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Help with Shutter Speed within a UAV platform (Camera hard to get to)

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Hello All...

To preface, I hope people don't think this is a lazy post; I am actively soaking in knowledge from the various sources regarding the CHDK framework.  I can't wait until I can become a poweruser!

The setup: I am trying to use the CHDK framework on a Canon SD1100IS that has been built within an R/C Airplane that has been setup for UAV (unmanned aerial vehicle).  This makes it very difficult to access the camera and play with the various CHDK settings; this requires an actual UAV flight to take pictures.

Currently, I have the SD1100IS setup using a USB Trigger Script and autoload.  The setup works very well, with the exception of 75% of the pictures coming out with blur.  I want to adjust the shutter speed and other settings, as the camera is oriented straight downward.  The images are always moving ~60 KPH.

I did four flights today after playing with the OSD settings, without much success.  I had to set these values each flight (pain in the butt):

- Main Menu
-- Extra Photo Operations
--- Value factor = 1
--- Override shutter speed = (tried both) 5 / 8.3

After the flights, I found that the images came out completely WHITE.  There were a few photos that actually did come out: when the plane was on the ground (thus a blury grass picture or a good shot of my shue).  Both cases I was in the shade and objects were close to the camera.

What I ultimately like is the following:

- All magical settings that need to work (i.e. a 1/1000 or ? ? ? shutter speed) set within my default USB trigger script. 

This way it is a fire and forget.  If anyone knows how to do that, .... :)

Else, can someone tell me why the pictures are pure WHITE and what I am doing wrong?  From my limited "Camera" knowledge, is this an issue because the ISO and sunlight is too much?  I am a technical guy, not a Photo guy. I am trying to learn the very basics.  So if anyone can tell me what settings I should try (and why, so I can learn); I would really appreciate it.

BTW, here is a build thread of the equipment / plane.  You can see some of the pictures it took with the basic USB script and default camera settings.  You may have to have an account to see the aerial photos.



Offline wontolla

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Re: Help with Shutter Speed within a UAV platform (Camera hard to get to)
« Reply #1 on: 17 / March / 2009, 21:18:16 »
Else, can someone tell me why the pictures are pure WHITE and what I am doing wrong?

- Main Menu
-- Extra Photo Operations
--- Value factor = 1
--- Override shutter speed = (tried both) 5 / 8.3
5 and 8.3 seconds is a pretty slow shutter speed, which might be the reason you get pure white pictures. Too much light hitting the sensor.

75% of the pictures coming out with blur...the camera is oriented straight downward...The images are always moving ~60 KPH.
Yes, that's why you get blurred pictures.

Don't use "Override shutter speed". Instead, set your camera to Av, using the widest aperture (lower number) and let the camera decide the shutter speed, otherwise you'll get over or underexposed photos. Try low ISO values first, if they are still blurred, you'll have to use a higher ISO.

You will need to get the highest shutter speed you can. 60km/h is fast and I guess the plane flies at low altitude. If possible, fix the camera pointing forward instead of downward.

Search the forum and google for KAP (Kite Aerial Photography). You can steal some scripts/ideas from those guys.


Offline fbonomi

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Re: Help with Shutter Speed within a UAV platform (Camera hard to get to)
« Reply #2 on: 18 / March / 2009, 03:35:26 »
your problem is not too far away from the one we had while flying a Sd1100 up to the stratosphere.

With another camera, the ideal solution would be to use Tv mode (aka Shutter priority, if you are not familiar with it see )

But, the SD1100 does not have an iris to adjust the aperture, therefore it does not have a Tv move (or Av mode either)

The sd1100 has a ND filter ( ) that automatically switches in when there's a lot of light. The camera "lies" to you and says it's changing aperture from 2.8 to 7.1, but in effects it's just switching the filter in, with a decrease in luminosity that is equivalent to the decrease in luminosity you would have changing the aperture from 2.8 to 7.1.

