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Lens choice

Pixy Hardware
#1

Hi,
I am trying to follow a human being at a distance of approx 20meters.

Could anyone suggest the right lens for this?

Also, is it correct that m12 1/3 sensor lenses are required? And must have IR cut filters?

Thanks,
Bob

#2

Pixy uses a 1/4" sensor, but a 1/3" lens is should work fine. An IR cut filter is required too to get good color response.

If you google around for “M12 IR cut lens” or “board camera lens IR cut” you’ll find online retailers.

thanks!

#3

Thank you for that info.

What focal length would you recommend for a human subject at 20 meters distance?

Ciao,
Bob

#4

Sorry man this is your experiment — I can say that you’ll probably want a focal length greater than 2.8mm :slight_smile: (what Pixy ships with)

There are lots of resources on the web

http://www.machinevision.ca/fieldofviewcalculator
http://petapixel.com/2013/06/15/a-mathematical-look-at-focal-length-and-crop-factor/

hope this helps!

#5

Hi,

Thanks for that info!

Now, I’m searching for a +/-6mm lens but this is not easy to find with IR-Cut !

Does anyone have any resources for this? I’ve searched a lot.

Or will it be ok to mount an IR-cut filter in front of the lens?

Thanks for all the help - sorry to be such a newbie…

Ciao,
Bob

#6

You can put the IR cut on either end of the lens.

#7

http://stores.ebay.com/RageCams-Wholesale-Outlet/CAMERA-LENSES-/_i.html?_nkw=m12&submit=Search&_fsub=5668665&_sid=86229

I haven’t purchased from them yet, but in an email exchange with them, they claimed that they “can put on an IR cut filter for you” if you ask for one.

Ag Primatic

#8

Actually, I found quite a good choice of lenses in the UK at:

http://www.stockoptics.com/board-lenses/ir-cut-board-lenses.html

All the replies have been very helpful.

Ciao,
Bob

#9

Bob,
Please share how successful you are at tracking a person 20 meters away.
The tricky part as I see it is that a Pixy Cam tracks colors, not shapes. If only there was a way to convert a Pixy Cam into thermal camera, that would work much better to track a person.

#10

Hi! Take a look of the attached picture of a traffic lights recognition with different lens, maybe it will give you an idea of how other lens work on Pixy. Both are taken with the camera in the same position (3 meters more or less away from the lights) The righ part is captured with the standard lens and the left part with a lens from www.stockoptics.com (I purchased it from Germany, so I don´t how can know for the people in America). Specifically I captured it with the one of 6.1mm of focal length and f/2 aperture (they are IR cut of course)

Hope this helps and greetings!

Roberto

#11

Hi Roberto!

Thanks for those images, they are really helpful.

I’ve seen the stockoptics lenses but have not purchased any yet.

Would you be able to post a photo of an object from say 20m? I am trying to determine what percentage of the screen a red helmet (on a person) target would occupy when taken from 10-25m distance, i.e. if it would still be recognized by pixy?

Cheers,
Bob

#12

Hi Bob. I do not see the problem if you select a camera with a longer focal length, there are lens up to 25 mm (but take into account that, i.e. a 25 mm focal length gives you barely 10 degrees of FOV). I am pretty happy with the results of my 6mm lens even with the photons lost due to the smaller sensor, but I could not assure how it would work for you another lens. It should work but always the best is try!

Cheers

Roberto

#13

I was also looking for a way to track a person when I came across the Pixy Cam.
The problem here is that Pixy tracks colors, not shapes, so you need to convince a person to wear that red helmet before you can track him.
Bob, I do not know whether your project’s goal specifically requires using a Pixy or using the best technology suitable for tracking a person, period. Since you have to dress a person for a Pixy anyway, I’d rather put a powerful IR LED on a person and use IR sensors to track him. IR tagging could be more reliable than using Pixy. Look at different tagging technologies. You need Arduino to process Pixy data anyway, so look at sensors that are suitable best for tracking and hook them up to an Arduino. I think that xbox does tracking; can you use the same technology? Google “SOLOSHOT2” - can you use this system to track your person? The common limitation of all these technologies (including Pixy) is that they require to tag a person before you can track him.
I wish that they made Pixy with the swappable sensor. Or even better - provide video input so that we can use an external sensor. Then you could use a thermal sensor, and the need to tag a person goes away.
This could be a great kickstarter idea! Produce a pixy with no onboard camera. Or does such thing already exist?

#14

Hello Yan,
You might find this interesting:

Edward

#15

Edward, I’ve seen this IR kit for Pixy, but again, it requires to tag a person with an IR LED before you can track.
Tagging won’t be necessary (since human skin temperature is different from surroundings) if Pixy had a true thermal sensor, or there was a way to use a video from an external thermal sensor like this one: