LtE in CMO #286

From Damian A PEACH



. . . . . . . Date: Thu, 25 Dec 2003 13:42:11 -0000

Subject: Re: [Saturn-ALPO] Re: Saturn on December 16th.

 

Hi Paolo,

 

The small spot spans 0.78" x 0.70" in size - well within the limits of the time window used. Check this formula calculated by a good friend which i have referred to:

 

Equat Merid drift = 3.14x Globe Diam" x Imaging Window minutes

--------------------------------------------------------

60 x Planet Rotation in hours

 

which comes out at 3.14 x 20.6" x 6mins/(60 x 10.2 hours)

 

= 0.63 arc-seconds, which is not much more than the 0.4 arc-sec theoretical resolution of a C11.

 

This puts resolving such a feature well within the limits of the windows used. I attach an R light animation (each was taken over 300 secs window, and show the feature clearly)

 

I would agree with you that this isnt an appropraite timing to reaching the theoretical limit of the telescope, but the fact remains that you are NEVER going to resolve low contrast spot-like features better than ~0.5", so the window works (as proved time and time again by Grafton/Myself.)

 

>>>The better is the seeing, the shorter should be the elapsed time

 

You are not taking into account noise is a major limiting factor in resolution of low contrast detail to this level. Halving the window would not improve resolution, as the image would be so much more noisey, resulting in this detail being lost in the noise. Why shorten the window when the one being used already works regardless of the seeing!?.

 

>>Congs indeed for your fast change!!!

Ferrari will be happy to have Damian in his F1 racing team!!! ;-)))

 

Lots of practice :-).

 

>>Yes, but don't forget if the crominance and the luminance are shifted, you'll go painting a detail with a wrong color!

 

This would be true yes, but what transient features on Saturn have any distinct colour?. With Jupiter i agree the window is much tighter for this, but with Saturn a couple of mins either way is not a problem (provided a Great White Spot outbreak isnt underway!.)

 

Merry Christmas to all - off to have my dinner :).

 

Best Wishes,

 

. . . . . . .Date: Fri, 26 Dec 2003 11:12:34 -0000

Subject: Re: [Saturn-ALPO] Re: Saturn on December 16th.

 

Hi Paolo,

 

>>How can you say this is the real size of the spot?

The above sizes are just the dimension of the spot imaged...

Maybe the real dimension or a stretched measure of it as well.

 

I never said this was the *real* size of the feature - its the size it measures from the images. Perhaps there is slight blurring, but this is not a concern to me. I consider it an achievement to even image such a feature. Check Christophe's 00:13 UT image of the same night (also faintly shows this spot.)

 

>>If you consider 0.4 arcsec for your C11 you're wrong!

The Encke is out there...How can you consider a 0.4 value when in your image there's a 0.1 value well captured?

 

Infact i am correct. You have not considered that the resolving power of the telescope on Planetary features depends on the contrast of those features, and the contrast the telescope delivers at focus dependant on obstruction/focus/seeing etc.) With high contrast detail such as Saturns ring divisions (Encke spans 0.05") which is 8x less the Dawes limit of the aperture it is only possible to resolve it with such an aperture because it presents a black line on a bright background. You will never resolve low contrast details to this level (such as Saturnian atmospheric spots) unless your using the Pic 1m Cassegrain, and even then it would be a struggle due to many issues.

 

I simply say that i am happy and accept a ~0.5" limit for detecting such features - i have no desire to try to detect a 0.1" spot because it will NEVER happen (see Ed's comments re: seeing.) How many times a year does the average site experience 0.5" seeing for long periods? - not very often!. And 0.2" seeing for long periods (at amateur sites probably once every few years!?.) Even at Pic du Midi such seeing occurs only a few times each year. All these reasons are why i choose to use a longer time frame to capture the data.

 

>>If you're able to capture 0.1 arcsec features, I think you must consider a time related to this value, so that a 6 times shorter window that gives 1 minute about.

 

Refer to above comments.

 

>>>Then, I guess why you use so long focal if you assume 0.5 arcsec as lower limit. It would be enough to use a 0.25 arcsec/pixel scale to image Saturn very well...

 

The original image scale is 0.135"/pixel.

 

>>I well know this!

While reducing the focal, you reduce also the noise and you can take a more contrasted image at the same time!

 

I desire to maintain a "natural" appearance to the data obtained in good seeing. This means a higher sampling is needed. I could easily use lower sampling, and produce a high contrasted image (which is useful) but this would mean losing out on producing the natural looking result. If i want a high contrast image i simply reduce the original.

 

Since the new BW CCD is much more sensitive, using F/31 is no problem at all with noise.

 

The red light animation i sent you is at the original sampling.

 

>>Because on this way you can also discover the smallest features in the equatorial belt! ;-)

 

Perhaps this would present some advantage but again, rarely do such spots occur in this region. Storms there are often large scale features, that are easily resolved.

 

>>Now you're just imaging very well the high latitudes only.

 

Spots that occur outside the equatorial zone is currently my primary interest in Saturn imaging, with the activity we have seen the last 2 years :-).

 

>>>A detail can be discovered because of different color and/or brightness respect to the background!

This is a guilt admission!!! :-)))

 

For Jupiter yes, but on Saturn thats highly unlikely. Even HST imagery rarely shows spots of distinctly different colours, so a couple of mins either way for the RGB data doesnt really present a problem.

