Long Exposure - How Long

[taxboy]

I've been trawling around the internet and come across some photographers using exposures running into 16 or 20 minutes - primarily for seascapes. This obviously has logistical issues regarding the amount of images you can take on a shoot.
My question for those experienced with LE is at what point does the law of diminishing returns start to kick in and the extra exposure time not render anything more within the image.

 

[TimHughes]

In my experience it all depends what you're trying to achieve, how much movement is going on in the scene and what you want to smooth out and what you want to keep sharp. For typical scenes e.g. waterfalls and suchlike, I find not much benefit beyond 120s for smoothing. That said, for example star trails, it could be all night (most likely combining a series of pics) on one end of the spectrum through to something like capturing snow being kicked up by horses racing on it could be still be a fraction of a second at the other end.

 

[taxboy]

In my experience it all depends what you're trying to achieve, how much movement is going on in the scene and what you want to smooth out and what you want to keep sharp. For typical scenes e.g. waterfalls and suchlike, I find not much benefit beyond 120s for smoothing. That said, for example star trails, it could be all night (most likely combining a series of pics) on one end of the spectrum through to something like capturing snow being kicked up by horses racing on it could be still be a fraction of a second at the other end.

Thanks for the reply. Apologies I didn't be more specific in my OP. I'm seeing seascape / landscape cloud shots running in the 16-20 min range and wondered if these were gaining anything over say a 2/3 minute exposure

 

[AndrewFlannigan]

I take it that you're allowing for reciprocity failure: https://shootitwithfilm.com/understanding-reciprocity-failure/

 

[sk66]

I take it that you're allowing for reciprocity failure: https://shootitwithfilm.com/understanding-reciprocity-failure/

Doesn't apply to digital exposures; probably not applicable since this isn't the "talk film" section...

 

[sk66]

Thanks for the reply. Apologies I didn't be more specific in my OP. I'm seeing seascape / landscape cloud shots running in the 16-20 min range and wondered if these were gaining anything over say a 2/3 minute exposure

Consider a calm evening with puffy clouds barely drifting across the sky... a longer exposure could be beneficial. But a stormy evening with stronger winds and faster moving clouds wouldn't benefit from the same.
That said, I find it hard to believe that 20 minutes would be required in most cases. And exposures that long tend to cause sensors to generate heat noise.

 

[AndrewFlannigan]

Doesn't apply to digital exposures; probably not applicable since this isn't the "talk film" section...

My mistake. I assumed it was a film question.

 

[TimHughes]

Thanks for the reply. Apologies I didn't be more specific in my OP. I'm seeing seascape / landscape cloud shots running in the 16-20 min range and wondered if these were gaining anything over say a 2/3 minute exposure

Thanks for the clarification, I'm struggling to think of circumstances where it would be worth 16-20 minutes vs 2-3 minutes for seascape / landscape with clouds.

 

[sk66]

My mistake. I assumed it was a film question.

I can see why... reciprocity failure could explain long exposures; especially larger formats at smaller apertures. (but 20 min? IDK).

 

[Nod]

I suppose extremely long exposures might render pedestrians invisible in cityscapes but I would thing that on coastal type shots a minute would be more than enough to get creamy waterlines and long streaky clouds.

 

[LeeRatters]

I shoot 20-70 minutes exposures at night on film.... Reciprocity actually helps out there!

Anyway, I think going up to 20 minutes digitally for land and seascapes isn't usually necessary. A minute or two for water can generally be enough and sometimes the same for the sky depending on wind speed.

 

[AndrewFlannigan]

I can see why... reciprocity failure could explain long exposures; especially larger formats at smaller apertures. (but 20 min? IDK).

There was a bloke I knew, many years ago, who did industrial stuff on 5x4. I think some of his available light stuff on Pan F could get that long, which is probably what put it into my head.

 

[Winslowe]

Thanks for the reply. Apologies I didn't be more specific in my OP. I'm seeing seascape / landscape cloud shots running in the 16-20 min range and wondered if these were gaining anything over say a 2/3 minute exposure

I don't know the answer, but if I did want to know I would take some 16-20 minute exposures and some 2-3 minute exposures, and compare them.
Edit: I think it's obvious that direct comparisons would be nigh on to impossible - way too many variables where weather is concerned. And of course there is bound to be differences in how various cameras deal with long exposure noise control.