From: "Tim" <tjp314@pacbell.net>

Date: March 20, 2007 10:50:29 AM MDT

To: Astro_IIDC@yahoogroups.com

Subject: Re: Saturn March 18th

Jim:

I can't remember if you specified anywhere what brand/type color

filters you are using.  If you don't already have a set, you might

want to get dichroic filters, rather than died glass filters.  The

died filters absorb too much of the wavelengths you're interested in,

and have a lot of "leakage" from other wavelengths in the wings.  

I agree with Alan also about the value of trying monochrome for the

luminance, but I would recommend you use green, as there are twice as

many green pixels as red or blue pixels.  Also, depending on the

optics you're shooting with, the best focus might also be in the green

(our eyes are most sensitive to green).  My 6" f/10 Jaegers refractor

does very well at green monochrome with a green filter.  I've tried

monochrome with red and blue separately, but the focus is still too

soft at those wavelengths even if I adjust the focus knob.  So, while

the Jaegers does very well visually on the planets, it doesn't do well

as a planetary color imager.  It does fine on DSOs, though, as the

color abberations aren't objectionable at f/10.

-Tim.

--- In Astro_IIDC@yahoogroups.com, Alan Friedman <alan@...> wrote:

Hi jim -

Great to see your two images a year apart sitting next to each other

in  

the files area - the learning curve is paying off.

Saturn is a really tough nut to crack - it demands good seeing perhaps  

more than any other planetary subject. You can get some help in  

moderate seeing by using the red filtered streams (maybe combined with  

green) for luminance - the steadiness is always better in red. But the  

light tradeoff with the red filter means using a much slower shutter,  

which negates much of the advantage (and of course you don't want to  

bin your luminance data). With my 10" at about f30 even 66ms at full  

gain is very dim and noisy - at 133ms the brightness is acceptable but  

the noise becomes evident quite quickly processing  a stack of 200  

frames. Really the only way to go is to use unfiltered streams for  

luminance (or a much smaller image scale) - and this requires 6-7/10  

seeing for a good result, I think.

Now the happy news is the Clear Sky Clock forecast for our region  

tonight!!

best -

Alan

On Mar 19, 2007, at 8:31 PM, jimchung2338 wrote:

Hey everyone,

I've given up on trying to get color data from my Unibrain webcam

for  

imaging Saturn and

turned to a filter wheel with my mono Flea. Much better results

in my  

opinion but still

ascending the imaging learning curve.

http://tech.groups.yahoo.com/group/Astro_IIDC/files/Planetary/ 

saturnmar18b copy.jpg

Jim