From: Alan Friedman <alan@greatarrow.com>

Date: March 21, 2007 11:47:34 AM MDT

To: Astro_IIDC@yahoogroups.com

Subject: Re: [Astro_IIDC] Saturn March 18th


ps -


A simple trick is to color code the file icons on your computer with r,g and b color labels. I always do this before I shut stuff down for the night. 


a.



On Mar 21, 2007, at 12:37 PM, Alan Friedman wrote:


Those are very good thoughts, Phil. I think it is valuable to block the IR in all of the RGB streams. These chips are very sensitive in the near IR wavelengths. After a while you get pretty good identifying the images (and the video on screen) from the different filters. The only ones I might get confused on now are R and IR - they look pretty similar, althought the IR is usually brighter with the same camera settings. I keep these two filters separated on my wheel and know them by their positions relative to the others. On almost any night, the "seeing" differences by wavelength would be enough to tell them apart - if it's 6-7/10 in red, it is 5/10 in green and 3/10 (or worse) in blue.


I find it hard to get good exposures in the RGB streams - often I have to drop the shutter down to 133 for red and blue (usually can get by with 66 for green) and still will need a high gain setting. Often the image looks OK outside in the middle of the night - then I'm shocked at how dark they are when I view them the next day (why don't I believe the histogram?). So I usually have to do some significant tweaking of the channels in Photoshop. I usually do this by selecting each channel separately and adjusting with curves or levels (remember to have the RGB channel enabled so you can see the effects.) I will keep a reference image or two open to compare. We've got enough filtration between the planet and our cameras running interference - no harm in making these adjustments to your captured data, IMO.


best -

Alan



On Mar 20, 2007, at 7:07 PM, Phil Houston wrote:


Jim,


Looking over your Saturn image reminded me of some color problems I've had using color filters on a monochrome camera.  If I remember correctly, two solutions come to mind, I apologize if this has been covered in a recent post.  The RGB filters I use allows way too much IR to pass and by adding an IR blocking filter I got rid of the excess red and could balance the colors.  The IR block filter may only be needed in combination with the red filter, but I use it with all colors captured.  The other solution to a few of my "poor color" images was to make sure that I did not inadvertently switch the red and green channels when assembling the RGB information. That also plays hell when trying to capture decent color, too.


This year was the first year I've used a monochrome camera (DMK) to capture Saturn and have found that by using the rings to obtain a white balance, the planet colors seem to look okay to me.  Before the DMK, I used a Toucam and found much greater variation in color from one image to another.  I have never had the chance to use a Flea camera.


Good luck with yours and I hope to see good Jupiter shots this year as well.


Phil


http://www.knology.net/~pkh111/astrophotos/Q6saturn.html





On Mar 19, 2007, at 9:31 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/saturnmar18bcopy.jpg 


Jim



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