What I have done in case of our balloon is:

A) forced to camera to keep the ND filter out of the way

To do this, in the main CHDK menu go under "Extra photo operations" and leave all the settings to their defaults, apart:
- ND filter state: Out (do not confuse it with "Off"!!)
- Clear override values on sta: Unchecked (do not confuse the menu item with the "Clear on start" that you find under "Zoom Override". This is one of the last items in the menu

This will activate a red alert on the display "ND FILTER: OUT". It's ok, it must be there. It's an alert because now (because of the ND filter always being out) if you shoot "normally" you might end up having badly over-exposed photos)

B) implement a sort-of shutter priority mode, where you set the shutter time and the camera (being unable to change aperture to get more/less light) changes ISO in order to be more/less sensible to light. This is made via a LUA script that I wrote

See this thread for dcshrum's original post:,2376.msg21970.html

I then joined the team (working on the the camera programming), and here:
you can see more info about the very succesful launch they made in Florida

In this thread I presented the results:,2877.0.html

particularly, give a look to thist post:,2877.msg27218.html#msg27218
where I give more details on the approach and the snippets of code you might need

Basically, all you need to do is have a loop that repeatedly calls my fast_tv shoot() function, with a small delay if you don't want to shoot too many photos.

If you aren't familiar with Lua scripting, this is an UNTESTED version of the script (I don't have the camera with me now).
Save this block as "test.lua" and run it

Code: [Select]

-- read current bv from scene
function read_bv96()
 while get_prop(115)==0 do
 return bv

-- Possible values of max_sv
-- 320 = ISO   50
-- 388 = ISO   80
-- 418 = ISO  100
-- 514 = ISO  200
-- 611 = ISO  400
-- 707 = ISO  800
-- 803 = ISO 1600

-- Ixus 80 has fixed aperture
av = 285 + offset

dbg("FAST TV")
dbg("bv " .. bv)

if bv==-1 then
 dbg("metered bv " .. bv)
 -- offset measured brightness

--if we shoot at fast_tv,
-- resulting sv would be
sv = av + fast_tv - bv

dbg("tv " .. tv)
dbg("sv " .. sv)

-- let's check if it's not too high
if sv>max_sv then
 -- how much must we reduce sv?
 reduce = sv-max_sv
 -- same reduction must be added to tv
 dbg("Reduced: ")
 dbg("tv " .. tv)
 dbg("sv " .. sv)

-- it might also happen than sv goes too low
-- arbitrary limit of 322 sv (abt ISO 50)
if sv<322 then
 reduce = sv-322
 dbg("INCREASED: ")
 dbg("tv " .. tv)
 dbg("sv " .. sv)

-- at last moment, set our parameters

-- set shutter time

-- set ISO


writelog("FTV", "Shoot " .. get_exp_count() .. " ".. bv .. " " .. tv .. " " .. sv .. " " .. av)

until get_prop(206)==0


function timestamp()
 return ( h .. ":" .. m .. ":" .. s)

function dbg(msg)
 -- uncomment for extra info il log file

function writelog(prefix, msg)
 print('###' .. prefix .. ' ' .. ts .. ' '  .. ' ' .. msg)

while true do
 -- min shutter 1/2000, max iso 200
 fast_tv_shoot(-1, 1053, 514, 32)

experiment by changing the very last lines of the script: sleep(1000) is a delay of 1 second between each shot while the parameters in fast_tv_shoot change the way the camera exposes. You  might want to try slower values such as
Code: [Select]
-- min shutter 1/1000, max iso 100
fast_tv_shoot(-1, 957, 418, 24)

hope this helps!
« Last Edit: 18 / March / 2009, 03:38:03 by fbonomi »

Re: Help with Shutter Speed within a UAV platform (Camera hard to get to)
« Reply #3 on: 18 / March / 2009, 11:33:49 »
Thanks a whole bunch!

I am so excited.  This is great information.

I will go try it out and report back my findings. :)

« Last Edit: 18 / March / 2009, 11:37:26 by RedRx7 »


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