Re: Webcam vs DSLR Target Field of View

On Apr 24, 7:08 pm, "whisky-dave" <whisky-d...@xxxxxxxxxxxxxxx> wrote:
"Hughes" <eugenhug...@xxxxxxxxx> wrote in message

news:69e0d238-c260-46b7-ab63-2b88c4675193@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
On Apr 24, 4:50 pm, "David J Taylor" <david-tay...@xxxxxxxxxxxxxxxxxxxx





part.nor-this.co.uk.invalid> wrote:
Hughes wrote:

[]

Details:
1/4" color progressive CMOS
640×480pixels

Lens Specification
F=2.4,f=4.9mm,View Angle 54

See:
http://www.a4tech.com/ennew/product.asp?cid=77&scid=89&id=253

So the lens has an entrance pupil of 2mm when wide open. Are you matching
your telescope to that?

David
}My 1000mm f/10 telephoto has aperture of 4 inches, so
}entrance pupil is 4 inches.
}I finally got to focus with my Webcam. I wasn't able
}to focus earlier because it was out of focus :)

What makes you think a webcam is suitable for this remember that the webcam
has both the sensor and the lens in a single unit they are fixed, they go
together.

}Now after checking. It is correct that the webcam
}can only image a very tiny portion of the target
}when using the 1000mm telephoto. Therefore
}it is really true that the lens of the webcam is
}able to take in the whole scene into the sensor,
}while that of telephoto can spread it to larger
}sensor.

Don;t think so.
What relevance is it that the telephoto spreads over a wider sensor. ?
A cameras lens is designed  so that the image produced covers the sensor
of any camera that the lens has been designed for, while the webcam
lens is only designed to cover the sensor in ONE camera the webcam and
nothing else.

}Now what's left to do is to look for the best webcam
}in the world.

I could look for the most expensive motorbike in the wolrd and expect it
to perform the same as a push bike because both have 2 wheels.

Not really a webcam is mostly used for moving images.
You could use a camcorder in the same way.
Why don;t people forget about DLSRs and just get a camcorder......
The optical quality is one reason.
If you want a large optical magnification then why not buy a camcorder
rathern than a DLSR or a webcam.

  }But first something I noticed. Digicam

}has pixel pitch the size of 2 micron while Webcam
}has pixel pitch the size of 5 micron. Why is the pixel
}pitch of Webcam larger?

Could it be the webcam has lower resolution.
Most webcams are for 72DPI viewing,
I don;t think any photographic lenses would sell with that spec,
they are expected to resolve at DPI is the 1000s

} It's large enough to match
}the pixel pitch of DSLR, is this one reason why
}astrophotography uses webcam a lot besides the
}ease of downloading images.

where have you got that idea from ?
Webcams might be use as spotting scopes.
I doubt the Hubble space telescope is using a webcam.

What you haven't consider (and which I just realised
today) is that when you take off the lens of a webcam,
and put the ccd in a big telephoto or even Hubble, the
resolution of it is equal to expensive dedicated CCDs or even DSLR
because the determining factor in getting
the pixel scale in arcsecond is the pixel size. So
if the webcam say has 4 micron and the Hubble
CCD has 4 micron, they would have similar resolution.
Surprise? Well, I was surprised to just learnt it today.

Hu


 Most Astrophotography uses specialist equipment of relatively large focal
lengths
unless they are mapping the sky.
webcams generally have wider fields of view in comparison.

}Now having mentioned that the pixel pitch of webcam
}and DSRL is similar in roughly 5 micron. What is
}the best webcam in the world in terms of noise
}suppression and color saturation that it can be
}at least 3/4 to that of DSLR in quality (or 1/2 if
}3/4 is not possible??) Anyone?

The thing about proper astrophotography regarding noise is the temperature
of the sensor,
they like to keep it to as close to absolute zero as possible which usually
requires
liquid nitrogen or better still liquid helium at around -270C.- Hide quoted text -

- Show quoted text -

.

Relevant Pages

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    ... So the lens has an entrance pupil of 2mm when wide open. ... What makes you think a webcam is suitable for this remember that the webcam ... has both the sensor and the lens in a single unit they are fixed, ... }has pixel pitch the size of 5 micron. ...
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