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Old Aug 8, 2007, 1:03 PM   #11
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Contriver wrote:
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So, to get to my question, I would just like to confirm this. Is it true that a point and shoot can capture this shot without filters while a dSLR requires a filter to block out some of the light?
No. It's not true. For a given lighting, ISO speed, f/stop and shutter speed, the exposure (how bright the image is) should be the same.

Even though most P&S models have lower available ISO speeds, you don't have apertures as small as you do on most DSLR lenses. So, if you can't get the shutter speeds as slow as desired with a DSLR shooting at ISO 200, you're not going to be able to accomplish it with a non-DSLR model shooting at ISO 50 either (since most have a smallest available aperture of around f/8 to f/11, and most lenses for DSLR models have a smallest available aperture of f/22 or smaller, which is greater than the 2 stop difference you typically see in the lowest available ISO speed).

Exposure is exposure is exposure, and the same concepts apply to film and digital (DSLR or not).

There is no difference there a non-DSLR and DSLR model (or film for that mattter) for the aperture, ISO speed and shutter speed needed to expose an image in the same lighting, as long as the manufacturer didn't "fudge" the ISO speed rating too much (some models may be a bit more or less sensitive than set to, but they should all be within about one stop). A number of combinations will give you identical exposure. See this handy online Exposure Calculator to get a better idea of the relationship between lighting, ISO speed, Aperture and Shutter speed. Note that film speed in the calculator is the same thing as ISO speed.

http://www.robert-barrett.com/photo/...alculator.html

If you try to use a shutter speed that's too slow for the lighting, aperture, and ISO speed, you'll get overexposed (too bright) images. If you try to use a shutter speed that's too fast for the lighting, aperture and ISO speed, you'll get underexposed (too dark) images.

If your shutter speeds are still faster than desired for a properly exposed image after setting your ISO speed to it's lowest value and your aperture to it's smallest opening (higher f/stop numbers), use a Neutral Density Filter or take the photos when there is not as much light. If you're real close to the desired speed after stopping the aperture down, you may also want to see if you can get by with a Polarizer (which will block around 2 stops if rotated just right, and also help with the reflections on the water).

Also note that most lenses are not as sharp at their aperture extremes (most lenses for 35mm or DSLR type cameras are sharpest about 2 stops down from wide open).

So, it's best to avoid using the largest or smallest available apertures if there is another approach.

If you really want very smooth water, you'll want to use a Neutral Density Filter with a Tripod, with shutter speeds around 1/4 to 1/8 second for the desired effect. In bright light at ISO 200, even with a lens stopped all the way down to it's smallest available aperture (higher f/stop numbers), your shutter speeds may still need to be faster than that for proper exposure.

It all depends on how much the water is moving and the effect you want (very smooth, just a bit blurred, etc.) and how bright the lighting is. If you get can there very early in morning before the sun comes up all the way, that would allow you to get a bit slower shutter speeds for any given aperture and ISO speed.

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Old Aug 8, 2007, 1:32 PM   #12
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Yes, I am using the 18-55 kit lens. Thats an interesting idea. However, from what I've learned (and what Jim mentioned as well) it appears that when you make theaperture smaller, the quality of the image decreases. In any case I do appreciate the idea


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What lens are you using? The 18-55 kit lens can go down to f/22 at 18mm, and f/40 at 55mm.
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Old Aug 8, 2007, 1:32 PM   #13
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JimC wrote:
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Exposure is what controls the brightess, try lowering your exposure...
That's what you're doing when you change the ISO, Shutter Speed and Aperture. ;-)

The only way to make an exposure darker or brighter is to change one of those values if the lighting is the same. There is no magic feature that you use that isn't changing one of those parameters. If you're referring to Exposure Compensation, all it's doing is varying the aperture or shutter speed so that the image is exposed brighter or darker than the camera's metering would normally expose it. That does not get around the camera's limitations for the smallest aperture and lowest ISO speed you can use.
IC your point, but as an example, i was takening soem night time shots, and had to use 30' shutter, and an aperture of atleast F18 but i used 22, and ISO 200. It was still pulling it a little bright, so i adjusted my exposure to not take so much light and it worked...so if my settings were at the max already, how did making the exposure change help?



