From: "Milton Aupperle" <milton@outcastsoft.com>

Date: January 9, 2006 12:13:38 PM MST

To: Astro_IIDC@yahoogroups.com

Subject: Image scale comparison for different pixel sizes


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