Teepee-Maïcé

Bonjour,Dans le logiciel 3D il y a peut être une option sur les diverses sortes de perspectives possibles. A mon avis le prob vient de ce que le dessin est à plat avec les lignes de vision parallèles alors que dans la réalité le télescope va être vu d'un point ce qui n'est pas la même chose, les lignes de vision ne sont pas parallèles. Je suppose que tu as calculé la valeur de l'offset. De toute façon le dessin le détermine automatiquement si le cône est vraiment un cône. Pour ceux que ça intéresse, il y a un calculateur en ligne bien pratique. http://www.bbastrodesigns.com/tm/diagonal.htm @+!!Thierry

Bonjour,Je lui ai posé la question il y a peut-être un an, il a répondu que les argentures étaient réservées au matériel professionnel...@+!Thierry

Bonjour,Normalement sur une cage secondaire en anneau ou susceptible de ne pas bloquer la lumière, il faut mettre un baffle à la sortie du porte oculaire et un autre baffle plus grand, de l'autre côté de la cage en face du P.O.Il y a la feuille de calcul de bafflage de Stathis Kafalis: http://www.geocities.com/dobsonstathis/kyklopas_fov_and_baffle_calculations.xls @+!Thierry

Bonjour,Paul Van Slyke pour les versions costaudes. http://www.observatory.org/turret.htm @+!Thierry

Re,Faut que ça tienne au chaud, au froid, à l'humidité etc. Le collage d'un secondaire au silicone c'est tout un art. http://astrosurf.com/altaz/508.htm#collage @+!!Thierry

La colle silicone ça colle pas trop des masses sur le PVC. Faire un essai préalable, mettre un petit tas de colle silicone sur du PVC et le retirer après 24h pour se donner une idée de la puissance du collage. Il y a une façon de faire tenir de la colle silicone sur des plastiques qui n'en veulent pas, c'est de faire des petits trous dans le plastique et faire pour que la colle les traverse, au moins ça donne une tenue mécanique.@+!Thierry

Bonjour,En fait le plus élégant serait de calculer le bafflage correctement de façon que la lumière parasite soit bloquée et que toute la lumière venant du miroir primaire arrive à l'oculaire, sans être diaphragmée par aucun dispositif.@+!Thierry

Il y a déjà plein de réponses ici: http://astrosurf.com/tests/image/image.htm#haut @+!!Thierry

Bonjour,Il s'agit d'un cabestan dans lequel l'oculaire ne tourne pas quand on fait la mise au point? Cela voudrait dire que la partie filetée n'est pas coaxiale à l'alésage du logement des oculaires, c'est vrai que c'est une condition qui n'est pas forcément facile à respecter si on ne fabrique pas les deux surfaces en une seule fois en laissant la pièce dans le mandrin du tour. Il y a une méthode de collimation avec le laser qui permet de minimiser l'influence de l'orientation du collimateur dans le porte oculaire, c'est la méthode laser + barlow inventée pas Nils Olof Carlin. http://www.atmsite.org/contrib/Carlin/collimation/kolli2.htm#barlowlaser Ca permet de régler la collimation du miroir primaire aussi précisément qu'avec le cheshire, ce qui revient à une collim très proche de celle effectuée sur étoile, et même supérieure en cas de turbulence moyenne. La position du laser dans le porte oculaire devient quasi indifférente dans le processus de collimation. Il faut toutefois régler le miroir secondaire normalement sans barlow. Rien n'est donc encore perdu!!@+!!Thierry

Re,Il y en a aussi chez Otelo mais j'ai pas le catalogue sous les yeux là. www.otelo.com @+!Thierry

Salut,Il y en a chez Selectronic mon gars. ref 50.8410-10 M3x16, 1.80 euros les 10. ref 50.8442-10 M3x20, 2.50 les 10. Il y en a en inox aussi. (J'ai aucune action dans ce magasin!)@+!Thierry

Re,Non, pas sur tous, le frein est en option. Je conseille de le prendre d'ailleurs car il est très utile en visuel aussi. Sinon oui, pour la photo je suppose que le feathertouch est parfaitement adapté. Il n'y a que pour la MAP électrique que faut plutôt se tourner vers JMI, Don Clement, Van Slyke... A moins de bricoler un système de MAP électrique car ce n'est pas prévu à première vue chez Starlight.@+!Thierry [Ce message a été modifié par Teepee-Maïcé (Édité le 15-09-2005).]