BTW i had it in manual mode.
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Old Aug 8, 2007, 1:37 PM   #14
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Jim, thanks alot for the comprehensive response. I have gottenshots at the same place using my point and shoot where I was able to get the "flowing" effect. But, it must have been thatthere was lessnatural light that day. It looks like what I want to do now is buy some filters



JimC wrote:
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Contriver wrote:
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So, to get to my question, I would just like to confirm this. Is it true that a point and shoot can capture this shot without filters while a dSLR requires a filter to block out some of the light?
No. It's not true. For a given lighting, ISO speed, f/stop and shutter speed, the exposure (how bright the image is) should be the same.

Even though most P&S models have lower available ISO speeds, you don't have ...(truncated)
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Old Aug 8, 2007, 1:43 PM   #15
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It's all subjective.

With most lenses for 35mm or APS-C formats, you start getting gradually softer images if viewed with close scrutiny, once you get more than about 3 stops or 4 stops down from wide open, and with most, you want to avoid aperture extremes (where most lenses are softest, although it's all a matter of what you perceive to be sharp).

The "sweet spot" is usually around 2, or sometimes 3 stops down from wide open with most lenses. So, around f/8 to f/11, depending on how much you're zoomed in, is probably about where your kit lens is sharpest. But, from most accounts, the Pentax lens is much better than average for this type of lens. So, you may be able to get away with much more.

IOW, as a general rule of thumb, don't shoot at f/22 if f/8 gives you the needed Depth of Field, shutter speed considerations aside, if you want the sharpest possible photos. ;-)

But, depending on your perception of quality, the viewing/print sizes needed, the DOF needed for the photo, the characteristics of a specific lens and more, you may be just fine using much smaller apertures. Try it and see what you think

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Old Aug 8, 2007, 2:19 PM   #16
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GigaS27 wrote:
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BTW i had it in manual mode.
Quit beating your head against the wall. Use the exposure meter in your camera.

Set the ISO to 200, use the Shutter Priority mode, set the shutter speed to 1/15, and see what the camera's exposure meter does with the aperture.
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Old Aug 8, 2007, 4:47 PM   #17
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GigaS27 wrote:
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IC your point, but as an example, i was takening soem night time shots, and had to use 30' shutter, and an aperture of atleast F18 but i used 22, and ISO 200. It was still pulling it a little bright, so i adjusted my exposure to not take so much light and it worked...so if my settings were at the max already, how did making the exposure change help?

BTW i had it in manual mode.
There is no Exposure Compensation in Manual Mode. It doens't work that way.

What do you mean by "adjusted my exposure". The only way to do that is by varying lighting, shutter speed, aperture or ISO speed. That's it. If you want to use Exposure Compensation, you have to use a non-Manual mode.

If you're shooting in Manual Exposure mode, there is no Exposure Compensation (because your aperture and shutter speed settings take the place of it since you're controlling both of these variables, although most cameras have a meter that shows you how your settings are impacting exposure).

Exposure Compensation lets you alter the way a camera's autoexposure/metering algorithms expose an image (brighten or darken it compared to the way the camera metered the scene). It's one of my most frequently used settings on most cameras.

A +EV value gives you a brighter exposure. The camera uses a slower shutter speed and/or larger aperture (smaller f/stop number) to get a brighter exposure, compared to what the camera's autoexposure/metering algorithms would have selected.

A -EV value gives you a darker exposure. The camera uses a faster shutter speed and/or smaller aperture (higher f/stop number) to get a darker exposure, compared to what the camera's autoexposure/metering algorithms would have selected.

If you're in Av Mode (Aperture Value, a.k.a., Aperture Priority) and use Exposure Compensation, the camera will vary the shutter speed (since you're setting the aperture). If you're using Tv (Time Value, a.k.a., Shutter Priority) mode and use Exposure Compensation, the camera will vary the Aperture (since you're controlling the shutter speed).

If you're in Auto (or other similar modes), the camera may vary aperture or shutter speed when you use Exposure Compensation. In low light, since your aperture is already wide open, it varies shutter speed if you use a -EV setting.

If you're shooting in Manual Exposure mode, there is no Exposure Compensation (because your aperture and shutter speed settings take the place of it since you're controlling both).

Correct Exposure comes down to the amount of light, the ISO speed, the shutter speed, and the aperture. A variety of combinations will produce identical exposure.

You use Exposure Compensation if you want a brighter or darker image compared to what the camera's metering would normally give you in the same conditions.

An example of when you may want to use a +EV setting is for a backlit subject, where the subject would normally be much darker than the rest of the image. Since the camera has a limited dynamic range, it doesn't know that you want the dark subject exposed properly (at the expense of the rest of the image). So, you can make the darker subject brighter for correct exposure (which might cause the rest of the scene to be overexposed some).

