long exposures

[Rickjs]

Not sure if this is the right forum, but here goes. I already have a little experience with ND filters for long exposure pictures. I have an app that tells me how long I can expose for depending on which filter or filters I use. If I want to go for a longer time can I just darken my exposure in my cameras exposure setting? If it means anything I have a Nikon D3200

 

[Ido]

If I want to go for a longer time can I just darken my exposure in my cameras exposure setting?

Do you mean the Exposure Compensation function? If so, no, that won't work.

As I hope you're aware, there are three variables that determine the exposure / brightness of your photo:

• aperture,
• shutter speed (exposure length/time),
• ISO.

These work in tight relation with each other—you change one, and you have to compensate the same amount with another to get the same exposure as before.

If you're in Aperture Priority, for example, you hard-set the aperture you want. Let's say you set it at f/16, and you also chose ISO 100 instead of Auto ISO. The camera picked a shutter speed automatically—1/100 sec. if shot in daylight.
Now let's say you screw a 3-stop ND filter on the lens. The camera compensated for it, and changed the shutter speed to 1/13.
If you use the Exposure Compensation function, it will change the shutter speed. If you go 1 stop darker, the shutter speed will go to 1/25, and the image will be darker. If you go a stop brighter, it will be 1/6—but the image will be overexposed (too bright).

If you use Manual mode, and hard-set all three variables, you shouldn't even have the option to tweak Exposure Compensation. The camera doesn't control anything automatically, so there's nothing there to override.

 

[Rickjs]

Thanks, yeah, I am aware of the aperture, speed and ISO variables and when I have done some long exposure I have gone into manual mode so I can use the setting the app gives me. I just never touched exposure composition and just thought about it the other day but haven't had a chance to see what it would do

 

[idcanyon]

If you use Manual mode, and hard-set all three variables, you shouldn't even have the option to tweak Exposure Compensation.

On most cameras you can still use EC, but all it does is change how your meter reads so that if you were to look at the meter to decide what exposure to dial in then you would get the compensated exposure. Like you are saying, its better to just dial in the exposure you want. In manual mode it should just be called "Exposure Confusion".

 

[dennybeall]

The ND filters will reduce the light coming into the camera. A chart of exposure based on time by filter number would have to be based on the light in the scene. Without that info the chart won't help much.
If the ambient light is too much once you've stopped the lens down as far as it will go then you can use the ND filter. If you add the ND filter to the exposure equation along with shutter, ISO and speed then you can adjust all to get the final result you want.

 

[Dikkie]

If I want to go for a longer time can I just darken my exposure in my cameras exposure setting?

If you set a longer shuttertime, your exposure will get more overexposed.
If you want to darken your exposure, you'll need to shorten your shuttertime.
Best to take 3 shots: a normal one, an underexposed and an overexposed one. Then you can see the results and choose the desired one that suits you.

OR, you can take one shot in RAW, and in your raw converter change the exposure less or more if the software allows you to.

 

[wfooshee]

The ND filter does not change the fact that closing the aperture, reducing the shutter speed, or lowering the ISO lessens the exposure.

Once you reach minimum aperture and minimum ISO, there's nothing you can do to decrease exposure further. If you want a longer exposure than you can get with your ND filter, you need a day with less light.

Or you could wade into the messy world of stacking another ND filter....... That only adds flat glass surfaces which may cause reflections, along with any other distortions caused by the filters if they are not optically and chromatically correct (i.e. cheap.)