From: Milton Aupperle <milton@outcastsoft.com>

Date: January 10, 2006 12:15:33 PM MST

To: Astro_IIDC@yahoogroups.com

Subject: Re: [Astro_IIDC] Re: Image scale comparison for different pixel sizes

Hi Tim;

On 9-Jan-06, at 6:19 PM, Tim wrote:

Milton:

Where this will become really interesting to me would be if you did a comparison of DSO

images taken with the two cameras. For example, I've cogitated about purchasing a

wonderfully compact Scorpion 1600x1200 camera (4.4 micron pixels and is uncooled) at

some point to compare with the sensitivity of my awesome but big, heavy, and bulky

ST2000XM, which has 7.4 micron pixels and is cooled. But the Scorpion is an expensive

camera, so I'm afraid to just buy one to find that out. ...so it'd be cool if you get a chance

to do DSO comparisons betwixt the Flea and the Dragonfly2.

Companies don't send me anything, so this isn't going to happen. And any camera I get in here for testing (I have to leave a credit card record on file to even get that far) I have to cover shipping both ways ($100 to $150 CDN) and pay taxes on them (7% if it's made in the USA, up to 18% from other countries). So if I get a $3000 USD camera in here, I wind up paying $250 CDN to $650 CDN up front just to get it out of customs.

The only reason I have the DragonFly2 camera here that Pt Gray is a Canadian company and they want Mac feedback on their prototype camera. Other than that,

For example, if you were to match the image scales for the two cameras by changing the

effective f/ratio, such that the same numbers of photons are hitting a single pixel with

both cameras, is there a difference in the resulting images?

It's the same image then.

...I suppose this opens a can

of worms with respect to the differences/similarities between film and ccds, and aperture

and focal ratios (like I've seen recently on other newsgroups). I would think that quantum

efficiency and well depth differences between the two cameras would be more important,

given the same image scales.

Well depth is essentially bit depth. Obviously a camera delivering 16 bit per pixel in it's A/D converter is going to have a better S/N than a 12 bit camera. Bigger pixel will always win hand down for collecting photons.

The smaller pixels might take longer to pull in the same

amount of light, but the greater number of pixels would make for a more aesthetically-

pleasing image, perhaps.

Your neglecting turbulence, which is going to be the limiting factor in what you get resolution wise.

The other major factor is readout noise and that's where a generic FireWire camera is not going to compete at all. SBIG's cameras don't run at 240 frames per second and their not concerned with high speed transfer rates. Their circuitry is designed to reduce noise as much as possible, which means changing the board layout to isolate components and connection lengths as much as possible. That's part of the reason that your ST2000XM is so bulky compared to a Flea that fits into you shirt pocket.

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