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FPV lenses and VIRTUAL ACCELERATION affecting Mobius, GoPro and Fatshark ?

#1
FPV lenses, being tiny, cause an exaggeration of distance, an elongation of it, like looking through the wrong end of a telescope. I noticed this because the paddock next door to my house became huge; and the village 2 miles away almost invisible, although perfectly visible to the naked eye. Annoying really because the church spire could have been a good landmark.

However, objects close up seem more or less what you would expect. It seems to me therefore that if one were flying towards a tree, at a constant speed, its approach will seem to accelerate as one draws closer to it, and that this acceleration is VIRTUAL not REAL. Has anyone else noticed this?

This effect might be a contributing factor to the frequency with which David W, following with his Tricopter, ends up getting too close: and the good-humoured, crazy-David explanation for mid-air contact wrong.
 
#2
I've quickly discovered that the tree, in fact, accelerates to match ones own approach speed, thus doubling the closing rate! Therefore, its not a virtual effect, but a real one. that's my story and I'm sticking to it! :)
 
#3
Richard, seriously though, now that you mention it, when I hit that tree yesterday it did seem to grow in my screen at an exponential rate in the last second before impact. Gah! If only my DVR hadn't chosen that particular flight to lock-up on me, I would have captured an excellent example of the phenomenon you describe.
 

jhitesma

Some guy in the desert
Mentor
#4
It's not so much the size of the lens as it is the focal length. Because you want a wide field of view with FPV you usually run a short focal length extreme wide angle lens. Unfortunately the wider you go the more distortion you get (go short/wide enough and you get into fisheye territory.)

The only real way around this is to use a longer lens with a narrower field of view - but then you can't see as well. Which could be compensated for with a head tracker and a motorized mount but that adds a lot of complexity compared to just learning to adapt to the optical quality of a short lens.
 

jhitesma

Some guy in the desert
Mentor
#5
One other thought I had on this in regards to David and his penchant for hitting planes he's filming ;)

Not only does the wide angle usually used for FPV cause distortion making things appear further than they actually are. But he also flies FPV through the gopro and there's a slight delay on the gopro video feed which is why a lot of people don't like to fly through it.

I understand the reasons why the FT guys like to fly through the go-pro since it makes framing more accurately when filming. But that delay is probably the major reason why they suffer so many collisions.

Two options for avoiding that:

1) Don't try to be cameraman and pilot at the same time. Most people shooting commercially with multis use a separate cameraman letting the pilot focus on flying and having the camera on a controllable gimbal that the cameraman controls with a second remote. I'm kind of surprised FT hasn't done this from time to time, they've done the buddy plane with different people controlling different parts of the plane...

2) Fly through a board camera that has a slightly larger field of view than the gopro and set it up so the gopro's field of view is within the board cam's - then setup some markers in an OSD to show the view of the gopro. Takes some more setup to keep it aligned and it's not 100% the same as looking through the gopro but eliminates the delay.

Both solutions add more weight and have other downsides like needing more people or not being 100% WYSIWYG. But if you're more worried about hitting things than getting exactly the footage you want and don't want the weight of extra gear and a second person.....

Personally I think they like the footage from hitting things so they aren't interested in trying to avoid it ;)