Long Exposures

[David995031]

It seems the accepted approach for long exposures is to control the light by using  a ND filter. Fine but my question is would I get the same result by adjusting the exposure compensation or would I be missing something?

[Black Pearl]

If you dial in exposure comp you change the exposure so it will be either over or under exposed. 

To increase the exposure time for a particular scene while still maintaining the correct exposure you need to lower your ISO, use a smaller aperture, shoot in lower light and/or use a ND filter to restrict the amount of light hitting your sensor. 

[David995031]

12 hours ago, Black Pearl said:

If you dial in exposure comp you change the exposure so it will be either over or under exposed. 

To increase the exposure time for a particular scene while still maintaining the correct exposure you need to lower your ISO, use a smaller aperture, shoot in lower light and/or use a ND filter to restrict the amount of light hitting your sensor. 

Thanks

[roicead]

generally you use an nd filter when you need to compensate beyond the exposure capabilities of your camera or if you need a particular setting.  nowadays they're used for scenarios like photographing waterfalls and getting movement in the water while shooting in daylight.  shooting exposure times of several seconds or more with a stopped down aperture and lowest iso will still result in an overexposed image.

[Black Pearl]

50 minutes ago, roicead said:

generally you use an nd filter when you need to compensate beyond the exposure capabilities of your camera or if you need a particular setting.  nowadays they're used for scenarios like photographing waterfalls and getting movement in the water while shooting in daylight.  shooting exposure times of several seconds or more with a stopped down aperture and lowest iso will still result in an overexposed image.

That should read - might result in an over exposed image if you don't pay attention to your meter. 

If the light levels are low enough then you could quite easily achieve a long exposure and correct exposure using a small aperture and low ISO.

[roicead]

24 minutes ago, Black Pearl said:

That should read - might result in an over exposed image if you don't pay attention to your meter. 

If the light levels are low enough then you could quite easily achieve a long exposure and correct exposure using a small aperture and low ISO.

correct.  but i'm not really lucky when it comes to getting to a waterfall and having a cloudy day on the same day.  i've always had to break out the nd filter with waterfalls..  but you're right, the meter rules.

[David995031]

On 3/17/2017 at 21:20, Black Pearl said:

If you dial in exposure comp you change the exposure so it will be either over or under exposed. 

To increase the exposure time for a particular scene while still maintaining the correct exposure you need to lower your ISO, use a smaller aperture, shoot in low and/or use a ND filter to restrict the amount of light hitting your sensor. 

Thanks

[David995031]

Thanks BP & Roicead - really helpful.

[ChrisLumix]

On 18 March 2017 at 11:41, roicead said:

generally you use an nd filter when you need to compensate beyond the exposure capabilities of your camera or if you need a particular setting.  nowadays they're used for scenarios like photographing waterfalls and getting movement in the water while shooting in daylight.  shooting exposure times of several seconds or more with a stopped down aperture and lowest iso will still result in an overexposed image.

Movement in water needs a shutter speed somewhere between ⅛ and 1/30 second. 'Whited out' water shows no movement whatever, just a solid white curtain.

[roicead]

11 hours ago, ChrisLumix said:

Movement in water needs a shutter speed somewhere between ⅛ and 1/30 second. 'Whited out' water shows no movement whatever, just a solid white curtain.

i prefer the smoother look of flowing water.  most of my waterfall shots are over 1 second, up to 30 seconds.  avg. for me seems to be about 5 seconds.

[ChrisLumix]

8 hours ago, roicead said:

i prefer the smoother look of flowing water.  most of my waterfall shots are over 1 second, up to 30 seconds.  avg. for me seems to be about 5 seconds.

That was my point - it stops "flowing" when you use a long exposure and just becomes a solid white lump. Waterfalls are where the water is already moving really fast, and I reckon 1/15 second would get some great motion, perhaps ⅛, but no slower. That's my opinion and experience anyway, based on photo mag tutorials in the 70s and 80s. As you may have realised I feel quite strongly on this subject! There's room for all views I feel, but when the vast majority follow what looks to me like a modern trend, and few adhere to the time-honoured principle, that's when I get up on my soapbox...

