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  #1  
Old May 26th, 2012, 02:53 AM
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Timelapse Photography and Exposure

I've been playing around with Timelapse Photography for a while now. I have a controller that will shoot at predetermined intervals over a period of time. The longest so far being about 12hrs.

Most of the shots taken during the daylight hours are exposed OK but when darkness begins to set results are not so good.

I've tried using Evaluative Exposure and this has a tendency to lighten the dark images - i.e it tries to bring each shot to the mythical 18% grayscale level.

I tried last night setting the exposure manually at the begining of the sequence but then the later shots look too dark.

You'll see the dilemma here

Image 3835 is the first of the sequence and 3858 is about 22minutes later. These were with the camera set on a fixed manual exposure, being that of the first image.

Image 3859 is when I switched back to Auto Exposure.

Any comments on Exposure control, given that I don't want to sit behind the camera all the time.

Thxs
Colin
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Old May 26th, 2012, 04:12 AM
Michel B Michel B is offline
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Colin,
I don't think there is an automatic process to compensate for the general luminosity rendering. Just like converting to black and white, optimizing a dark 'low key' image is an artistic process to recreate the visual impression.

So, the technical problem is to get the most information from your sensor not to lose any meaningful detail. And that is what you are already getting when shooting raw with the evaluative exposure.

I have followed the long and heated discussions by various gurus at Dpreview about the 'isoless' camera.
The scientific data converge to prove that especially on recent captors, you get no advantage by 'upping' the ISO in camera compared with compensating in the raw convertor.

Since you have to manually correct and compensate, I would rather try to find various custom 'presets' to correct for the low light shots to get the correction rapidly.
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Old May 26th, 2012, 01:38 PM
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Thanks for the reply, Michel.

I always shoot RAW so that helps considerably. Also the best results I've had so far are using Evaluative Metering and then compensating in LR. This isn't a great deal of work since LR is very affective at batch processing lots of images that need the same adjustments.

Colin
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Old May 30th, 2012, 04:17 PM
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Hi Colin, does your controller allow you to take more than one picture once every hour? If so you could set the camera to bracket the exposure. Although you'll end up with some wasted, over exposed shots earlier on, you would get some better exposed images as well as the under exposed ones as the light falls.

Nice pics by the way!

Ivor
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Old May 31st, 2012, 03:11 AM
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Thanks Ivor....

Yes the controller is very flexible and does allow for bracketing. I have considered this and may give it a try next time.

I'll let you know how it goes.

Colin
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Old June 1st, 2012, 11:42 AM
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I've had second thoughts on bracketing. It means that I only get 1/3rd of the images to work with. Of course I could buy larger memory cards or even work in tethered mode but I think post processing in LR may be the solution initially.

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Colin
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Old June 1st, 2012, 01:33 PM
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This is not something I have tried, but may well do in the near future so am interested in your experiments.

Do you come a point when under exposing will decrease the signal to noise ratio so much that recovering the shadows will be too noisy?

Would this work:

work out the perfect exposure for the current lighting conditions in manual mode,
change to aperture priority,
apply exposure compensation for the picture to achieve the correct shutter speed that you chose in manual,
start your shooting sequence and allow the camera to change the shutter speed as light drops so maintaining a correct exposure.

Thinking about that, I suppose that as the light drops you will get longer exposures and moving water will appear more milky and moving objects will blur or disappear from the shot. If that was an issue then I might apply an ND filter so all shots had long exposures.

Or buy a HUGE flash!

Ivor

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Old June 1st, 2012, 02:29 PM
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Quote:
Originally Posted by Ivor View Post
This is not something I have tried, but may well do in the near future so am interested in your experiments.

Do you come a point when under exposing will decrease the signal to noise ratio so much that recovering the shadows will be too noisy?

