What is the best script for Time-Lapse Astropphotography??? - page 2 - Script Writing - CHDK Forum
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What is the best script for Time-Lapse Astropphotography???

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Offline fe50

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Re: What is the best script for Time-Lapse Astropphotography???
« Reply #10 on: 01 / July / 2012, 19:25:56 »
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Quote from: apfrsscf on 01 / July / 2012, 12:51:14
Is there a way to shut it off (without shutting the whole camera down)?
Yes, switch to playback mode.
The sensor & also parts of the electronics are disabled in playback mode, the power consumption is much lower...
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Offline waterwingz

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Re: What is the best script for Time-Lapse Astropphotography???
« Reply #11 on: 01 / July / 2012, 19:40:40 »
Quote from: waterwingz on 01 / July / 2012, 11:56:41
People have done some fun work making scripts more efficient - even to the point of switching to "playback" mode automatically between shots because somebody did the measurements and found out that "playback" uses somewhat less power.
Quote from: fe50 on 01 / July / 2012, 19:25:56
Yes, switch to playback mode.  The sensor & also parts of the electronics are disabled in playback mode, the power consumption is much lower...
Glad we agree on that one.   Here's a couple of links to the data :

https://www.box.com/s/tscho3m30j/1/55257469/1370873701/1
https://www.box.com/s/tscho3m30j/1/55257469/1370873395/1

Update : if the links don't automatically start a download - you want the two that start with the word "bugsplatter"
« Last Edit: 01 / July / 2012, 19:43:10 by waterwingz »
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Offline reyalp

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Re: What is the best script for Time-Lapse Astropphotography???
« Reply #12 on: 01 / July / 2012, 20:58:09 »
Quote from: apfrsscf on 01 / July / 2012, 12:51:14
Is there a way to shut it off (without shutting the whole camera down)? I notice that the CMOS chip gets quite warm which also increases noise. Wouldn't giving the CMOS chip a rest save power and reduce thermal noise?
If your shooting interval is long, then you can also set the display off interval short enough that it will turn off between exposures. This should shut down all the sensor hardware too.

Some cameras have a "sleep" function you can assign to the print button, but a quick look at the sx230 manual suggests it doesn't have anything like this. On cameras with an optical view finder, turning the display off likely turns off sensor as well.
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Offline outslider

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Re: What is the best script for Time-Lapse Astropphotography???
« Reply #13 on: 02 / July / 2012, 03:00:17 »
Quote from: apfrsscf on 01 / July / 2012, 11:42:49
Question: How exactly do I change the correction parameters of the script to adjust the brightness?

It's not easy, you have to decrease the parameters:

"Bv96 correction @ Bv = -500"
"Bv96 correction @ Bv = +500"

When I shot sunsets/rises I set them like that:


Bv96 correction @ Bv = -500    [  -250]
Bv96 correction @ Bv = +500    [   70]

In general when you set negative values for "@ Bv = -500" and positive values for "@ Bv = +500" you'll get darker images when it's dark and brighter when it's bright. Try to play with params and get the correct values by experiments ;)
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Offline apfrsscf

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Re: What is the best script for Time-Lapse Astropphotography???
« Reply #14 on: 02 / July / 2012, 21:28:28 »
1) My sx230 does not have shish-ka-bob port, but it did come with a mini-usb to TV cable that shuts off the LCD screen.

2) I will have to play with the "@BV = " settings when I get a chance.
I do want to say that so far the exposures have been pretty much right on the money.  :D
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Offline apfrsscf

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Re: What is the best script for Time-Lapse Astropphotography???
« Reply #15 on: 08 / July / 2012, 12:47:00 »
Greetings CHDK
1) I ran another test of "Intervalometer with auto shutter time". I started with a fully charged battery. After 80  exposures the camera shut down due to exhausted battery.

2) "Intervalometer with auto shutter time" totally miscalculated exposures containing the Full Moon (bright as day). I played with adjusting the "Bv96 corrections" but I did not get very far with that.

3) I down loaded "Sunset4" and ran that last night. I got about 171 exposures before the fully charged battery ran out, but the exposures were totally wacky. For a while they were OK, but then the ISO continued to increase up to 5266. That resulted in 'bright as day' images. I suppose I could have manually limited the ISO with the params, but I was hoping that it would limit itself.
I do like the feature that it increase the Tv up to a limit and then increases the ISO.

4) I tried downloading "Sunset14.lua", but it does not run. I get error message: ":54: module 'fb-lib' not found: 00no field package. preload [ 'fb-lib']". I checked that the "fb-lib" file is in the same directory as "set_b-14".
The simple "Intervalometer.Lua" that came with the original CHDK download runs, so Lua scripts do in fact run.

5) I am seeing a lot of strange numbers in the programming side of things. For instance "Sunset4"  says to use 960 for ISO5000 and -414 for 20 seconds. And those Bv96 corrections of + or - 500. What is with all those strange numbers? How can I de-code them?

Clear Dark Skies
apfrsscf
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Offline outslider

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Re: What is the best script for Time-Lapse Astropphotography???
« Reply #16 on: 08 / July / 2012, 15:02:09 »
Well... First of all you'd like to read this:

http://dougkerr.net/pumpkin/articles/APEX.pdf

This document describes so-called APEX - The Additive System of Photographic Exposure. What does it mean? There are parameters that result in exposure: aperture, ISO and shutter time. But the effect of change of each parameter is different. That's where APEX comes. shutter time, ISO and aperture are there changed into APEX values: Tv, Sv and Iv. There's also Bv which means brightness of the scene itself (while exposer says how dark/bright is the image). They all can be merged into one equation:

Ev = Bv + Sv -Av -Tv

And this equation shows, how changing of one value causes changes in exposure. For example if you add '2' to Sv (increasing ISO) then you can for example increase Av +2 and the exposure will be intouched. relations between Sv, Av or Tv and ISO, aperture and shutter time are described in APEX.

