Fresnal lens

planecrazy

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Okay,  I've found all kinds of useful info here, but now that my cam is built, I have a question.  Will the Radio Shack sensor not work from behind plexiglass?  
 



Gumboyaya

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Just a tip. I built 3 cameras but the last two I mounted the rs pir fresnal lens with the wrong side facing the sensor (when you take it apart it easy to do because the rough side looks like it should face outward, not so).

It still detects motion out to 30 ft with no problem, but I checked it against my "good" one and the correctly place lens picked my motion up out to 40 + ft.

Hope this helps someone.
Gumbo
 

Tinhorn

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makes me wonder if the MS20's sensitivity could be reduced with that method.....

Tinhorn
 

jayber

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I've got some each way and they detect pretty much the same.  I mount any new ones I build with the smooth side out because the rough side looks like it could collect debris fairly easy.
 

kmitch

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I use the MS20 PIR's. On one of my cameras I removed the MS20 from the housing. I epoxied the circuit board to a larger piece of 1/8" thick lexan sheet so I could mount it with four long machine screws, one at each corner. Then I glued the fresnel lens behing a 3/4" opening in my box. The PIR board is mounted behind the lens on the long machine screws. I use the machine screws to adjust the distance from the board to the lens. Changing the board to lens distance changes the detection distance of the PIR.  By desensitizing the PIR I get it's range to match the range of the camera flash. This seems to eliminate photos with no game included.  

Keith
 

Tinhorn

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Good Job kmitch,

I copied your tip over to Random Thoughts

Thanx

Tinhorn
 

TNDEERHUNTER

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Thats a good tip. You never know what your going to find if you keep reading on this forum. Thanks guys.
 

kmitch

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Glad to be able to contribute. I know I've benefitted from the info others have been willing to share here.

Keith
 

kfen

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I know this has proubably been asked before. What size hole is the best for the fresnal lens opening ? I have always built my cameras with out removing the sensor from the housing. I think they look more profesional mounted out of the housing. Also what is the proper distance to mount the sensor away from the fresnal lens? Thanks to everyone I have always gotten great advice.
 

h2obobh2o

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KFEN...

I use a 7/8" hole in my enclosure, and I have never (knock on wood) had any problems with getting an animal that trips the PIR in the whole "frame" of the picture.  I use the RS 49-425 PIR, and I use a set of "calipers" that I use for reloading, I set my distance with a piece of dowel rod that is .762 ", that is pretty much what the factory setting is. And I cannot complain about my "sensitivity", infact, sometimes I think the PIR is too "sensitive", I sometimes get some pictures of "eyes" that are beyond the capabilities of the OWL PF's flash range.
 

TNDEERHUNTER

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I use a 1" hole on mine and mount them about 3/4" away from the lens. Works well I have six like this.LOL
 

kmitch

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I use a 1" hole and concur that smaller is better. You always want the camera field of view to be greater than the PIR detection envelope. I have a roll of landscape pictures that is evidence of what happens when you don't do this. With the MS20 PIR and the MS20 fresnel lens I space the PIR side of the board at 1.35" from the lens which is the spacing in the original housing as best I can measure.

One thing I've pointed out before is you can decrease the sensitivity of the PIR by adjusting the PIR element to lens spacing. I find the MS20's have a far greater detection range that the flash of the cameras. So to avoid some pictures with no aparent game it's sometimes better to decrease the PIR range a little. This time of year it's not so critical because the body temps and air temps are much closer than in the winter.

On one camera I mounted the PIR board on four long machine screws with multiple nuts so I could adjust the PIR to lens spacing. Of the two I had out last season I got more good pictures from it than the other which was using the MS20 in it's original housing. Everything I've built lately has been fixed distance. I was hoping to find an electronic method of adjusting the gain without affecting the bandwidth. Not there yet.

Keith
 

SouthernStyle

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Guys,

When you are using the MS20 board without the original housing are you using the fresnel lens that comes with it or does a different type fresnel lens work better when placed "flat"?

Thanks,
Scott
 

davered1

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Use the same lense and make sure you line it up properly, look at lens there are a bunch of skinny lines on top and a bunch of fat lines on bottom. The fat lines see down and skinny lines see out.

In a 1" hole put the short fat rows about 1/4 of way up and 3/4 skinny lines rest of the way. this is the way it is centered in original housing.

Hole size for PIR also depends on what camera you are using and if you have a refresh pulse keeping flash charged. A PF without a refreshneeds a bigger hole because it takes longer than a AF to fire .

A 1" hole will work for all but if you want animals more centered in picture then for a AF I would run a 3/4" hole
 


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