This was taken at 1/20 second and shows what I think is good motion, but I accept I could have gone slower - say 1/10 second - and it would still be 'moving water', i.e. motion blur.

[roicead]

you've got a very nice photo.  thanks for sharing.  

here's one of mine at 30 seconds.  i definitely wouldn't shoot a large solid waterfall like bridalveil falls in yosemite national park like this, but for broken up waterfalls i think the effect is nice.  this waterfall is about 30' high

[ChrisLumix]

That's nice ... but I bet you'd have got the same effect at about ½ second?

[Black Pearl]

1 hour ago, ChrisLumix said:

That's nice ... but I bet you'd have got the same effect at about ½ second?

That simply isn't accurate.

At 1/2 sec you will get some blur but you would still retain a fair amount of detail, lots of structure to the water surface meaning you wouldn't get anywhere near the same smoothing affect. 

[Black Pearl]

A 1/2 second exposure time of a similar scene - the difference is immediately obvious....

[ChrisLumix]

I still see largely white water there BP. We'll have to agree to differ on this.

[roicead]

a lot of it also depends on the flow of the water.  yes, you might get a fair amount of blur with 1/2 sec on a large waterfall that's reached maximum velocity with the help of gravity.  on a slow trickling creek you might need 5 minutes.  on a raindrop sliding down your car after the rain has ended you might lose to evaporation.  this was a slow trickle during a drought, the water on the rocks in the foreground is usually about a foot deep, it was just a few inches when i was there..

 

chris, i think you're seeing a large amount of white because you're looking at such a small area.  look at these photos close up and you'll see details, ebbs and flows around where rocks jut out, pathways taken by the water or trails where leaves or other debris passed through.  that's the one place where digital fails, if everyone's looking at a 900px size photo on a computer screen they only see the big picture and don't see the smaller details like you'd see on a 16x20" print.

[ChrisLumix]

16 hours ago, roicead said:

a lot of it also depends on the flow of the water.  yes, you might get a fair amount of blur with 1/2 sec on a large waterfall that's reached maximum velocity with the help of gravity.  on a slow trickling creek you might need 5 minutes.  on a raindrop sliding down your car after the rain has ended you might lose to evaporation.  this was a slow trickle during a drought, the water on the rocks in the foreground is usually about a foot deep, it was just a few inches when i was there..

 

chris, i think you're seeing a large amount of white because you're looking at such a small area.  look at these photos close up and you'll see details, ebbs and flows around where rocks jut out, pathways taken by the water or trails where leaves or other debris passed through.  that's the one place where digital fails, if everyone's looking at a 900px size photo on a computer screen they only see the big picture and don't see the smaller details like you'd see on a 16x20" print.

I think it's also because BP's picture was of a much slower moving river, where water bubbles over rocks like mini-weirs, whereas your picture was of a full size near vertical waterfall where the water is accelerating at 32 feet per second squared, i.e. much faster, and moving predominantly downwards rather than forward with the current. For that, you could get great motion blur at a faster shutter speed simply because the water is moving so much faster.

[Black Pearl]

You couldn't achieve that blur with a 1/2 second exposure, not even close to it, regardless of the water flow as you will still pick up structures within the flow that longer speeds blur away. 

[riddell]

ND filters only come into play when there is too much light. i.e. you are already on minimum ISO, say 100 or 50 and you'd need particular settings, such as perhaps you want to capture moving water with some movement blur and you want a narrow depth of field. You might need f3.2 and 1/50 of a second to achieve that.

Of course normally to capture the right exposure you'd simply narrow your aperture and shorten your shutter speed, or of course one or the other. I'm using a little bit of a extreme example here, or maybe a more niche example, but one which is still very valid.

The problem is that that because you want the movement blur and because you want the narrow depth of field, adjusting either the aperture or shutter speed is going to lose that effect. And that's where a ND filter comes into play, allowing you to keep those settings whilst cutting down on the amount of light.

Of course you can use flags to cut down on the amount of light, but its not really the same. If we assume that in this example we are shooting a stream outside then not only would this mean carrying a huge flag as opposed to a tiny little filter, but also that the flag is going to actually block the light meaning you'll probably lose all that lovely play of light bouncing on and refracting through the water.

Paul

Edited August 8, 2017 by Phil
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