From: "mihalco" <mihalco@pacbell.net>

Date: January 15, 2006 3:41:57 PM MST

To: Astro_IIDC@yahoogroups.com

Subject: Re: Image scale comparison for different pixel sizes

Hi Milton,

I'm new to the group and in the process of choosing a camera. After 

reading through the messages, I'm leaning to the Dragonfly2 from Pt 

Grey. I just wanted to point out that both the Flea and Dragonfly2 

are available either with the 7.4 micron (640 x 480) or 4.65 micron 

(1024 x 768)pixel Sony imagers.  The Dragonfly 2 is also capable of 

12 bit like the Flea.  I think I'll be going with the larger pixel, 

lower res mono version.  Thanks for the group - lots of good info 

here.

Regards,

Kurt Mihalco

--- In Astro_IIDC@yahoogroups.com, "Milton Aupperle" <milton@o...> 

wrote:

Hi Folks;

In the "Other" folder of the Files section, is a jpeg image entitled

"FleaVersusDragonFly2.jpg". I took the images on the same night

(seeing was really poor, about 2 to 3 out of 10) with the same scope

and focal length but using two different color cameras, a 640x480 

Flea

and a 1024x768 DragonFly2 camera. The 1024x768 DragonFly2 camera can

"crop" out portions of the CCD and delivers 640x480, 800x600 or

1024x768 video, so for this test I ran it in 640x480 mode so that it

can be directly compared to a 640x480 Flea camera.

The images show what difference pixel size makes with respect to 

image

scale, which is a factor of 1.59 times. The Flea CCD has 7.40 micron

sized pixels where as the Dragon Fly CCD has 4.65 micron pixels. So

the larger the pixel, the less magnification you get for the same

pixel area. To achive the same scale would require increasing the

focal length by 1.59 times.

The flip side of this is the light collecting capability of the CCD

for pixel size. Even though both cameras have 1/3" CCD, the Flea CCD

captures more light (2.5 times) than the DragonFly2 CCD did. The 

Flea

camera used less gain (36% verusus 48%) and less exposure time

(19.35ms versus 33.33 ms) to achieve the same brightness level.

So now you have some idea as to what difference pixel size makes 

with

respect to imaging when selecting a CCD for a particular camera.

TTYL...

PS: I uploaded a new lunar quarter image that I took January 4th to

the Lunar section.

Milton Aupperle