Hello,Prends le Feathertouch si tu as les sous, ou le Moonlite si t'es fauché. Ne prends pas de PO en 1"1/4 vu que tu serais obligé de le remplacer un jour ou l'autre. D'ailleurs qu'est ce qu'il y a de bien en 1"1/4? Le cabestan est moins pratique que le crayford car quand on tourne un cabestan, ça fait pas mal bouger le télescope et la mise au point est plus difficile en fait. Alors qu'avec le feathertouch la molette démultipliée tourne au moindre effleurement. Je parle pour l'utilisation Dobson. Pour la photo, c'est un autre problème. En tous cas prends un PO avec démultiplication, c'est vraiment un plus.@+!Thierry[Ce message a été modifié par Teepee-Maïcé (Édité le 15-09-2005).]

Bonjour,Il faut vérifier que la grosse molette de serrage en altitude ne tourne pas dans le vide. En fait le serrage en altitude est le point faible mécanique de l'etx. De la graisse migre toujours dans l'embrayage et il faut serrer de plus en plus fort pour que ça tienne, sinon lors des goto, ça glisse et le pointage est mauvais. Donc entre parenthèses quand on peut serrer et que ça glisse encore, il faut dévisser la grosse molette et enlever le produit huileux qui est entre les parties en contact de l'embrayage. Le prob c'est que le système de serrage ne peut supporter un serrage très important car ça tire sur un insert en laiton qui est pris dans le plastique et ça finit par se craqueler et s'arracher. Donc vérifier que le serrage efficace se situe vers le "demi gorille", vu que si on serre d'un "gorille" ben ça va casser. L'unité "gorille" étant la force qu'une poigne costaude peut déployer en forçant pas mal. Si ça ne serre plus du tout c'est que c'est cassé.L'etx peut servir comme chercheur/viseur goto quand on passe à un diamètre très supérieur comme un bon dobson. Il faut l'équiper d'un quickfinder. La chose intéressante dans l'etx est justement le goto, car c'est vrai que le diamètre limite son utilisation aux amas ouverts, et aux objets de Messier les plus visibles. La puissance de ce télescope se situe aussi dans la poignée de la valise de transport. On se sent plus fort quand le télescope est petit.@+!Thierry

Bonjour,On a parlé de ça ici il y a qq jours: http://www.astrosurf.com/ubb/Forum2/HTML/014465.html @+!!!Thierry

Bonjour,12mm en avant du focuser complètement rentré, c'est le strict minimum. Il vaut mieux prévoir entre 20 et 25mm pour être tranquille. Un lien utile pour calculer le rayon du champ de pleine lumière et l'offset du miroir secondaire: http://www.bbastrodesigns.com/tm/diagonal.htm @+!!Thierry

Le Nagler 20mm T5 il est super très bien corrigé pour un f/d4. Prends le, tu prendras un 26mm T5 plus tard pour la Rosette etc. Le Nagler 9mmT6 il est super. Un Pentax 5mm je n'ai pas essayé. Moi celui que j'utilise le plus pour les galaxies c'est le Nagler 13mmT6. Pour moi c'est l'oculaire de base. Confortable, pas d'ombres volantes, grand champ, un peu de déformation en coussin certes, belle luminosité. Pour grossir un peu, le Nagler 7mmT6. Sur les amas globulaires il est top. Ceci pour le ciel profond et planétaire occasionnel, pour quelqu'un qui ne porte pas de lunettes en observant. Pour avoir un cran au dessus en planétaire, il faut la bino de qualité et les bons oculaires. Il vaut mieux avoir le suivi aussi. @+!Thierry

Il faut tous les grossissements. Il y a toujours un objet qui est trop grand pour le champ et un autre sur lequel on voudrait grossir plus. Il faut une bino aussi. Mais tu n'es pas obligé de prendre tout en même temps.@+!!!Thierry

Bonjour,Il va y avoir quand même une grande différence entre les deux montages, c'est le grossissement. A oculaires identiques (j'ai vu qu'il était question de 19mm), il y aura beaucoup plus de champ et moins de grossissement avec les 2 lunettes. Les montages sont difficilement comparables à cause de ça.@+!Thierry

Encore moi,Pour Alain Maury, Oui, j'ai aussi un filtre OIII de marque ICS qui d'après Markus Ludes serait identique au OIII Astronomik, ce filtre ne passe que du vert/ cyan, pas trace de rouge, en fait avec ce filtre on voit M20 gris sur tout le champ. Mais elle sort bien. Je ne vois pas ce que le superpolich a à voir là dedans? Intox? Non comprendo.@+!Thierry

