A1400 and ND filter ** help appreciated ** - General Help and Assistance on using CHDK stable releases

Michel2e

A1400 and ND filter help appreciated

« on: 19 / July / 2014, 05:21:56 »

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I'm using A1400 for short kap session with a simple script similar to intervallometer.
Camera is in P mode and when the scene becomes very bright the ND filter comes in, reducing the shutter speed significantly.
I've tried to use the following command
set_nd_filter 2
but the ND filter is still active.
also put it "out" in the chdk menu but still active.
last I've tried the kap and uav script with 1/800 as minimum speed. It works for the min speed but, I would have anticipated to have overexposed pics with strong ligth and actually the ND filter comes in, despite setting the correct "out" position in the script menu.
Any idea to avoid this ?

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waterwingz

12088

Re: A1400 and ND filter help appreciated

« Reply #1 on: 19 / July / 2014, 09:37:47 »

Quote from: Michel2e on 19 / July / 2014, 05:21:56

I'm using A1400 for short kap session with a simple script similar to intervallometer.
Camera is in P mode and when the scene becomes very bright the ND filter comes in, reducing the shutter speed significantly. I've tried to use the following command
set_nd_filter 2
but the ND filter is still active. also put it "out" in the chdk menu but still active.

I took a look at the code for the A1400 and it appears to be using the correct function calls for controlling the ND filter. You did not post your script here, but be aware that you need to issue the command in your script before every shoot command - not just once at the start of the script.

One other thing to be aware of is what this will do to the exposure. When you are shooting in "P" mode, the camera will decide if it needs the filter (usually because the scene is too bright for the maximum shutter speed and minimum ISO setting), insert it, and lower the shutter speed to compensate. If you manually force the ND filter out, the Canon firmware will not know that your script has done that, and will still lower the shutter speed, resulting in an over exposed image. To fix this, your script needs to also override the shutter speed (Tv) to a higher value when the ND filter is forced out. There is quite a bit of code in the kap_uav.lua and CHDKplus.lua scripts to handle this - it's not hard but there are some tricks to consider.

Quote

last I've tried the kap and uav script with 1/800 as minimum speed. It works for the min speed but, I would have anticipated to have overexposed pics with strong light and actually the ND filter comes in, despite setting the correct "out" position in the script menu. Any idea to avoid this ?

You might be using an older version of the script? There is no longer an "out" option - the current choice is to allow the script to use the ND filter or not. There have been a couple of updates to improve the ND filter handling - the current version of the script is 3.1 https://app.box.com/s/a5tbl1xasp8m3a57fclx

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Ported : A1200 SD940 G10 Powershot N G16

Michel2e

Re: A1400 and ND filter help appreciated

« Reply #2 on: 19 / July / 2014, 12:54:22 »

Quote

If you manually force the ND filter out, the Canon firmware will not know that your script has done that, and will still lower the shutter speed, resulting in an over exposed image. To fix this, your script needs to also override the shutter speed (Tv) to a higher value when the ND filter is forced out. There is quite a bit of code in the kap_uav.lua and CHDKplus.lua scripts to handle this - it's not hard but there are some tricks to consider.

It will be too tricky I guess for my purpose.

Quote

You might be using an older version of the script? There is no longer an "out" option - the current choice is to allow the script to use the ND filter or not.

You're right: actually I used the correct version but confused the menu with the CHDK menus. Sorry for this.
I will stick to this version of script for current need.
Thanks again, this script is very interesting. I'll have a look next winter if I could get more familiar with Lua. (Actually the script seems quite readable for me, after a year fighting with ubasic script, but writing it to implement my own ideas would be another story !!).

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waterwingz

12088

Re: A1400 and ND filter help appreciated

« Reply #3 on: 19 / July / 2014, 12:59:09 »

Quote from: Michel2e on 19 / July / 2014, 12:54:22

Thanks again, this script is very interesting. I'll have a look next winter if I could get more familiar with Lua. (Actually the script seems quite readable for me, after a year fighting with ubasic script, but writing it to implement my own ideas would be another story !!).

No problem - I'm always open to new ideas if you want to go that way.

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Ported : A1200 SD940 G10 Powershot N G16

Michel2e

Re: A1400 and ND filter help appreciated

« Reply #4 on: 10 / August / 2014, 15:54:00 »

Using the script for kap initiation, I confirm it works perfectly.
I've tried to adapt it a bit to include a zoom change, but unsuccessfully. I was overestimating my ability to understand the script: I still have to make efforts on learning LUA to be able to do it.

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