Exposure time limit?

JFSebastian

« on: 15 / July / 2011, 16:07:37 »

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I do aerial photography from a multirotor helicopter with an A480, remote shutter from USB.
The heli obviously vibrates a lot, and most shots with exp time higer than 1/500 turns out blurry.
I tried maintaining the exp with override time in A480's P mode, and although it works for most shots I miss the auto exp function, as example, a white house in bright sunlight needs like 1/1250 to capture the details.

Is there any way that I can limit the exp time to not go slower than let's say 1/500?

Thanks

Sebastian

« Last Edit: 17 / July / 2011, 03:35:43 by JFSebastian »

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Microfunguy

4037

Re: Exposure time limit?

« Reply #1 on: 15 / July / 2011, 17:24:02 »

Quote from: JFSebastian on 15 / July / 2011, 16:07:37

Is there any way that I can limit the exp time to not go higher than let's say 1/500?

Hello Sebastian and welcome.

Do you really mean "not go higher than let's say 1/500" ?

Don't you mean not go slower than 1/500" ?

If so, someone in Las Vegas is testing this right now as I write this post.
He is comparing 1/2000 and 1/4000" shots taken with a fast moving camera.

This is for a flight to the stratosphere using a balloon.

I have added a new command to SDM called shoot_fast_at.

You use it like this :-

set_max_iso 320
shoot_fast_at 1/2000

If you want to try it, let me know.

« Last Edit: 15 / July / 2011, 17:25:50 by Microfunguy »

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fudgey

1705
a570is

Re: Exposure time limit?

« Reply #2 on: 16 / July / 2011, 02:15:32 »

I'm assuming you are using a CHDK script for this.

Then it shouldn't be hard to modify the script to limit Tv. E.g. instead of just 'shoot()', do something like (Lua):

Code: [Select]

-- in script start:
@param z tv96 limit
@default z 828
tv96_limit = z
propcase=require("propcase")

-- put following code in place of shoot():

press("shoot_half")
-- wait for exposure
repeat 
  sleep(1)
until get_shooting() == true
-- override tv if it's too slow
tv96=get_prop(propcase.TV)
if tv96 < tv96_limit then set_prop(propcase.TV, tv96_limit) end
click("shoot_full")
release("shoot_half")

Now this will obviously cause darker exposures. In your case it will probably never be many Ev stops, but if it still bothers you, you could could increase ISO by the amount you changed Tv (that would go before click shoot full and you would be increasing sv96 by tv96_limit - tv96 and maybe you'd want to set a maximum ISO as a script parameter too).

tv96 is APEX exposure time value multiplied by 96 for easy integer calculation in Canon's firmware. You should find APEX.pdf if you aren't familiar with the system.

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JFSebastian

Re: Exposure time limit?

« Reply #3 on: 17 / July / 2011, 03:29:45 »

Quote from: Microfunguy on 15 / July / 2011, 17:24:02

Quote from: JFSebastian on 15 / July / 2011, 16:07:37
Is there any way that I can limit the exp time to not go higher than let's say 1/500?

Hello Sebastian and welcome.

Do you really mean "not go higher than let's say 1/500" ?

Don't you mean not go slower than 1/500" ?

If so, someone in Las Vegas is testing this right now as I write this post.
He is comparing 1/2000 and 1/4000" shots taken with a fast moving camera.

This is for a flight to the stratosphere using a balloon.

I have added a new command to SDM called shoot_fast_at.

You use it like this :-

set_max_iso 320
shoot_fast_at 1/2000

If you want to try it, let me know.

Thanks, and yes, i meant slower than XX, it was late at the time I posted.

Looking good, I'd love to try it, but will it let the exp time operate in auto within a preset range?

« Last Edit: 17 / July / 2011, 03:37:44 by JFSebastian »

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JFSebastian

Re: Exposure time limit?

« Reply #4 on: 17 / July / 2011, 03:43:03 »

Quote from: fudgey on 16 / July / 2011, 02:15:32

I'm assuming you are using a CHDK script for this.

Then it shouldn't be hard to modify the script to limit Tv. E.g. instead of just 'shoot()', do something like (Lua):

Code: [Select]
-- in script start: @param z tv96 limit @default z 828 tv96_limit = z propcase=require("propcase") -- put following code in place of shoot(): press("shoot_half") -- wait for exposure repeat sleep(1) until get_shooting() == true -- override tv if it's too slow tv96=get_prop(propcase.TV) if tv96 < tv96_limit then set_prop(propcase.TV, tv96_limit) end click("shoot_full") release("shoot_half")Now this will obviously cause darker exposures. In your case it will probably never be many Ev stops, but if it still bothers you, you could could increase ISO by the amount you changed Tv (that would go before click shoot full and you would be increasing sv96 by tv96_limit - tv96 and maybe you'd want to set a maximum ISO as a script parameter too).

tv96 is APEX exposure time value multiplied by 96 for easy integer calculation in Canon's firmware. You should find APEX.pdf if you aren't familiar with the system.

Thanks, it's a little over my head, but I'll start reading.

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Microfunguy

4037

Re: Exposure time limit?

« Reply #5 on: 18 / July / 2011, 04:58:03 »

Quote from: JFSebastian on 17 / July / 2011, 03:29:45

will it let the exp time operate in auto within a preset range?

You set a required shutter speed.
SDM sets a suitable ISO for correct exposure at that speed.
If ISO reaches the maximum you wish to use, the shutter speed will be as fast as possible.

This is from a script.

Not sure if CHDK auto ISO works and will do this in normal shooting mode (without a script).

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