Voici encore de la lecture, en anglais certes, ne pas compter sur moi pour traduire ! On est en plein dans le sujet. C'est long, mais c'est une mine d'infos. Grand merci à l'internaute qui m'a passé ces messages!Thierry > From: "David W. Knisely" <KA0CZC@...> > Date: Fri Jul 14, 2000 10:37 am > Subject: Re: [amastro] Some thoughts on color in faint objects KA0CZC@... > Send Email > > As with Jay, I also have seen some color in some of the brighter nebulae > using my ten inch Newtonian. However, the colors have been extremely > pastel, and color in the Trifid was not clearly seen. I regularly note > reddish hues in M42 and M8 when doing my quick comparisons of the views > using the Lumicon OIII and UHC and Lumicon's Multi-filter selector. The > OIII I have has a booming red passband, and with it, reddish hues in the > outer areas of M42 are occasionally visible, whereas the UHC just shows > blues and bluish-green hues. I have also seen some red in M8, although > it is nowhere near as prominent as in M42. One night with the Lumicon > H-beta filter, M20 did look a bit reddish (as does M42), but the > reflection nebula was killed, and it might have been a little wishful > thinking. I do recall many years before filters having some children > look at M20 with a 12.5 inch Newtonian, and they reported a reddish hue > as well, although I could not see it. The only other DSO which showed > much red was good old IC 418, which I call "the Pink Planetary". Some > people probably just have enhanced color sensitivity, and thus might see > color in some objects that the rest of us. Clear skies to you. > -- > David Knisely KA0CZC@... > > ============== > > > From: Roger N Clark <rnclark@...> > Date: Sat Jul 31, 1999 11:47 pm > Subject: [amastro] Re: (red objects) M20 rnclark@... > Send Email > > Just to add to the M20 color discussion. When I was younger (high school- > early college) I often saw color in M20. Best view I remember was > through 8 and 10-inch telescopes in eastern Washington state (early > 1970's). The magnification was such that m20 filled the field of view. > And the northern portion (the reflection nebula) appeared blue! > Others saw this too. We often saw the reds in other observing > sessions, but only one the blue. The reds and blues appeared > pastel (not real vivd red or blue). Faintest stars were ~7.5 unaided eye. > > Later, in my 30s and now 40s, observing from lower latitudes, including > hawaii, through 8 to 13-inch apertures, I've not seen those colors, except > for > maybe a faint hint of pastel pink. > > (I've just returned from a couple of weeks vacationing and doing large > format > photography of colorado wildflowers and trying to catch up to seemingly > hundreds of amastro emails. --Amastro: what a great resource!) > > Roger Clark > > Lew Gramer wrote: > >>Alan Goldstein wrote: >> > I have seen M20 red at the TSP years and years ago. It was with a 12" >>scope. >> > We also looked at M8... it was not red. Curious... > > > ================================= > > From: Lew Gramer <dedalus@...> > Date: Tue Jul 20, 1999 5:27 am > Subject: [amastro] Re: (red objects) dedalus@... > Send Email > > > Alan Goldstein wrote: >>I have seen M20 red at the TSP years and years ago. It was with a 12" >>scope. >>We also looked at M8... it was not red. Curious... > > My own relatively limited experience agrees with Alan's: I've never seen > or > (until now) heard of any color being seen in M8, other than possibly a > pale > green - probably just the harbinger of incipient color perception for > some. > > However, I myself have seen and independently confirmed color in M20: in > fact, > the confirmation came from two VERY fresh young observers, at the Summer > Star > Party in Savoy MA last year, and it was merely with my 20" f/5. The > observation > consisted not merely in seeing reddish hue in the emission region, but > also > (most likely a contrast effect) pale green and blue in the reflection > region! > The confirmation was "double-blind" - a simple question from me as to what > two > teenager amateurs saw in my eyepiece, with no mention of color. > > This seems to eliminate both visual training and aperture as likely > factors in > color perception for THIS object at least. However, for me it does point > to > contrast: my own Limiting Magnitude that night (not that LM is > unambiguous!) was > 7.2. Meanwhile, just two months ago from New Hampshire, with LM closer to > 6.6 or > so, I could log no color at all in M20 with a friend's 36" f/ 5... > > Clear skies all! > Lew Gramer > ==================================== > > From: Thom Ahl <tiahl@...> > Date: Sat Jul 15, 2000 2:28 am > Subject: Re: [amastro] Some thoughts on color in faint objects tiahl@... > Send Email > > Way back when I lived in San Jose, while observing at Fremont Peak, my > 13.1" > Odyssey would show a pale green with M42/43, M8 & M20. Up here in > Washington, > the only place that I have been that allowed me to see any hint of color, > has > been at Table Mt. Here in the Tri-Cities it just doesn't get dark enough > (light > pollution) to give a good view, either naked eye or with a light bucket. > {Miss > observing in California} > > Thom > ============================ > > > > puis une suite de message sur le sujet: > > From: Jay Reynolds Freeman <freeman@...> > Date: Fri Jul 14, 2000 9:44 am > Subject: Some thoughts on color in faint objects freeman@... > Send Email > > Recent events have given me some thoughts on the occasional > controversy about seeing color in faint objects, I don't really have any > new information, just some personal observations that suggest some > things to wonder about. > > When I was on the side of Mauna Kea, at the 9000-foot level, in the > week after Memorial Day, I had several nice views of the Trifid Nebula > with my 10-inch Dobson at 106x. I was well dark-adapted, and had no > difficulty seeing the two lobes with classic nursery-room colors -- pale > pink for the large one with prominent dark lanes, baby blue for the > other. That's of course the way they are "supposed to look", so I could > in principle have been deceiving myself, but for what it is worth, I > thought the colors were pretty obvious, though not by any means intense. > > On one of those occasions I showed the Trifid to a professional who > was staying at the dormitory. With no prompting about what colors might > be there, I asked if he saw any color in the object. He replied that > the large lobe -- the one I saw as pink -- looked greenish. > > I thought about that for a while, and came up with two things that > might have explained the difference in our experience of the color, that > I didn't know anything about. (Not to say these are the only two > things.) First, the other observer was certainly less well dark adapted > than I was; I had been outside in low light levels for several hours, he > for rather less than one. Second, I wondered -- and did not think to > ask till after he had left -- whether he had been using averted vision. > The Trifid was bright enough, in the 10-inch, not to require it. > > My own past experience has certainly been that I am much more > likely to see color in faint fuzzies when I am well dark adapted than > when I am not. And on