Re: [ATM] webcam question

[Dominic-Luc Webb <dlwebb@canit.se>]

On Tue, 20 Sep 2005, Bob May wrote:

> Focusing with a webcam can be fun as it is more critical.  You
> also need to look at the camera's images of normal things to see
> how good the focus can be with it.  The pixel size is really
> quite small and longer focal length telescopes will often not
> produce a spot that is smaller than a single pixel but rather
> occupy several pixels.

You hit on some excellent points there, Bob, and every word looks
to be spelled correctly. :)

This pixel matter takes on a whole new meaning these days. The
chips are tiny, yet they are really packed with some remarkably
small pixels. Since the poster is tinkering with this camera,
he can take a peak at the active surface and compare the pixel
dimensions. Last I checked, they can easily be under 2 microns
these days. Comparing to some theoretical limits of some of my
designs, only perfectly focused light right smack on the optical
axis would fit into a single pixel, and this would expect perfect
alignment of optical components, and probably atmospheric
turbulence would be a major factor.

Getting back to the camera (yeah, my brain oscillates between
thoughts), the digital cameras these days are generally color
which means a filtering system. They are generally not very
sensitive and cannot take long exposures. Looking to the lenses
(maybe a little pun intended), even the cheapest webcams have
excellent optical components. I have tried replacing these
with expensive optics only to find very little or no difference.
I am guessing you can and do remove the lens, although for the
aurora borealis, I keep it on and use no scope.

One major problem with these cheapie cams is "smoke". I do not
know exactly what this is, but it gets worse at higher resolution.
If you can get away with 2x2 binning, this could make a big
improvement. It could help with detecting stars, although, you
obviously are not going to see much detail.



> If you have any refractive optics in the light path, you will
> find that you will never get a good focus because refractive
> optics does have a problem with focusing all of the light to one
> spot with the infrared (where the camera is really snesitive!) to
> the UV bening a complex curve of wavelength vs. focus point.
> Bob May
> bobmay at nethere.com
> http: slash /nav.to slash bobmay
> http: slash /bobmay dot astronomy.net
> Addresses have been munged tp lee[ spammers from bothering me.
> replace the obvious words with the proper character.
> Thank you for your understanding!
>
> _______________________________________________
> ATM mailing list http://www.atmlist.net/
>

_______________________________________________
ATM mailing list http://www.atmlist.net/