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

Date: November 6, 2008 3:11:17 PM MST

To: Astro_IIDC@yahoogroups.com

Subject: Re: Question about Deep Sky techniques at Cedar Key

--- In Astro_IIDC@yahoogroups.com, "doodlebun" <gbleser@...> wrote:

Would you recommend that I purchase a monochrome DMK31AF03 with more 

pixels (but slightly smaller pixels)? I assume the smaller pixels 

would result in longer exposure times than the DMK21AF04. I can't 

seem to find many deep sky shots posted with that camera.

The smaller the pixel, the longer the exposure.

If it's the same CCD model (i.e. monochrome Sony) you can calculate

the difference in exposure time if you know the CCD pixel size in microns.

For example if a CCD has 7.0 micron pixels and another CCD had 3.5

micron pixels, then the light gathering ability is proportional to the

square of the pixel size.

So for 7.0 micron CCD it's 7.0 * 7.0 which is 49.0

and for the 3.5 micron CCD it's 3.5 * 3.5 which is 12.25.

The ratio of 49.0 / 12.25 is 4.0 times.

So you need to expose the 3.5 micron CCD for 4 times the exposure time

than you would for a 7.0 micron CCD to capture the same brightness.

Or should I, like Milton, sell the farm and get a another camera with 

more pixels and sensitivity? I would prefer staying with the 1.25 

inch cameras. Milton has spent plenty of time considering these 

issues but I know his modus operandi. He slaps a Peltier cooler on 

every camera that comes into his house. So this confuses the non-

Peltier modifiers like myself when I try to interpret his photos.

All the IIDC cameras use a C or CS mount interface, so you can get

C-Mount to 1.25",  C Mount to 2" adapters and C-Mount to TS adapter

too. So size doesn't matter, just interface does.

For camera physical size comparisons, see my shots comparing a TIS

camera to PGR Flea / Flea 2 and PGR Grasshopper cameras and  a 1.25"

eyepiece in the "Files" Section of the "Other" folder with these two

files:

TIS_GRASSHOPPEr_FLEA2_Side.jpg

and

TIS_Grasshopper_Flea2Top.jpg

All the TIS cameras are the same size and have the same box form

factor, regardless of the size of their CCD's. The PGR cameras are

lighter and a lot smaller than the TIS are. You can fit four flea /

flea 2 cameras in the same space as one TIS camera.

The 6 megapixel StarShoot Pro looks tempting but I would like to 

continue using Astro IIDC and not jump into Windows with BootCamp on 

my white MacBook.

For long term usability that may be your only option. Steve says you

don't need Firewire, there fore that's all there is too it.

HTH..

Milton