From: Milton Aupperle <milton@outcastsoft.com>

Date: September 5, 2006 12:08:43 PM MDT

To: Astro_IIDC@yahoogroups.com

Subject: Re: [Astro_IIDC] Re: Questions on FireWire Camera Purchase

Hi David;

On 5-Sep-06, at 8:13 AM, David Illig wrote:

David wrote:

My old ToUCam (USB) has died and my iBot (FW) is OK, but no

better than OK...

(Milton Aupperle and Alan Friedman both replied with timely and useful

information that is much appreciated.)

Alan Friedman wrote:

Maybe you want to consider a monochrome camera and filterwheel? You would

notice the increased sensitivity of the monochrome DMK cameras over your

ToUcam.

I thought I understood that, but when I compare the specs of the

supported cameras in my price range, the DMK 21AF04 monochrome and

the DBK 21AF04 color, the published sensitivity specs are identical:

"Sensitivity 0.5 lx at 1/30s, gain 20 dB

Dynamic range ADC: 10 bit, output: 8 bit

SNR ADC: 9 bit at 25 °C, gain 0 dB

There has to be a "Yes, but you must also consider..." in there somewhere,

but I don't know what it is! Help!

Lux numbers are pretty well useless, because no one ever fully explain how they derived them (i.e optics, light source, light frequencies, filters used / not used etc.).

The only sensitivity numbers I sort of trust are from the Sony specification reports for each CCD model. The usually list a sensitivity value in the "Image Sensor Characteristics" table.

http://www.sony.co.jp/~semicon/english/90203.html

http://www.sony.co.jp/~semicon/english/img/sony01/a6805251.pdf

http://www.sony.co.jp/~semicon/english/img/sony01/a6805849.pdf

The monchrome CCD is more sensitive as it has no Bayer color filter array grafted on it. It has an average sensitivity of 700 mV, where as the Color (both Bayer and YUV models) are 580 mV, which works out to be 21%.

However this is still apple's and oranges comparisons, as they measure total sensitivity for monochrome cameras and only measure green sensitivity for the color cameras. I seem to recall from my own tests comparing the mono and color you wind up with around 30% less light being accumulated with color than mono - but it depends on what sort of light the target generates.

Hope That Helps..

Milton J. Aupperle

President

ASC - Aupperle Services and Contracting

Mac Software (Drivers, Components and Application) Specialist

#1005 - 815 14th Avenue. S.W.

Calgary Alberta Canada T2R0N5

1-(403)-229-9456

milton@outcastsoft.com