LtE in CMO #286

From Paolo R LAZZAROTTI

® . . . . . . . . Date: Wed, 24 Dec 2003 10:16:31 +0100

Subject: Re: Saturn on December 16th.

Damian Peach wrote:

> Hi all,

> Here is a Saturn image from December 16th. Seeing conditions were good

> to excellent. A small dark spot was captured. The full data set

> follows to the relevant people.

Very impressive result, Damian!

I see you finally work with a video ccd camera...

But there's something strange: 3000 frames multiplied 0,1 secs gives 300 secs (5 minutes!!!), a too longer time for a "spinless" Saturn imaging! Further, I don't believe you used all the frames captured, so the elapsed time should be still longer! But you also managed a CCD setup with the webcam (1-2 minutes?) and a 250 secs RGB color avi through it. The total time elapsed should be about 10 minutes for your final LRGB image!!!!

Please, let me know.

Thanks and best Christmas greetings.

> For this image:

> 00:21 UTC (CM1=318.4, CM3=331.6.)

> 11" (28cm) SCT @ f/31. ATK-1HS CCD (Luminance) and Philips ToUcam pro

> (RGB.)

> L: ~3000 x 1/10th secs. (ATK)

> RGB: ~1000 x 1/25th secs. (ToUcam.)

® . . . . . . . .Date: Thu, 25 Dec 2003 10:22:44 +0100

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

Damian Peach wrote:

> Hi Paolo,

> >>But there's something strange: 3000 frames multiplied 0,1 secs gives

> 300 secs (5 minutes!!!), a too longer time for a "spinless" Saturn

> imaging!

> Thanks for your mail. Infact, you are not correct in that 300secs is

> too long. CCD images produced by Ed Grafton and Myself using windows

> of 360secs using cooled CCD indicates this is fine for Saturn.

> Infact, Ed's images were the very first to discover the white spots at

> -40s on Saturn, and this was done with such an imaging window. Also,

> all the images i produced last apparition were done using 300secs

> window, and no notable blurring occurs, when spots were present on the

> globe.

You're only partially correct! Yes, it might be true when you say 360 secs is a correct time, BUT when you image high latitudes ONLY through a large image scale!!! In fact the WOS you captured is well definied with any blur. In the equatorial belt there's no minimal detail, and this is quit strange in a so well definied image!

I attach you a formula by astronomer Paolo Tanga (who's reading us in CC) measuring the Tmax for a correct planetary imaging:

Tmax [sec] = 1150xPxM/D

Where: P is the rotation's period of a planet [hours]; M is the max rotation allowed at the CENTER of the disc [arcsec] and D its apparent diameter [arcsec]. Assumed a resolution power of 0.43 arcsec for your C11, Nyquist says you have to put this separation in 2 pixels; so you would have a 0.21 image scale with you. But you also well know this is an high value for a fine imaging, so I agree with you to use smaller values as you are doing.

Assumed you didn't resample your final image, you managed a 0.09 arcsec/pixel, so this is M parameter of the above formula.

Tmax = 1150x10.5x0.09/20.5 = 53 secs.

You are definitively far away from an appropriate timing. The math says this, not me! :-(((

For any discussion about the formula listed above, please ask to P. Tanga.

> >>Further, I don't believe you used all the frames captured, so the

> elapsed time should be still longer!

> I used 3000 of 3600 images. Seeing was very good, so little change

> between each raw frame occurs.

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

> >>But you also managed a CCD setup with the webcam (1-2 minutes?) and

> a 250 secs RGB color avi through it.

> Changing between cameras takes about 10 secs, and about 10-15secs

> refocus for the RGB data.

Congs indeed for your fast change!!! Ferrari will be happy to have Damian in his F1 racing team!!! ;-)))

> This doesnt affect the final LRGB image since the atmospheric details

> present in the image are resident in the L image, while the RGB is

> simply the colour information.

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

> Both cameras can be controlled from the same software, so this is very

> convenient.

This is good.

® . . . . . . . .Date: Fri, 26 Dec 2003 11:07:23 +0100

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

Ed Grafton wrote:

>>Assumed you didn't resample your final image, you managed a 0.09

>>arcsec/pixel, so this is M parameter of the above formula.

>>Tmax = 1150x10.5x0.09/20.5 = 53 secs.

>Hi Guys

>For this discussion lets assume that the 2x sampling for max resolution is

>correct, although I am no longer as convinced of this as I once was. Let me

>also state that I have not see a rigorous mathmatical proof to to refute the

>2x rule as applied to our application.

>The application of this rule DOES NOT extend to the time window of gathering

>images for later averaging or "stacking". The 2x rule is satisfied by the

>image scale ( sampling) and the TIME WINDOW OF A SINGLE FRAME. All the

>SAMPLING CRITERIA is completed on the INDIVIDUAL FRAMES. Stacking or

>averaging the individual frames is a REGISTRATION issue not a sampling

>issue. During the registration and "stacking" ones hopes to maintain the

>resolution already captured on the individual frames and improve the S/N.

>The resolution captured on each frame would be at best .43 arcseconds. If

>the planet rotated less than .43 it was not resolved by the scope. The

>window calculated from the formula given by Paolo's formula would then be 253

>seconds.