Now what's this correction parameter:

The script calculates the Tv value from modified equation:

Tv_new=Bv+Sv-Av-Ev

let's imagine you'r camera has calculated, that the brightness of the scene (Bv) is -500 (at night). And let's say other parameters result with Tv_new=120.
If you have set parameter

@-500    [ -100 ]

then the camera understand, that when brightness of the scene is -100 you want to decrease resulting exposure 100 APEX units. So the Tv_new will be changed 100 units up, which results with shorter shutter time and darker image.

Let's say you have set:

@+500   [200]

and the measured brightness is +500. So the camera will decrease Tv_new of 200 APEX units causing in brighter image.

And at the end: the correction is linear. Imagine you have set both parameters as above and camera see scene with brightness = 0. So the correction will be in the middle of -100 and 200, literally: +100.

I hope I help you a little;)
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Offline apfrsscf

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Re: What is the best script for Time-Lapse Astropphotography???
« Reply #17 on: 27 / July / 2012, 20:59:04 »
Dear Outslider
Thank you for your programming and assistance.
I have been reading APEX and “Intervalometer with auto Tv”, as well as taking several field trips to dark sky sites including Pine Mountain Observatory.
I have some questions about calculating numbers:
 
APEX says: Av+Tv=Bv+Sv
Which means Bv=Av+Tv-Sv
 
 
Exposure #70: (exposure determined manually)
ISO2999 (Apex value 9.91)
Tv 16 sec (Apex -4)
F 3.2 (Apex 3.36)
Ev=Av+Tv (-0.64)
Bv=Av+Tv-Sv (-10.55)
Tv_new=Bv+Sv-Av-Ev = (-3.36)

 
 
Exposure #135 (underexposure determined by “autoexp”)
ISO4829 (Apex 10.59)
Tv 2.9 sec (Apex -1.54)
F 3.2 (Apex 3.36)
Ev=Av+Tv (1.82)
Bv=Av+Tv-Sv (-8.77)
Tv_new=Bv+Sv-Av-Ev = (-3.36)
 
 
The APEX concept makes sense to me, but I am not coming up with anything close to the 500ish range.
 
Looking at “autoexp”, I see:
A=h-l
The default value for h = +500
And the default value for l = -500
So A=h-l = +500- -500 = +1000
 
B=(l+h)/2
So B= (-500 + +500)/2 = 0/2 = 0
 
Bv_COR=Bv*A/1000+B = Bv *1000/1000+0 = Bv*1+0 = Bv
 
Tv_new=Tv_new-Bv_COR
So in the case of Exp#135; Tv_new= (-3.36) – (-8.77) which comes out to 5.41 or about 2/85 sec. Yet the script calculated a Tv of 2.9 sec.
 
Ok, so what am I doing wrong?
 
Respectfully
apfrsscf
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Offline outslider

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Re: What is the best script for Time-Lapse Astropphotography???
« Reply #18 on: 28 / July / 2012, 05:14:00 »
Quote from: apfrsscf on 27 / July / 2012, 20:59:04
The APEX concept makes sense to me, but I am not coming up with anything close to the 500ish range.
 
Looking at “autoexp”, I see:
A=h-l
The default value for h = +500
And the default value for l = -500
So A=h-l = +500- -500 = +1000
 
B=(l+h)/2
So B= (-500 + +500)/2 = 0/2 = 0
 
Bv_COR=Bv*A/1000+B = Bv *1000/1000+0 = Bv*1+0 = Bv
 
Tv_new=Tv_new-Bv_COR
So in the case of Exp#135; Tv_new= (-3.36) – (-8.77) which comes out to 5.41 or about 2/85 sec. Yet the script calculated a Tv of 2.9 sec.


Not exactly... default for both: h and i are 0. So with default you'll have:

A=0
B=0

A and B are just parameters of the linear equation. A is directional factor and B is the Y-intercept. You can imagine, that you have coordinate system, where X is Bv and Y is BV_COR. The h and l mean the values of BV_COR when Bv=500 and Bv=-500 respectively. The linear equation is:

Y=A*X + B

in our case:

BV_COR=Bv*A/1000+B

1000 is just a constant coeficient.

So Correction@500 and Correction@-500 are being used to calculate the linear parameters of the correction. The correction is applied depending on the measured Bv.

Imagine you have set Cor@500 = -100 and Cor@-500=200

A=h-l=-100-200=-300
B=(l+h)/2=50

The equation:

BV_COR=Bv*(-300)/1000+50

So when measured Bv is for example 0 the BV_COR will be 50 and then the image will be brighter of 50 APEX units. When for example measured Bv=-100 BV_COR=-30+50=20 and the image will be 20 units brighter. When measured Bv=-1000 then BV_COR=-250 and image will be 250 APEX units darker...

I don't know how to say this in other words...
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Offline MeBeJedi

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Re: What is the best script for Time-Lapse Astropphotography???
« Reply #19 on: 21 / October / 2012, 23:14:57 »
This script gives me an error. It says the camera is shaking (should I turn that off manually?) And I get a yellow square in the middle of the screen with an exclamation point.
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