several occasions since returning from Mauna Kea, > I turned my C-14 to the Trifid, at 98x, to investigate averted vision. > What I found on those occasions, on all of which I have been well dark > adapted, is that when I use averted vision, I see the pink and blue > colors as mentioned before, with the addition that the pink hue is more > prominent at the periphery of the large lobe than at the center -- the > center looks whiter, though brighter. Yet when I use direct vision, I > find it difficult or impossible to detect blue in the smaller lobe, and > the big lobe looks greenish, with the green more intense nearer the > center of the lobe, where the nebula appears brightest. All this is > repeatable, but that might mean very little, since I have looked at the > Trifid scores of times, and know what it is "supposed to look like". > > What I wonder about is two questions: > > 1) How does the color sensitivity of the dark-adapted eye vary > across the retina, in particular, from the fovea to the peripheral area? > > 2) What is the time scale for dark adaptation of color vision? > > A little more broadly, I believe there are four visual pigments > involved in the eye -- one for the rod cells, and three more for the > three kinds of cones. We might ask about positional variation in > sensitivity and about time scale for dark adaptation, for each of those > four pigments or kinds of cells. Most common information about dark > adaptation and peripheral vision applies, I believe, only to the rod > cells and their pigment. If the other cells or pigments are different, > it is important to know what the differences are in comparing > observations of colors of faint objects. > > Does anyone have any information or ideas? > > -- Jay Freeman > > =================================== > > (celui ci est déjà écrit au dessus) > From: "David W. Knisely" <KA0CZC@...> > Date: Fri Jul 14, 2000 10:37 am > Subject: Re: [amastro] Some thoughts on color in faint objects KA0CZC@... > Send Email > > As with Jay, I also have seen some color in some of the brighter nebulae > using my ten inch Newtonian. However, the colors have been extremely > pastel, and color in the Trifid was not clearly seen. I regularly note > reddish hues in M42 and M8 when doing my quick comparisons of the views > using the Lumicon OIII and UHC and Lumicon's Multi-filter selector. The > OIII I have has a booming red passband, and with it, reddish hues in the > outer areas of M42 are occasionally visible, whereas the UHC just shows > blues and bluish-green hues. I have also seen some red in M8, although > it is nowhere near as prominent as in M42. One night with the Lumicon > H-beta filter, M20 did look a bit reddish (as does M42), but the > reflection nebula was killed, and it might have been a little wishful > thinking. I do recall many years before filters having some children > look at M20 with a 12.5 inch Newtonian, and they reported a reddish hue > as well, although I could not see it. The only other DSO which showed > much red was good old IC 418, which I call "the Pink Planetary". Some > people probably just have enhanced color sensitivity, and thus might see > color in some objects that the rest of us. Clear skies to you. > -- > David Knisely KA0CZC@... > > ===================== > > From: "Don" <don@...> > Date: Fri Jul 14, 2000 5:11 pm > Subject: Re: [amastro] Some thoughts on color in faint objects don@... > Send Email > > I, too, have seen shades of "dark rose" and "peach" in M42, mostly with a > UHC or > OIII > filter. Very few other objects are bright enough to show color in my 8". > One > thing I've > noticed is that the bluish color of many planetaries changes to green with > a > filter. Even > though the details become more apparent, looking at the planetaries > without a > filter > first is still essential to get an idea of true color. > DonPensack > > =================== > From: Jeff Medkeff <medkeff@...> > Date: Fri Jul 14, 2000 10:20 pm > Subject: Re: [amastro] Some thoughts on color in faint objects > medkeff@... > Send Email > > At 08:11 AM 7/14/00 -0700, you wrote: > >>I, too, have seen shades of "dark rose" and "peach" in M42, > > When I got my current 10" Newtonian, I turned it toward M42 and had my > wife > have a look. She peered into the eyepiece and exclaimed "oh, part of it is > maroon, how interesting!" > > Having never prior to that date seen color in M42 at all, I was slightly > miffed. But since my wife was rather oblivious of the arguments concerning > the perception of color in the M42, I can't really say she had reason to > imagine it. > > Not one of my brighter moments as an amateur astronomer.... > > > -- > Jeff Medkeff > > ============================ > From: Jay Reynolds Freeman <freeman@...> > Date: Fri Jul 14, 2000 11:22 pm > Subject: Re: [amastro] Some thoughts on color in faint objects > freeman@... > Send Email > > I should have said, that all the Trifid observations I mentioned, wre > \\\ were made without any filter. -- Jay Freeman > =========================== > From: HEALYHealyDave@... > Date: Sat Jul 15, 2000 12:42 am > Subject: Re: [amastro] Some thoughts on color in faint objects > HEALYHealyDave@... > Send Email > > Years ago, I asked by daughter, who was nine at the time, what color M42 > looked in my C8. Matter of factly, and without any prompting, she said > "green." To me it appeared strictly in shades of gray. Don't children have > greater color perception than adults at low light levels? > > And, for that matter, don't M42 and other emission nebulae fluoresce in > both > red and green bands? If so, differing sensitivity to low-level colors in > different individuals might account for the "green" and "maroon" answers > to > the question "what color is M42?" > > Dave Healy > Huachuca > ===================== > From: Alan Whitman <awhitman@...> > Date: (Date unavailable) > Subject: Re: [amastro] Some thoughts on color in faint objects > awhitman@... > Send Email > > At 06:42 PM 7/14/2000 EDT, Dave Healy wrote: >>Years ago, I asked by daughter, who was nine at the time, what color M42 >>looked in my C8. Matter of factly, and without any prompting, she said >>"green." To me it appeared strictly in shades of gray. Don't children have >>greater color perception than adults at low light levels? > > At 16 years of age I always saw M42 as greenish in my 60mm refractor; at > 54 > years of age M42 is now only grey in my 16-inch Newtonian! Ouch. > > Other colour notes over the years for M42 (all without filters of course): > 13-inch at age 38: "pink or puplish northern fringe" > 16-inch at age 49: "the nebula was definitely reddish-brown-rust colour, > except for the blue-grey Huyghenian region" (transparency superb, seeing > very good) > 16-inch, eleven days later: "Again, parts of M42 were faint reddish-brown" > 8-inch at age 52: "the Huyghenian region is tinted greenish-gray" > > My 16-inch collects 44 times as much light as the 60mm refractor of my > teenage years did and yet the greenish glow that was always seen then is > not > visible now with my 16-inch and 54 year old eyes. > > Best, > > Alan Whitman > > ========================= > From: deepskyspy1@... > Date: Sat Jul 15, 2000 3:24 am > Subject: Re: [amastro] Some thoughts on color in faint objects > deepskyspy1@... > Send Email > > I noticed the pink color in the Trifed at the TSP about 2 decades ago with > a > 12" scope, but don't recall seeing it in any other instrument at other > localities. I have wondered why nearby M8 always looks bland. Does the > star > cluster overwhelm the color? M42 has either been vivid green or a ruddy > color > with a variety of instruments and conditions. The nucleus of M31 looks > yellow > to me with moderate to high magnification and a 13.1" scope. A variety of > planetaries are green or blue - I haven't targeted the pink one with a > decent > scope. I hope my eyes don't go "gray" on me, because looking for color has > always been something I enjoy. Does anyone have a list of colorful > objects? > > Alan Goldstein > > ================== > From: "David W. Knisely" <KA0CZC@...