If your subject is much brighter than the rest of the image, you may want to use a -EV setting for Exposure Compensation so that your subject is not overexposed (making the rest of the image darker, too).

The camera has a limited range of bright to dark that it can capture. So, it makes choices so that most of the iimage is correctly exposed, depending on your metering mode. Sometimes that may not be what you want. That's where exposure compensation comes in.

If you reach the camera's ISO speed limits and your shutter speeds are still slower than desired, you can also use exposure compensation to get faster shutter speeds by deliberately underexposing using a -EV Setting. Then, brighten the images later using software so that they appear to be correctly exposed.

But, this will increase noise levels, just as if the camera had an even higher ISO speed available (especially after you brighten the underexposed images with software), and deliberately underexposing and brightening images later also results in some loss of dynamic range. So, don't use this technique unless you have to.

Exposure Compensation is not some kind of magic setting that can get around the basics of proper exposure within the limitations of your camera and lens. It's only varying aperture and/or shutter speed to give you a brighter or darker exposure than the camera's metering would have normally selected.
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Old Aug 9, 2007, 10:24 AM   #18
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JimC, i have to apologize. Your expertise is correct. I'm sorry for the miss confusion, but i'm sorta new, and my camera has an auto ISO mode (Nikon D40) so that it adjust the ISO setting correctly or automaticly. Also after grabbing my camera and messing with the settings, the exposure is disabled in M mode like you stated. Now that i think about, i must have been in 2 different modes because i did use the exposure mode when i was practicing night shots and it did effect the brightness which it could have messed with the aperture or shutter.



So my apologies for the confusion.
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Old Aug 9, 2007, 11:00 AM   #19
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No need to apologise. I'm glad you brought it up, since that is something that confuses many users (how Exposure Compensation works).

You keep using the term Exposure versus Exposure Compensation (which is what you seem to be referring to).

In manual mode, you're controlling the Exposure with your settings for aperture and shutter speed (and your meter will show you if the camera thinks they will result in under or overexposure, much in the same way it will show you if your Exposure Compensation settings in non-manual modes will expose brighter or darker).

Although we have a lot of automation with newer camera models (both film and digital), the concepts of exposure still work the same way as they do with old manual only cameras.

You still have only 4 main variables to take into consideration for exposure (and I use the term "main" since there are a lot of nuances to how you measure the light, as well as different film characteristics if shooting film, and camera settings if shooting digital for the desired tone/contrast curve within an image and more). Once you have a better idea of how these 4 variables work together to give you a properly exposed image, the other fancy features will make more sense.

1. Light (typically measured as EV for Exposure Value in Photography).

2. Aperture (which works similar to the pupils in your eyes, where you can open up the aperture iris wider to let in more light, or close it down to let in less light). If you let in more light with a wider aperture, you can expose the film or sensor faster. If you let in less light with a smaller opening, it takes longer to expose the film or sensor. Note that aperture is normally expressed as f/stop, which is a ratio between the focal length of the lens and the diameter of the aperture iris. So, smaller values represent a larger iris diameter.

3. ISO speed. This is how sensitive the film or sensor is to light and is the same thing as the older ASA rating for film. The higher the ISO speed, the faster you can expose it.

4. Shutter Speed (this is how long the camera's shutter stays open to expose the film or sensor).

IOW, it all boils down to how senstive the film or sensor is to light (which you control via the film you use with film, or the ISO speed settings you use with digital), and how much light you need to let it see to "expose" the iimage (which you control via the aperture opening size and shutter speed).

So, you've got lots of fancy features on newer cameras to automate what settings it uses, and let you vary it's behavior to expose an image darker or brighter than the camera's metering would normally expose it. But, it really boils down to the camera changing the same things you had to worry about with a strictly manual camera without a fancy metering system, Automatic Exposure modes, etc.

So, Exposure Compensation is just another tool you have to work with, allowing you to expose an image brighter or darker than the camera's metering would normally expose it when using non-manual modes, and it varies shutter speed and/or aperture to accomplish that. With manual exposure, you're controlling those variables (and your viewfinder scale for the metering will let you know if your setttings are exposing brighter or darker than the camera's metering thinks is needed).


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Old Aug 9, 2007, 12:04 PM   #20
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Yeah, I didn't know what exposure compensation did either, I thought it was basically like a brightness adjustment so I never used it. And, I too never realized that it wasn't available in manual modes and now I know why

Thanks Giga and Jim!
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