LtE in CMO #272

From Maurice P VALIMBERTI

From: "Maurice Valimberti"

To: "David M Moore"

Cc: "Masatsugu MINAMI" 　

Subject: Re: Mars - April 25, 2003

Hi Dave, Thanks for sending me your Mars images from the 25th - good job..

I was interested to receive the comment from Mr Minami regarding the B bandpass of the ToUcam. I too have been uncertain of using this as my camera of choice. I have concerns more so about its G characteristics, as they appear to cut into much shorter B wavelengths than a standard BVR set.

I believe that the CCD used in the ToUcam is the Sony ICX098BQ, and so have attached a page from the data sheets for this device which shows it's transmission curves. Also attached is a diagram showing a UVBRI set used at Kitt Peak. The longest wavelengths which pass in B are about 570nm for both. The G curve on the other hand, skews right back to start at about 400nm for the ToUcam, and about 470nm for V in the UVBRI set. This, of course, does not take into account the IR component for the ToUcam because the 'standard imaging conditions' as specified by Sony require the addition of an IR cut filter.

I will try to do as you have done, and image with an IR block in place. Hopefully this may clear up some of the B 'ghosting' anomaly mentioned by Mr Minami. As to the G response - I'm not sure. Of course, this all presumes that the transmission curves as quoted are accurate... I would be keen to hear your opinion.

(27 April 2003 email)

Hello again! It has been a while since our last correspondence - I hope you are well.

Sorry for the upside-down image which I sent to you recently - I'll make sure that mine are in the correct orientation in future. It was a lapse on my part - maybe due to my being in the southern hemisphere ? :)

I have attached here the original version (with correct orientation), as well as the more recent blue channel enhanced one for your perusal….Also, you will find a raw, stacked version, as well as a single raw frame (my images suffer from dispersion effects too; as you can see) - these last two have been resampled 2x from their original size - I tend to do this when processing.

The edge effect which you mention appears to be at least partly an artefact of my processing. When the seeing is good, I try to extract as much fine detail as I can out of my images, whilst trying to minimize noise. This for me usually means choosing a small unsharp mask radius & large contrast enhancement. If the edge shows a slight limb arc, as it does in this case (see the raw stacked set, as well as the single frame), then the higher contrast at the edge combined with the small mask radius accentuate the problem. I could use a larger mask radius together with less contrast enhancement, but this would be at the expense of fine detail. I would not get as noticeable a 'dark line', but the limb arc size would be exaggerated.

I guess that its a balancing act - at least for me it is. I believe that it is in the very nature of unsharp masking, that this effect develops. The lower frequency image components remain nearly as in the original image, whereas the contrast of the high frequency components is increased by the contrast factor used.

If you examine the stacked, but otherwise unprocessed frame which I have sent; the area around Syrtis Mj, N & f is about 3% darker than the surroundings. My processing exaggerates this for the reasons described above. Maybe this is part of the effect which you note? We have spoken before of the color 'skew' which can be expected of using the ToUcam; perhaps this is also playing a part in the 'strange' data?

I appreciate your note of my image of the 5th April. There is much I have to learn about Mars!

Kind regards

(11 May 2003 email)

Thank you for forwarding this to me...interesting idea. I look forward to seeing the results of images taken with this method.

(14 May 2003 email)

Dear Masatsugu, I am happy that my image is of use to you. As you say, it is difficult to make an appropriate judgement with the ToUcam data.

Visually, I could not detect the colour well. The C14 which I am using is an old one and tends to 'warm' the colours (I believe that the older C14's had uncoated float glass correctors).

I will try and image the region of interest again tonight, & will forward the results to you if they are favourable. As we are expecting rain here soon, this may be my last chance at this long. for a while..

I have attached another image, taken only two minutes earlier, for cross reference purposes.

(23 May 2003 email)

Subject: Images from this morning - 23rd May UT

Attached is a set from this morning........

Subject: Follow-up images to Thaumasia activity

Attached is a preliminary set from this morning... Will follow with final captioned image soon.

Subject: Final image 24th May UT

Attached is the final version (captioned) of the data taken this morning. Very bright am. limb in "R" (from camera) on 17:11 UT image.

Maurice VALIMBERTI (Melbourne, Australia)

mauricev@ozemail.com.au

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