> > Date: Sat Jul 15, 2000 7:09 am > Subject: Re: [amastro] Some thoughts on color in faint objects KA0CZC@... > Send Email > > Alan Goldstein wrote: >>The nucleus of M31 looks yellow >>to me with moderate to high magnification and a 13.1" scope. > > I am really glad that somebody else has seen this! I recall a look last > year at the Nebraska Star Party through a 30 inch Obsession at the core > of M31, and it looked almost orangish yellow (definitely off-white). I > had also once seen some color in M15 one evening with that same 30 inch > when Betelgeuse was just up in the east, and the cluster looked almost > the same shade or orange. M42's main core has always looked a bluish > color with hints of green not using filters, but the outer regions never > showed much color unless I used the OIII (Lumicon model). Clear skies > to all. > -- > David Knisely KA0CZC@... > > ====================== > From: Jay Reynolds Freeman <freeman@...> > Date: Sat Jul 15, 2000 8:35 pm > Subject: Re: [amastro] Some thoughts on color in faint objects > freeman@... > Send Email > > I had a couple of interesting experiences regarding color in M57 > lately. > > On April 29-30, 2000, observing with my C-14 at 489x from the > Henry Coe State Park outer parking lot, with no filter, on a night of > superb seeing, my logbook reads as follows: "... M57 is wonderful. > The central star is intermittantly visible, as are several others both > in the bright "doughnut" and in the hole. The bright part of the > nebula looks curdled or mottled. Patchy faint illumination spans the > hole. Another observer called my attention to a color difference, > saying that the outer periphery of the doughnut appeared red, the rest > green. It's subtle, but I think he's right. Someone said that > whereas at lower magnification and smaller aperture, M57 resembles a > Cheerio, tonight it was like a peach cut in half." > > And from Lick Observatory on June 23-24, 2000, observing with the > 36-inch refractor at 496x (one of the perks of being a docent), "Shows > central star and color -- mostly green, with reddish outer tinge." > On this occasion, when I mentioned the color, another observer also > mentioned seeing it earlier in that session. (I came in from the outside > when observing of M57 was in progress, so I don't know whether anyone > remarked on the color before I did.) I had had my C-14 set up outside on > the occasion, but had not noted any color, and was part way through > taking down when called in to look through the 36-inch. > > I probably wasn't as well dark-adapted with the C-14 at Lick as at > Coe, due to local lights. I don't recall who the other observers > seeing color were, and I didn't take names. > > -- Jay Freeman > > ========================== > From: "Dave Mitsky" <djm28@...> > Date: Sat Jul 15, 2000 9:13 pm > Subject: Re: Some thoughts on color in faint objects djm28@... > Send Email > > --- In amastro@egroups.com, "David W. Knisely" <KA0CZC@n...> wrote: >>Alan Goldstein wrote: >> > The nucleus of M31 looks yellow >> > to me with moderate to high magnification and a 13.1" scope. >> >>I am really glad that somebody else has seen this! I recall a look > last >>year at the Nebraska Star Party through a 30 inch Obsession at the > core >>of M31, and it looked almost orangish yellow (definitely > off-white). > I >>had also once seen some color in M15 one evening with that same 30 > inch >>when Betelgeuse was just up in the east, and the cluster looked > almost >>the same shade or orange. M42's main core has always looked a > bluish >>color with hints of green not using filters, but the outer regions > never >>showed much color unless I used the OIII (Lumicon model). Clear > skies >>to all. >>-- >>David Knisely KA0CZC@n... > > I have also seen the stars of M13 and M15 appear as a pale yellow > through John Vogt's 32" f/4 Dob. M42 usually looks greenish white to > me but I have perceived its "wings" as a ruddy shade through 20" and > larger scopes. > > Dave Mitsky > > ========================== > From: Nick Martin <bonnyton@...> > Date: Mon Jul 17, 2000 1:01 am > Subject: Re: Some thoughts on color in faint objects bonnyton@... > Send Email > > Some objects in which I have have perceived colour. > When only 18 I recorded M42 on a very clear night as a vivid green using > an > 8" relector and low power. Currently at 57 I still see it as greensih at > low > power with my 20inch Dobsonian but not a vivid grren. I can also perceive > some of the outer parts of the nebula as having a reddish tinge. We do > have > a 16 year oold member in ouir local Astro society who perceives the whole > nebula as pink. > I observed M27 the dumbell nebula, using some care to maintain colour > vision by having an increased ambient light level ( from a hall light), > checked by observing a printer colour test chart inclined so its incident > illumination was roughly the same as the apparent brightness of the > nebula. > The brighter upper and lower edges of the dumbell showed a distinct > reddish > tinge. The bright HII region in M33 showed a distinct orange tinge. I got > an > inexperienced observer to say what colour he saw it and he too reported > that > it had an orange tinge. The cat's eye nebula under low power showed a > definite red colour. > Clear and dark skies( ours are twilight for another two weeks) > Nick > Nick Martin, Bonnyton House, By Ayr, Ayrshire KA6 7EW ,Scotland, UK. > Latitude 55 24'56" Longitude 4 26' 00". > > ============================ > From: "David W. Knisely" <KA0CZC@...> > Date: Mon Jul 17, 2000 6:20 am > Subject: Re: [amastro] Re: Some thoughts on color in faint objects > KA0CZC@... > Send Email > > Nick Martin Posted: >>The cat's eye nebula under low power showed a >>definite red colour. Clear and dark skies( ours are twilight for >>another two weeks) >>Nick >>Nick Martin, Bonnyton House, By Ayr, Ayrshire KA6 7EW ,Scotland, UK. >>Latitude 55 24'56" Longitude 4 26' 00". >> > > If by "the Cat's Eye" you mean NGC 6543, then I can't confirm this red > color in a 30 inch. At last year's NSP (the first Saturday evening), > the object was almost lime green through and through. We could see the > spiraling arcs shown in the HST images (nowhere near that level of > detail however), as well as the tattered pieces of the faint outer > shell, as well as the central star, but no red. Clear skies to you. > -- > David Knisely KA0CZC@... >

