which camera for low-altitude aerial photography (for use with PhotoScan)?

[jan]

Hi all,

I'm sure some people here make their own aerial pictures with a balloon, kite or drone (and use these as input for the PhotoScan software).

Which camera do you use/recommend?

I currently use a Ricoh GX200, but the intervalometer with this camera is limited to 5 seconds. However, I would like to have a camera with an intervalometer range starting from 1 or 2 seconds. The only one I found with this specification is a Pentax Q10, but this camera has no lens of 24 mm (35 mm equivalent) focal length, which I prefer.

Anybody suggestions?
thank you,
Jan

[RalfH]

Most Canon Powershot cameras can run an interval script under CHDK, and it is possible to set any interval time. I use this a lot with a Canon G12 working with intervals between 4 and 6 seconds. In real life there are some issues with short intervals (which the CHDK people may be working on). One option for very short intervals would be to run a script that forces continuous-mode shooting (no change of focus or exposure settings between photos, and also no possibility to adjust interval time - just running at several images pers second); another option would be to preset focus and then use a interval script that does allow setting interval time, but I think still would not get into the 1-2 second range. If you want the camera to adjust focus and exposure settings for every photo, it will be slower. The G12 being somewhat on the top end of the line of the Powershot series, I don't know if another one would be much faster.

[hsmith]

Here is an interesting link on a discussion on how to reduce the cycle time for CHDK enabled Canon Powershots to about 1 second per exposure. The key is to disenable auto-focus, focus, and exposure, and to have a fairly short and clean script.

http://chdk.setepontos.com/index.php?topic=9188.0

I've got a SX130 down to about 1.3 seconds.
Hope this help.

Harold

[RalfH]

Thanks for the link, Harold!

[mwillis]

I use cheap Canon point and shoots with CHDK for all my KAP, BAP, and PAP.

Here is a sample from KAP:
https://vimeo.com/40083174

If you haven't been there check out the KAP Forum and this post in particular:
http://arch.ced.berkeley.edu/kap/discuss/index.php?p=/discussion/1595/microsoft-photosynth-possible-kap-use/p1

You'll see the genesis of SfM as we know it today.

Mark (aka Horus on the KAP forum)

[jan]

Thank you all for the info, I will delve into it...

[jan]

after some googling,

I assume that the "Canon Powershot S100" is a good option since it has 24 mm focal length, and is capable of running CHDK scripts.

However, this camera has no intervalometer (or time-lapse) option by default. Is it than still possible to introduce, and to parameterize an intervalometer with a CHDK script in this camera?

Another question:
which camera focal length do you use/prefer with low-altitude areal photography? Does it matter that much, as probably a longer focal length can be compensated by just flying higher above the ground? Or are there other side-effects of this compensation?

regards,
Jan

[Oli63]

I think that currently there is only one choice concerning the best compromise in weight, resolution and lens quality: Sony NEX-7 with the 16 mm lens, which is in use by quite a lot of UAV operators. It has around 400 g and 24 MP. Disadvantage is the lousy interface for the shutter release, but this can be overcome.

[Santiago]

The Sony Nex 5, 5N or 7 are all great choices. They are low in size and weight, which can be controlled with an infrared controller by your RC. They also have interchangeable lens which will give you an advantage for what you're looking. Either way you should always take into account the size and weight of the camera and that will depend on which UAV you have. If you have a multirotor they can handle many cameras, but the heavier, the less flight time you'll get.

In my opinion the sony Nex 7 is one of the best cameras out there for low altitude aerial photography, but if you aren't looking for something that good the sony nex 5n will do and it is between 600-700 US$.

Regards,

Santiago

[RalfH]

jan,

the Canon S100 will be able to run an interval script under CHDK (any Canon Powershot capable of running CHDK can run interval scripts); however, it does not support all options of loading CHDK. Were you thinking about the S100 because of the built-in GPS?

[jan]

Hello RalfH,

thanks, I was thinking about the S100 because of the 24mm wide angle and it's manual focus option (I assume that autofocus will limit the maximum shooting frequency in the CHDK script). Also the GPS is a plus

[RalfH]

With CHDK scripts, you have complete control over your camera, even if the regular firmware does not provide the desired functionality. For example, you could write a simple script which waits for a specified time (so as to not waste memory while the UAV gains height), sets focus to infinity (a good choice for most aerial photography) and then shoots at regular intervals or shoots in continuous mode for a specified time. For KAP, I have used a Canon A3000IS (not the best image quality though) with a script with an initial delay and interval shooting that focusses, shoots, reads focus distance and shuts down the camera if focus distance is less than 5 metres (to protect the lens when getting close to the ground), but this only works well if the camera can always focus well (i.e., no strong movement and no textureless surfaces), because otherwise the camera occasionally shuts down when it's still far from the ground. For PAP, I use a Canon G12.

[jan]

Thanks RalfH, good to know this,
Jan

[jan]

We've finally bought a Canon Ixus 220hs, and it seems to work fine, at least on the ground. With a CHDK script I've managed to set the frequency of the intervalometer to a bit less than 1 picture a second. Other camera properties are also nice (only 140 gram, only 140 euros, 24 mm focal length)

I'm now wondering what shutter speed, ISO value combination I should use. Of course I will trial and error on the field, but maybe somebody knows a good initial parameter combination to start from?

I will use the UAV at 20 m height, and it will fly 15 km/h. Does somebody has experience with estimating good shutter speed and ISO value combinations with UAV photography? I will take pictures in very sunny areas (in the desert).

[RalfH]

jan,

you can calculate this as follows:

The camera's angle of view (http://en.wikipedia.org/wiki/Angle_of_view) depends on it's focal length. For 24 mm (equivalent) focal length, the angle of view is 53° (image height) or 74° (image width). One pixel width thus equals 53°/3000 or 0.0177°. At a distance of 20 metres from the camera, one pixel therefore equals 6.2 mm on the ground. If you fly the camera at 15 km/h (4.2 m/s), one pixel width on the ground goes by in 1/677 second. Your shutter speed should be faster than this to avoid motion blur. With a UAV, you will usually have other movement as well (pan, roll, tilt, vibrations), so you might need an even faster shutter speed. Rotations about any camera axis are usually a bad thing, because they are angular rather than linear movements, and (as shown above), each pixel equals a very tiny angle of approx. 1/60 of a degree per pixel. Shutter speed therefore has to be faster than this (i.e., if maximum camera rotation rate in pan or tilt is 0.1 full rotations or 36° per second, shutter speed has to be faster than 1/(36x60) or 1/2160 second to avoid pan/tilt blur). Rotation about the camera's optical axis is the worst, because in this case the problem gets bigger from the centre to the edges of the image. Having the rotation axes not go through the camera will improve the situation, but fitting the camera off-center under a UAV is very unpractical, so what you can do is either use a UAV with good flight stability (or fly under low-turbulence conditions if possible) or use a faster shutter speed. All these things can of course be found out by trial and error. Knowing nothing about the actual camera rotations, I'd start with 1/1000 second and see if shutter speed still has to be faster.