Hi Ed,

What you say is correct; the M parameter of my formula is referred to the max blur accepted.　If you don't want any blur in your final image, that means the first frame and the last one have to be captured before the planet would spin 1 pixel at least at the center of its disk. If your image is sampled at 0.4 arcsec/pixel, that means you can accept a max blur of 0.4 secs; if you sample at 0.2 arcsec/pixel, you can accept a max blur of 0.2 secs and so on.

I assumed Damian's image scale as 0.09 arcsec/pixel, so my consideration is right. But if he was 2x resizing the final image, than the appropriate value to consider is 0.18. This is clear!

>In practice it would take 10/10 seeing for several minutes to acheive the

>.43 arcseconds resoltion, which I have never seen. In fact the seeing might

>have to be .43 arc seconds/2 to achieve the .43 arcseconds resolution since

>that is the sampling being performed by the required nyquest 2x rule!

Yes, the discussion we're feeding is based on the math.

>>Damian Peach wrote:

>>I would agree with you that this isnt an appropriate 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.)

>>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!?.

>This S/N point is a good one. None of the low contrast spots that I have

>imaged have shown on any one frame. The resolution is there but it is lost

>in the noise and can only be recovered by improving the S/N by "stacking"

>many images. The latest dark spot that Damian imaged is a good example. The

>low contrast .7 arc second spot imaged by Damian would have gone undiscoverd

>if the S/N would have been lower than he achieved, due to a less a less

>productive imaging strategy having been employed, ie a shorter window.

I agree at all; read at my last reply to Damian. I only disagreed Damian about the focal length.

® . . . . . . . .Date: Fri, 26 Dec 2003 10:46:55 +0100

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

Damian Peach wrote:

> Hi Paolo,

> The small spot spans 0.78" x 0.70" in size - well within the limits of

> the time window used.

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.

> Check this formula calculated by a good friend which i have refered 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 gives further reason to me! 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? 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. This is the same result come out from Tanga's formulae, too. It would be a pity to loose the finest detail detectable in order to have an estetical image only...

> 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)

Yes, but this animation, as for your image, can't say anything about the

REAL size of the spot.

> I would agree with you that this isnt an appropriate 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.)

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 longer is the focal, the larger is the noise and the lower is the contrast.

> >>>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.

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!

> Halving the window would not improve resolution, as the image would be

> so much more noisy, resulting in this detail being lost in the noise.

> Why shorten the window when the one being used already works

> regardless of the seeing!?.

Because on this way you can also discover the smallest features in the equatorial belt! ;-) IMHO, sizing the focal according to the resolution power or the seeing condition you're able to capture all the features detectable over a planet! Now you're just imaging very well the high latitudes only.

> >>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?.

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

> 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!.)

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

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

To you, too!

® . . . . . . . .Date: Fri, 26 Dec 2003 15:04:03 +0100

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

Damian Peach wrote:

> 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.

Ok, now we're clear! ;-)

> Perhaps there is slight blurring, but this is not a concern to me. I

> consider it an achievment to even image such a feature. Check

> Christophe's 00:13 UT image of the same night (also faintly shows this

> spot.)

You're a step from having images close to the perfection when the seeing does cooperate; I'd like to see pictures from you as near as possible to the "atmospheric limitation" only!

> >>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 obsruction/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 atmopsheric spots) unless your using the Pic 1m

> cassegrain, and even then it would be a struggle due to many issues.

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. At this point, you must decide what to blur and what to reproduce in a still image. 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; 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 think my opinion now is clear.

> 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.

Ok, this is very clear. If you want to accept 0.5 arcsec as limit of your instrument, then you have to stay ANY CASE below the 140 secs. Any larger window time will be introducing >0.5 arcsec blurring. In fact the 0.5" power limit has to drop within 2 pixels for the Nyquist criteria; I think it's enough to have it into 3 pixel to get some blurring.

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 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.

I don't understand what do you mean for "natural" appearance: can you give me an explanation? Further, I usually see Saturn more yellowish with my eyes.

> Since the new BW CCD is much more sensitive, using F/31 is no problem

> at all with noise.

Where can I find more info about your camera?

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

I like better the original format!

> >>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.

I don't believe this is a good reason to make this zone blurred...

> >>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 :-).

You're an ultra-specialized planetary imager!!! :-ooo :-)))

® . . . . . . . .Date: Sat, 27 Dec 2003 15:26:46 +0100

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

Damian Peach wrote:

> 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 occuring 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.

I don't mean you have to stay within 1 minute recording; I'm just saying you have to size the window time according to the real resolution in order to avoid partial blurring into your images.

> >>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.

Then, you have to stay in a window time capable of freezing up to 0.6" detail, nothing more nothing less.

> >>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 to 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!! ;-).

You're definitively correct in your statement until you stay in the high latitudes. Equatorial storms are supposed to be larger than spots, so they are less critical BUT this is not a good reason any way to stretch them!

> >>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.

Damian, I'm sure you had a better image through the 120" avi frames stacking...but the critical point it's always the same: the larger time is good ONLY on the mid-high latitude zones!!! 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!!!

> >>>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.

Ok, thanks.

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

> Saturn's globe definatly isnt yellow! :-).

"｣$%&/()=??????????

The cases are 2:

1. you're colour-blind;

2. sky over England is polluted with pink dust.