shutter speeds effects on background

Hey wetpixelators,

So if I take a light reading and work it out to be 1/60th at f8 (for example) If I slowed down/increased my shutter speed but kept the light the same via widening/closing the aperature, what would the outcome be for my image?

Eg foreground, background etc

Excluding motion blur.

On that note, whats the slowest you can shoot under without motion blur? Macro vs wide

Cheers,

Cal

Hey wetpixelators,

 

So if I take a light reading and work it out to be 1/60th at f8 (for example) If I slowed down/increased my shutter speed but kept the light the same via widening/closing the aperature, what would the outcome be for my image?

 

Eg foreground, background etc

 

Excluding motion blur.

 

On that note, whats the slowest you can shoot under without motion blur? Macro vs wide

 

Cheers,

 

Cal

Hi Cal,

The most important thing about changing aperture is it will change the depth of focus in your picture. There are other things that change at very small apertures (high number) and very large apertures (low number) but those are not that important at this point for you. The smaller the aperture (higher number) the more of the picture behind and in front of your subject will be in focus, and visa versa. So by widening your aperture you will make your background more out of focus and blurry and by closing it you will tend to make it more sharp.

Cal,

I was recently playing with shutter speed to try to get a realistic blue-green background, I'll post links to the results below -

Shot 1

Black background with shutter speed at 1/125th sec

Shot 2

Nice blue-green background similar to actual conditions during the dive with shutter speed at 1/20th sec, aperture constant at f9.1.

As regards motion blur, I think the maximum amount is down to taste, I've seen some incredible shots of deep wrecks etc with blurred fish due to the extreme slow shutter speeds.

Hope this is of help,

TDD

(Just re-read the question and realise this is not quite the same thing as I am altering the total amount of light entering, D'Oh)

Hi Cal,

Jeff (loftus) pretty much nailed it with respect to simultaneously adjusting shutter speed and aperture for a given exposure, but you may also want to consider what adjusting each in isolation does to your exposure.

Lets say that you have a typical wide angle/close focus subject so the subject is very close to you and will be primarily exposed by your strobe while the distant background will be illuminated by ambient light. You also determine that the optimal exposure will be 1/60s at F8 with strobe power set at 1/2.

-if you change the shutter speed while leaving the aperture and strobe power the same you will change the background exposure while leaving the foreground untouched. So, if you change you aperture to 1/120s then your background will be 1stop underexposed but you foreground will be unchanged. This is because your foreground is primarily illuminated by your strobe. Since the strobe flash is so much faster (~1/1000s) than your shutter speed, the entire flash duration will be captured by the sensor regardless of what shutter speed you choose (within reason of course).

-if you change aperture while leaving strobe power and shutter speed constant, then you entire exposure will be affected. So, changing your aperture from F8 to F5.6 will result in both your foreground and background being overexposed by 1 stop. As mentioned by Jeff, you're depth of field will also be affected (reduced).

-if you change strobe power, but leave aperture and shutter speed unaltered, then you foreground expose will change, but your background exposer will be unaffected. Decreasing strobe power from 1/2 to 1/4 will result in a foreground that is underexposed by 1 stop, but your background will be unaltered.

There are many other things that will influence results, but this is a good starting point.

With respect to how slow of shutter speed you can use... that's pretty subjective. A general rule of thumb is 1/focal length (35mm equivalent) so if you using a 12mm lens on a DX sensor you should be able to get away with a shutter speed down to 1/18s. That is, if your careful and have steady hands (and good buoyancy). However, don't be afraid to try slower if the situation demands it. When shooting film in dark temperate waters, I was often forced to shoot at 1/8 or even 1/4 at F4 to F5.6 to get the exposure. There were lots of tossers, but a few worked out. For macro, shutter speed generally doesn't matter as your primary source of illumination is your strobes which will freeze the motion. But again, this depends on what you want your background to look like (inky black vs deep blue).

Cheers,

Mike

Wow.......

Those were some brilliant responses

Thanks guys, you completely answered my question

Cal

Wow.......

Those were some brilliant responses

 

Thanks guys, you completely answered my question

 

Cal

Cal,

You can also increase your ISO to get your shutter speed to a acceptable speed.

Roy