LtE in CMO #271

From David M MOORE

. . . . . . . . . . Subject: Mars - 24 April, 2003


All: First useable (probably debatable!) Mars images this apparition. Was concerned the ToUCam may not be a good camera choice for a small Mars. It is hard to adjust the image and not get a hot spot in Red. Focus does not appear to be the same in all colors, as the Blue light images tend to be more blurry. Hopefully, this is only a product of the seeing. After viewing Maurice Valimberti's images of Mars with the ToUCam, I am hopeful this is the case. Awesome images for only 7.8" from down under! See


Does anyone have Maurice's email address?

I hope to image soon with my HX-5 as well. Am putting the finishing tweaks of collimation on my 14" cass.


(24 April 2003 email)


. . . . . . . . . .Date: Thu, 24 Apr 2003 10:54:22 -0700

From: "David M Moore" <>

To: <>

Subject: Re: RE:Mars - 24 April, 2003


Masatsugu: Good hearing from you again. The issue of using the webcam strictly for RGB purposes is probably not a good idea, hence the reason I want to use my HX-5. The filtering over each pixel is probably not as stringent as our RGB filters with IR blocker. Most assuredly, without the use of an IR blocker, the Blue images are being tainted. I will experiment with an IR blocker in the morning, seeing permitting. Perhaps the results will be better. On second thought, that should prevent the Red images from being so hot and may cut back on the distortion in Blue. Good idea Masatsugu! It will mean longer exposures however, or more gain. Always a trade off!!

Of course, if my images are worthy, please use them on your CMO website as you see fit.


Thanks for Maurice's email address.



. . . . . . . . . .Date: Thu, 24 Apr 2003 11:24:11 -0700

From: Tim Parker <>

Subject: Re: Mars - 24 April, 2003


Dave: Have you tried splitting the RGB channels and re-registering them to compensate for atmospheric refraction? I've done this before with the 3com camera, and it works - to a point. The success will be limited because most color ccds (the Toucam, tou?) have cmy and green pixels (with green being by far the most abundant), where red AND blue are derived from the cyan and magenta filters (so you can't really split them effectively). It would be interesting to know whether any of the webcams use RGB on-chip filter ccds. But Apogee tried them without success (and Terry Platt says he experimented with the RGB color version of the HX5's ccd, and found it too insensitive for low light), so I guess I doubt this. Also, Mars is mostly red, and since the red will always have some of the smear from refraction of the magenta filter across the red-blue range, this might be part of the problem as well.

Wouldn't it be nice if there were a grayscale version of the Toucam that you could use a filter wheel with? (I guess you could "make" one by taking the IR block filter out of the camera, using the one in your filter wheel instead, and running the camera in "grayscale" mode).

planetary regards,



. . . . . . . . . .Date: Thu, 24 Apr 2003 11:53:36 -0700

From: "David M Moore" <>

To: "Tim Parker" <>

Subject: Re: Mars - 24 April, 2003


Tim: Thanks for your reply. I have tried splitting the images and reopening them in Astroart, messing with the histogram and restacking them.. I have not yet tried to realign them in the manner you describe however. I will try it next time.


Yes, I was just discussing the merits of using the ToUcam for Mars with Masatsugu, and his concerns regarding Blue images. I told him much the same as you have just described. The chips do not use RGB pe se, but we split them like it does. Not using an IR blocker, may well be part of the problem too. I will try using a IR blocker in the morning and see if this does not improve the Blue images and possibly stop the hotspot in Red. Also, I doubt the filters over each pixel are very strict on their exact wavelength preferences. There is some wavelength bleed over from one filter to the next. I feel the webcams do a fine job of extracting data in color for monitoring of overall changes and of course the esthetics. For exacting purposes of studying Mars in specific wavelengths, they no doubt fall short. This has been a concern of mine.




Dave MOORE (Phoenix, AZ, USA)

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