Re,Voici un message posté sur la liste Amastro, (accessible par l'interface yahoosgroups)qui traite des couleurs visibles en visuel sur les nébuleuses. Je pense que c'est dans le sujet du post. > Malcolm Currie, professional astronomer and amateur meteor observer, > asked me for my thoughts about visually observable colors in objects > of the deep-sky. Here is my response: I welcome input (including the > occasional polite brickbat) from other deep-skyers on this subject, > even considering that much has already been said on both these fora > about this topic in previous years... > > > Malcolm notes regarding colors: >>Stars without question. I can see colour in M42 and some planetary >>nebulae. I'm not a great visual deep-sky observer, and from Britain >>most of the best objects are low in the haze, so there cold be more. >>I must try looking through a big Celestron at Hale Pohaku [Hawai'i]. > > > Not too much time at work today for astronomy (funny how that happens > at times! :> ), but here are my quick "thinking points" on this, based > purely on my own experiences with visual deep-sky color: > > > 1) Visibility of color in "nebular" objects *is* dependent on both ap- > erture and magnification - though clearly in non-linear, non-monotonic > ways. Again, some put forward theoretical reasons why this shouldn't be > so... Nonetheless, my comments derive purely from personal experience, > rather than any theoretical considerations - however interesting. > > > 2) Visibility (and optimal aperture and power for seeing it) is also > highly dependent on sky contrast and transparency - in ways which are > too complex for my limited experiences to characterize. (And on this > topic, some theoretical input would be very welcome indeed!) > > > 3) Relatively MANY amateur-observable PNe show color, including many > which are nearly stellar, and so infrequently observed. In fact, so > many PNe show either a green, blue-green, or blue, that I'd exclude > them from this discussion! Same goes for stars - from the blue-white > of an O-class star, to the deep crimson of an M, RC or RN star. Again, > *not everyone* will see these colors - and some will call green what > others call unequivocally blue-green or even blue. But the EXISTENCE > of visual color in such object classes is not in question, I think. > > > 4) Individual perception plays an overriding role... Some people do in > fact see color in M42 naked-eye! Others cannot see this at any aperture > or magnification. More interestingly, some are most likely to perceive > pale green in M42 before any other color; while others may see nothing > but the "default" pearly gray, until suddenly (at the right power, sky > contrast, and aperture) they will perceive reddish tinges first. > > (Malcolm, this "wild" scatter in color perception is certainly borne > out by the available data on fireball colors... One might assume that > there was little room for perception variation in descriptions of an > object of mag -3 or brighter - yet this is decidedly NOT the case!) > > > 5) Objects (excluding stars & PNe) in which I definitely logged color > are listed below, with minimal data about the WORST (or in some cases, > ONLY) instrument and conditions under which color was logged so far: > > M42 (6" scope in Bortle 3 sky); M8 (12.5" scope in Bortle 2 sky); M20 > (20" scope in Bortle 2 sky - both red in the emission area and lovely > contrasting pale blue in the reflection region!); M45 nebulosity (I > have seen color only once, in a 6" under Bortle 3(!) skies - a very > pale blue in the Merope nebulosity); pale yellow in core of M22 (30" > scope in Bortle 1 skies of NE New Mexico); very pale red in NGC 281 > (again, 30" in Bortle 1 sky). > > I noted that extraordinary yellow in the core of M22 while doing a > very unusual sort of observing: exploring the globular at ABSURDLY > high power, seeking a small PN superimposed on the inner regions... > (I finally logged the presence of the PN by "blinking" the field at > about 1000x with a UHC filter. Obviously the yellowish tinge in the > core was only seen when the UHC was NOT interposed on the field! :> ) > > > Clear skies, > Lew Gramer > > > >

