Re: CCD Camera Data

Joe Lippencott Nov 26, 2003

Bill,
Here is a dialog I had with the LPI yahoo group, starting with my
first request for data:
--------------------------------
"--- In autostarsuite@yahoogroups.com, "Joe Lippencott" <lippen@r...>
wrote:
> Does anyone know for sure what the pixel array size (X by Y) and
the
> pixel dimensions (in microns) are for the LPI?
> I need to set up the frame size in a separate planetarium program
I
> use for autoguiding.
>
> Joe L.

How about 3.6mm x 4.9mm, measured empirically through a shot of the
Sun.

Take care,

Don
----------------------------------
Don,
Just curious, but how did you arrive at these numbers? I would
really know how this sort of thing is measured. The method might
come in handy for other applications.
Joe L.
-----------------------------------
I took an image of the Sun with a 480-mm refractor, used TheSky to
find the diameter of the Sun at that time, and by measuring the size
of the image in pixels, was able to calculate 3.22 arc-seconds per
pixel. The image is here if you'd like to measure it:

http://www.tabbutt.com/sun.htm

I then input those values into Ron Wodaski's CCD Calculator program
to come up with the answer (actually 3.6 x 4.8 mm, not 4.9...a typo).

This will only be close, because the refractor's focal length is
probably not exactly 480-mm, the measured diameter of the Sun could
be off by a few pixels, and atmospheric refraction of the low Sun
may have made it slightly larger in the image than it really is.

But my take is it's very close.

Take care,

Don
--------------------------------
The ElecVision EVS350A CMOS sensor matches exactly the empirical
measurements I have made, comes in a 48-pin package like the one in
the LPI, and is supported by the controller chip in the LPI.

It's data are (briefly):

VGA output (640x480)
7.5 um square pixels
VGA chip size: 4.8 x 3.6 mm

I've uploaded the data sheet to the Files section in the Hardware
folder.

Regards,

Don
-------------------
END OF DIALOG

Apparently this is the best estimate so far for this chip. I will
add it to CCDS.NAM for my copy of Guide. I guess it is close enough
for now but feel a little uncomfortable about not having absolute
data, especially when someone at Meade actually knows the chip ID,
but is reluctant to release the info. (I really don't understand
their attitude on these issues - everything is such a big secret -
"proprietary information", they call it). You may want to wait
until the "official" numbers are verified before publishing it on
your website.
Meanwhile, I will try to pry this info out of Meade. I predict this
new camera is going to be very popular with the masses. It is
incredibly cheap, very easy to use, and produces fairly decent
images. From what I have seen, the images are competitive with
webcam images and the 1/5 sec. exposure limit barrier is broken with
the LPI's 15 sec. exposure time. Not a SAC or a modified ToUCam, but
enough camera for most casual amateurs.

I am a diehard fan and supporter of Guide and recommend it to
everyone. Price, features, accuracy, costomizability (is that a
word?), to me, it has it all. I hope Guide becomes classed up there
with some of the more mainstream "Planetarium" programs.

BTW, do you think you could publish more of the "undocumented"
features of Guide? For example, it was a bit of work for me to find
out how to edit the CCD fle to add another camera. It wasn't in the
manual and I couldn't find it on the website. Also, it would be nice
to be able to have labels on the FOV circles for different EPs.

Keep up the good work, excellent program!

Joe

--- In guide-user@yahoogroups.com, Bill J Gray <pluto@p...> wrote:
> Hi Joe,
>
> Hmmm... hadn't heard of this one, but a Google search turned
> up assorted comments on the Meade LPI. (Be warned that aside from
> the glowing comments of those selling it, most remarks were
somewhat
> negative. The software appears to be okay, but the image quality
> isn't quite up to, say, a modified Webcam. But you _can_ use it
> right out of the box; you don't have to play with a soldering
iron.)
> Nobody seems to know anything about what chip it might use, except
> that it's a color CMOS one.
>
> I'll take a guess that it uses the same chip as either the SAC7
> or Philips Vesta. These both use 640x480 color CMOS chips with 5.6
> micron square pixels. I doubt we'll get the info from Meade, but
> I've generally seen excellent technical data on Meade products from
> third parties. At some point, someone will take an image with
> this camera, measure the pixel scale, compare it to the focal
> length of the scope, and do the math to determine the size of the
> pixels in microns... and then we can add it to 'ccds.nam'.
>
> -- Bill