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70mm F1.6 3.98° lens allows for clear 500m distant video

Sat Nov 17, 2018 9:50 pm

I have a 70mm F1.6 3.98° lens I originally bought for Raspberry camera microscope. This lens did cost 9$ with free shipping on aliexpress and is most expensive of the lenses I own:

After it turned out that best resolution with Raspberry Pi camera and that lens (0.125µm/pixel!) was beaten by 20° lens (0.12µm/pixel) I had no more use for that 3.98° lens.

Lately I lost an RC airplane in 30m height of tree, and a drone searching for that in 22m height of tree (and another drone searching for 1st drone in 16m height of tree).

Now that all leaves have fallen from the tree where most likely the RC airplane still is in, I wanted to see whether I can sport the yellow airplane from ground. But my eyes are not good enough. So I thought of having a Raspberry camera looking up from ground for getting a picture from the plane. For good image I wanted to minimize the lense angle and remembered the 3.98° lens.

Today I played with that lens, and it was mounted on a v1 NoIR camera. That camera came with M12 mount and another lens when I bought it, but I added M12 mounts to "normal" v1 and v2 cameras as well. This is the setup of today's experiment:

I took videos out from secondary living place, through closed window in 2nd floor, far over fields to first houses of next small town Altdorf. Distance to the big house on right side of the video is 512m, measured with gmaps pedometer:

I took the video with this command (25fps because that is the framerate youtube assumes on .h264 video upload):

Code: Select all

$ raspivid -md 5 -w 1296 -h 730 -p 0,0,1296,730 -t 10000 -fps 25 -pts t1.pts -o t1.h264

During the 10 seconds a car drove from left to right on the street just before that 512m distant house. I am really impressed how good the car and house look more than 500m distant (I am novice to photography, did not do any videos before using Raspberry cameras): ...

The house right/left in previous picture is the house top/bottom in this Google maps 3D view: ... !1e3?hl=en

The camera is named 2MP, that is the reason I took 1296x730 resolution.
There were 0 frame skips in the video recorded at 25fps, this is frame delta analysis:

Code: Select all

$ ./ptsanalyze t1.pts 0
creating tstamps.csv
246 frames were captured at 25fps
frame delta time[us] distribution
      4 39976
     22 39977
     29 39978
    129 39979
     32 39980
     21 39981
      6 39982
after skip frame indices (middle column)
0 frame skips (0%)

After I got surprisingly good video of 500m distant scene, I am curious whether I can spot yellow 33cmx25cm Piper RC airplane in 30m height of tree without leaves from ground.

v1 camera mode 5 has full FOV (horizontally): ... /

Slightly better resolution can be obtained by v2 camera (my v2 camera is a NoIR camera as well).
Last edited by HermannSW on Sat Nov 17, 2018 11:31 pm, edited 1 time in total.

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Re: 70mm F1.6 3.98° lens allows for clear 500m distant video

Mon Nov 19, 2018 2:29 pm

I extended the 512m long line until it hits the distant trees on Google maps -- the trees are 4.5km distant. Will see whether I can get clear pictures of those trees by adjusting lens.

I measured the angle between blue line and house wall of right house in video, roughly 60°. I measured the length of house wall to be 10m with gmaps pedometer, and gimp says that house wall of right house covers 300 of the 698 horizontal pixels in youtube screenshot.

The house length orthogonal to blue line is therefore 8.7m, and the length of whole horizontal range orthogonal to blue line is therefore 20.1m. Scaling back to my target distance of 30m to airplane in tree gives 1.2m for full horizontal view. 0.33mx0.25m RC airplane airplane should be well visible in 1.2m horizontal view:

Code: Select all

$ bc -ql

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Re: 70mm F1.6 3.98° lens allows for clear 500m distant video

Mon Nov 19, 2018 3:12 pm

Slightly bigger sensors, but in a previous job doing CCTV control systems we could get some pretty nice pictures of Ely cathedral from Bar Hill (CB24) - Bing says that's around 14 miles.

The camera was probably a Philips LTC0600 with a chunky lens (a Rainbow 20x zoom? H20X10MEA?).
The main problem was the wobble from the 12m pole :D
Perhaps I should ask one of my ex-colleagues if they had a spare one lying around to play with!
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Re: 70mm F1.6 3.98° lens allows for clear 500m distant video

Mon Nov 19, 2018 3:16 pm

Another problem you get with long distances is heat giving air movement and 'wobbly' pictures.

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Re: 70mm F1.6 3.98° lens allows for clear 500m distant video

Mon Nov 19, 2018 6:00 pm

Thanks for the comments wrt air movement and wobbly pictures:

I looked art the video again and saw some wobble. ...

But that was no air movement, but my wife moving through the room and producing slight camera position changes.
We were on a hurry Saturday and I had no time during daylight to create another video.

Yesterday and today I came back to secondary living place when it was already dark.
I will do another video with same setup and no in room disturbance to see whether air wobble is an issue.
Maybe more in summer than now, maximal day temperatures are 2°C currently in Holzgerlingen.

I guess air wobble will be less of an issue for my main application, finding yellow RC airplane at "only" 30m height in tree from ground.

I took >60 videos searching for RC airplane with 1st drone lost in another tree.
Only in 3 videos I was able to see the airplane.
I did capture from the animated gif I created the two where the airplane can be seen quite well.
I hope the tree without leaves I think the airplane crashed into is the correct one.
Otherwise (or additionally to search from ground) I will do another video with E52 drone and vertically direction camera.
But this time bringing drone very high (40m?) before moving above the tree -- I don't want to loose another drone before having at least released one of the other lost drones.

I need the airplane in order to build a Stratolaunch type airplaine together with identical 2nd plane at home:

Of course I could just buy another airplane for 20$, but searching and trying to rescue the lost airplane is more fun -- even if I (hopefully temporarily) lost two drones that way in addition ;-)

In case my payload drop mechanism developed for that will not help to release the airplane or the lost drones, I already thought on a Kamikaze style flight of E52 drone with full speed into airplane or one of the lost drones to get both falling to ground hopefully (after the respective trees will have no more leaves).

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Re: 70mm F1.6 3.98° lens allows for clear 500m distant video

Thu Nov 22, 2018 8:38 pm

I did new videos of same 500m distant houses as discussed.

I did shoot first video through open window, warm inside, cold outside, much air movement, very wobbly result: ...

After I closed the window and waited for indoor air movement to settle, I took this video of same scene. Still a little wobbly, but far less than in previous video. Looks similar to first video wrt wobblyness, seems that not indoor movement was cause as I first thought for first video: ...

Next I took a (again 1296x730) video of advertisement attached to house on other side of rail track, distance between camera and advertisement was 59m:

Quite a detailed view of the (big) advertisement letters, this is photo from smartphone camera (the previous videos recorded the house before the crane far distant -- right click to see photo in original 5MP size). The horizontal length of Raspberry video is slightly more than 2m -- promising for my search 30m height in tree RC airplane effort:

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