Thanks for helping to describe a parabola!
Lots of people think a shotgun does the same job as a parabola. Here, many
birders spend 100 USD on a video-camera shotgun, mostly with a 5 mm
electret, and get disappointed.
To inform that a shotgun is not a parabola seems to be an everlasting
project. Yes, it gets boring, and probably also un-necessary disqualifying
the shot-gun users.
Klas.
At 05:57 2002-08-06 -0400, you wrote:
>At 10:47 AM 8/4/02 -0400, you wrote:
>>They will call if it rains, so we ran a sprinkler. Their call is so soft
>>that most calls you can't hear if they are at your feet. And I was
>>having to deal with the various house air conditioners in the
>>neighborhood. The frogs were in the leaf litter under some thick low
>>bushes in the yard. I ended up recording with the Telinga from a
>>distance of about 2', the tops of the bushes, probably something of a
>>record for close mic work with a parabolic. The reflector helped to cut
>>down the noise from the air conditioners. It's still going to take a lot
>>of filtering.
>
>Headline:
>PARABOLAS BAFFLE NATURE RECORDISTS, NOT AIR-CONDITIONERS.
>
>Parabolas have a known physics; they are lenses, and when you bring
>the object closer, as with an optical lens, you need to focus them to
>have the image continue to fall near the microphone. They do NOT
>filter the sound, they do NOT gather the sound, they focus the sound,
>and they probably make a bad choice as a baffle, compared to overcoats,
>pillows, beer coolers or foam mattresses.
>
>The lens relation is:
>
>reciprocal image distance + reciprocal object distance = reciprocal focal
>length.
>
>or
>
>1/I + 1/O = 1/F
>
>(this reads: one over eye plus one over oh equals one over eff.)
>
>Say the focal length is 40 cm (I have no idea what it is for a Telinga).
>With many recordings, the object is so far away the 1/O approaches zero.
>So setting the mic AT the focal length (as the relaxed eye is set at infinity)
>works very well for distant recordings.
>
>When the object is very close, the image gets startlingly far away, but we are
>usually so glad to be near our subject that we just record anyway and forget
>these nicities. With a frog call that is "hard to hear", however, we might
>want to try: a one-to-one setting, where Object distance, O is EQUAL to the
>Image distance, I. In this case each would then be at 80 cm. (about 2 1/2
>feet).
>
>1/80 + 1/80 = 2/80 = 1/40
>
>This means moving the mic TWICE AS FAR from the parabola as it usually
>is, again I have no idea how hard this would be for a Telinga, but it is an
>interesting point, because the mic and the frog actually are AT the exact
>same spot, 80 cm from the dish, and there is no NEED for a parabola,
>except, as Walt says, to sort of shield off the suburban noise. Truly,
>a baffling usage.
>
>In this F = 40 cm example, having the frog at 2 ft would mean properly
>moving the mic to about 3 1/2 ft! Think about that.
>
>Or, if you insist on using a parabola, ;^) you can put the animal at the
>parabola focal point and you can move your mic back to infinity - e.g. your
>bedroom, - providing the animal and parabola never move and it is all
>pointed exactly at your house! A veritable sound-flashlight, indeed.
>
>At this point, a shotgun mic user, perhaps a bit tired of hearing people
>on this list repeatedly berate his equipment as "only shutting off sound",
>would likely burst a gut, laughing - just point the mic itself at the creature
>and forget the parabola! Oh yes, and maybe turn the mic around so it can
>hear the frog better. We all know there must be a real limit to the word
>"omnidirectional".
>
>
>
>you also wrote:
>With that I'm down to one Georgia frog I've not recorded, Brimley's
>Chorus Frog. They won't be calling until February or so, and are very
>rare in Georgia, I've been trying for them for a couple years already.
>
>
>Good luck, Walt, they are retiring. The Brimley's I caught in South Carolina
>were calling in April, but they were not in chorus (under roadside boards)
>and I am sure you are much more aware of their entire season than I,
>who only visited their range that one time.
>
>my very best,
>
>Marty Michener
>MIST Software Associates
>PO Box 269, Hollis, NH 03049
>
>
>coming soon : EnjoyBirds, bird identification software for all AOU area.
>
>
>
>
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>
>
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