what the camera "sees"

opening the aperture while shortening the shutter keeps the same amount of light falling on the sensor so that doesn't change.

You will find at very small apertures and very large ones that you loose sharpness. you may also find that you get more lens flare or a little soft glow or loss of contrast when the aperture is wide open on a very fast lens (I get a soft glowy effect on my 85mm at f1.2 but it's gone by f1.8) Different lenses can vary between them, some are more contrasty, some are more saturated, some are crisp and razor sharp then some are very soft and dreamy.

If you already know about motion blur and depth of field and the light isn't visibly pulsing, strobing or shimmering, then you'll find the look the same. As they say in PJ circles, "f8 and be there" ie. it's more about looking for the shot then messing with your settings.

dstainer

There would be no difference in the light as it relates to ideal exposure. It’s just a matter of creative effect and artistic intent. Do you want shallow depth of field or deep; freeze action or blur? No matter what combination of aperture or shutter you choose to use to achieve an ideal exposure (all things being equal, there is only one ideal exposure value for any given scene, but many different exposure variations that can be used to achieve different creative effects). Exposure variation for creative effect is basically the concept behind most DSLR “Program” modes—wherein the aperture and shutter can be changes in unison based on available light.

Let’s take for example a picture of tree in a field. You can shoot the tree at f/2.8 with a shutter speed of 1/500s. In this example (irrespective of focal length, distance to subject, and subject distance to background), your depth of field will be shallow. The same photo at f/16 and 1/30s will yield the same exposure (as far as light is concerned), but your depth of field will be much greater. The light has not changed, and the exposure should be similar. But the creative effect has changed.

The only impact on image quality would be in regards to raising or lowering ISO, possible light diffraction issues that may be present when you close down the aperture too much, and other blur and/or noise issues associated with long shutter times (along with lens variations, as was suggested above).

Now if you consider the effect on lighting outside of exposure (especially as it relates to how light affects subject form, color, tone, texture, etc.), different settings will impact how a photo is perceived and interpreted. In my tree example above, if you are shooting the scene wide open and have achieved shallow depth of field (which is accompanied by creamy background out-of-focus bokeh), the light may appear more diffused, and the objects in your scene (behind the tree) may exhibit a subtler rendering of contrast, color, form and texture.

gvf

Now if you consider the effect on lighting outside of exposure (especially as it relates to how light affects subject form, color, tone, texture, etc.), different settings will impact how a photo is perceived and interpreted.

Right. Seems to me you don't see light; practically speaking you see objects, scenes, people illuminated. So, the effect of a photo may be different and will be of course if the radically shift DOF - or the blurrines/sharpness of moving elements even if the "amount" of light is the same.