re,Bon, il est donc bien possible que cette perception de couleurs soit une illusion, en fait la chose que j'ai trouvée étonnante est que les deux parties de la nébuleuse me soient apparues l'une bleue et l'autre marron, en vision directe ou décalée. C'est ce qui m'a fait dire qu'il y avait quelque chose, lié aux vraies couleurs de M20. Ceci dit, le filtrage est à première vue une manoeuvre qui devrait supprimer toute nuance de couleur, on est tous bien d'accord. Il faut toutefois remarquer que les filtres Lumicon laissent passer pas mal de rouge, à tel point que certains sont roses dans l'axe, ce qui est assez bizarre en effet, mais constaté par moi aussi sur un filtre Hbeta qui est vraiment rose ce qui m'a d'ailleurs fait croire que le Hbeta était une longueur d'onde dans le rouge. (En fait le Hbeta est bleu, comme l'est mon filtre UHC) http://home.freeuk.com/m.gavin/grism2.htm On peut voir tout cela sur ce lien. On y voit que plusieurs modèles de filtres laissent passer du rouge, en plus du vert/ bleu. Moi ce que j'ai vu c'est du rouge et du bleu, ce qui ne me paraît finalement pas si bizarre que ça. Excuse moi Quasar04 d'avoir parlé de filtrage sur ton post, le titre que tu as donné c'est "couleurs de M20" et j'ai pensé être dans le sujet. En ce qui concerne la pollution dans le site où nous avons observé, ben non, c'est un site très peu pollué, bien dégagé vers le sud, lors d'une soirée bien claire. Certes M20 n'est pas au zenith. Le télescope n'est pas pourri, pas de vapeurs de bibine, etc. Et pas question de remplacer les Naglers.@+!!!Thierry