 

Best Wishes,

 

. . . . . . .Date: Fri, 26 Dec 2003 18:45:09 -0000

Subject: Re: [Saturn-ALPO] Re: Saturn on December 16th.

 

Hi Paolo,

 

>>I'm going to think we're making confusion between low contrast spots and high contrast divisions. Of course a Saturn's division doesn't need of timing limitation, so you can push the duration until your hard disk is full! So, the only limitation is given by the planet's rotation. You'll agree with me when I say the blur is coming whenever you go over the image scale value, isn't it?

Hope yes.

 

Yes, i agree some blur is occurring when you go over the "ideal" value. However, i simply use a technique that works well enough to record these spots, and i am happy with that. To narrow the window down to say 60secs would not be practical at all, even in good seeing - the result would be to noise ridden, and details would be lost.

 

>>At this point, you must decide what to blur and what to reproduce in a still image.

 

 

The question is how much blur is acceptable? In this case, ~0.6" worth of rotation is acceptable to me in producing an image, as it will reveal all the features i can capture on Saturn.

 

 

>>If your target is the high latitude spots, ok, you can push up to 5-6 minutes imaging through the image scale you're now using;

 

 

This has been my point....

 

>>if you want a still image of the WHOLE planetary disc, you MUST reduce the window time of your imaging until the faintest spot detectable from your instrument at the equator can be frozen into your CCD.

 

I still say the amount of blur incurred during the time window used is simply too small to be concerned with under real conditions. I have imaged storms in the EZ using the 300sec time window. I accept this isnt "theoretically ideal" but it works, and works well...not unless all the spots weve found are artifacts!! ;-).

 

 

>>Much more dramatical will be the next Jup imaging where also the smallest WOSs will be nicely contrasted! I suppose you'll have to stop your CCD at 1 minute or less.

 

I did a very interesting experiment while on Tenerife imaging Jupiter. Using the same image scale (0.13") i imaged the Planet for 60 secs, then imaged it for 120 secs (the seeing was excellent.) I then produced stacked raws of both and processed them. You could tell no difference in the detail in either, accept the 60secs had more noise. I am quite sure youd say using more than 60secs isnt ideal - but yet again look at the Jupiter images at my website - all done using 120secs window.

 

>>>I don't understand what do you mean for "natural" appearance: can you give me an explanation?

 

I mean an image that doesnt look to processed, but presents an accurate and realistic image of the Planet. This needs good seeing, and careful processing.

 

>>>Further, I usually see Saturn more yellowish with my eyes.

 

 

Saturn's globe definitely isnt yellow! :-).

 

>>>Where can I find more info about your camera?

 

rtripa@perseu.pt

 

>>I like better the original format!

 

I prefer the more lightly processed larger result...:-)

 

Best Wishes,

 

. . . . . . .Date: Sat, 27 Dec 2003 15:39:32 -0000

Subject: [Saturn-ALPO] Saturn on December 16th - Final reply.

 

Hi Paolo,

 

>>>I'm strongly sure if you had had an ideal CCD camera capable of webcam performance without the noise, you'd have had the best result through the 60" avi film; the longer one would have been showing some blurring in the EZ. In the practice, you found out a good compromise between the EZ blurring and the global disc noise. I might put my hand on the fire to defend this!!!

 

Currently a webcam doesnt exist that is true 16bit, and peltier cooled. When it does, then i am sure 60sec window would be fine for producing good images. With current technology it isnt. I have certainly no reason to complain at the results ive obtained with my "flawed method" ;-))).

 

>>>Saturn's globe definitely isnt yellow! :-). "$%&/()=??????????

The cases are 2: you're colour-blind; sky over England is polluted with pink dust.

 

Basically, under good seeing i find Saturn's globe to not be yellow at all really, but rather "reddish brown" tone, with blues/greys, and sometimes greens. A multitude of colours can sometimes be seen.

 

I find Saturn to look yellow in poor seeing, or small apertures. Certainly, high resolution images of Saturn dont show it to be yellow at all :-). But i am NOT going to be drawn into a debate on this, as we will still be here this time next year :-).

 

Best Wishes,

 

. . . . . . .Date: Sat, 27 Dec 2003 18:00:30 -0000

Subject: Webpage update

 

Hi all,

 

Just a quick note i updated my webpages with many new images.

 

http://www.theplanets.cjb.net/

 

Best wishes for the new year to all,

 

. . . . . . .Date: Mon, 29 Dec 2003 00:14:23 -0000

From: "Damian Peach" <dpeach_78@yahoo.co.uk>

To: "Don Parker" <park3232@bellsouth.net>,

"Richard McKim" <RMckim5374@aol.com>,

"Masatsugu Minami" <vzv03210@nifty.com>

Subject: Mars with 4.2m

 

Hi all,

 

One of the chaps who works at the observatories on La Palma, sent me some raw test images to process they took using their new Adaptive Optics system on the 4.2m William Herschel Telescope.

 

The attached I filter Mars image is the best from a set of 30 or so, taken back on July 13th, 2003. The resolution is very good for 19" diam. Some interesting details inside the SPC are visible.

 

The line artifacts are due to the Planet being position across 4 CCDs, and some hot pixels are also present.

 

Hope you find it of interest.

 

Best Wishes,

 


Damian PEACH (Loudwater, Buckinghamshire,UK)

ALPO/BAA Jupiter Sections; BAA Saturn Section
email

Homepage: http://www.damianpeach.com/


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