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Long exposure noise reduction

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momech View Drop Down
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Post Options Post Options   Quote momech Quote  Post ReplyReply Direct Link To This Post Topic: Long exposure noise reduction
    Posted: 10 September 2017 at 13:39
At what point do you turn this off or do you leave it on for everything. I've been experimenting with long exposures. Getting up into the five-and-a-half 6-minute range and the long wait for processing can be a problem as well as the battery drain.
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artuk View Drop Down
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Post Options Post Options   Quote artuk Quote  Post ReplyReply Direct Link To This Post Posted: 10 September 2017 at 13:47
One answer could be... with it turned on, when does the camera start to take black frame shots to reduce noise? That is the camera makers view of when it starts to be required.

As you may know, the problem is that when the sensor is active during long exposures, it heats up, which creates resistance, which leads to more noise (SNR goes down). Additionally, you may get hot pixels and so on. The black frame afterwards allow the sensor noise to be subtracted from the image, therefore removing it from the raw.

From my limited experience of "Long exposures" (I have rarely shot longer than 30 seconds for my work in cities etc), I would say if you are leaving the shutter open for 5-6 minutes, you need black frame noise subtraction.

The other option - turn it off, shoot, then see how the files look when you get home - or make a comparison on and off with the same scene, and decide yourself if you need it or not. Surely that's the best idea?
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Post Options Post Options   Quote sybersitizen Quote  Post ReplyReply Direct Link To This Post Posted: 10 September 2017 at 16:54
Originally posted by momech momech wrote:

At what point do you turn this off or do you leave it on for everything.

With me, it's always enabled ... meaning it happens with every shot that is one second or longer. I don't take many looong exposures, so I appreciate the convenience factor.

Getting up into the five-and-a-half 6-minute range and the long wait for processing can be a problem as well as the battery drain.

LENR is just an automated form of dark frame subtraction. Dark frame subtraction is very useful for the type of thing you're talking about, so the wait is worthwhile. You can do some testing with and without it and judge for yourself.

However ... if you take several looong exposures of the same duration in the same session, you don't have to wait for the camera to produce an individual dark frame for each individual shot. You can instead turn off LENR and shoot your own single dark frame of that same duration, then perform dark frame subtraction in PP, using that one dark frame for all the shots. That can save you time and battery consumption in the field.
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momech View Drop Down
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Post Options Post Options   Quote momech Quote  Post ReplyReply Direct Link To This Post Posted: 10 September 2017 at 17:05
You're right, it does need the noise reduction one way or the other.

I really like Roger Rex's long exposures with the silky smooth water and skies, trying to teach myself the technique using NDs of varying strength. I'm making progress but still only at the stage of guestimating exposure times, and having those long waits tends to break my concentration.

Best thing I can come up with is break out my old A900 and alternate shots with the A99 II. That should cut the down time in half.

Thanks for the response     



Ooops, Syber posted while I was composing my own response.

Thanks, that should really help.
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Post Options Post Options   Quote mikey2000 Quote  Post ReplyReply Direct Link To This Post Posted: 10 September 2017 at 21:37
I don't do much long exposure conventional photography as I'm always seemingly on-the-run and my tripod almost never leave the house.


However, I do the occasional astro shoot where having to shoot a dark frame for each shot would be unimaginably inconvenient, so Long Exposure NR is definitely turned off for me.    For astro, I shoot dark frames separately. This maxises the exposure time I can get under the stars.

For conventional photography, I'd no doubt do the same and use one of the Dark Frame NR techniques out the on the interweb.   Of course, you need some some sort of PP software to achieve this but I imagine GIMP can easily do this kind of thing.

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Post Options Post Options   Quote aarif Quote  Post ReplyReply Direct Link To This Post Posted: 10 September 2017 at 21:52
always off
 



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Post Options Post Options   Quote wetapunga Quote  Post ReplyReply Direct Link To This Post Posted: 10 September 2017 at 23:22
Originally posted by aarif aarif wrote:

always off


Likewise. It cuts too much into composition times in the field. I prefer to do NR later on the PC.
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Post Options Post Options   Quote Miranda F Quote  Post ReplyReply Direct Link To This Post Posted: 11 September 2017 at 12:57
Usually on in daylight (ND10) or dusk, but I do turn it off for star fields - I figure a few more 'stars' aren't an issue.
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Post Options Post Options   Quote Mark Twain Quote  Post ReplyReply Direct Link To This Post Posted: 11 September 2017 at 17:03
Usually I leave it on for convenience. But when doing multiple long exposures (for example when photographing stars/milky way) I turn it off because the waiting times are not only boring and battery consuming but also pose a problem in terms of composition and framing because sometimes I use a startracker and make a separate picture for the foreground and the night sky.

Interestingly I can never remove all hot pixels with a dark frame that I produce manually - must do something wrong all the time...
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