Par rapport au métal, le bois a principalement l'inconvénient de se déformer progressivement sous la charge et de ne pas revenir en position. Les déformations sont aussi inhomogènes, en fonction du sens des fibres. Dans un barillet il peut y avoir des déformations tant qu'elles sont semblables sur tous les appuis. Ainsi il n'y a que du refocus à effectuer, les déformations ont peu d'influence sur la collimation. Le point à vérifier est au niveau des butées latérales qui pourront introduire de l'astigmatisme selon que le barillet est flexible, que les butées glissent mal, que le miroir est fin etc. @+!thierry [Ce message a été modifié par Teepee-Maïcé (Édité le 04-07-2005).]

A l'utilisation ces oculaires sont très proches, pour les différences il y a moins de déformation en "coussin" sur le 12mmT4 et plus de relief d'oeil. Mais le 13mmT6 a aussi des choses pour lui, un placement de l'oeil moins critique, le phénomène d'ombres volantes est totalement absent, et le poids plus léger. Pour la qualité de l'image, moi je serais tenté de dire égalité, la finesse est excellente sur les 2 oculaires et le contraste élevé. Le 13mm T6 a un peu plus de lumière que l'association 26mmT5 + powermate x2, ceci pour les objets à la limite de la détection. Le 13T6 a un rendu légèrement plus "chaud" que le 12T4. Moi personnellement comme je ne porte pas de lunettes en observant, je préfère le 13mmT6 dont le relief d'oeil est plus petit que le 12T4, mais qui délivre les images plus facilement, ce qui fait une différence en utilisation réelle, (je parle pour moi). Pour les porteurs de lunettes, il vaut mieux le 12mmT4. Pour les problèmes de poids, normalement avec un 400mm il ne devrait y avoir aucun problème, le scope devrait pouvoir rester équilibré, le 12T4 n'est pas si lourd que ça. Il faut pouvoir équilibrer aussi pour des poids plus lourds en prévision de bino, etc.@+!Thierry[Ce message a été modifié par Teepee-Maïcé (Édité le 24-06-2005).]