Would this work:

work out the perfect exposure for the current lighting conditions in manual mode,
change to aperture priority,
apply exposure compensation for the picture to achieve the correct shutter speed that you chose in manual,
start your shooting sequence and allow the camera to change the shutter speed as light drops so maintaining a correct exposure.

Thinking about that, I suppose that as the light drops you will get longer exposures and moving water will appear more milky and moving objects will blur or disappear from the shot. If that was an issue then I might apply an ND filter so all shots had long exposures.

Or buy a HUGE flash!

Ivor

Ivor
Ivor,

Have a look at this thread from Dpreview
http://forums.dpreview.com/forums/re...ssage=38911351

You may be surprised...
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Old June 2nd, 2012, 10:26 AM
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Quote:
Originally Posted by Michel B View Post
Ivor,

Have a look at this thread from Dpreview
http://forums.dpreview.com/forums/re...ssage=38911351

You may be surprised...
I've read it three times and ooh, my brain hurts.



I'm trying to work out how to reconcile that discussion with this article about exposing to the right. If Colin allows his camera to under expose as light drops, wont the detail in the dark areas be lost amongst the increase in noise? And therefore, isn't it better to get the correct exposure.



Ivor
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Old June 2nd, 2012, 11:31 AM
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Quote:
Originally Posted by Ivor View Post
I've read it three times and ooh, my brain hurts.

Ivor
Yes, sorry, that was to be expected...
Just to place this discussion in context, it may be important to note that at least 4 of the forum users there are really experts in processors, digital circuitry and signal/noise theory : lfinger, Johnsheehy, ejmartin, Bobn. They are all also knowledgeable photographers and don't rely only on theory, but have made extensive tests on many cameras.
Historically, this discussion including not only the proponents of this 'isoless' camera but also clear opponents took place after the first heated rounds about the theory had cooled down. So, you'll find side links to a number of other articles or discussion.

I quote :
"Steen Bay wrote:
Just noticed a new and quite interesting article (linked below) by Michael Reichmann. It's somehow related to this discussion, except that he seems more concerned with optimizing the exposure at base ISO (ETTR) and pulling it back afterwards, than he is with pushing an 'underexposed' base ISO image.
The ideas are not contradictory. Different situations require different priorities, and what one can gamble is different (if anything needs to be at all). I really don't know why people think that approaches discussed are universal.
For a landscape photographer, there is usually no point in doing anything other than ETTR at base ISO. They don't need to freeze motion. I just glanced through the article, but it seems to suggest that there should be an ETTR exposure mode, which is something I have felt for a long time.
I would replace the EC functionality in that mode with a logarithmic "highlight escape" control. IOW, the camera would meter with the sensor itself, and a user setting would determine what percentage of pixels are allowed to clip."

After some time, the former opponents seemed to admit that the theory has not only good grounds, but it can be proven by experimentation.
For those opponents to be able to exchange ideas usefully, a few themes had to be cleared first:
- Noise : The theorists have no doubt about it (or about the two flavours of noise). It's a scientific and measurable fact. The pure photographers have another view.
- Sensors : the ability of sensors and digital circuitry to provide this 'isoless' feature may be very different. I happen to have a Canon 20D which is in the worst category, whereas Sony sensors are leading in the field!
- Raw converters. Before the above thread, this was not clear. And it appears that the Adobe converter does not behave well to support the 'isoless' camera.
- This discussion took place after very creative ideas about how to implement such an 'isoless' camera.

Quote:
Originally Posted by Ivor View Post
I'm trying to work out how to reconcile that discussion with this article about exposing to the right. If Colin allows his camera to under expose as light drops, wont the detail in the dark areas be lost amongst the increase in noise? And therefore, isn't it better to get the correct exposure.
Ivor
My personal ideas after testing both approaches is that to a certain extent I can compensate for underexposure without visible degradation. I am also convinced that recent cameras are much better in this respect (dynamic range) due to the comparative tests and resulting competition. Just like I would not change ACR for Raw Therapee, I believe you should stay with what works for you now.
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