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Timelapse with variable shutter speed

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Offline avatorl

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Re: Timelapse with variable shutter speed
« Reply #40 on: 02 / May / 2008, 09:27:54 »
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Quote from: fbonomi on 02 / May / 2008, 09:15:06
Hi avatorl,

thanks for sharing! Where is it?


It is the view through mine apartment windows in Kyiv, Ukraine.
Not so fine to make beautiful video, but enough to test the script :)
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Offline vine

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Re: Timelapse with variable shutter speed
« Reply #41 on: 02 / May / 2008, 09:36:05 »
Quote from: avatorl on 02 / May / 2008, 09:27:54
It is the view through mine apartment windows in Kyiv, Ukraine.
Not so fine to make beautiful video, but enough to test the script :)
Man you gotta take a video of the mother motherland monument then!
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Offline avatorl

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Re: Timelapse with variable shutter speed
« Reply #42 on: 02 / May / 2008, 09:52:34 »
Quote from: vine on 02 / May / 2008, 09:36:05
Man you gotta take a video of the mother motherland monument then!

:) This is the view (at 12x zoom) from my previous apartment

I really hope to take a video of sunset|sunrise|clouds movement in Carpathian Mountains soon.
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Offline vine

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Re: Timelapse with variable shutter speed
« Reply #43 on: 02 / May / 2008, 10:51:08 »
Quote from: fbonomi on 30 / April / 2008, 06:24:24
@param b Limit Tv
@default b -414
rem (-414=20 sec; -384=15 sec; -320=10 sec; -224=5 sec.)

@param d Limit Sv
@default d 776
rem (776=1250 ISO; 960=5000)

I have trouble finding the mathematical formula underlying the sv96 and tv96 values.
(ISO => sv96 and seconds => tv96)
Could someone enlighten me, so I can put them in a spreadsheet on my handheldPC?
Forum and Wiki search didn't find me anything sadly :( (I'm sure this information must exist somewhere, but I couldn't come up with the proper search terms it seems.)
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Offline fbonomi

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Re: Timelapse with variable shutter speed
« Reply #44 on: 02 / May / 2008, 10:59:34 »
Quote from: vine on 02 / May / 2008, 10:51:08
I have trouble finding the mathematical formula underlying the sv96 and tv96 values.
(ISO => sv96 and seconds => tv96)

There you go!

In the first row, you enter the TV96 value (in the bold cell) and it converts to other units.

Below, there is a ready-made conversion table

For ISO, I found out that the values were offset by a constant value (1.56 in my case)

I mean, if I set Sv96 to 768 the EXIF data gives ISO 1250, not 800.

That's why you have two columns (ISO and real ISO).

I don't know which is more reliable....

« Last Edit: 02 / May / 2008, 11:03:21 by fbonomi »
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Offline fbonomi

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Re: Timelapse with variable shutter speed
« Reply #45 on: 02 / May / 2008, 11:26:51 »
Quote from: PhyrePhoX on 02 / May / 2008, 09:16:18
could you elaborate on these changes?

The idea is to use shot N to adjust exposure for shot N+1.

For example, if I am exposing 40", the CCD data (the ones read by getBV) are useless to tell me if I am under- (or over-) exposing.

But aust after every shot, (at the beginning of raw_savefile might be the best place) I examine the image raw data and see if its exposition was ok.

If (for example) the shot was onder-exposed, I will expose next shot a little bit longer.

The difficoult part is to decide what a "correct" exposure is for a night shot.

Night shots (if they have artificial light in them) have HUGE contrasts and the standard algorigthms to see if an image is well exposed make no sense here.

So, basically, I think some custom algorithm will be needed, maybe with some parametrization to decide if one wants to have
1) a night look (dark night with stars)
2) a day look (luminous sky, but no stars and over-exposed town lights)

I have done some of the coding already, after having done the shot, I do a (sub-sampled) histogram of the RAW data and I save it to disk.

I repeat this for a large set of exposures of the same scene (from 1" to 64" in 1/3 stops) and try to see if I can develop a program that looks at the histohgrams and tell me which is the "best" exposed photo.

But, as I was saying, best is very subjective here :-)
« Last Edit: 02 / May / 2008, 11:28:34 by fbonomi »
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Offline PhyrePhoX

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Re: Timelapse with variable shutter speed
« Reply #46 on: 02 / May / 2008, 11:32:31 »
good idea. although better timelapses is the primary goal here, i guess there could be more advantages to that. way to go :)
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Offline vine

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Re: Timelapse with variable shutter speed
« Reply #47 on: 02 / May / 2008, 11:37:04 »
Thanks. Here is the Pocket Excel (CE3.0) file for on-the-fly calculation in return.
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Offline fbonomi

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Re: Timelapse with variable shutter speed
« Reply #48 on: 02 / May / 2008, 11:41:41 »
Quote from: PhyrePhoX on 02 / May / 2008, 11:32:31
good idea. although better timelapses is the primary goal here, i guess there could be more advantages to that.

Exactly, this could be used for a "delayed auto-exposure for night scenes" mode...

1) shoot at ISO 1600, 2"
2) evaluate exposure
3) shoot at ISO 200, 15" (or 10", or 25", if the camera finds more appropriate)
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Offline vine

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Re: Timelapse with variable shutter speed
« Reply #49 on: 02 / May / 2008, 11:45:09 »
Quote from: fbonomi on 02 / May / 2008, 11:41:41
Exactly, this could be used for a "delayed auto-exposure for night scenes" mode...

1) shoot at ISO 1600, 2"
2) evaluate exposure
3) shoot at ISO 200, 15" (or 10", or 25", if the camera finds more appropriate)

Or you could always go the lazy mans route and just take a bunch of different exposures and sort them out later I guess ;)
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